BG4.2

EDI
Biogeochemistry of coastal seas and continental shelves

The coastal ocean has been increasingly recognized as a dynamic component of the global carbon budget. This session aims at fostering our understanding of the roles of coastal environments and of exchange processes, both natural or perturbed, along the terrestrial / coastal sea / open ocean continuum in global biogeochemical cycles. During the session recent advancements in the field of coastal and shelf biogeochemistry will be discussed. Contributions focusing on carbon and nutrient and all other element's cycles in coastal, shelf and shelf break environments, both pelagic and sedimentary, are invited.

This session is multidisciplinary and is open to observational, modelling and theoretical studies in order to promote the dialogue. The session will comprise subsections on coastal carbon storage, and on benthic biogeochemical processes.

Co-organized by OS3
Convener: Helmuth Thomas | Co-conveners: Alberto V. Borges, Arthur CapetECSECS, Katarzyna Koziorowska-Makuch, Craig Smeaton, Sonia Silvestri, Manudeo Singh, Beatrice Maria Sole Giambastiani
Presentations
| Tue, 24 May, 08:30–11:49 (CEST), 15:10–18:27 (CEST)
 
Room 3.16/17

Presentations: Tue, 24 May | Room 3.16/17

Chairpersons: Arthur Capet, Katarzyna Koziorowska-Makuch
08:30–08:35
08:35–08:42
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EGU22-483
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ECS
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Presentation form not yet defined
Celeste Kellock, Craig Smeaton, Nadeem Shah, William Austin, and Christian Schroeder

Mid-latitude fjords have recently been identified as important environments for carbon storage. This research highlights the importance of the lateral transport of carbon from land to sea as we assess the influence of catchment land use (primarily forestry) on carbon transport and sediment carbon burial. Establishing the influence of land use, specifically forestry, on coastal biogeochemical cycling is particularly important if afforestation is to help mitigate climate change impacts, and to better understand the impact of deforestation. The relationship between carbon and iron in fjord sediments is the focus of this study. We provide insights into carbon and iron coupling in a mid-latitude fjord. Here we show the variability of carbon burial, and how this is influenced by terrestrial inputs and iron speciation in fjord sediments. We use bulk organic carbon and elemental data, isotopic analysis, Mössbauer spectroscopy and chemical extractions to better understand the relationship between carbon and iron. Observed decreases in organic carbon from the upper to lower basin are influenced by the input of terrestrial material. Organic carbon is up to three times higher in the upper basin and terrestrial organic carbon is ~20% higher in comparison to the lower basin of the fjord. The strength of the reactive iron signal is found to vary vertically (with depth, over time) and laterally (from upper – lower basin) within this fjord. Results highlight that there is a changing relationship between iron and carbon within this system. Understanding land-sea controls on coastal carbon transport and burial is crucial during this period of climate change.

How to cite: Kellock, C., Smeaton, C., Shah, N., Austin, W., and Schroeder, C.: Source to Sea: the relationship between carbon and iron in mid-latitude fjord sediments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-483, https://doi.org/10.5194/egusphere-egu22-483, 2022.

08:42–08:49
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EGU22-853
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ECS
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On-site presentation
Benthic foraminifera as bioindicators of anthropogenic Pollution in the Red Sea Coast, Saudi Arabia
(withdrawn)
khaled alKahtanya, Mohamed Youssef, and Abdelbaset El-Sorogy
08:49–08:56
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EGU22-3170
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ECS
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On-site presentation
Rhiannon Grant and William EN Austin

The UK and Scottish Governments have committed to improve and preserve marine habitats including protecting 10% of Scottish waters through the creation of new Highly Protected Marine Areas (HPMAs). Within these commitments, an innovative management perspective was introduced where areas are proposed for protection based on their blue carbon value.  Understanding the physical properties of these environments and establishing evidence for their vulnerability to human impacts is therefore becoming increasingly important. This research identifies “blue carbon hotspots” in the Firth of Clyde. The Firth of Clyde is a sheltered fjord on the west coast of Scotland which has been fundamental to Scottish industry and fishing for hundreds of years. In this study, the vulnerability of these marine carbon stores from direct seabed disturbances is investigated to highlight areas most at risk of carbon loss due to human impacts. Elemental analysis of surface sediment samples were used to identify “blue carbon hotspots” across the basin. Furthermore, the carbon stored in different sediment types was determined using particle size analysis combined with existing broad-scale mapping of this region.  Thermogravimetric analysis indicated the stability of organic carbon within marine sediment providing a useful assessment of the quality of the carbon present. The impacts of benthic fishing (indicated by VMS data) were used to assess the existing pressures on these blue carbon stores together with MPA mapping and environmental properties (such as bathymetry and sedimentology). Mapping results produced in this research can be used in policy and decision making for the prioritisation of protecting blue carbon alongside other designation criteria for the protection of marine habitats in Scotland. Growing recognition of the climate benefits from protecting long-term natural carbon stores mean these findings can be integrated to highlight a blue carbon climate service in addition to implications for local and national management of marine habitats.

How to cite: Grant, R. and Austin, W. E.: The quantity and quality of organic matter in the sediments of the Firth of Clyde: A new tool to assess the vulnerability of “blue carbon hotspots” in Scotland’s inshore waters., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3170, https://doi.org/10.5194/egusphere-egu22-3170, 2022.

08:56–09:03
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EGU22-103
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ECS
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Highlight
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Virtual presentation
Kirsty Black, Craig Smeaton, and William Austin

Shelf and coastal seas hold vast quantities of sedimentary carbon, which if left undisturbed, will contribute towards long-term carbon and underpin natural ocean climate services. It is estimated that within the UK exclusive economic zone, 524 Mt of organic carbon is stored within sediments (Smeaton et al., 2021). However, the stability and potential vulnerability of this key component of global natural capital remains poorly quantified, particularly under anthropogenic stressors, such as benthic fishing activity. Benthic trawling activity is the most significant cause of anthropogenic disturbance to the seabed, leading to massive sediment resuspension events and wide scale impact to benthic communities. The impacts of trawling on benthic ecosystems and communities are well reported within the literature (e.g. Hughes et al., 2014); however, a knowledge gap remains regarding the impact of trawl-induced disturbance events on sedimentary carbon stores.

In order to improve our understanding of the areas where sedimentary carbon is potentially at greatest risk from trawling events, we have developed a carbon vulnerability ranking to signify the areas of the seabed where preventative protection would be most beneficial to help maintain our current carbon stocks while further research continues to shed light on the fate of carbon after trawling (e.g. carbon remineralization, transport, and consumption etc.). These maps have been modelled within GIS via fuzzy set theory by making use of currently available fishing intensity, carbon and sediment distribution, and sediment lability datasets (ICES, 2014; Smeaton et al., 2021).

Our results show that the fjordic west coast of Scotland represents one of the key areas where sedimentary carbon is highlighted as being potentially at risk from bottom trawling. This is largely due to the high lability of the sediments as a function of both sediment type and the elevated organic carbon content present within these sediments. In addition, higher occurrences of repetitive trawling activity within inshore waters may add to these pressures. Our research shows that these organic carbon hotspots are potentially at risk of disturbance from benthic trawling activity and should be prioritized for future safeguarding measures to ensure avoided emissions are minimized and to protect this natural carbon capital resource.

References

Hughes, K.M., Kaiser, M.J., Jennings, S., McConnaughey, R.A., Pitcher, R., Hilborn, R., Amoroso, R.O., Collie, J., Hiddink, J.G., Parma, A.M., Rijnsdorp, A., 2014. Investigating the effects of mobile bottom fishing on benthic biota: A systematic review protocol. Environ. Evid. 3. https://doi.org/10.1186/2047-2382-3-23

ICES, 2014. OSPAR request on mapping of bottom fishing intensity using VMS data, Special request, Advice September 2014.

Smeaton, C., Hunt, C.A., Turrell, W.R., Austin, W.E.N., 2021. Marine Sedimentary Carbon Stocks of the United Kingdom’s Exclusive Economic Zone. Front. Earth Sci. 9, 1–21. https://doi.org/10.3389/feart.2021.593324

How to cite: Black, K., Smeaton, C., and Austin, W.: Assessing the Potential Vulnerability of Sedimentary Carbon Stores to Benthic Trawling within the UK EEZ, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-103, https://doi.org/10.5194/egusphere-egu22-103, 2022.

09:03–09:10
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EGU22-1547
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ECS
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Virtual presentation
Craig Smeaton, Pauline Gulliver, and William Austin

Annually, continental shelf sediments bury an estimated 137 Mt of organic carbon (OC) making these sedimentary systems an integral component of the global carbon (C) cycle. Within continental shelfs individual sedimentary environments can range between inshore fjord to offshore non-deltaic settings each vastly differing in their ability to trap and lock away OC. Of these different environments fjord sediments have been shown to be hotspot for the burial and storage of OC burying and estimate 18 Mt OC yr-1, which equates to ~11% of all marine C burial (Smith et al., 2015). In Scotland, the postglacial sediments of the mid-latitude fjords are estimated to store 252 ± 62 Mt OC (Smeaton et al., 2017) with a further 84,000 tonnes of OC being trapped and stored each year (Smeaton et al., 2021). It is clear that fjord sediments are an integral element of the global C cycle and could potentially be crucial long-term climate mitigation. Yet these systems do not exists in isolation and how these system interact with other marine sedimentary systems remains an open question.  

Current research is largely focused on the close interactions between fjord sediments and the terrestrial environment (Cui et al., 2016; Smeaton and Austin, 2017) but recent research in Scotland and Norway has indicated the marine environment can play as large if not greater role in the OC dynamics of fjords than terrestrial ecosystems (Faust and Knies, 2019; Smeaton et al., 2021).

Here we explore the interactions between the sediments of the Loch Linnhe fjord complex on the West coast of Scotland and the adjacent continental shelf. Using an array of geochemical techniques the source, age and depositional history of the OC held within the sediments will be investigated to understand the geochemical processes driving OC burial and storage in both the fjord and continental shelf sediments. By integrating state-of-the-art spatial analytics with the geochemical measurements we further seek to quantify how these different sedimentary settings interact and how these processes drive OC dynamics across a continental shelf.    

 

References

Cui, X., Bianchi, T.S., Savage, C. and Smith, R.W., 2016. Organic carbon burial in fjords: Terrestrial versus marine inputs. Earth and Planetary Science Letters451, pp.41-50.

Faust, J.C. and Knies, J., 2019. Organic matter sources in North Atlantic fjord sediments. Geochemistry, Geophysics, Geosystems20(6), pp.2872-2885.

Smeaton, C., Austin, W.E., Davies, A.L., Baltzer, A., Howe, J.A. and Baxter, J.M., 2017. Scotland's forgotten carbon: a national assessment of mid-latitude fjord sedimentary carbon stocks. Biogeosciences14(24), pp.5663-5674.

Smeaton, C. and Austin, W.E., 2017. Sources, sinks, and subsidies: Terrestrial carbon storage in mid‐latitude fjords. Journal of Geophysical Research: Biogeosciences122(11), pp.2754-2768.

Smeaton, C., Yang, H. and Austin, W.E., 2021. Carbon burial in the mid-latitude fjords of Scotland. Marine Geology441, p.106618.

Smith, R.W., Bianchi, T.S., Allison, M., Savage, C. and Galy, V., 2015. High rates of organic carbon burial in fjord sediments globally. Nature Geoscience8(6), pp.450-453.

How to cite: Smeaton, C., Gulliver, P., and Austin, W.: Carbon Connections: understanding the carbon interactions between adjacent marine sedimentary environments. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1547, https://doi.org/10.5194/egusphere-egu22-1547, 2022.

09:10–09:17
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EGU22-2401
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On-site presentation
Oliver Schmale, Sebastian Jordan, and Tina Treude

Benthic microorganisms transported into the water column potentially influence biogeochemical cycles and the pelagic food web structure. In our present study in the coastal waters of the Coal Oil Point seep field (California) and the Blowout site in the North Sea (abandoned well site 22/4b), we proved the dislocation of microorganisms from the sediment into the water column via gas bubbles released from the seabed. These studies showed that the transport efficiency of benthic methanotrophic bacteria into the water column was dependent on the gas flux intensity from the gas-releasing vent site. Cold seeps represent hot spots of seabed-derived methane emissions to the water column, where physical and biological barriers regulate transport of methane to the atmosphere. In our study, we combined field measurements with a particle-tracking model and demonstrated that sediment resuspension and gas-bubble-mediated inoculation of the water column with methane oxidizing bacteria decreased the methane turnover time by a factor of five. Our findings impressively demonstrate that the bubble-mediated transport of microorganisms influences the pelagic microbial abundance and community composition at gas-releasing seep sites. For cold seeps sites this newly discovered bentho-pelagic transport mechanisms creates a positive feedback on the pelagic methane sink and it seems obvious that this mechanism influences other biogeochemical processes in the vicinity of gas seeps, too.

How to cite: Schmale, O., Jordan, S., and Treude, T.: Bubble-mediated transport of benthic microorganisms into the water column and its implication on pelagic biogeochemical cycles., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2401, https://doi.org/10.5194/egusphere-egu22-2401, 2022.

09:17–09:27
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EGU22-724
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ECS
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solicited
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Presentation form not yet defined
Vlad Macovei, Ulrich Callies, Paulo Calil, and Yoana Voynova

Marine uptake of carbon dioxide limits the atmospheric concentration growth. Continental shelf seas are important areas for this uptake, but are also highly variable environments, with indications that their sink capacity is weakening. A way to reduce uncertainty of budgeting is to increase our observational capacity, such as through FerryBox installations on Ships-of-Opportunity. Here, we compare FerryBox observations in the North Sea for periods of interest in the autumn seasons of 2019 and 2020. We show that short-lived and small to medium-scale events can be identified when the sampling resolution is adequately high, and that these events cause changes in some essential environmental variables on the same magnitude as seasonal cycles. In particular, these events rapidly lowered seawater pCO2 by 8-10%. In September 2019, an advectively-driven event caused a previously carbon source area (flux of 1.3 ± 0.6 mmol m-2 day-1) to be in relative balance with the atmosphere (new flux of −0.04 ± 0.34 mmol m-2 day-1). In November 2020, a late autumn bloom caused another previously carbon source area (flux of 2.7 ± 2.1 mmol m-2 day-1) to potentially become a carbon sink (flux of −0.6 ± 1.4 mmol m-2 day-1 during the bloom). We demonstrate the importance of including such events in regional carbon budget assessments and advocate for the tuning of models in order to capture this small-scale variability.

How to cite: Macovei, V., Callies, U., Calil, P., and Voynova, Y.: Quantifying how small-scale, short-lived, advective and biologically driven processes alter the carbon uptake capacity in a shelf sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-724, https://doi.org/10.5194/egusphere-egu22-724, 2022.

09:27–09:34
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EGU22-2412
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On-site presentation
David Curbelo Hernández, Juana Magdalena Santana Casiano, Aridane González González, David González Santana, and Melchor González Dávila

The spatio-temporal variability of the surface CO2 system and its air-sea fluxes were studied in the Strait of Gibraltar based on high-resolution underway field data collected between February 2019 and March 2021 by a surface ocean observation platform (SOOP) aboard a volunteer observing ship (VOS). The surface CO2 distribution was strongly influenced by the seasonal and spatial variability in the depth of the Atlantic-Mediterranean Interface layer and by upwelling of deep-water drove by the tidal and easterly winds. The variability of the CO2 fugacity (fCO2,sw) and fluxes were mainly driven by temperature despite the significant influence of non-thermal processes in the southernmost part. The thermal to non-thermal effect ratio (T/B) reached higher values values in the northern section (>1.8) compared with the southern section (<1.30) due to the enhancement of biological activity and vertical mixing related to the seasonal wind-induced upwelling along the African coast. The fCO2,sw increased with temperature by 9.02 ± 1.99 µatm ºC (r2=0.86) and 4.51 ± 1.66 µatm ºC (r2=0.48) in the northern and southern sections, respectively. The annual cycle (referenced to 2019) of total inorganic carbon normalized to a constant salinity of 36.7 (NCT) was attended. The net community production processes described 93.5-95.6% of the total NCT change, while the contribution of air-sea exchange and horizontal and vertical advection was found to be minimal (<4.6%). According to the seasonality of air-sea CO2 fluxes, the region behaved as a strong CO2 sink during the cold months and as a weak CO2 source during the warm months. The Strait of Gibraltar acted as annual net CO2 sink, with higher net ingassing along the southern section (-1.01 mol C m-2) compared to the northern section (-0.82 mol C m-2). The calculated average CO2 flux for the entire area was -7.12 Gg CO2 yr-1 (-1.94 Gg C yr-1).

Keywords: Air-sea CO2 fluxes, CO2 system, VOS line, Surface Ocean Observation Platform, Strait of Gibraltar.

How to cite: Curbelo Hernández, D., Santana Casiano, J. M., González González, A., González Santana, D., and González Dávila, M.: Variability of the air-sea CO2 exchange in the Strait of Gibraltar based on measurements from a VOS line., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2412, https://doi.org/10.5194/egusphere-egu22-2412, 2022.

09:34–09:41
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EGU22-2975
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ECS
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Presentation form not yet defined
Effect of ocean margin calcification dynamics on global carbon transfer – a box model study
(withdrawn)
Anne Kruijt, Appy Sluijs, and Jack Middelburg
09:41–09:48
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EGU22-3085
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ECS
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On-site presentation
A model set-up for future scenario simulations in the northwest European shelf
(withdrawn)
Himansu Kesari Pradhan, Ute Daewal, Sebastian Grayek, Joanna Staneva, and Corinna Schrum
09:48–09:55
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EGU22-3504
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ECS
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Virtual presentation
Blanca Ausin, Sarah Paradis, Gina Bossert, Negar Haghipour, and Timothy Eglinton

Marine sediments comprise the primary long-term sink of organic matter (OM) in marine systems. A key mechanism for stabilization of OM in marine sediments occurs via protection on mineral surfaces. However, fine-grained minerals are prone to resuspension and redistribution prior to final burial, potentially further exposing OM to degradation. Here, we examine the sedimentological properties and geochemical characteristics of organic carbon (OC) in surface sediments from the Western Mediterranean Sea to shed light on the origin of OM and the underlying mechanisms that determine its fate in this semi-enclosed basin. We analysed the isotopic (ẟ13C, ẟ15N, and Δ 14C) and elemental (carbon and nitrogen content and C/N) composition of OC in 104 surface sediments retrieved from the Western Mediterranean Sea and the adjacent Atlantic Ocean, west of the Strait of Gibraltar. Corresponding grain-size and mineral surface area data were used to shed light on OM-mineral relationships and sedimentary transport mechanisms. The influence of this latter process was further evaluated by comparing the 14C age of OC and planktic foraminifera and analysing excess 210Pb concentration in surface sediments. The OC content and ẟ13C and Δ 14C signatures depict a clear SW-NE gradient defined by strong differences between the westernmost (Alboran Sea) and the easternmost sub-basins (Northwestern and Balearic Sea). This gradient is attributed to differences in local primary productivity and delivery of terrestrial OC. When explored in a sedimentological context, our results suggest that both OM protection via association with mineral surfaces and selective degradation of labile OM during secondary transport plays an important role magnifying the contrast between endmembers manifested in these geochemical gradients.

How to cite: Ausin, B., Paradis, S., Bossert, G., Haghipour, N., and Eglinton, T.: Controls on the characteristics and distribution of sedimentary organic matter in the Western Mediterranean Sea , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3504, https://doi.org/10.5194/egusphere-egu22-3504, 2022.

Coffee break
Chairpersons: Sonia Silvestri, Beatrice Maria Sole Giambastiani, Manudeo Singh
10:20–10:25
10:25–10:32
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EGU22-2901
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Virtual presentation
Ricardo Martinez Prentice, Raymond D. Ward, Miguel Villoslada Peciña, and Kalev Sepp

Coastal wetlands provide a range of ecosystem services and can support quite high biodiversity as a result of their high productivity. There are a range of techniques applied to monitoring and assessing ecological status and ecosystem service provision, however, traditional techniques can be quite time consuming and costly. In recent years, there has been a strong push to use remotely sensed data to evaluate ecological condition as well as estimate a range of ecosystem services within coastal wetlands.  Unmanned Aerial Vehicles (UAV) platforms have increasingly been used in the field of remote sensing of coastal wetlands because they provide detailed radiometric data to carry out the classification of the high-resolution images. Classifications using supervised Machine Learning algorithms can be performed on those images, providing robust datasets for a range of variables.

However, in spite of the flexibility of performing flight plans to monitor coastal wetlands with high accuracy, it is often not feasible to capture large areas using UAV systems. Satellite imagery can be used to undertake evaluations of a wide range of environmental variables in coastal wetlands over much larger areas. Finding synergies between images taken from UAVs and satellite could provide the possibility to extend local observations of plant functional diversity or ecosystem service provision in coastal wetlands to larger areas or to regions. Using validation techniques based on ground-truth data, high-resolution UAV derived images can be used to characterize terrain and ecological features, such as plant communities and then upscale them to satellite resolutions.

The present study presents a methodology to compare images taken from a UAV multispectral camera and the freely available Multispectral Instrument (MSI) sensor images from the Sentinel-2 satellite because their spectral bands overlap with those commonly used for plant community assessments in coastal wetlands using drones. First, each pixel of Sentinel-2 image is characterized by the most frequent category of plant communities obtained from a ML supervised classification of high-resolution UAV image. Then, the results of classifying the study areas with the Sentinel-2 image are compared with the previous process by analyzing the differences and similarities of categories in each pixel. By this way, synergies between the UAV and Sentinel-2 images can be found in order to have a reliable upscaling of UAV-based data. 
Keywords: Remote Sensing, UAV, Machine Learning, Upscaling

How to cite: Martinez Prentice, R., D. Ward, R., Peciña, M. V., and Sepp, K.: Image Upscaling Assesment From UAV To Sentinel-2 In Coastal Wetlands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2901, https://doi.org/10.5194/egusphere-egu22-2901, 2022.

10:32–10:39
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EGU22-4664
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ECS
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Virtual presentation
Margaux Brandon, Nathalie Lefèvre, Dimitry Khvorostyanov, and Denis Diverrès

Spatial and temporal evolution of sea surface temperature, salinity and CO2 properties are studied in the English Channel (EnC) (48.8°N-5.2°W and 51.2°N-1.5°E) from 2006 to 2021. In situ measurements are collected using voluntary observing ships (VOS) as part of the ICOS program, during repeated transects every year, providing a good temporal coverage to study monthly to interannual variability in the area. The analysis of the longitudinal distribution of the parameters highlights a strong east-west difference. SST decreases from West to East in winter and spring, while the opposite gradient is observed at the end of summer and in autumn. During the month of July, a strong SST gradient up to 3 °C is observed around 3°W. Along the transect, the salinity slightly decreases from West to East, with a higher variability in the Eastern EnC. Mean SST in the EnC varies between 9 in March and 17°C in August-September and the mean difference between sea-water fCO2 and atmospheric fCO2 (ΔfCO2) ranges from -45 µatm at the end of spring/beginning of summer to 40 µatm in autumn. Differences in seasonality and variability are observed between the Western and Eastern EnC. For example, a strong sink of CO2 is observed in summer in the Western EnC, while in the Eastern EnC, the strongest sink occurs in spring. These CO2 sinks are associated with a rise in biological activity as shown by the very high surface Chl-a concentrations observed from satellite images. To better understand the physical and biological processes behind the fCO2 variations, relations between parameters are examined. Finally, interannual evolution of SST, SSS and CO2 properties are discussed to assess the long-term changes in this region.

How to cite: Brandon, M., Lefèvre, N., Khvorostyanov, D., and Diverrès, D.: Spatial and temporal distribution of physical and CO2 properties in the English Channel based on voluntary observing ships between 2006 and 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4664, https://doi.org/10.5194/egusphere-egu22-4664, 2022.

10:39–10:46
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EGU22-4789
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ECS
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On-site presentation
Sarah Cryer, Stacey Felgate, Peter Brown, Filipa Carvalho, James Strong, Terry Wood, Gilbert Andrews, Samir Rosado, Arlene Young, Millie Goddard-Dwyer, Socratis Loucaides, Richard Sanders, and Claire Evans

The Mesoamerican Barrier Reef, the second largest barrier reef in the world, is vitally important to the ecology and economy of Belize and neighbouring countries. Coral reefs are inherently vulnerable to ocean acidification and those exposed to significant riverine input may be under enhanced threat. In tropical rivers pCO2 levels may be linked to land use in their catchment, with conversion of pristine forest to agricultural land potentially enhancing carbon flux to the coastal ocean. We investigated the effect the Belize River may have on the carbonate chemistry of surrounding coastal ocean, applying a multidisciplinary methodology. Water samples were collected and measured for: total alkalinity; dissolved inorganic carbon (DIC); and δ13CDIC; and were complemented by pH and pCO2 data acquired from sensors mounted on an autonomous surface vehicle. Samples were collected from the source of the Belize river to the mouth and out past the barrier reef.  pCO2 measuring >1000-µatm at the mouth of the Belize River suggests local high levels of respiration and low pH water being discharged into the coastal ocean. δ13CDIC samples were taken to identify terrestrial DIC signatures and used in combination with sensor data to identify potential controls on coastal pH. There was a distinct difference in δ13CDIC along the river with a range of 27 ‰ to - 13‰, while coastal δ13CDIC was heavier with a range of  -11.5‰ to 1.5 ‰. These results demonstrate the complexity of processes that control coastal ocean acidification, which has implications for coastal economies that are heavily dependent on healthy coral reefs as a resource.

How to cite: Cryer, S., Felgate, S., Brown, P., Carvalho, F., Strong, J., Wood, T., Andrews, G., Rosado, S., Young, A., Goddard-Dwyer, M., Loucaides, S., Sanders, R., and Evans, C.: The role of the Belize River in localised coastal ocean acidification. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4789, https://doi.org/10.5194/egusphere-egu22-4789, 2022.

10:46–10:53
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EGU22-5326
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ECS
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On-site presentation
Emilia Chiapponi, Beatrice M.S. Giambastiani, Denis Zannoni, Marco Antonellini, and Sonia Silvestri

Coastal wetlands play a strategic role in the context of mitigating climate-change thanks to their ability of sequestering large amounts of organic carbon (C) and store it in the ground. However, methane (CH4) may form in the sediments of freshwater wetlands, so that these ecosystems may switch from a net sink to a net source of greenhouse gases (GHGs). Salinity is known to be one of the main inhibitors of CH4 production; however, its influence in brackish water systems is still poorly studied. Our study aims at understanding how the consequences of climate change (sea-level rise, salinization, and temperature increase) may affect the C storage in vegetated coastal wetlands.

Here we present the results of almost one year of measurements performed in four wetlands located along the northeast Adriatic coast near Ravenna, Italy. Despite a very limited distance among the four sites (1-4 km), they present a significant salinity gradient, going from fresh- to brackish waters. Air and soil temperatures and solar irradiance were continuously monitored through a network of sensors. Carbon dioxide (CO2) and CH4 fluxes from soils and waters, water head levels, surface, and ground water physical-chemical parameters (redox potential (Eh), temperature (T), pH, conductivity (EC), sulphate and sulfide concentrations) were measured monthly. Finally, soil samples were collected at each site in order to determine soil properties, i.e. organic matter content, bulk density, granulometry. 

We used multivariate statistics to investigate emergent relationships between GHGs fluxes from water and soil and environmental factors. The results of the principal component analysis (PCA) suggest that air T, water T  and irradiance play a significant role in both CH4 and CO2 emissions from water and soil. On the other hand, water head level and EC have been found to be limiting factors of the GHGs emissions. Soil properties seem to be secondary factors both in soil and water emissions.

The results obtained from these and other analyses will be presented to provide a critical insight on correlations between GHGs emissions and the environmental drivers in temperate coastal wetlands. A remote-sensing approach to upscale the results obtained on the four studied wetlands, to the adjacent coastal wetland system will also be presented. Remote sensing turns out to be a key method to extend the assessment on C fluxes to areas difficult to access and that could not be characterized otherwise.

How to cite: Chiapponi, E., Giambastiani, B. M. S., Zannoni, D., Antonellini, M., and Silvestri, S.: Exploring the driving factors of CH4 and CO2 emissions in coastal wetlands: a case study in the Ravenna Province, Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5326, https://doi.org/10.5194/egusphere-egu22-5326, 2022.

10:53–11:00
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EGU22-7230
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ECS
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Presentation form not yet defined
Guillaume Goodwin, Marco Marani, Luca Carniello, Andrea D'Alpaos, and Sonia Silvestri

Seagrass meadows are a famously productive habitat found globally in intertidal and shallow subtidal shelves, hosting a rich biodiversity and efficiently sequestering carbon. They also exert an influence on coastal morphodynamics by modifying tidal flat roughness and erodibility, affecting sediment dynamics in coastal environments in a way that is not yet fully documented.

Due to their sensitivity to environmental change and anthropogenic pressure, seagrass is prone to widespread die-off, which can be worsened by punctual degradation events such as dredging. Conversely, high primary productivity allows degraded meadows to recover rapidly, as well as expand through clonal and sexual reproduction. This potential for rapid change, however, is not currently matched by the frequency of observations of seagrass meadows, making it difficult to assess the spatial and temporal dynamics of seagrass meadows and their impact on intertidal zones.

Using a novel method combining machine learning and time-series analysis, we extract seasonal maps of seagrass cover in the Southern Venice Lagoon from over 150 Landsat images over the 1999-2021 period and over 100 Sentinel images over the 2017-2021 period. By analysing changes in seagrass distribution over time, we identify seasonal extrema in seagrass surface area and observe their decadal evolution. Furthermore, we record the frequency and magnitude of sudden seagrass die-off events as well as recovery times. From these data we identify regions of preserved root mat, and by coupling seagrass dynamics with additional environmental data such as water temperature, sediment concentration and wave height, propose a set of possible degradation drivers and conditions for seagrass meadow recovery.

With this contribution, we show how high-frequency mapping of seagrass distribution can reveal spatio-temporal dynamics of a highly productive coastal ecosystem, as well as offer keys to their response to environmental change.

How to cite: Goodwin, G., Marani, M., Carniello, L., D'Alpaos, A., and Silvestri, S.: High frequency spatio-temporal dynamics of seagrass meadows in a mediterranean lagoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7230, https://doi.org/10.5194/egusphere-egu22-7230, 2022.

11:00–11:07
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EGU22-8266
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Presentation form not yet defined
Ulf Mallast and the KiSNet - Königshafen Submarine Groundwater Discharge Network

Submarine groundwater discharge (SGD) as a pathway for water and elements between land and ocean is a rather young topic and was for a long time neglected by the scientific community and coastal managers. However, the subject has increasingly attracted attention since the turn of the millennium. In this emerging field, measurement techniques and quantification methods strongly depend on individual research groups, but the high spatio-temporal variability of SGD, in general, leads to low confidence in its estimates at a regional scale.

The Königshafen Submarine Groundwater Discharge Network (KiSNet) seeks to form an interdisciplinary group of SGD experts to initiate and intensify collaborative ties across research groups. The aim is to bring together various methods from all disciplines to a common enclosed study area, Königshafen bay in Sylt, Germany. The strategy of measuring simultaneously results in a) a reliable groundwater picture of the bay, but also b) the possibility to suggest optimal combinations for qualitative and quantitative SGD methods that may serve as basis for a future more standardized SGD research.

Here we present first results from remote sensing, marine and terrestrial ground-based geophysics, seepage meters, temperature rods, natural tracers, numerical simulation from terrestrial and marine disciplines, and outline a preliminary concept of synergetic method combinations.

How to cite: Mallast, U. and the KiSNet - Königshafen Submarine Groundwater Discharge Network: Königshafen Submarine Groundwater Discharge Network (KiSNet) - first monitoring results from a multi-sensor and multidisciplinary approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8266, https://doi.org/10.5194/egusphere-egu22-8266, 2022.

11:07–11:14
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EGU22-8929
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ECS
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Virtual presentation
Zhicheng Yang, Davide Tognin, Enrica Belluco, Alice Puppin, Alvise Finotello, Sonia Silvestri, Marco Marani, and Andrea D’Alpaos

Salt marshes are coastal ecosystems of high importance from ecological and geomorphological perspectives which have been disappearing fastin thelast centuries. Halophytic vegetation can support marsh survival through complex ecomorphic feedbacks. A better understanding of vegetation distribution and related variations in response to environmental changes is of central importance to analyze marsh evolution. Towards this goal, we analyzed the vegetation-elevation relationship in a microtidal marsh  in the Venice Lagoon (the San Felice marsh) by coupling in-situ measurements in different years (between 2000 and 2019) and multi-spectral and Light Detection and Ranging (LIDAR) data. The vertical distribution of above-ground biomass (AGB) was also analyzed by using NDVI and an empirically estimated AGB (eAGB). Our results suggest that: 1) the known species sequence with increasing elevations maintained constant over the monitored period and at the whole marsh scale, although the overall increase in relative sea level rise altered the relative vertical position of each species; 2) the in-situ observed species sequence is found to be reliable and consistent at the whole marsh scale; 3) AGB increases with marsh elevation, values of NDVI and eAGB being generally higher in higher marsh portions. We also observed the dieback event of Spartina and the invasion of Salicornia in the San Felice marsh. All these results bear important implications for future marsh eco-morphodynamic analyses concerning landscapes populated by multiple vegetation species.

How to cite: Yang, Z., Tognin, D., Belluco, E., Puppin, A., Finotello, A., Silvestri, S., Marani, M., and D’Alpaos, A.: The vegetation-elevation relationship in salt marshes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8929, https://doi.org/10.5194/egusphere-egu22-8929, 2022.

11:14–11:21
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EGU22-9687
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ECS
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Virtual presentation
Regine Anne Faelga, Beatrice Maria Sole Giambastiani, and Luigi Cantelli

Nowadays Unmanned Aerial Vehicle (UAV) is one of the most utilized tools in the field of coastal geomorphology studies due to its efficiency and cost-effectiveness to carry out high-spatial and temporal resolution topographic surveys. The images produced by UAV surveys can be processed using Structure from Motion (SfM) photogrammetry, which allows 3D reconstruction of the terrain from the series of overlapping images. This research aimed to utilize UAV topographic surveys to characterize the geomorphological evolution of a portion of the dune belt that was subjected to a restoration in 2016. The study site is located in the protected natural area of the Bevano River mouth in Ravenna, (Northern Adriatic Coast, Italy). The reinforcement of the dune system was initiated since the zone is primarily characterized as a low-lying coastal area and is subjected to increasing environmental risks, such as coastal erosion, storm surge, groundwater and soil salinization. The restoration measure included two windbreak wooden fences, which were installed in front of the dune foot and parallel to the coast to stop wind and facilitate sand deposition and accumulation, to favor embryo dune formation and prevent sand loss toward the inland, out of the sedimentary cell. UAV topographic survey, coupled with GPS ground survey using Real-time Kinematic (RTK) positioning, were carried out from 2016 to 2021 in order to assess the geomorphological evolution of the area over time. SfM photogrammetry was carried out to generate the point cloud and orthomosaic images for each survey year using Agisoft Metashape Professional. Point cloud data were interpolated in ArcMap to create Digital Elevation Models (DEMs), while the orthomosaic images were utilized to confirm the possible sources of data noise in the model and assess vegetation changes. The collected GPS data points, including Ground Control Points (GCPs) and several dune profiles, were used to validate the DEMs. Then, the volumetric changes in sediment storage over time were calculated by using the DEM of Difference (DoD) approach under the Geomorphic Change Detection (GCD) extension toolbar in ArcMap. Probabilistic thresholding was used as the uncertainty analysis method for the volume calculation. The changes in dune height and slope were assessed using both the GCD and 2D profiler toolbar as well. The results show that the windbreak fence has proven to be an effective intervention to prevent dune erosion since significant geomorphological changes and vegetation colonization have occurred. Based on volume calculations, main sand accumulation was observed along the dune foot where the fences were established. The sand deposition has also reduced the slope steepness of the dune and some profiles exhibit embryo dune development. Erosion has only been evident in the northern beach portion towards the end of the fence. An increase in both pioneer species and stabilizing plants were also noticed on the dune front and crest, respectively.

How to cite: Faelga, R. A., Giambastiani, B. M. S., and Cantelli, L.: Using UAV topographic surveys for monitoring geomorphological evolution and restoration of the dune belt in Ravenna (Northern Adriatic Coast, Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9687, https://doi.org/10.5194/egusphere-egu22-9687, 2022.

11:21–11:28
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EGU22-12725
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Virtual presentation
Inga Monika Koszalka, Foucaut Tachon, and Agnes ML Karlson

Algae blooms, specifically cyanobacterial blooms, are frequent in the Baltic Sea and pose major environmental problems for the marine ecosystem and coastal societies. Surface accumulations of algae exacebate eutrophication, limit access to oxygen and can be toxic to humans and marine life. They affect marine services including drinking water resources, marine operations, tourism and fishing. Monitoring of algae blooms based on satellite-borne and in-situ data have been ongoing for years. However, a proper assessment of monitoring needs to cover complex spatio-temporal variability of the blooms as well as reliable early warning and forecasts systems are still lacking, owing to the complexity of physical and biological processes involved in algae growth and too sparse data to constrain complex marine ecosystem models. As algal blooms are expected to intensify under the observed long-term warming of surface waters, developing relevant monitoring-early warning systems is a priority.

Our interdisciplinary collaboration aims at a tantalizing task of building a framework tailored for monitoring and forecasting of algae blooms in the Baltic Sea. The framework combines surface drift observations, in-situ observations, remotely-sensed chlorophyll products as well as numerical simulations of Lagrangian (drifting) trajectories driven by the ocean state forecast available at the Copernicus Marine Environment Monitoring Service (CMEMS). The first step toward this goal consisted of collecting observations of the surface drift in the Baltic Sea relevant to the dispersion of algae accumulations. To this end, we deployed 6 CARTHE Smart surface drifter platforms in Western Gotland Basin in August 2021. The CARTHE drifter platforms are designed to sample sea currents close to the surface compared to other standard drift measurements, provide a very accurate positioning data at 15 minute intervals, and their floating parts are biodegradable. We will present data from this experiment as well the results from a comparison between the observed surface drift and CMEMS-driven Lagrangian simulations. The results using relative dispersion statistics point to a good skill of the model-driven drift forecast (a few km error in mean dispersion over a two day scale). We extend the analysis including Lagrangian ecosystem modelling, spectral analysis and clustering approaches, taking into the consideration sparseness of in-situ data.

How to cite: Koszalka, I. M., Tachon, F., and Karlson, A. M.: A new observational-modelling framework for algae bloom monitoring and forecast in the Baltic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12725, https://doi.org/10.5194/egusphere-egu22-12725, 2022.

11:28–11:35
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EGU22-13460
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Virtual presentation
Tom Hull, Naomi Greenwood, Ben Loveday, Tim Symth, Mathew Palmer, Charlotte Williams, and Jan Kaiser

The coastal shelf seas are a vitally important human resource for numerous ecosystem services, including food, carbon
storage, biodiversity, energy, and livelihoods. These highly dynamic regions are under a wide range of stresses, and
as such future management requires appropriate monitoring measures.  

A key metric to understanding and predicting future ecosystem change are the rates of biological production. Assessing
the variability in production at appropriate temporal and spatial scales is essential to accurately determine the fate
of carbon, and ecosystem health in these regions.  

Using high frequency data from a fleet of instrumented submersible gliders, we calculate oxygen based net community
production for an 18-month period in the central North Sea; a productivity hotspot and challenging environment for
long term monitoring with autonomous vehicles.
From these data we determine an annual depth integrated carbon budget, and we observe both the interannual and
seasonal changes in production.  

We compare these net community production estimates to the PAR and chlorophyll fluorescence based net primary
production estimates using the same glider fleet and supported by satellite earth observations. 

These observations and analysis are part of the AlterEco project, which seeks to demonstrate a novel monitoring
framework to deliver improved understanding of key shelf sea ecosystem drivers. 

How to cite: Hull, T., Greenwood, N., Loveday, B., Symth, T., Palmer, M., Williams, C., and Kaiser, J.: AlterEco: Annual shelf sea net production from a fleet of autonomous gliders , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13460, https://doi.org/10.5194/egusphere-egu22-13460, 2022.

11:35–11:42
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EGU22-12823
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ECS
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Virtual presentation
Aida Beye, Eric Machu, and Luis Felipe Artigas

Abstract

The Senegalese coastal and shelf systems comprises a southern part of the Canary Islands upwelling system. The present study focuses on the study of phytoplankton from meso- to submesoscale during the transition period from the warm West African monsoon season to the cold upwelling season. This period coincides with the return of sardinella from their northward migration to its second most important spawning area resulting in a high retention on the southern coast, as well as possible events of the Senegalese fishermen's skin disease (as it was the case in November 2020). This is a very poorly documented period. The last studies allowing the study of the phytoplankton compartment date from the 1980s. Several data on phytoplankton were collected during the period from 29 November to 02 December 2017 for addressing phytoplankton distribution and dynamics: pigmentary data, microscopic counts, metabarcoding analysis of plankton diversity, single-cell analysis and characterization of optical groups by automated (in vivo) flow cytometry (CytoSen) as well as in vivo characterization of spectral/pigmentary groups by multispectral fluorometry (Fluoroprobe). Environmental data was supplied by CTD RBR concerto and the analysis of several physical and chemical parameters. In particular, FluoroProbe continuous subsurface measurements and profiles made it possible to considerably improve the spatial and temporal resolution of measurements and the dynamics of phytoplankton groups at submesoscale. Moreover, it was possible to follow spatial and temporal changes in the phytoplankton community, particularly at stations sampled twice at few days interval. Many unknown species characterized this period, especially in the nanophytoplankton size range. Distinct communities were found in the upwelling on the coastal fringe and in the old waters offshore, as shown by multispectral analysis. Phytoplankton blooms were observed, some of which being caused by the upwelling of cold water, but intermittently and weakly. In some stations, toxic species were found, such as species belonging to the genus Pseudo-Nitzschia.

 

Keywords: Upwelling, multi-spectral fluorometry, CTD, automated flow cytometry, metabarcoding, microscopy, phytoplankton diversity and dynamics.

How to cite: Beye, A., Machu, E., and Artigas, L. F.: Meso and submesoscale study of the phytoplankton compartment over part of the southern Canary Islands system during the transition period between the warm West African monsoon season and the cold upwelling season, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12823, https://doi.org/10.5194/egusphere-egu22-12823, 2022.

11:42–11:49
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EGU22-7492
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ECS
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Highlight
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On-site presentation
Jonas Fredriksson, Volker Brüchert, Karl Attard, and Christian Stranne

Coastal benthic hypoxia and anoxia develop in thermally stratified coastal waters during warm summer months. They alter the chemical composition, biogeochemical cycling, and ecosystem functioning at the seafloor and can render the benthic habitat uninhabitable for higher life forms. With more and longer heatwaves expected due to global warming, the strength and persistence of stratification is expected to increase leading to longer and more extensive bottom water hypoxia in the coastal ocean. However, on short timescales benthic oxygen availability can be dominated by highly dynamic lateral transport and transient vertical mixing events that can compensate for the sediment oxygen demand through short-term ventilation events. The occurrence, temporal dynamics, and quantitative impacts of these ventilation events have so far been poorly understood.

We present results of a two-week summer field campaign at a 38 m deep thermally stratified  coastal site in the western Baltic Sea. An autonomously operating benthic lander system equipped with stationary oxygen optodes at fixed depths, a continuously profiling multiparameter probe, a high-frequency downward-looking ADCP was deployed together with an eddy correlation system, within 50 meters distance. The setup enabled the study of the vertically resolved temporal evolution of oxygen in relation to hydrodynamic parameters in the bottom waters at a second- and centimetre-scale resolution for a 280-hour long deployment period together with continuous measurements of the benthic oxygen consumption. At the beginning of the deployment bottom-water free-flow velocities were on average 1.6 cm/s consisting of a translatory and a rotating diurnal oscillatory component. Weakening of the translatory current component gradually turned the system into an almost pure oscillatory state with free-flow velocities of about 0.8 cm/s. Bottom-water oxygen concentrations were constant down to 5 cm above the sediment at an initial normoxic concentration of 170 μmol l-1 that decreased with decreasing flow velocity to hypoxia below 63 µmol l-1 by the end of the measurement series. During purely oscillatory flow the balance between sediment oxygen uptake and vertical transport resulted in a net bottom water oxygen loss of 6.4 μmol l-1d-1 increasing to -14.5 μmol l-1d-1 following a resuspension event. Even at low-flow velocities the bottom water remained well mixed. Bottom water oxygen loss was not continuous and instead varied between +43.5 and -45.2 μmol l-1d-1 corresponding to changes in lateral transport. Temporary changes (<2 hours) up to 30 μmol l-1 were found due to convergence/divergence events of the bottom water during flow reversals.

These dynamic bottom water changes would have been undetectable using conventional shipboard tools due to their close proximity to the sea floor. We suggest that areas undergoing frequent hidden hypoxia and re-ventilation are more common than previously thought and have so far unexplored effects for benthic ecosystem functioning.

How to cite: Fredriksson, J., Brüchert, V., Attard, K., and Stranne, C.: Hidden Hypoxia in Coastal Waters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7492, https://doi.org/10.5194/egusphere-egu22-7492, 2022.

Lunch break
Chairpersons: Katarzyna Koziorowska-Makuch, Craig Smeaton
15:10–15:17
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EGU22-4012
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ECS
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On-site presentation
Dunia Rios-Yunes, Justin C. Tiano, Dick van Oevelen, Jeroen van Dalen, and Karline Soetaert

Estuarine systems filter nutrients and organic matter from riverine input and lower concentrations reaching the sea. Sediments within these ecosystems play a significant role in the mineralization and retention of nutrients and organic matter within the estuary. Such processes are influenced by abiotic (e.g. salinity, temperature, etc.) and biological (e.g. fluctuations in the benthic community) parameters which may contrast remarkably between intertidal or subtidal zones. Despite their relative importance, few studies have investigated the biogeochemistry of intertidal sediments with high spatiotemporal resolution. This study reports the results of monthly biogeochemical monitoring in intertidal muddy sediments along the salinity gradient of the Western Scheldt estuary (NL). Budgets of OM mineralization and nutrient retention were calculated for the fresh, brackish, and marine water zones. Temperature controlled sediment oxygen consumption rates and nutrient fluxes. Fresh and brackish sediments had a net influx of dissolved inorganic nitrogen (DIN) (-1.62 mmol DIN m-2 d-1 and -2.84 mmol DIN m-2 d-1, respectively), while the freshwater area had the only net influx of phosphate (-0.07 mmol m-2 d-1). Marine sediments showed net effluxes of DIN and DIP. Despite the net influx observed in freshwater sediments, geospatial analysis showed that their contribution to the total estuarine filtering capacity was minimal due to their small area. In contrast, brackish and marine regions had a more important contribution to the estuarine filter because of their larger surface area. Overall, sediments removed 11% (1,500 t N y-1) and 15% (~200 t P y-1) of the total nitrogen and phosphorus entering the estuary from riverine input. Our findings highlight the importance of using spatially-resolving remineralization budgets to improve models and nutrient cycling estimates in estuarine systems.

How to cite: Rios-Yunes, D., Tiano, J. C., van Oevelen, D., van Dalen, J., and Soetaert, K.: Intertidal sediments exhibit different nutrient filtration capacity along the estuarine salinity gradient, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4012, https://doi.org/10.5194/egusphere-egu22-4012, 2022.

15:17–15:24
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EGU22-5152
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ECS
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Virtual presentation
William Hiles, Craig Smeaton, and William Austin

Globally, fjords are recognised as hotspots for the burial and storage of organic carbon (OC). The role of fjords as nationally and globally important carbon sinks is now well established, yet the long-term drivers and evolution of OC burial and storage in these coastal systems remains largely unknown. The location of fjords at the land-ocean interface in combination with their geomorphology results in a large proportion of the OC that is trapped in their sediments deriving from the terrestrial environment, yet the processes driving the delivery of terrestrial carbon into fjords over long timescales is often poorly constrained. In order to better understand these important processes, an understanding of terrestrial landscape change in conjunction with sedimentological data for carbon storage is required. Understanding the drivers of the carbon transfer at the land-ocean interface throughout the mid- to late-Holocene can provide insights into the sensitivity of catchments to climatic and anthropogenic pressure, which will be crucial to predicting future carbon loss, burial and storage scenarios across the land-ocean interface.

We present a new multiproxy palaeoenvironmental dataset developed from a core from Loch Eriboll, a large fjord in northern Scotland, spanning the last 5,000 years. Pollen data, taken to represent catchment-scale vegetation change, is used to investigate landscape change in response to natural and anthropogenic forcing mechanisms. Sedimentological and geochemical data are then used to reconstruct changes in the delivery of carbon into the fjord system via soil erosion. Comparison of two age models, developed from bulk radiocarbon dating and dating of shells, respectively, provide data on the relative age of carbon being reworked from the terrestrial system into the fjord.

We present evidence for links between the terrestrial and fjord systems throughout the mid to late Holocene. Throughout the record is a consistent radiocarbon age offset of approximately 800 years in the bulk data, and increases in this offset coincide with marked changes in the terrestrial vegetation on three discrete occasions: a significant reduction in Pinus, an increase in herbaceous pollen, and an expansion of heathland pollen. Complemented by a suite of geochemical proxies, including inorganic and organic geochemical signatures, these datasets provide insights into the sensitivity of fjordic systems to changes in the adjacent terrestrial system on centennial timescales.

How to cite: Hiles, W., Smeaton, C., and Austin, W.: Long-term carbon transfers at the land-ocean interface: evidence from Loch Eriboll, northern Scotland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5152, https://doi.org/10.5194/egusphere-egu22-5152, 2022.

15:24–15:31
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EGU22-3723
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ECS
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On-site presentation
Pierre Chabert, Xavier Capet, Vincent Echevin, and Alban Lazar

In addition to the wind seasonal cycle, Eastern Boundary Upwelling Systems undergo intraseasonal fluctuations. These synoptic fluctuations are characterized by an intensification or a relaxation of upwelling favorable winds of a period of about 10 days and are believed to have a major impact on the upwelling dynamics. Here we focus on the South Senegalese Upwelling System (SSUS) which is located south of the sharp Cape Verde peninsula which acts as an abrupt coastline break and has a particularly shallow continental shelf. Previous studies described not only the SSUS climatological dynamics but also the importance of synoptic events that play a major role in the observed variability. However, their precise impacts on the 3D dynamics on the shelf remain unclear and consequences on biogeochemistry are unknown. We identify the key dynamical and biogeochemical processes of the coastal ocean in its response to synoptic events. This is done using a modeling experiment that consists in applying idealized synoptic wind intensification and relaxation to climatological SSUS states (with CROCO-PISCES). We find that synoptic fluctuations affect the regional circulation and shape robust anomalies of temperature, boundary layer depth, sea surface height,  surface and subsurface currents. Nutrients supply in the euphotic layer is significantly affected by synoptic fluctuations (+-30%). We find asymmetrical responses in nitrate, iron and silicate concentrations both between intensification and relaxation and between the inner and outer shelf regions. Persistent nitrate depletion is observed over the inner shelf. Phytoplanktonic ecosystem response to synoptic wind intensification thus differs spatially, with enhanced development of diatoms over the outer shelf and of nanophytoplankton over the inner shelf. Consequences on the zooplanktonic ecosystem are observed with a time delay and space shift, consistent with typical prey - predator relationships. Processes at play in the nutrients supply and planktonic ecosystem structure in response to synoptic fluctuations are discussed. 

How to cite: Chabert, P., Capet, X., Echevin, V., and Lazar, A.: Dynamical and biogeochemical responses of the South Senegalese Upwelling System to synoptic wind variability: a modeling approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3723, https://doi.org/10.5194/egusphere-egu22-3723, 2022.

15:31–15:38
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EGU22-3999
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ECS
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On-site presentation
Mareike Paul, Martijn Hermans, Sami A. Jokinen, Inda Brinkmann, Helena L. Filipsson, and Tom Jilbert

Sedimentary molybdenum (Mo) and uranium (U) enrichments are often used as redox proxies to reconstruct bottom water redox changes. However, the reliability of these redox proxies may be compromised by secondary depositional environmental factors, such as the depth of the sulfide front in porewaters. Fjords vary greatly in their depositional environments due to their unique bathymetry and hydrography, and they are highly vulnerable to anthropogenic and climatic pressures. Currently, it is unknown how Mo and U sequestration is affected by variable depositional conditions in fjords. Here, we aim to improve the reliability of Mo and U redox proxies in such systems by comparing two silled fjords on the Swedish West coast with contrasting depositional environments and bottom water redox conditions. We use a sequential extraction method designed for sedimentary trace metals and pore water data, to improve the understanding of Mo and U enrichment pathways in fjord sediments. Our data suggest that sedimentary authigenic Mo and U pools differ between the two fjords. In the seasonally hypoxic Gullmar Fjord, Mo largely binds to manganese (Mn) oxides and to a lesser extent to iron (Fe) oxides; Mo sulfides do not play a major role due to low sulfate reduction rates. U largely resides in labile carbonates and residual phases. Overall enrichment factors (EF) of both elements (relative to upper continental crustal values, UCC) are close to 1, implying minimal authigenic enrichment despite low-oxygen conditions. In the seasonally euxinic Koljö Fjord, Mo is significantly enriched relative to UCC (EF: 20.2-78.5) due to binding with more refractory organic matter complexes, thiomolybdates, and to a lesser extent to pyrites. U is also moderately enriched (EF: 1.9-5.4) and largely resides in refractory carbonates and organic matter complexes. Our data demonstrate that the pore water redox zonation (i.e., the sulfide front), and the rate of shuttling of carrier oxide phases, control the efficiency of Mo and U sequestration in seasonally hypoxic and euxinic fjords to such an extent that enrichments do not systematically record bottom water redox conditions. These results may help to explain the large variability in trace metal enrichments observed across sites of similar bottom water redox conditions.

How to cite: Paul, M., Hermans, M., Jokinen, S. A., Brinkmann, I., Filipsson, H. L., and Jilbert, T.: Sedimentary molybdenum and uranium sequestration in silled fjords on the Swedish West coast: implications for trace-metal based paleo redox proxies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3999, https://doi.org/10.5194/egusphere-egu22-3999, 2022.

15:38–15:45
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EGU22-4133
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Virtual presentation
Yue Ming

The flocculation, triggered during estuarine mixing and having an important role on land-to-sea interactions, is a fundamental issue in near-shore oceanographic studies. Identifying the in situ flocculation in large-river estuaries is quite a challenging work, because of the complex seawater circulation and heterogeneous SPM composition in those areas. In this study, three cruises were conducted in the Changjiang (Yangtze) River Estuary and the adjacent area in March, May, and July 2016. Vertical profiles of suspended particulate matter (SPM) total volume, mean size, and size spectra were determined using laser in situ scattering and transmissometry (LISST) measurements at 66–89 stations during the three cruises. Stable isotopic ratios of δ13C were also measured in the organic carbon contents of SPM collected at the surface, middle, and bottom layers of the sampling stations. The LISST data were used to successfully identify flocculation occurring in the field as well as to trace SPM size spectrum changes before and after the flocculation process. The δ13C values were utilized to study the response of biogeochemical parameters to the flocculation. Phytoplankton blooms occurring in May largely resulted in the discontinuous variations of LISST parameters and δ13C from March to July. Although SPM size spectra involved in flocculation showed different patterns in different seasons, however, the flocculation processes were always contributed by smaller particles with sizes of several tens of µm aggregating into larger ones > 300 µm. Using LISST and δ13C measurements together greatly improves our understanding of SPM dynamics in estuarine and coastal areas, in which estuarine flocculation is a critical component.

How to cite: Ming, Y.: Identification of flocculation during large-river estuarine mixing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4133, https://doi.org/10.5194/egusphere-egu22-4133, 2022.

15:45–15:52
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EGU22-4174
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Virtual presentation
Mengyu Wang

Four research cruises were carried out during March and July in 2015 and 2016 in the Changjiang (Yangtze) River Estuary and the adjacent shelf. Nutrient concentrations (regarded as static parameters) were measured in the surface and bottom waters collected at 86–99 stations over the course of these cruises. In addition, unfiltered seawater samples were incubated onboard for 48 h to measure the potential change rates of nutrients (regarded as dynamic parameters). These parameters can help directly elucidate non-conservative behaviors of nutrients in order to determine whether seawater serves as a source or a sink. Large nutrient sinks (with more negative variation rates) were consistently found at the surface during the two July cruises at the stations just along the outside edge of the turbidity maximum zone near the mouth of the river. Negative rates, although with much smaller magnitudes, were also found in most bottom water samples in July and at both the surface and bottom in March. The high net nutrient uptake rates at the surface in the summer triggered bloom events later at the seaward stations, showing that high net nutrient uptake is the cause and high chlorophyll-a is the consequence of the bloom. Such information about biogeochemical cycling of nutrients and the mechanisms and development of bloom events occurring in large river estuarine and coastal areas could not have been obtained if these static and dynamic parameters had not been studied together.

How to cite: Wang, M.: New insights into the non-conservative behaviors of nutrients triggering phytoplankton blooms in the Changjiang (Yangtze) River Estuary., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4174, https://doi.org/10.5194/egusphere-egu22-4174, 2022.

15:52–15:59
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EGU22-4666
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ECS
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Presentation form not yet defined
Martin Vodopivec, Filip Strnisa, and Gregor Kosec

With more than 50 variables, the Biogeochemical Flux Model (BFM) is one of the most advanced and complex marine biogeochemical models available. In addition to several phytoplankton and zooplankton groups, it also includes bacterioplankton, and its modular structure allows for the relatively straightforward addition of new plankton functional types (PFT). The BFM is used in the Copernicus Marine Service products for the Mediterranean Sea and these should provide ideal initial and boundary conditions for more detailed regional studies. Here we present the coupling of the BFM with the Coastal and Regional Ocean COmmunity model (CROCO; based on ROMS_AGRIF and SNH). The latter is a non-hydrostatic, terrain-following, free-surface ocean model with a highly efficient time-stepping algorithm, making it very suitable for high-resolution simulations and topographies with a wide range of depths. The models are directly coupled without an intermediate coupler and can be executed in parallel via Message Passing Interface (MPI). We present the results of an idealized case and these are in a good agreement with a similar configuration of a coupled MITgcm-BFM run (Cossarini et al., 2017). Not surprisingly, the coupled system CROCO-BFM proves to be computationally intensive given the large number of variables, and we explore different speed-up possibilities.

How to cite: Vodopivec, M., Strnisa, F., and Kosec, G.: Coupling the Coastal and Regional Ocean COmmunity model (CROCO) with the Biogeochemical Flux Model (BFM), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4666, https://doi.org/10.5194/egusphere-egu22-4666, 2022.

15:59–16:06
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EGU22-5273
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ECS
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Presentation form not yet defined
Elisa Lovecchio, Stephanie Henson, Filipa Carvalho, and Nathan Briggs

The northern Benguela Upwelling System is characterized by significant oxygen and particle anomalies due to the lateral influx of both oxygenated water from the south and low-oxygen water that flows south across the northern Angola-Benguela front (ABF). Mesoscale features developing at the front and in the shelf region of the upwelling system further modulate these anomalies. Here we present the results of a study based on high-resolution glider data collected from the surface to 1000 m depth in February – June 2018 at 100 km off the coast of the northern Benguela (18°S). These in-situ data are further interpreted and generalized using high-resolution model output from the physical Regional Ocean Modeling System (ROMS) coupled to the Biogeochemical Ecosystem Cycling (BEC) model. Using the glider data, we discuss the prevalence of low oxygen events characterized by O2 < 120 µmol (sub-lethal level), O2 < 60 µmol (hypoxia) and O2 < 30 µmol (severe hypoxia) as a function of depth and time. We present two different impacts of eddies on oxygen concentrations: extreme hypoxia associated to a subsurface anticyclone generated at the Benguela shelf, and mixing between high and low oxygen water at the rim of a large surface anticyclone generated at the ABF. Through a spike analysis of the glider data, we study the distribution of large and small particles as a function of depth and time, and relate them to the identified mesoscale structures. We find that the subsurface eddy corresponds to a local low in small particle concentrations, while the frontal anticyclone is associated to a deep export event of both small and large particles. Further, we find that the region is characterized by a deep particle layer between 300 m and 500 m. Using the model output, we identify the drivers of this deep particle layer and deep export events and discuss the relative role of physics and biology in the determination of the vertical distribution of particles in the region of study.

How to cite: Lovecchio, E., Henson, S., Carvalho, F., and Briggs, N.: Meso and submesoscale oxygen and particle variability in the northern Benguela Upwelling System from glider and model data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5273, https://doi.org/10.5194/egusphere-egu22-5273, 2022.

16:06–16:13
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EGU22-5776
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ECS
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On-site presentation
Katarzyna Koziorowska-Makuch, Beata Szymczycha, Helmuth Thomas, and Karol Kuliński

The spatial variability in hydrography (salinity and temperature) and carbonate chemistry (alkalinity - AT, total inorganic carbon concentration - CT, pH, CO2 partial pressure - pCO2, and the saturation state of aragonite - ΩAr) in high meltwater season (summer) was investigated in four Spitsbergen fjords - Krossfjorden, Kongsfjorden, Isfjorden, and Hornsund. It was found that the differences in hydrology entail spatial changes in the CO2 system structure. AT decline with decreasing salinity was evident, however, this relationship was highly heterogenous. Significant surface water AT variability (1889-2261 µmol kg-1) suggests multiple freshwater sources having different alkalinity end-member values and biological processes occurring in the water column. Most of the AT values were within the dilution lines of Ocean Water with freshwater having alkalinity from 0 to ~600 μmol kg-1. However, the distribution of AT against salinity suggests that locally the freshwater A maybe even higher. The effect of AT fluxes from sediments on the bottom water was rather insignificant, despite high AT values (2288-2666 μmol kg-1) observed in the pore waters. Low pCO2 results in surface water (200-295 μatm) points to intensive biological production, which can strongly affect the CT values, however, is less important for shaping alkalinity. It has also been shown that the freshening of the surface water in the fjords reduces significantly ΩAr (an increase in freshwater fraction contribution by 1% causes a decrease in ΩAr by 0.022). Although during the polar day, due to low pCO2, ΩAr values are still rather far from 1 (they ranged from 1.4 to 2.5), during polar night, when pCO2 values are much higher, ΩAr may drop markedly.

This study highlights that the use of salinity to estimate the potential alkalinity can carry a high uncertainty, while good recognition of the surface water AT variability and its freshwater end-members is key to predict marine CO2 system changes along with the ongoing freshening of fjords waters due to climate warming.

How to cite: Koziorowska-Makuch, K., Szymczycha, B., Thomas, H., and Kuliński, K.: The effect of seawater freshening on the marine carbonate system variability in the high Arctic fjords, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5776, https://doi.org/10.5194/egusphere-egu22-5776, 2022.

16:13–16:20
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EGU22-5922
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ECS
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Virtual presentation
Uliana Kazakova, Alexander Polukhin, Anna Kostyleva, Julia Pronina, Evgeniy Yakushev, and Alexander Osadchiev

A large volume of river runoff influences the Kara Sea annually. The water masses coming from estuaries form a surface desalinated layer, which propagates under the influence of the wind forcing. A water during the melting of sea ice contributes to the desalination of the surface layer as well. At the end of the summer period of 2021, the presence of ice cover was observed in the northern and northeastern parts of the Kara Sea. The hydrological regime of rivers at the end of the summer period is characterized by a decrease in water consumption and, accordingly, a small volume of incoming river runoff.

Together with the fresh waters of the Ob, Yenisei and other rivers, various nutrients are transported into the sea. A part of nutrients is deposited in the estuaries of the Ob and Yenisei gulfs within the frontal zone. The other part is carried out to the open sea and serves as the basis for the activity of marine organisms in coastal ecosystems. The observed climatic changes in the Arctic affect the change in the distribution of parameters of the carbonate system, which, in turn, affects the marine ecosystem.

The main purpose of the work is to analyze the temporal and spatial variability of the hydrochemical structure and carbonate parameters at the end of the summer period of 2021.

The work uses the data obtained during the 58th cruise of the RV "Academik Ioffe" in august 2021 and the 86th cruise of the RV "Academik Mstislav Keldysh" to the Kara Sea in October 2021. The hydrochemical parameters that were determined included biogenic elements, dissolved oxygen, pH of hydrogen, alkalinity and components of the carbonate system.

Several groups of parameters are identified depending on the nature of the distribution of biogeochemical values in the water column of the Kara Sea. These groups include parameters that clearly mark the influence of river runoff, parameters in the distribution of which extremes in the frontal zone are distinguished, and parameters characterized by heterogeneity of distribution in the zone of mixing of fresh and marine waters.

The hydrochemical structure was characterized by great temporal and spatial variability associated with the influence of hydrological, meteorological and hydrobiological factors.

The temporal variability of biogeochemical parameters at the end of the summer period is considered. The change in the hydrogen pH index during the period under review is characterized by a decrease in the range of values. In august, the pH varied in the range of 7.5-8.5, in November - from 7.5 to 7.9. The partial pressure of carbon dioxide in August ranged from 136 ppm to 1260 ppm, in October - from 267 ppm to 850 ppm. The aragonite saturation varies from 0.07 to 2.4 in august and 0.2-1.75 in November.

The research is implemented in the framework of the state assignment of the Shirshov Institute of Oceanology (theme No. 0128-2021-0007), with the support of the Russian Scientific Foundation (project № 19-17-00196) and the grant of the President of Russian Federation № МК-3506.2022.1.5

How to cite: Kazakova, U., Polukhin, A., Kostyleva, A., Pronina, J., Yakushev, E., and Osadchiev, A.: INFLUENCE OF THE CONTINENTAL RUNOFF ON THE BIOGEOCHEMICAL STRUCTURE OF THE KARA SEA SURFACE LAYER in 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5922, https://doi.org/10.5194/egusphere-egu22-5922, 2022.

16:20–16:27
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EGU22-5936
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ECS
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Presentation form not yet defined
David González-Santana, J. Magdalena Santana-Casiano, Quentin Devresse, Helmke Hepach, Carolina Santana-González, Birgit Quack, Anja Engel, and Melchor González-Dávila

Iron is an essential nutrient that limits primary productivity in up to 30% of the world’s ocean. Redox and complexation reactions control its solubility and therefore the fraction of dissolved and bioavailable iron. The iron (II) oxidation kinetic process was studied at 25 stations in coastal seawater of the Macaronesia region (around Cape Verde, the Canary Islands and Madeira). Laboratory experiments were carried out to study the pseudo-first-order oxidation rate constant (k’, min-1) over a range of pH (7.8-8.1) and temperature (T; 10-25ºC). Measured k’ varied from the calculated k’ (k'cal) at the same T, pH and salinity (S) at most stations. Measured iron (II) half-life times (t1/2=ln2/k’; min) at the 25 stations ranged from 1.8-3.5 min (mean 1.9±0.8 min) and for all but two stations were lower than the theoretically calculated t1/2 of 3.2±0.2 min. The biogeochemical context was considered by analysing nutrients and variables associated with the organic matter spectral properties (CDOM and FDOM). A multilinear regression model indicated that k’ can be described (R=0.921, SEE=0.064 for pH=8 and T=25ºC) from a linear combination of three organic variables.

k’OM = k’cal -0.11* TDN + 29.9 * bDOM + 33.4 * C1humic

where TDN is the total dissolved nitrogen, bDOM is the spectral peak obtained from coloured DOM analysis when protein-like or tyrosine-like components are present and C1humic is the component associated with humic-like compounds obtained from the parallel factor analysis (PARAFAC) of the fluorescent DOM. Experimentally, k’ and kOM provide the net result between the compounds that accelerate the process and those that slow it down. Results show that compounds with nitrogen in their structures mainly explain the observed k’ increase for most of the samples, although other components could also present a relevant role.

How to cite: González-Santana, D., Santana-Casiano, J. M., Devresse, Q., Hepach, H., Santana-González, C., Quack, B., Engel, A., and González-Dávila, M.: The organic matter effect on Fe(II) oxidation kinetics within coastal seawater, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5936, https://doi.org/10.5194/egusphere-egu22-5936, 2022.

16:27–16:34
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EGU22-6425
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ECS
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Virtual presentation
Nadine Lehmann, Markus Kienast, Claire Normandeau, Peter Thamer, and Carolyn Buchwald

The northwestern North Atlantic, and the extensive Northwest Atlantic Shelf in particular, are among the areas of the world’s ocean most dramatically affected by ongoing climate change. Profound alterations of nitrogen (N) cycling both in the water column and in the sediment are expected in response to rapidly changing ocean and biogeochemical conditions. Despite the importance of bioavailable nitrogen in shaping this marine environment and ultimately sustaining large commercial fisheries, significant uncertainties remain regarding the main sources and sinks of this key macronutrient.

In this study, we use hydrographic data (T, S, O2) and nutrient concentrations collected during the Atlantic Zone Monitoring Program (AZMP) in an extended Optimum Multiparameter Analysis (eOMPA) to quantify the fractional contribution of nearshore versus slope waters on the Scotian Shelf. In combination with nitrate N and O isotope ratios (δ15NNO3 and δ18ONO3) these results will help to constrain the relationship between physical forcing (on-shelf nutrient transport) and biologically mediated sources and sinks of bioavailable N on the Scotian Shelf. Tracer distributions indicate different hydrographic sources between coastal and offshore slope stations. Nearshore subsurface (> 50 m) waters are characterized by low temperatures and a pronounced deficit in nitrate relative to phosphate (-4 µmol/L; assuming Redfield stoichiometry), highlighting the dominance of cold, fresh water from the Gulf of St. Lawrence along the inner shelf. Off-shelf, higher temperatures along with higher salinity and lower O2 concentrations indicate the presence of nutrient-rich slope waters, with contributions from both the Labrador Sea and the Gulf Stream. N and O isotope ratios show lower δ18ONO3 (0.0 – 0.4‰) and higher δ15NNO3 (~5.0‰) near the coast relative to stations further offshore (> 2.0‰ and ~4.0‰, respectively). Increased temperatures along with higher values of δ18ONO3 (~2.0‰) and a surplus in nitrate over phosphate (4 µmol/L) reflect the intrusion of warm slope waters into deep basins on the shelf. Tracer distributions further show an imprint of remineralization on bottom water properties along the shelf. These new data and results from the eOMPA will be discussed in the context of the regional circulation and N biogeochemistry.

How to cite: Lehmann, N., Kienast, M., Normandeau, C., Thamer, P., and Buchwald, C.: On sources and sinks of bioavailable nitrogen on the Scotian Shelf: Insights from nutrient distributions and nitrate isotope ratios, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6425, https://doi.org/10.5194/egusphere-egu22-6425, 2022.

Coffee break
Chairpersons: Helmuth Thomas, Alberto V. Borges
17:00–17:07
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EGU22-6911
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On-site presentation
Martijn Hermans, Erik Gustafsson, Bo G Gustafsson, Caroline P Slomp, and Tom Jilbert

Marginal marine systems, such as the Baltic Sea, are naturally susceptible to bottom water oxygen (O2) depletion due to strong stratification and restricted horizontal water exchange. In recent decades, bottom water hypoxia (O2 < 63 μM) and anoxia (O2 = 0 μM) have been further exacerbated in coastal areas due to excessive anthropogenic nitrogen (N) and phosphorus (P) inputs. Feedback mechanisms in the coupled biogeochemical cycling of P, iron (Fe) and sulphur (S) play a major role in controlling bottom water O2 conditions. Phosphorus release from the seafloor amplifies when bottom water O2 availability is low due to reductive dissolution of iron (Fe) oxide-bound P and preferential P regeneration from organic matter. This Fe oxide-bound P feedback mechanism has been suggested to play a key role in the rapid transitions at the onset and end of multidecadal hypoxic events in the Baltic Sea. Currently, the coupled biogeochemical cycling of Fe, P and S is not explicitly described in Baltic Sea models. For example, BALTSEM, the principal model used in decision making under the Baltic Sea Action Plan, does not include a representation of coupled Fe, P and S cycling and therefore utilises simplified parameterisations to mimic feedback mechanisms. A critical deficiency is that such parameterisations are calibrated for present-day state only, and do not take into account large-scale changes in the spatial distribution of Fe, P and S over long time-scales. Therefore, it can become difficult to predict possible future changes or to reproduce past events. Here, we introduce a new model extension for BALTSEM, so-called Fosferrox, that simulates the coupled dynamics between Fe, P and S in response to changes in bottom water oxygen for present day (1850-2100 A.D.). The implementation of such a mechanistic coupled biogeochemical cycling between Fe, P and S, and its associated feedback mechanisms in Baltic Sea models is fundamental to better understand how changes in, for example, P loading might impact water column redox conditions, as well as to improve hypoxia abatement strategies. The main impetus is to extend the functionality of Fosferrox to gain a better mechanistic understanding of how the coupled Fe, P and S feedback mechanisms drive the multidecadal oscillations in Baltic Sea hypoxia.

How to cite: Hermans, M., Gustafsson, E., Gustafsson, B. G., Slomp, C. P., and Jilbert, T.: Fosferrox: A biogeochemical model extension for coupled iron, phosphorus and sulphur dynamics in response to changes in bottom water oxygen in BALTSEM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6911, https://doi.org/10.5194/egusphere-egu22-6911, 2022.

17:07–17:14
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EGU22-7491
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On-site presentation
Birgit Wild, Nicholas Ray, Céline Lett, Amelia Davies, Elena Kirillova, Henry Holmstrand, Elizaveta Klevantceva, Alexander Osadchiev, Ivan Gangnus, Evgeniy Yakushev, Denis Kosmach, Oleg Dudarev, Örjan Gustafsson, Igor Semiletov, and Volker Brüchert

Nitrous oxide (N2O) is a strong greenhouse gas and a major ozone depleting agent. Almost a quarter of global N2O emissions stems from the ocean, but projections of future releases are uncertain due to scarce observations over large areas and limited understanding of the drivers behind. Here, we focus on the vast continental shelf seas north of Siberia, a hotspot area of global change that experiences rapid warming and high nitrogen input via rivers and coastal erosion; yet N2O measurements from this region are extremely scarce. We combine water column N2O measurements generated during two expeditions with on-board incubation of intact sediment cores to fill this observational gap, constrain N2O sources and assess the impact of land-derived nitrogen that is expected to increase with permafrost thaw. Our data show elevated nitrogen concentrations in the water column and sediments near the mouths of large rivers, suggesting that land-derived nitrogen might promote primary production, but also nitrification and denitrification in the region. However, N2O concentrations were only weakly influenced by elevated nitrogen availability near river mouths. Comparison with a range of environmental parameters suggests that N2O concentrations might be controlled by interactions of nitrogen availability with turbidity and possibly temperature. Surface water N2O concentrations were on average in equilibrium with the atmosphere, but high spatial variability indicates strong local N2O sources and sinks. Water column profiles of N2O concentrations and low sediment-water N2O fluxes do not support a dominant sedimentary source or sink, but point at production and consumption processes in the water column as main drivers of N2O dynamics in the Siberian shelf seas. The projected increases in water temperature and input of freshwater, nitrogen and suspended material from rivers and coastal erosion with land permafrost thaw have the potential to affect not only net N2O production rates, but also N2O solubility in the water, and increase N2O emissions from the Arctic Ocean.

How to cite: Wild, B., Ray, N., Lett, C., Davies, A., Kirillova, E., Holmstrand, H., Klevantceva, E., Osadchiev, A., Gangnus, I., Yakushev, E., Kosmach, D., Dudarev, O., Gustafsson, Ö., Semiletov, I., and Brüchert, V.: Nitrous oxide dynamics on the Siberian Arctic Ocean shelves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7491, https://doi.org/10.5194/egusphere-egu22-7491, 2022.

17:14–17:24
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EGU22-7494
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ECS
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solicited
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Highlight
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On-site presentation
Jan Kossack, Moritz Mathis, and Corinna Schrum

It has been suggested that continental shelves disproportionally contribute to global oceanic CO2 uptake from the atmosphere, in particular through the efficient CO2 sinks of the biologically productive mid- and high latitude shelves. For the North Western European Shelf (NWES), contributions of different biological and hydrodynamic drivers of the shelf carbon pump, however, remain poorly constrained. We here use the flexible coupled hydrodynamic-biogeochemical modeling system SCHISM-ECOSMO to investigate how tidal forcing, as one of the dominant hydrodynamic features on the NWES, influences the efficiency of the continental shelf pump. Tidal impacts on biological productivity and carbon cycling are assessed by comparing hindcast simulations with and without tidal forcing. We show that tides substantially increase net primary productivity on the NWES and find a significant contribution from vertical mixing induced by internal tides. Our results further demonstrate that the enhanced productivity and inorganic carbon sequestration in the tidal scenario translates into an increased oceanic CO2 uptake, even though tidal currents reduce particulate carbon deposition in the shelf sediments. This suggests that tides play an important role for the efficiency of the continental shelf pump by promoting net carbon export from the NWES to the adjacent North Atlantic.

How to cite: Kossack, J., Mathis, M., and Schrum, C.: Impact of tides on the North Western European shelf carbon pump, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7494, https://doi.org/10.5194/egusphere-egu22-7494, 2022.

17:24–17:31
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EGU22-8316
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ECS
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On-site presentation
Sarah Paradis, Kai Nakajima, Negar Haghipour, and Tim Eglinton

Continental margins play a central role in the global carbon cycle, but the heterogenous OC origin, sediment transport processes, and depositional environments lead to complex patterns of distribution and accumulation of OC that render it challenging to quantitatively assess their role in global biogeochemical cycles. While previous studies have focused on predicting the distribution of sedimentary OC, comprehensive spatial constraints that link the provenance and composition of OC with the processes affecting its storage on continental margins are lacking. For example, radiocarbon is a powerful tool for understanding the origin and depositional fate of OC but it is not extensively used due to its cost and measurement accessibility, leading to sparse data coverage on continental margins.

The Modern Ocean Sediment Archive and Inventory of Carbon (MOSAIC) database (Van der Voort et al., 2021) was recently established to compile and curate data on the OC content and its composition in continental margin sediments worldwide together with relevant sedimentological and environmental variables. This database is continuously being revised and presently includes > 60 % more published and unpublished data, > 100 % more variables, and executes harmonization techniques designed to increase its richness and utility. Using this new database in combination with geostatistical and geospatial techniques, we aim to explore relationships between depositional settings and the content and composition of organic carbon, with the goal of ultimately predicting sedimentary organic carbon properties over a range of spatial scales.

Here, we use the East Asian marginal seas as a case study. This expansive marginal sea (~4 million km2) is characterized by highly heterogenous OC inputs, dynamic sediment transport processes, and diverse depositional environments, while presenting a wealth of sedimentological and geochemical data, which makes this area the perfect natural laboratory to assess the influence of these environmental factors on the spatial distribution of sedimentary OC content, composition, and age. A spatial model predictor was developed with over 2000 data points of organic carbon and its isotopic composition (δ13C, 14C) as well as sedimentological properties extracted from the updated version of MOSAIC, coupled with relevant spatial environmental explanatory variables. Results indicate that the distribution of sedimentary organic carbon throughout this margin is non-stationary due to the regional influences of different depositional environments. Observing this on a regional scale emphasizes the need to incorporate the local effect of depositional environments to accurately predict the fate of organic carbon in marine sediments worldwide.

Van der Voort, T. S., Blattmann, T., Usman, M., Montluçon, D., Loeffler, T., Tavagna, M. L., et al. (2021). MOSAIC (Modern Ocean Sediment Archive and Inventory of Carbon): a (radio)carbon-centric database for seafloor surficial sediments. Earth Syst. Sci. Data 13, 2135–2146. doi:10.5194/essd-13-2135-2021

How to cite: Paradis, S., Nakajima, K., Haghipour, N., and Eglinton, T.: Predicting spatial variability in sedimentary organic carbon content and composition on continental margins – the East Asian marginal seas as a case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8316, https://doi.org/10.5194/egusphere-egu22-8316, 2022.

17:31–17:38
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EGU22-8393
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ECS
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Virtual presentation
Jannine M. Lencina-Avila, Jens Daniel Müller, Stefan Otto, Michael Glockzin, Bernd Sadkowiak, and Gregor Rehder

Coastal regions are under the threat of surface water acidification, which its ecological and socioeconomic impacts need to be better constrained. However, pH measurements in coastal waters are challenging and are still primarily measured discretely, compromising spatial or temporal scales. Therefore, directly measuring an acidification parameter, such as pH, with high spatial and temporal coverage could improve our understanding of the changes in the water acid-base balance and, thus, potential changes in the biogeochemical processes in these highly dynamic regions. Contributing to coastal management, we analysed continuous surface spectrophotometric pH measured on board the Ship of Opportunity "Finnmaid" along the Baltic Sea over the year 2020. We observed a pronounced seasonality of isothermal (25 oC) pH (total scale, pHT), with higher pH values in warm seasons (8.206 ± 0.148) and lower in colder seasons (7.959 ± 0.065), with maximum (8.792) and minimum (6.971) pH observed in the Gulf of Finnland during the summer. Consistently, surface pCO2 mirrored pH, with general averages of 299.6 ± 103.5 µatm (spring) and 279.4 ± 108.0 µatm (summer). In addition, the high-frequency measurements enable us to investigate biogeochemical processes at the submesoscale and, thus, better resolve sub-basin and sporadic coastal processes, such as river discharge and upwelling events. For this purpose, the Baltic Sea was sub-dived into three basins along the ship track: the German coast, the Gotland Sea, and the Gulf of Finland. Data in the Gulf of Finland indicated higher biological productivity during the warm season (spring-summer), depicted by a more significant surface pCO2 drawdown (minimum of 181.2 µatm) compared to the Gotland Sea (237.3 µatm) and German coast (200.8 µatm) minima. Consequently, pH values followed this pattern, reaching maxima of 8.792, 8.433, and 8.562 in summer, respectively. The results indicate that seasonal pH variations are controlled mainly by biological processes, which, in turn, vary regionally due to differences in the external conditions (e.g., light availability), the hydrographical setting (e.g., temperature and water column structure) and nutrient availability. Furthermore, the high spatiotemporal resolution of pH measurements achieved here allows for tracking the minimum and maximum pH values encountered in the surface water over the entire year, which can support current efforts towards the development of an acidification indicator within HELCOM.

How to cite: M. Lencina-Avila, J., Müller, J. D., Otto, S., Glockzin, M., Sadkowiak, B., and Rehder, G.: Seasonal and regional pH variation determined from continuous spectrophotometric measurements on a ship of opportunity in a coastal region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8393, https://doi.org/10.5194/egusphere-egu22-8393, 2022.

17:38–17:45
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EGU22-9239
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Virtual presentation
Teodoro Ramírez-Cárdenas, Esperanza Liger, and Luís Miguel Fernández-Salas

This work analyses the spatial variability of organic matter (phytopigments, proteins and carbohydrates) in surface sediments from the Gulf of Cadiz (SW Iberian Peninsula). Sediment samples were taken in summer 2019 during the oceanographic cruise “INPULSE-19” at different stations with depths ranging from nearly 500 m to 1000 m depth. The distribution of the different organic matter fractions showed a high variability with marked differences between stations. The spatial distribution of phytopigments (PHYTOPIG) in the upper sediment layer (0-1 cm below the seafloor) evidenced high degree of accumulation at two close stations, where the higher PHYTOPIG concentrations were found, while PHYTOPIG concentrations were one other of magnitude lower at other sampling stations. Protein and carbohydrate concentrations in the water-soluble fractions (PROTWS and CHOWS) from the upper 0-1 cm sediment layer were correlated with each other, although they exhibited some differences in their spatial distribution pattern. Moreover, PROTWS in the 0-1 cm sediment layer was highly correlated to PHYTOPIG, suggesting a similar origin for both fractions, while the correlation with CHOWS was weaker. Alkaline extractable proteins and carbohydrates (PROTALK andCHOALK) were one order of magnitude higher than the concentrations in their respective water-soluble fractions. PROTALK andCHOALK in the 0-1 cm sediment layer were highly correlated with each other, showing a quite similar distribution pattern. The PROTWS/CHOWS ratio, an index of organic matter lability, ranged between 0.3 and 2.1 in the upper sediment layer, while the PROTALK/CHOALK ratio ranged between 1.6 and 3.6 The observed variability in these ratios indicates differences in the lability of sedimentary organic matter at different stations, which might affect the bioavailability of organic matter in the sediments.

How to cite: Ramírez-Cárdenas, T., Liger, E., and Fernández-Salas, L. M.: Spatial variability of organic matter in marine sediments from the Gulf of Cadiz, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9239, https://doi.org/10.5194/egusphere-egu22-9239, 2022.

17:45–17:52
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EGU22-9444
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ECS
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On-site presentation
Mona Norbisrath, Johannes Pätsch, Kirstin Dähnke, Tina Sanders, Gesa Schulz, Justus E. E. van Beusekom, and Helmuth Thomas

The Elbe Estuary and its biogeochemistry are strongly influenced by tidal cycles of the North Sea, high nutrient and organic matter loads from the catchment area, and dredging of the navigation channel to maintain the connection between the North Sea and Germanys largest seaport in Hamburg.

Due to large phytoplankton blooms upstream of the port, the input of organic matter is high and provides high metabolic activity within and downstream the Hamburg port.

Here, we combined carbon, oxygen, and nitrogen data to elucidate their relationship and distribution along the Elbe Estuary. We used a box model approach to balance the budgets of dissolved inorganic carbon (DIC), oxygen (O2), and nitrogen in form of nitrate (NO3-). To complete carbon and oxygen, we included atmospheric exchange of carbon dioxide (CO2) and O2.

DIC generation and O2 consumption reveal the highest metabolic activity in the Hamburg port area, decreasing downstream. In contrast, NO3- budgets are stable along the estuary, indicating a strong decoupling of carbon and nitrogen in the Elbe Estuary. This decoupling can be explained by anaerobic processes such as denitrification in the port area, but it also implies lateral nitrogen sources further downstream.

How to cite: Norbisrath, M., Pätsch, J., Dähnke, K., Sanders, T., Schulz, G., van Beusekom, J. E. E., and Thomas, H.: Coupling and decoupling of carbon, oxygen, and nitrogen in the Elbe Estuary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9444, https://doi.org/10.5194/egusphere-egu22-9444, 2022.

17:52–17:59
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EGU22-3493
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Virtual presentation
Johannes Paetsch, Helmuth Thomas, and Mona Norbisrath

Recent studies have shown that anaerobic remineralisation in estuaries of the North Sea, a semi-enclosed shelf sea of the Northeast Atlantic, generates a large amount of alkalinity which is subsequently flushed into the North Sea basin. The anaerobic processes within the estuaries fed by high anthropogenic nitrate loads peaked in the 1980s. Under pristine conditions, these nutrient loads are lowered by about 90 %.

On the other hand, the goals of the 2015 Paris agreement can only be achieved with zero or even negative CO2 emissions. Such scenarios often include the use of terrestrial bioenergy requiring an increasing usage of fertilizers. Simply by leakage, such applications induce additional nutrient (and thus alkalinity) loads into the adjacent seas.

Using a 3-D biogeochemical model for the Northwest European shelf, we investigated the North Sea – wide consequences of the different scenarios described above. Assuming only aerobic regeneration within the estuaries of the North Sea, the annual uptake of atmospheric CO2 is reduced by about one third within a coastal band of 100 km width. More drastic changes of alkalinity discharge into the North Sea, described above, also impact areas of the central North Sea and are able to alter the annual CO2 uptake in the order of the magnitude of the air-to-sea flux itself.

How to cite: Paetsch, J., Thomas, H., and Norbisrath, M.: Variations of estuarine metabolic alkalinity loads: Consequences for the biogeochemistry of a shelf sea (North Sea), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3493, https://doi.org/10.5194/egusphere-egu22-3493, 2022.

17:59–18:06
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EGU22-10390
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ECS
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On-site presentation
Chantal Mears, Helmuth Thomas, Hendrik Wolschke, Yoana Voynova, and Anton Schrader

The long-lived radium isotopes, 226Ra (t1/2= 1600 yrs.) and 228Ra (t1/2 = 5.8 yrs.), are established shelf-sea tracers, capable of discerning key water-mass compositions and distribution patterns from source to sea. Within the North Sea, radium has not only been recognized as a suitable tool for identifying water-mass characteristics, but 228Ra has also been found to effectively trace total alkalinity (AT). Within the known continental shelf pump system of the North Sea, this indirect link between radium and the carbonate system has recently enticed greater interest for climate mitigation strategies, such as Artificial Ocean Alkalinization (AOA). But, prior to initiating intentional anthropogenic perturbations on the complex coastal North Sea, it is imperative to understand the initial state of the system. In order to do just that, our study builds on the previous knowledge of water-mass distributions within the North Sea, distinguishing the sources and mixing patterns which contribute to the three main water-masses (with particular focus placed on further identification of the North Atlantic input source components). Quantitatively, these patterns are further supported through the use of inverse modelling techniques, which highlight the importance of end members for each of the water-masses. Overall this study provides a more in-depth baseline understanding of water-mass distribution and mixing within the North Sea.

How to cite: Mears, C., Thomas, H., Wolschke, H., Voynova, Y., and Schrader, A.: Using long-lived radium isotopes as water-mass tracers in the North Sea and investigating their use for tracking artificial ocean alkalinization., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10390, https://doi.org/10.5194/egusphere-egu22-10390, 2022.

18:06–18:13
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EGU22-12509
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Highlight
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Presentation form not yet defined
Decadal variability southern North Sea pH: ocean acidification in reverse?
(withdrawn)
Matthew Humphreys, Cecile Hilgen, Yasmina Ourradi, Jos Schilder, and Gert-Jan Reichart
18:13–18:20
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EGU22-13372
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On-site presentation
Marit van Erk, Olivia Bourceau, Chyrene Moncada, Subhajit Basu, Colleen Hansel, and Dirk de Beer

We investigated the influence of reactive oxygen species (ROS) on microbial mineralization in intertidal permeable sediments. These sediments are crucial for coastal carbon cycling. Permeable intertidal sediments are further prone to variable surface oxygenation and active iron-sulfur cycling, and are therefore likely sites of intense ROS formation. We incubated sediment slurries from an intertidal sandflat in the German Wadden Sea over a transition to anoxic conditions, and found that removal of ROS by enzymes increased rates of aerobic and anaerobic respiration, including sulfate reduction. We additionally found high concentrations of the ROS hydrogen peroxide in sediment porewaters. Sulfate reduction was absent during the oxic period, but directly resumed upon anoxia.

This study shows the regulating effect of ROS on microbial mineralization and the impact of ROS and transient oxygenation on marine sediment biogeochemistry.

How to cite: van Erk, M., Bourceau, O., Moncada, C., Basu, S., Hansel, C., and de Beer, D.: Reactive oxygen species control mineralization in permeable intertidal sediments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13372, https://doi.org/10.5194/egusphere-egu22-13372, 2022.

18:20–18:27
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EGU22-12627
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ECS
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On-site presentation
Julia Meyer, Yoana G. Voynova, Bryce Van Dam, Dagmar Daehne, Lara Luitjens, and Helmuth Thomas

Coastal regions are highly variable ecosystems and play a crucial role in the global carbon cycle. In the North Sea, the CARBOSTORE project aims to investigate some of the benthic and pelagic reservoirs of carbon. This study focuses on the seasonal and inter-annual changes in the Southern North Sea and the North Frisian Islands in the Wadden Sea. Large regional and seasonal variability has been documented in previous studies of total alkalinity and carbon in these regions, but the driving factors are still being investigated.

Since the start of the CARBOSTORE project in spring 2021, two seasonal cruises were completed in July and October 2021. The dissolved inorganic carbon (DIC) and total alkalinity (TA) in the southern North Sea and intertidal regions around the North Frisian Islands were measured, along with several other biogeochemical parameters measured using a Ferry Box. These surveys allow insights into the regional distribution and the seasonal cycle of TA and DIC and will help elucidate the potential sources of carbon. In addition, a close collaboration to colleagues investigating the benthic processes in this project will allow for coupling the benthic and pelagic dynamics.

Preliminary results show a gradient in TA and DIC from land to sea, as well as regional variability. In the intertidal zones, TA and DIC values are higher overall than in the southern North Sea. Higher TA and DIC values were measured in July compared to October. What is more, the intertidal regions near the Ems River show some of the highest TA and DIC values, suggesting a potential influence from riverine inputs.

How to cite: Meyer, J., Voynova, Y. G., Van Dam, B., Daehne, D., Luitjens, L., and Thomas, H.: Seasonal changes in total alkalinity and dissolved inorganic carbon in the southern North Sea and intertidal regions around the North Frisian Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12627, https://doi.org/10.5194/egusphere-egu22-12627, 2022.