BG4.2

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.

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 Letters, 451, pp.41-50.

Faust, J.C. and Knies, J., 2019. Organic matter sources in North Atlantic fjord sediments. Geochemistry, Geophysics, Geosystems, 20(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. Biogeosciences, 14(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: Biogeosciences, 122(11), pp.2754-2768.

Smeaton, C., Yang, H. and Austin, W.E., 2021. Carbon burial in the mid-latitude fjords of Scotland. Marine Geology, 441, 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 Geoscience, 8(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.

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.

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 (fCO_2,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 fCO_2,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 (NC_T) was attended. The net community production processes described 93.5-95.6% of the total NC_T 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.