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-MakuchECSECS, Craig SmeatonECSECS
vPICO presentations
| Tue, 27 Apr, 13:30–17:00 (CEST)

Session assets

Session summary

vPICO presentations: Tue, 27 Apr

Chairpersons: Helmuth Thomas, Katarzyna Koziorowska-Makuch, Alberto V. Borges
Aaron Alorda-Kleinglass, Isabel Ruiz-Mallen, Marc Diego-Feliu, Valentí Rodellas, and Jordi Gracia-Orellana

Coastal environments have experienced a rapid transformation due to the expansion of tourism. This growth may enhance problems as over-saturation of spaces or environmental pollution. One of the main problems is associated with the collapse of environmental infrastructures, which may become saturated during high seasons. Indeed, wastewater treatment plants (WWTP) can be located in coastal areas delivering high concentrations of nutrient effluents into the marine environment. Alternatively, WWTP effluents are introduced into coastal aquifers via injection wells, given that the geological matrix is used to filter naturally the transported effluent solutes. However, the injection of significant amounts of WWTP effluents can modify the hydrogeological dynamics and enrich substantially the solute concentrations in groundwaters. Zones with a hydraulic connection between the coastal aquifer and the sea, these contaminated groundwaters may be transferred to coastal environments via Submarine Groundwater Discharge (SGD). Thus, SGD may act as a pathway delivering part of the WWTP-derived nutrients and pollutants into the marine environment, which may lead to eutrophication or harmful algal blooms. More importantly, such process may become threatening for society when the discharge occurs into bathing waters, affecting the ecosystem and perception of stakeholders.

In this study, we evaluate the role of SGD as a conveyor of nutrients from a karstic coastal aquifer affected by the injection of WWTP effluents to the Deià cove in Mallorca (Balearic Islands). Results show that the tourism seasonality changes the coastal aquifer natural dynamics during the dry season, delivering via SGD, nutrients concentrations above the maximum limits established by the Spanish and European water framework directives. Due to those enriched nutrient fluxes, the coastal water ecosystem has registered the highest values of ∂15N in Posidonia oceanica in the Balearic Islands and suffers periodic algal blooms, creating a conflict among stakeholders.

How to cite: Alorda-Kleinglass, A., Ruiz-Mallen, I., Diego-Feliu, M., Rodellas, V., and Gracia-Orellana, J.: Submarine Groundwater Discharge: The invisible mechanism that degrades the quality of crystalline bathing water in the Balearic Islands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15714,, 2021.

Roger Carvalho da Silva, Hannelore Waska, Kai Schwalfenberg, and Thorsten Dittmar

Submarine groundwater discharge (SGD) is an important connection between fresh groundwater and the marine ecosystem. The scientific interest in SGD has grown considerably during the last decades due to the recognition of SGD in coastal environments as a significant source of nutrients and pollutants.  The Sahlenburg area (Northern Germany) is known by its highly permeable sediments and high rainfall precipitation that produces a large reservoir of groundwater.  Such characteristics are essential for industry, agriculture and drinking water supply with a large regional importance. In addition, this groundwater discharges in the form of highly productive springs directly into the adjacent tidal flats, with so far unknown effects on the local biogeochemistry.  The aim of this study was to characterize the spatial distribution of salinity, fluorescence dissolved organic matter (FDOM), dissolved organic matter (DOC) and total dissolved nitrogen (TDN) of the springs of Sahlenburg tidal flat area in Cuxhaven, Germany. We hypothesize that the SGD composition is changing on its way through the tidal flat due to biogeochemical factors. This may affect the composition of the water in the final part of the pathway with more influence of seawater. Porewater springs were sampled in February 2019 during low tide in three different types of locations in the tidal flat area: nearshore where the springs are located close to the vegetated shoreline (salt marsh), offshore approximately 70 meters from the vegetation and in the middle from both locations. In addition, porewater from a nearby sandy beach (around 500 meters away from the area of spring sampling), and surface samples from a nearby lake and seawater, were obtained. Salinity and FDOM were measured in situ, and DOC and TDN in the laboratory.  The preliminary data showed low average values for salinity in all springs (0.2-1.4), as well as in beach porewater, indicating strong influence of fresh groundwater in the whole area. When comparing the three spring location types, the lowest salinities were found offshore, and the highest nearshore. This difference could be due to the size of the springs, since nearshore springs usually were smaller when compared to offshore springs. Furthermore, depressions in the tidal flat relief close to nearshore springs favored seawater retention in pools during low tide. Additionally, we found higher average values for DOC and FDOM in the nearshore when compared with the other spring areas, but lower compared to the lake, beach porewater and seawater. The average values for TDN (272-452 µmol L-1) in the groundwater springs were higher when compared to all other sample types (beach porewater, seawater, and lake water) in this study. These values suggest an anthropogenic input (e.g., agriculture influence) in the surrounding watershed and might stimulate primary productivity in the tidal flat. We conclude that groundwater springs in Sahlenburg tidal flat differ locally in their biogeochemistry due to different residence times, heterogeneity of sediment layers, and size of the springs.


How to cite: Carvalho da Silva, R., Waska, H., Schwalfenberg, K., and Dittmar, T.: Submarine groundwater discharge (SGD) in the springs of Sahlenburg tidal flat, Germany: a geochemical approach. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10833,, 2021.

Greg Siemens, Ryan Mulligan, and Delaney Benoit

The characteristics of waves breaking on a beach can have significant impacts on how water infiltrates and influences coastal groundwater flows. The effects of continuous wave action on groundwater in coastal aquifers is important to understand to predict subsurface flows in beaches. This investigation will study how coastal wave dynamics in the swash zone impact the groundwater table using physical laboratory modelling and detailed image analysis that allows for high density spatial and temporal resolution degree of saturation measurements using unsaturated transparent soil as illustrated in Figure 1. Transparent soil methods will be applied to observe simulated wavedriven subsurface flows in a cross-section of a sandy beach. The objective of this study is to extend the current knowledge of how waves drive groundwater fluctuations by experimentally quantifying the time and length scales of flow within a beach.

Figure 1.

Transparent soil can be used to experimentally measure subsurface fluid/air flow and is used to quantify spatial and temporal saturation conditions every few seconds during an experiment. Digital image analysis allows for millimeter spatial resolution throughout the domain. Transparent soil is formed are applied by using crushed quartz rock in place of sand and an oil mixture with an identical refractive index to the grains (Peters et al. 2011). When the pores of the crushed quartz are saturated with the oil, the mixture appears transparent. When dry, the crushed quartz appears opaque. Change in colour is quantified, through digital image analysis, to measure degree of saturation throughout the domain (Sills et al. 2017)

This study applied transparent soil techniques in its first application to understand coastal processes by observing how incident waves infiltrate beaches and induce groundwater table fluctuations. Four tests are reported with variations in beach slope and wave properties, and the images are processed to quantify spatial and temporal degree of saturation variation. In each test, the swash interacted with the groundwater table by forming a partially saturated zone above the saturated zone of the beach. This partially saturated mound followed a consistent shape, that varied in size and rate of change primarily due to beach slope. The partially saturated zone is formed by a combination of capillary forces and downward infiltration, forming a continuously dampened zone in the beach. Finally, the results show a strong inverse correlation between the wetting front formed in a beach and the slope of the swash zone. Steeper slopes displayed much larger partially saturated mounds and were observed to do so in a slower manner compared to flatter slopes.


Peters, S. B., Siemens, G., and Take, W. A. (2011). “Characterization of Transparent Soil for Unsaturated Applications.” Geotechnical Testing Journal, 34(5).

Sills, L.-A. K., Mumford, K. G., and Siemens, G. A. (2017). “Quantification of Fluid Saturations in Transparent Porous Media.” Vadose Zone Journal, 16(2), 1–9.

How to cite: Siemens, G., Mulligan, R., and Benoit, D.: Physical Modelling of Wave-Driven Groundwater Flows in a Sand Beach Using Transparent Soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13923,, 2021.

Werna Werna and Stefan Forster

The benthic oxygen consumption rate (OCR) has been widely used to measure the total benthic organic carbon degradation rate, while the oxygen distribution provides the general biogeochemistry state of marine sediments. In shallow coastal environments the light driven photosynthesis by benthic microalgae, resulting in large diurnal oscillations of oxygen concentration, further affects the oxygenation of the sediment. Yet, for permeable sediments, studies incorporating pore water advection driven by physical forces into oxygen consumption and distribution measurements are  still limited. Here we examine the combined effect of benthic oxygen production and advective oxygen transport on oxygen dynamics and consumption rate in a microphytobenthos-dominated sediment (permeability k =2 x 10-11 to 5 x 10-11 m2) in a laboratory simulation with stirred benthic chambers at 40 rpm. Under alternating light (50 μE m−2 s-1) and flow regimes, oxygen concentration, penetration depth and consumption rates were monitored by means of micro-profiling and planar optode measurements. In all cases, we found that oxygen penetration depth increased up to a factor of 2 with pore water flow simulation. On the other hand, advective transport was found to reduce maximum oxygen concentration in the sediment by up to 30 %.  The OCR were up to 2-times higher with only light (28 ± 3.5 µM/min) compared to combined light and flow simulation, however the total oxygen uptake was generally uniform in all chambers (41.83 ± 5.9 mmol/m2 d-1), suggesting the local redistribution of oxygen with flow without marked overall changes in O2 consumption. Our result emphasized the importance of advective transport controlling benthic oxygenation in photic permeable sediment.

How to cite: Werna, W. and Forster, S.: Benthic Oxygen dynamics: Influence of pore water advection and microphytobenthos in a permeable sediment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1239,, 2021.

Pei-Chuan Chuang, Matthias Zabel, Stefan Sommer, Florian Scholz, Paul Vosteen, and Andrew W. Dale

The availability of major nutrients, nitrogen (N) and phosphorus (P), largely controls primary productivity in eastern boundary upwelling systems. The oxygen minimum zone (OMZ) on the Namibian shelf is characterized by high productivity and extraordinarily high particulate organic carbon (POC) contents (up to 19 % dry weight) in the surface sediments. The anaerobic degradation of POC by bacterial sulfate reduction leads to the production of hydrogen sulfide (H2S) that supports extensive communities of large sulfur bacteria Thiomargarita namibiensis in surface shelf sediments. These bacteria oxidize sulfide by reducing nitrate (NO3-) to either ammonium (NH4+) or dinitrogen (N2). Thiomargarita also affect phosphorus cycling by intracellular incorporation of polyphosphates and extracellular formation of hydroxyapatites. In order to understand and quantify the complexity of the coupled benthic cycles of C, N, P, S, Fe in the Benguela Upwelling System, a reaction-transport model (RTM) was used to simulate sediment biogeochemical data collected from the RV Meteor cruise (M157, August 4th-September 16th 2019) off Namibia. This allowed deeper insights into the role of sulfur-oxidizing bacteria on P and N fluxes across the sediment surface. Results are presented that point toward potentially strong feedbacks by Thiomargarita on primary production in response to ongoing global warming and ocean deoxygenation.

How to cite: Chuang, P.-C., Zabel, M., Sommer, S., Scholz, F., Vosteen, P., and Dale, A. W.: Impact of Thiomargarita on the rates of N, S and P turnover in mudbelt sediments from the Benguela Upwelling System: a model study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1837,, 2021.

Dana Hellemann, Sanni-Leea Aalto, Eero Asmala, Tom Jilbert, Mikko Kiljunen, Boris Koch, Joanna Norkko, and Alf Norkko

Excess bioavailable nitrogen (N) is the key driver of coastal eutrophication, thus knowledge on the fate of N in coastal systems is imperative for improving eutrophication mitigation measures. In the coastal Baltic Sea, benthic heterotrophic denitrification, the main process of bioavailable N-removal from a coastal system, has recently been suggested to be seasonally limited by labile organic carbon (OC) availability1 - despite the system´s richness in labile organic matter from long-term eutrophication. This challenges our common understanding of the intrinsic link between C- and N-cycling, and highlights the need for a more advanced concept of OC availability. Hence, in this project, we (i) extensively characterized the biochemical composition of coastal OC beyond traditional descriptors of ‘lability’, applying techniques such as isotopic fingerprinting and Fourier transform ion cyclotron resonance mass spectrometry, and (ii) concurrently quantified benthic nitrate reduction rates both with and without addition of easily degradable OC (glucose), to ultimately confirm and understand proposed OC-limitation of denitrification in coastal sediments. All measurements were done in high temporal and spatial resolution at the southern coast of Finland, covering a three-month period from late winter to early summer that included the peak annual input of fresh organic matter to the benthic system by the phytoplankton spring bloom. First results will be presented and their implications for understanding seasonal N turnover and coastal eutrophication dynamics will be discussed.

1Hellemann D, Tallberg P, Aalto SL, Bartoli M, Hietanen S (2020) Seasonal cycle of benthic denitrification and DNRA in the aphotic  coastal zone, northern Baltic Sea. Mar Ecol Prog Ser 637:15–28

How to cite: Hellemann, D., Aalto, S.-L., Asmala, E., Jilbert, T., Kiljunen, M., Koch, B., Norkko, J., and Norkko, A.: Unraveling seasonal carbon-limitation of benthic nitrate-reduction in the coastal Baltic Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2924,, 2021.

Zuzanna Borawska, Beata Szymczycha, Marc J. Silberberger, Marta Szczepanek, Katarzyna Koziorowska-Makuch, and Monika Kędra

Dissolved silica (DSi) is an important macronutrient in the marine environment, necessary for growth of many aquatic organisms. Yet, DSi marine cycle is still not fully recognized, especially in dynamic, coastal zones. Although DSi is mainly transported to the sea by rivers, benthic fluxes of DSi, which originate from dissolution of the siliceous remains in the sediments, can also represent an important source of bioavailable silicon in the ocean. Benthic DSi fluxes are mainly powered by diffusion, but their rates are strongly shaped by the benthic fauna. Still, the role of benthos in these processes is not fully recognized. The main goal of this study was to investigate how various environmental factors and benthic fauna may shape the coastal cycle of Si in coastal environments during different seasons.

Our study was conducted in the shallow coastal ecosystems of the southern Baltic Sea characterized by contrasting environmental conditions: shallow, brackish and enclosed Szczecin Lagoon (Oder river estuary), dynamic open waters near Łeba with relatively low anthropogenic influence, enclosed Puck Bay and Vistula prodelta. We investigated both shore ecosystems (app. 0.5 m depth) and deeper areas (from 6 up to 60 m depth). DSi concentrations in the bottom waters and environmental characteristics (T, S, O2, sediment organic matter) were investigated at 6 stations, during three seasons (winter, spring and autumn) in years 2019-2020 with s/y Oceania (IOPAN) and directly from the shore. Additionally, samples from shore stations were collected during summer. DSi benthic fluxes were determined at each station by performing ex situ incubations of sediment cores (n = 4-5) with natural benthic assemblages. The benthic organisms in studied cores were collected, identified, counted, and weighed.

The lowest fluxes were measured at sandy stations while highest return fluxes were observed at muddy sites. High variability in DSi benthic fluxes along studied localities was observed, ranging from -1.11 mmol d-1m-2 in summer at shore station in the Puck Bay and up to 6.79 mmol d-1m-2 in Szczecin Lagoon in autumn. We used  Gaussian Generalized Linear Models (GLMs) to estimate the role of environmental conditions, benthic fauna characteristics  and interactions among them in the variability of DSi benthic flux across studied localities. The most important predictors for the fluxes were all pair-wise interactions of temperature, total organic carbon, the C/N molar ratio, and the density of benthic macrofauna. Both interaction terms that included C/N ratio, a measure of organic matter quality (i.e. low C/N ratio indicates higher quality), were associated with increased DSi uptake by the sediment. Further, the interaction term between T and benthic marcofauna density was also linked to negative benthic fluxes of DSi. In contrast, the interaction of T and TOC caused a strong increase in DSi return fluxes.

How to cite: Borawska, Z., Szymczycha, B., Silberberger, M. J., Szczepanek, M., Koziorowska-Makuch, K., and Kędra, M.: Spatial and seasonal variation in dissolved silica benthic fluxes in the shallow zones of the southern Baltic Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5163,, 2021.

Anne-Christin Melcher, Susann Henkel, Thomas Pape, Anette Meixner, Simone A. Kasemann, Male Köster, Jessica Volz, Henriette Wilckens, Elda Miramontes, Walter Geibert, Tilmann Schwenk, Thomas Frederichs, Michael Staubwasser, and Sabine Kasten

The Argentina Continental Margin represents a unique geologic setting to study interactions between bottom currents and sediment deposition as well as their impact on (bio)geochemical processes, particularly the cycling of iron (Fe). Our aim was to determine (1) how different depositional conditions control post-depositional (bio)geochemical processes and (2) how stable Fe isotopes (δ56Fe) of pore water and solid phases are affected accordingly. Furthermore, we (3) evaluated the applicability of δ56Fe of solid Fe pools as a proxy to trace past diagenetic alteration of Fe, which might be decoupled from current redox conditions. Sediments from two different depositional environments were sampled during RV SONNE expedition SO260: a site dominated by contouritic deposition on a terrace (Contourite Site) and the lower continental slope (Slope Site) dominated by hemipelagic sedimentation. Sequentially extracted sedimentary Fe [1] and δ56Fe analyses of extracts and pore water [2,3] were combined with sedimentological, radioisotope, geochemical and magnetic data. Our study presents the first sedimentary δ56Fe dataset at the Argentina Continental Margin.

The depositional conditions differed between and within both sites as evidenced by variable grain sizes, organic carbon contents and sedimentation rates. At the Contourite Site, non-steady state pore-water conditions and diagenetic overprint occurs in the post-oxic zone and the sulfate-methane transition (SMT). In contrast, pore-water profiles at the Slope Site suggest that currently steady-state conditions prevail, leading to a strong diagenetic overprint of Fe oxides at the SMT. Pore-water δ56Fe values at the Slope Site are mostly negative, which is typical for on-going microbial Fe reduction. At the Contourite Site the pore-water δ56Fe values are mostly positive and range between -0.35‰ to 1.82‰. Positive δ56Fe values are related to high sulfate reduction rates that dominate over Fe reduction in the post-oxic zone. The HS- liberated during organoclastic sulfate reduction or sulfate-mediated anaerobic oxidation of methane (AOM) reacts with Fe2+ to form Fe sulfides. Hereby, light Fe isotopes are preferentially removed from the dissolved pool. The isotopically light Fe sulfides drive the acetate-leached Fe pool towards negative values. Isotopic trends were absent in other extracted Fe pools, partly due to unintended dissolution of silicate Fe masking the composition of targeted Fe oxides. Significant amounts of reactive Fe phases are preserved below the SMT and are possibly available for reduction processes, such as Fe-mediated AOM [4]. Fe2+ in the methanic zone is isotopically light at both sites, which is indicative for a microbial Fe reduction process.

Our results demonstrate that depositional conditions exert a significant control on geochemical conditions and dominant (bio)geochemical processes in the sediments of both contrasting sites. We conclude that the applicability of sedimentary δ56Fe signatures as a proxy to trace diagenetic Fe overprint is limited to distinct Fe pools. The development into a useful tool depends on the refining of extraction methods or other means to analyse δ56Fe in specific sedimentary Fe phases.



[1]Poulton and Canfield, 2005. Chemical Geology 214: 209-221.
[2]Henkel et al., 2016. Chemical Geology 421: 93-102.
[3]Homoky et al., 2013. Nature Communications 4: 1-10.
[4]Riedinger et al., 2014. Geobiology 12: 172-181.

How to cite: Melcher, A.-C., Henkel, S., Pape, T., Meixner, A., Kasemann, S. A., Köster, M., Volz, J., Wilckens, H., Miramontes, E., Geibert, W., Schwenk, T., Frederichs, T., Staubwasser, M., and Kasten, S.: The impact of depositional conditions on biogeochemical cycling of iron and stable iron signatures in sediments of the Argentina Continental Margin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8356,, 2021.

Constance Lefebvre, Felipe S. Freitas, Katharine Hendry, and Sandra Arndt

The Arctic Ocean is currently experiencing rapid oceanographic shifts and significant sea-ice loss as a result of regional atmospheric and oceanic warming. The Barents Sea is a notable example of these phenomena, having seen a near 40% decline of its April sea-ice extent since 1979, and a progressive northward expansion of Atlantic Water (i.e., Atlantification). Such changes affect primary productivity and nutrient cycling in ways that remain poorly understood. Longer ice-free periods and the inflow of warmer Atlantic Water are expected to lead to extended bloom seasons on short, near-future timescales and therefore increase nutrient uptake in upper water layers. The benthic recycling of nutrients is believed to play an important part in replenishing nutrient inventories in overlying waters thus maintaining high primary productivity over the continuously expanding growth season. Therefore, it is crucial to increase our understanding of nutrient dynamic controls in changing oceans to make more accurate predictions and decipher the complex feedbacks involved in these evolving environments. However, most efforts to constrain and quantify nutrient fluxes so far have been directed at silicon, nitrogen or iron. This study aims to provide specific insight into phosphorus (P) cycling through its response to OM fluctuations and coupling with iron cycling. An integrated data-model approach was used to investigate the dynamics of P cycling at the sediment-water interface across five locations along the 30°E meridian that were drilled in the framework of the ChAOS project in the Barents Sea. The model approach allowed to explore the sensitivity of P cycling to plausible ranges of reactive iron and OM inputs. Greater inputs of reactive iron were found to decrease benthic phosphate fluxes (JPO4) whereas greater inputs of OM increased phosphate return to the water column. The quality of these inputs is equally significant: JPO4 decreased when iron hydroxides were made more reactive and increased with more reactive OM. Our findings indicate that variation in climatically sensitive processes, such as burial of terrestrial sediments and iron cycling, could represent powerful feedbacks on JPO4 through adsorption/desorption mechanisms. Results also reveal significant oceanographic controls on JPO4, suggesting Atlantification of the Barents Sea will play into future phosphate availability.

How to cite: Lefebvre, C., S. Freitas, F., Hendry, K., and Arndt, S.: Benthic Cycling of Phosphate in the changing Arctic Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8754,, 2021.

Natalia Herran, Martin Schmidt, Volker Mohrholz, and Heide Schulz-Vogt

On the seabed of oxygen minimum zones (OMZ), embedded in organic-rich sediments, large sulfur bacteria (LSB) fulfil an important ecological role by detoxifying the overlying bottom waters. Thiomargarita Namibiensis and Beggiatoa spp. are chemoautotrophic microorganisms that reduce sulfur compounds to create biomass and link by doing so the carbon, sulfur, oxygen and nitrate cycle very efficiently. This particular ability make life in suboxic and hypoxic coastal waters feasible. Nevertheless, due to the complexity of sulfur oxidation and its various pathways the quantification of such activity is of great complexity. Hereby, we describe a model framework of LSB activity to implement intrinsic properties of the bacteria based on field observations and numerical modelling validations, linking the stoichiometry and energy conservation efficiency of LSB while counting for the reduced sulfur pools and its partitioning sub-products.

How to cite: Herran, N., Schmidt, M., Mohrholz, V., and Schulz-Vogt, H.: The role of large benthic sulfur bacteria in biogeochemical cycles - a model approach., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13368,, 2021.

Alexander Ulyantsev, Svetlana Bratskaya, Nikolay Belyaev, Oleg Dudarev, and Igor Semiletov

The modern East Siberian Arctic shelf represents a fascinating area with a vast expansion of subsea permafrost that holds a large pool of frozen immobilised organic carbon (OC). Amplified climate change at high latitudes has raised growing concerns about potential positive carbon–climate feedbacks. Degradation of permafrost in the Arctic could constitute a positive feedback to climate change due to activation of this OC stock, while recognizing the origin and peculiarities of organic matter (OM) is useful for predicting the potential for involving the ancient OC in modern carbon cycling. This paper emphasises the molecular composition of lignin-derived phenols (LDP) in bottom sediments and subsea permafrost from the Laptev Sea shelf as a proxy to describe the main sources, distribution, and preservation of terrestrial OM. The compositional pattern and concentration of LDP revealed irregular dynamics of terrigenous OM supply in the study area, that were governed primarily by continental flows. The OC concentration in the studied sediments varied from 0.04% to 23.1% (mean 1.74%, median 1.07%). The concentration of LDP in the studied 126 samples from five sediment cores obtained from Buor-Khaya Bay varied from 0.7 to 13191 (mean 539, median 63.5) µg/g of dry sediment as the sum of vanillyl, syringyl, and cinnamyl (VSC) compounds and from 0.03 to 27.6 (mean 1.61, median 0.76) mg/100 mg of OC content. All OC-rich samples showed higher concentrations of LDP and virtually non-oxidized lignin. Vegetation proxies suggested that vascular plant tissues account for a significant fraction of the lignin in the examined samples, with a strong share of gymnosperms. The concentration of LDP correlates to OC content, indicating a strong supply of terrestrial OC to the study area. Degradation proxies indicate a predominant supply of wood-rich non-oxidized terrestrial OM. The well-preserved lignin revealed in the studied deposits represents a specific feature of Quaternary lithodynamics of the Laptev Sea and is not typical for the majority of bottom sediments of the World Ocean. Good correlation between OC and lignin concentration suggests that terrigenous fluxes were the main contributor to OM supply. Distribution of specific lignin phenols and related ratios coupled with lithology and grain size revealed that fluvial processes have been leading here.

This research was supported through the Russian Scientific Foundation (grant no. 19-77-10044) within the framework of the state assignment of the Shirshov Institute of Oceanology RAS (grant no. 0149-2019-0006).

How to cite: Ulyantsev, A., Bratskaya, S., Belyaev, N., Dudarev, O., and Semiletov, I.: Compositional pattern of lignin derived phenols of sediments as a proxy of accumulation of terrestrial organic matter in coastal zone of the Laptev Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4726,, 2021.

Tina Liesirova, Tobias Aarenstrup-Launbjerg, Lasse Riemann, and Maren Voss

Benthic nitrogen fixation by heterotrophic non-cyanobacterial diazotrophs (NCDs) is common in anoxic marine sediments, however, it is currently unclear how resuspension of sediments affects this activity. Moreover, physical mixing processes are strongest in shallow coastal waters where permeable sediments prevail and anoxic conditions rarely occur. It is therefore of interest to understand whether such coastal sites provide ecological niches for NCDs. In order to gain insight into NCD nitrogen fixation during sediment resuspension, slurry incubations were carried out with nearshore sediments from stations along the Southern Baltic coastline and, for comparison, with anoxic sediments from the Gdansk Deep. Parallel to this, we carried out separate incubations treated with sodium molybdate, an inhibitor of sulfate reducing bacteria (SRB), to differentiate SRB activity from total NCD activity. Our data show low rates of nitrogen fixation by NCDs and indicate that SRBs (e.g. Desulfovibro) are actively fixing nitrogen. Nitrogen fixation rates varied greatly between locations, influenced by sediment grain size and POC-loading. Interestingly, nitrogen fixation took place despite of micromolar concentrations of inorganic nitrogen, which implies that NCDs may be more resilient towards N-stress than formerly expected. In conclusion, our experimental study supports previous findings of stimulation of nitrogen fixation by sediment resuspension, even in permeable sediments, however, at low rates.

How to cite: Liesirova, T., Aarenstrup-Launbjerg, T., Riemann, L., and Voss, M.: The impact of sediment resuspension on non-cyanobacterial nitrogen fixation along the Southern Baltic coastline, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11032,, 2021.

Natalia Shulga, Sergej Abramov, Sergej Gavrilov, and Konstantin Ryazantsev

This work is based on ferromanganese nodules, crusts and underlying sediments collected from the different parts of the Kara Sea shelf (Arctic). The geochemistry, morphology and organic matter content of nodules, crusts and sediments were determined with ICP-MS, SEM-EDS and GC/MS. The associated microbial communities were identified with 16S rRNA (gene) sequencing. Nodules from the Kara Sea shelf significantly differ from their more common abyssal analogues. These shelf nodules have an irregular tabular morphology and relatively low abundances of Mn (up to 19 wt.%), Fe (up to 24 wt.%), other trace metals and the REYs. The Kara Sea nodules show concentric layering that is also typical of deep-sea diagenetic nodules. Samples subdivided into two groups: Mn-rich (Mn/Fe = 0.35 on av.) and Fe-rich (Mn/Fe = 1.65 on av.). The negative Ce anomaly suggests a diagenetic origin of the nodules and crusts. The input of organic matter to the ore deposits in the study area has three main sources (according to n-alkane composition): 1) marine (planctonogenic); 2) low-transformed terrestrial organic matter derived from river run-off; 3) microbial-derived source. Microbial communities of nodules and crusts are substantially different from benthic microbial communities in sediments. They dominated by taxa involved in N cycle, particularly responsible for denitrification (Cyclobacteriaceae and Kiloniellaceae), nitrification (“Candidatus Nitrosopumilus” and Nitrosomonas), comammox (Nitrospira) and anammox (Nitrosococcaceae) [1]. Dissimilatory Fe(III)- and Mn(IV)-reducing Geopsychrobacter was identified in Fe-rich ore samples. This taxon can be involved in Fe(III)- and Mn(IV)-dependent anaerobic oxidation of methane [2]. In contrast, microbial community of underlying sediments dominated by sulfate-reducing bacteria (SRB). Some of the identified SRB (e.g. Desulfobulbaceae and Desulfosarcinaceae) are able to form syntrophic associations with anaerobic methanotrophic archaea [3]. Identified n-alkanes can be oxidized by Anaerolineaceae growing in syntrophic association with methanogens. Furthermore, we revealed that manganese nodules and crusts can be used potentially as important electron acceptors for oxidation of organic compounds by Geopsychrobacter, Desulfuromonadales and Colwellia. Applied multi-disciplinary approach to the study of the Fe-Mn nodules and crusts will help to determine their contribution in formation of unique biogeochemical environments in the Kara Sea.

This work was supported by the Russian Science Foundation (grant 19-77-00107).

How to cite: Shulga, N., Abramov, S., Gavrilov, S., and Ryazantsev, K.: Composition of the Fe-Mn nodules and associated microbial communities of the Kara Sea, Arctic Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15925,, 2021.

Yan Ding and Dongqi Wang

Inter-tidal wetlands at mangroves, salt marshes and sea grass bed are important carbon reservoirs that play a significant role in climate change mitigation. However, the lack of large-scale quantification and source identification of sediment organic carbon (SOC) in inter-tidal wetlands hampers the assessment of carbon storage potential in these systems. In this research, we hypothesized that SOC in the inter-tidal wetlands of Chinese East Coast were mainly from three potential sources (terrestrial soil, marine phytoplankton, local C3 and C4 plants as mangrove and salt marsh plants ). Based on elemental ratios and stable carbon isotope of core sediment from the inter-tidal wetlands along the east coast of China, we quantified the contribution of organic carbon (OC) sources and explored the hydrological and plant drivers controlling the variations of OC source contribution among different coastal environmental settings. We found SOC in the large estuaries (river runoff more than 50 billion m3/a) originated predominantly from terrestrial soil OC (46±9%), while the primary OC source of the smaller estuaries was marine phytoplankton OC (61±14%). These results suggested that the contribution of terrestrial soil OC increased with river runoff, whereas the share of marine phytoplankton OC decreased with runoff. Moreover, while mangroves played a substantial role in carbon storage at the southern part of the coast, our estimates revealed a sharp decline in the contribution of mangrove OC since the 1980s. These findings indicate carbon storage in the inter-tidal wetlands varies among contrasting coastal environmental conditions and among wetlands with different ages, providing implications for inter-tidal wetlands as an important carbon sink in the global carbon budget.

How to cite: Ding, Y. and Wang, D.: Identification and Quantification of Sediment Organic Carbon in the Inter-tidal Wetlands of Eastern Coast of China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3699,, 2021.

Mareike Paul, Niels A. G. M. van Helmond, Caroline P. Slomp, Sami A. Jokinen, Joonas J. Virtasalo, Helena L. Filipsson, and Tom Jilbert

Deoxygenation in response to eutrophication and climate change in coastal systems is increasing worldwide. Low oxygen conditions cause the chemical transformation of redox-sensitive trace metals (e.g. molybdenum and uranium) in seawater, and their subsequent transport to the sediment. Sedimentary trace metal contents can therefore be used as a record of changes in bottom water oxygen conditions allowing the history of deoxygenation to be reconstructed. However, most trace metal studies have focused on strongly reducing and sulfidic settings, leaving mildly reducing and oxygenated (but eutrophic) settings vastly understudied. Currently, it is unknown to what extent existing trace metal redox proxies are applicable to reconstruct oxygen conditions in coastal zones experiencing mild deoxygenation, despite the fact that such areas occupy vast stretches of the coastal oceans. Here, we study trace metal enrichments in 13 European coastal marine sites with varying bottom water redox conditions and depositional environments. Our data demonstrates that sedimentary molybdenum and uranium contents are sensitive to deoxygenation across a range of settings, although the mechanisms of enrichment may vary. Improved understanding of molybdenum and uranium dynamics in mildly reducing coastal settings will facilitate the development of reliable and widely applicable molybdenum and uranium-based redox proxies.

How to cite: Paul, M., van Helmond, N. A. G. M., Slomp, C. P., Jokinen, S. A., Virtasalo, J. J., Filipsson, H. L., and Jilbert, T.: Sedimentary trace metals: improving proxies for deoxygenation in coastal European seas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5499,, 2021.

Sarah Cryer, Claire Evans, Filipa Carvalho, Sara Fowell, Urska Martincic, Gilbert Andrews, Samir Rosado, Arlene Young, Antoine de Ramon, and Socratis Loucaides

Tropical coral reefs are both biologically diverse and economically important ecosystems, yet are under threat globally, facing a multitude of stressors including global warming, ocean acidification, nutrient loading, over-fishing and sedimentation. Reef building corals precipitate an aragonite skeleton (CaCO3), which forms the base of the coral reef ecosystem, but it is this skeleton, which makes them sensitive to changes in ocean pH. To precipitate their skeletons, corals raise their internal pH, as seawater pH decreases this increases the energy demands needed to facilitate calcification. Furthermore, reductions in coral calcification has significant implications for reef health, potentially altering community structure with reef-wide consequences. Global ocean pH is decreasing due to rising atmospheric concentrations of CO2, however, dynamic ecosystems, alongside carbon and freshwater input from land, may result in coastal ocean pH being lower than is predicted by open ocean models. While it is predicted than ocean pH will decrease by 0.3 units by 2100 if emissions are not curbed, coral reefs, particularly those near major river outflow, may already be experiencing pH values similar to that of future scenarios.

Our aim was to determine the factors which influence pH in coastal reef systems and thus potentially mitigate or exacerbate atmospheric CO2 mediated ocean acidification. This was achieved by contrasting reefs in distinct environmental settings and collecting data over a sufficient temporal resolution to permit the identification of pertinent drivers. To accomplish this we deployed fixed point observatories in the distinct reefs of Belize (fore and back reef sites), Fiji and Dominica. These custom-built platforms were equipped with a spectrophotometric pH sensor and a conductivity, temperature and dissolved oxygen (CT-DO) sensor from which data was logged at 30-120 minute intervals.

A strong diel cycle in pH, O2 and temperature was observed at all reef sites in response to the changing balance of respiration and photosynthesis. However, the range of these changes varied between the different sites - Belize fore reef (pH 7.849­ – 8.000), Belize back reef (pH 7.897 – 8.039), Fiji (pH 7.951 – 8.0950) and Dominica (pH 7.843 – 8.144). Meteorological conditions, such as wind direction, affected the amplitude of diurnal pH variability and its relationship with other parameters, likely by influencing mixing and the spatial distribution of seawater and freshwater endmembers. The relationship between pH and O2 varied between sites reflecting differences in ecosystem processes (e.g. calcification and primary production) and ecosystem composition (e.g. hard coral and algae cover, proximity to seagrass). Our data confirms that different reef sites are subject to varying degrees of ocean acidification and that controls on pH vary between environments. Furthermore, it highlights the need for widespread high-resolution monitoring to identify, and where possible enact protective measures, in vulnerable reef regions. As coral reefs continue to experience ocean acidification our data also serves to document baseline conditions against which future changes can be assessed.


How to cite: Cryer, S., Evans, C., Carvalho, F., Fowell, S., Martincic, U., Andrews, G., Rosado, S., Young, A., de Ramon, A., and Loucaides, S.: Ecosystem composition and environmental factors as drivers of pH on Barrier Reefs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12156,, 2021.

Chairpersons: Arthur Capet, Craig Smeaton, Helmuth Thomas
Celeste Kellock, Craig Smeaton, Nadeem Shah, William Austin, and Christian Schroeder

There is strong evidence that the source of terrestrial carbon and iron geochemistry play an important role in organic carbon transport and preservation in coastal and marine sediments 1,2,3. There is a global drive to increase forestry and Scotland is undergoing a period of afforestation4. A portion of this is being planted in sea loch (fjord) catchments; however the effect of this increase in forestry on coastal carbon transport and storage is poorly understood. Fjord systems have recently been identified as significant terrestrial carbon stores5 therefore understanding how afforestation of these catchments changes the carbon dynamics from source to sea, is key.

In this study Mossbauer spectroscopy, XRD and XRF are used to examine how iron concentration and speciation differs within Scottish fjord sediments. This preliminary data provides insight of the variation in iron speciation in fjord systems, processes controlling iron transport and speciation and potential mineral binding mechanisms in coastal sediments. This enables us to start addressing key knowledge gaps in the transport of organic carbon and iron from land (forested source areas) to sea (fjords). Thus, contributing to our overarching aim of tracing the movement and interactions of organic carbon across the terrestrial - aquatic interface.

Through this project, further analytical techniques such as biomarker analysis, isotopic analysis and SEM, will be used to improve our understanding of source to sea processes in fjord systems throughout the northern hemisphere. This will hopefully enable improved understanding and quantification of local and national carbon stocks. Further insights into carbon and iron burial mechanisms may allow us to tailor land use and management around fjord environments to maximise natural carbon storage.

How to cite: Kellock, C., Smeaton, C., Shah, N., Austin, W., and Schroeder, C.: Source to Sea: Transport of organic carbon and iron from forested environments to coastal waters and sediments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12008,, 2021.

E. Elena Garcia-Martin, Richard Sanders, Chris D. Evans, Vassilis Kitidis, Dan J. Lapworth, Andrew P. Rees, Bryan Spears, Andy Tye, Jennifer L. Williamson, and Daniel J. Mayor

The flux of terrigenous organic carbon across estuaries is an important and changing component of the global carbon cycle, but it is poorly understood. It has been proposed that estuaries can act either as a transporter of terrestrial dissolved organic carbon (DOC) to the ocean or as a reactor system in which DOC can be buried or transformed into carbon dioxide and released to the atmosphere. However, there is no clear understanding of the factors that drive estuaries to behave in one way or the other. Here we present the results from a study conducted in thirteen British estuaries which drain catchments of diverse land-uses under different hydrological conditions. Our data show that land-use influences the composition of the dissolved organic matter (DOM), the mixing dynamics of DOC and the quantity of DOC exported off the estuaries. Estuaries, whose catchments are less intensively managed and represent more natural ecosystems (average proportion of arable and (sub)-urban land-use ~12 %), contain a higher proportion of biologically-refractory “humic-like” DOM, which is transported conservatively across the salinity gradient. In contrast, estuaries whose catchments are more intensively managed (average proportion of arable and (sub)-urban land-use ~32 %) contain a high fraction of “protein-like” DOM which is transported non-conservatively, and thus suggest the existence of additions and removal processes across the salinity gradient. Furthermore, estuaries with more intensively managed catchments tend to export more DOC to coastal areas than they receive from rivers. Our results indicate that future changes in land-use have the potential to alter aquatic fluxes of terrigenous DOM and the fate of the constituent carbon.

How to cite: Garcia-Martin, E. E., Sanders, R., Evans, C. D., Kitidis, V., Lapworth, D. J., Rees, A. P., Spears, B., Tye, A., Williamson, J. L., and Mayor, D. J.: Influence of land-use on the dynamics, quantity and composition of the organic matter transported across estuaries, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1298,, 2021.

Agathe Laes, Gabriel Dulaquais, Alexandre Hemery, Matthieu Waeles, Romain Davy, Jeremy Devesa, Ricardo Riso, and Stefan Lalonde

The aim of FeLINE project (Fer Ligands In the aulNe Estuary) was to determine the distribution of iron and associated ligands concentrations along the land sea continuum of the Iroise Sea (Bay of Brest, France). Iron porphyrin like ligands (Fe-Py) such as heme and hemoproteins are relevant complexes in iron biogeochemical cycling as they can persist in seawater and on marine particulates. This work reveals for the first time the distribution of Fe-Py concentrations (dissolved plus reactive particulate) along a temperate macrotidal estuary. Unfiltered samples were collected in October 2019 across a transect of the Aulne river and estuary / Rade of Brest / Iroise Sea during low tidal coefficient (39). Fe-Py concentrations were determined using flow injection analysis with chemiluminescence detection adapted from Vong et al. (2007). Various interferences (organic, metallic, pH and salinity) were tested. The detection limit attained was 11 pmol.l-1 and the time of analysis 1min30s per sample. The Fe-Py concentrations varied from 0.007 ±0.002 nmol.l-1 for S=33.98 and 1.177 ±0.007 nmol.l-1 for S = 0.92. The Fe-Py concentrations clearly showed a non-conservative behavior due to various processes other than simple mixing of natural and seawater. The highest values revealing a Fe-Py enrichment were observed in the Estuarine Turbidity Maximum (ETM) for which concentrations varied between 1.177 ±0.007, S = 5.2 and 0.738 ±0.004 nmol.l-1 S = 8.59. This positive anomaly of Fe-Py concentrations (40%) also corresponded to the lowest pH values (pH =7.27-7.32). The distal part of the transect displayed a negative anomaly for salinities comprised between 15 and 25 (loss of 37%). The four last points geographically corresponding to the Bay of Brest (S>35) exhibited low and stable Fe-Py concentrations of 0.007±0.002 and 0.024 ± 0.003 nmol.l-1. The supply and removal fluxes were respectively estimated at 2.4±0.2g/d and 8.1 ± 0.8g/d, revealing an average Fe-Py removal of 39.8% that is probably due to particle flocculation.

How to cite: Laes, A., Dulaquais, G., Hemery, A., Waeles, M., Davy, R., Devesa, J., Riso, R., and Lalonde, S.: Distribution of iron porphyrin like complexes along the land sea continuum of the Iroise Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-183,, 2021.

Johannes Paetsch and Helmuth Thomas

Since the early eighties of the 20th century nitrogen and phosphorus loads of the River Elbe, a river entering the North European Shelf at the southeastern coast, have decreased by a factor of about four. This resulted in a reduction of the eutrophication status in the adjacent German Bight and the coastal waters west of Denmark. In addition, benthic carbon and alkalinity pools have changed due to 1- changed carbon loads and, 2- changed decay pathways of benthic organic carbon.

We investigate the consequences of observed nutrient and organic loads by rivers with a 3D-biogeochemical model including a 3D-early diageneses model within the sediment for the time 1979 - 2014.   

The results show a strong decrease of benthic carbon rather due to decreasing nutrient loads and subsequent autochthonous biological production than changes in organic loads. The export of inorganic carbon from the sediment is related to the magnitude of benthic organic carbon and cannot explain the strong decrease of the benthic POC pool. During the time until the early nineties aerobic degradation increases, whereas denitrification and sulfate reduction as organic matter degradation pathway decreases.

Alkalinity production due to benthic organic matter degradation decreases over the first half of the investigated time interval and keeps constant during the second half. Denitrification and sulfate reduction dominate the mechanisms decreasing the alkalinity export. Benthic nitrification consuming alkalinity strongly increases during the first half of the time dampening the decrease of alkalinity export.

How to cite: Paetsch, J. and Thomas, H.: Consequences of nutrient load reductions for carbon and alkalinity dynamics within the region of freshwater influence of River Elbe, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1716,, 2021.

Tihana Novak, Blaženka Gašparović, Ivna Vrana Špoljarić, and Milan Čanković

Marine phytoplankton are crucial for ecosystem function and responsible for almost half of world’s primary production. In order to grow and reproduce phytoplankton need sufficient amount of macro and micro nutrients. Nutrient concentrations are changeable in different water mases and dependable on different natural and anthropogenic sources such as terrestrial water inputs, recycling by sloppy feeding, remineralization with bacteria and atmospheric deposition. High nutrient input to oligotrophic regions raises phytoplankton biomass that leads to higher organic matter production and heterotrophs` development.  Anthropogenic nutrient inputs are considered as the main cause of coastal eutrophication. Marine lipids, dominantly produced by phytoplankton, are good biogeochemical traces of organic matter origin and processing in marine environment and phytoplankton adaptation to environmental perturbations. They are important for multiple cell mechanisms functioning.

The goal of this research was to investigate the influence of a point source of nutrients on organic matter production and lipid composition as a consequence of phytoplankton acclimation to different nutrient loads. We sampled at two geographically close stations in the Krka River Estuary mouth, oligo- to mesotrophic Martinska station and station in vicinity of the town of Šibenik that is under high anthropogenic influence. Samples were taken from three depths (above, on and below halocline) and in four different seasons covering annual cycle. Lipid classes were characterized by thin–layer chromatography–flame ionization detection. Data are supported by hydrographic, dissolved organic carbon and particulate organic carbon parameters. We will discuss the changes of organic matter accumulation and estuarine lipid biogeochemistry caused by human activity.



This research was financed by the Croatian Science Foundation project BiREADI (IP-2018-01-3105).

How to cite: Novak, T., Gašparović, B., Vrana Špoljarić, I., and Čanković, M.: High local nutrient input influence on oligotrophic phytoplankton production and lipid biogeochemistry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15187,, 2021.

Valentina Sergeeva and Olga Vorobieva

Pronounced changes in the climate system that lead to a significant reduction in sea ice cover and active glacier melting provoke the great interest in ecosystem studies of archipelago bays in the high Arctic. In addition to increasing the duration of the open water period, the glacier melting increases the fresh water discharge from the archipelagos and thereby affects the coastal ecosystems of the Arctic region. There is practically no information about the ecosystems of the archipelago bays of the seas of the Russian Arctic due to the inaccessibility. Within the framework of the program “Investigation of the Russian Arctic ecosystems” in 2007-2020 held by Shirshov Institute of Oceanology, modern comprehensive studies of ecosystems of Novaya Zemlya bays, including phytoplankton (as primary producer of organic matter) were carried out. The most frequent observations were conducted in Blagopoluchiya Bay (North Island of Novaya Zemlya Archipelago), which has several coastal runoffs of glacial origin flow.

We found that despite the constant enrichment with allochthonous suspended matter and nutrients with runoff from Novaya Zemlya to the Blagopoluchiya Bay there was no increase in phytoplankton production during the summer open water period (Borisenko et al. Thesis EGU21-9528). On the contrary, the quantitative characteristics of phytoplankton in euphotic layer were extremely low: 0.2-0.7 mkgC/l and 0.03 - 0.15 mkgChl/l. Obviously the inclusion of allochthonous nutrients in local production cycles over the sea part of the bay was difficult.

To clarify the reasons of such low phytoplankton productivity against the background of the enrichment with nutrients of ​​Blagopoluchiya Bay, multifactorial experiments were carried out on the monoculture of the cosmopolitan diatom Thalassiosira nordenskioeldii Cleve, 1873, which is one of the dominant species in the Novaya Zemlya bays. Algae culture was isolated from the phytoplankton community of the Kara Sea and adapted to a salinity of 31 psu, typical for Novaya Zemlya bays. In addition to routine cell counting under microscope we used PAM-fluorometry to control the growth characteristics of algae that makes it possible to observe the photosynthetic activity of algae.

It was shown that the functioning of algae is greatly influenced by a significant gradients in salinity. When fresh runoff from Novaya Zemlya is mixed with the seawater of the bay, marine planktonic algae experience significant osmostress and immediately settle down and die off. With a slight dilution (up to 29-30 psu) of sea water by freshwater from the archipelago, the algae functioned well and doubled their biomass for 2-3 days. At the same time, we found that the algae were well adapted to a significant range of illumination: 40-200 µE, which apparently allows them to maintain high level of photosynthetic activity under the changing arctic illumination during the Arctic summer at high latitudes.

This study was performed within the framework of the state assignment of IO RAS, (topic no. 0149-2019-0008) and supported by the Russian Foundation of Basic Research (projects no. 18–05–60069Arctic and 19-04-00322 А).

How to cite: Sergeeva, V. and Vorobieva, O.: Functioning of phytoplankton in the bays of Novaya Zemlya Archipelago, Kara Sea ​​ (Blagopoluchiya Bay) during summer., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11895,, 2021.

Peihang Xu, Christian Furbo Christiansen, and Carolin Löscher

Both oxygenic and anoxygenic phototrophic bacteria (OPB and APB, respectively) are widely distributed in the ocean and play significant roles in carbon cycle and marine productivity. These organisms capture light as energy source via chlorophyll or bacteriochlorophylls-based photosystems. While OPB are relatively well studied, information on APB is rather scarce although they have been shown abundant in some ocean ecosystems and may play an important role in oxygen depleted environments. Here, we investigate the spatial profile of OPB and APB, gene abundance and expression of the key functional marker gene pufM (APB specific photosynthetic reaction center subunit M), in one fjord and three basins of the Baltic Sea using 16S rRNA amplicon sequencing and qPCR. Among the microbial community, abundances of OPB and APB were found to be similar thus emphasizing a potential importance of APB, with APB representing 1.6-17.5% and OPB representing 0.5-20%. Among APB, we identified eleven different orders, with Rhodobacterales being quantitatively dominant. The identified seven orders of OPB were dominated by Synechococcales. OPB were more abundant than APB in surface waters (<8m), while APB were comparably more abundant in deeper waters. Besides a depth-dependent distribution, we observed an impact of salinity on the distribution of APB and OPB, both of which being suggestive of distinct niches for those primary producer clades. pufM gene abundance ranged from 104 to 109 copies/L, with highest counts detectable in the mixed layer (<40m), however, even in deeper waters where gene abundances decreased APB pufM gene expression was high with up to 104 copies/L. These results indicate APB may play a more important role in marine primary productivity which has been underestimated before. 

How to cite: Xu, P., Christiansen, C. F., and Löscher, C.: The role of anoxygenic phototrophs in the Baltic Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2348,, 2021.

Gennadii Borisenko, Alexander Polukhin, and Valentina Sergeeva

In the frames of the scientific program “Investigation of the Russian Arctic ecosystems” in 2007-2020 held by Shirshov Institute of Oceanology, comprehensive studies of the bays of the Novaya Zemlya archipelago (NZA) were carried out. There is very little information in the scientific literature on the dynamics and hydrochemical structure of the waters of the bays. Our investigations have revealed that the concentration of nutrients (first of all, nitrates and silicate) in the bays of NZA was higher than in the surrounding water area of ​​the Kara Sea. The most well studied and open for investigations is the Blagopoluchiya Bay in the northern island of NZA. Blagopoluchiya Bay is a fjord-type bay with several streams of the glacier origin.

The concentrations of nutrients (N, P, Si, C) in the streams were observed in August-September (0-1.53 µM of PO43-, 6.4-50.2 µM of SiO32-, 0.6-11.2 µM of NO2-+NO3-, 732-4815 µM of DIC). The observed content of nutrients in the waters of the bay was on average 2 times lower, but not lower than the level limiting the development of phytoplankton.

We suppose that high concentrations of nutrients in NZA bays in August-September were supported by increasing glacial runoff from NZA during the summer open water period and the removal of products of degradation of shore rocks with it. Despite the constant enrichment of nutrients, the concentration of phytoplankton in Blagopoluchiya Bay was extremely low (0.2-0.7 mkgC/l) in comparison with the adjacent marine part of the Kara Sea in all years of research.  Perhaps it was due to osmostress of planktonic algae during desalination of the bay by the NZA runoff.

This work was supported by the State Agreement of The Ministry of Science and Education of Russian Federation (theme №0128-2019-0008); Russian Foundation for Basic Research project 18-05-60069 (processing hydrochemistry data); Russian Scientific Foundation project 19-17-00196 (data obtaining); by the Grant of the President of the Russian Federation MK-860.2020.5 (processing carbonate chemistry data).

How to cite: Borisenko, G., Polukhin, A., and Sergeeva, V.: Content and variability of nutrients in the water area of ​​Blagopoluchiya Bay (Novaya Zemlya, Kara Sea), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9528,, 2021.

Mona Norbisrath, Jeannette Hansen, Kirstin Dähnke, Tina Sanders, Justus E. E. van Beusekom, and Helmuth Thomas

The Elbe is the largest river entering the German Bight. Its estuary is a heavily used waterway connecting the sea to Germany’s biggest port in Hamburg. The Elbe navigation channel is continuously dredged, and agricultural fertilizer input from the catchment ensuing large phytoplankton blooms in the river Elbe exerts additional anthropogenic pressure. Biogeochemistry in the estuary is additionally governed by the North Sea and its strong tidal cycles, which ensure an exchange of fresh and marine waters.

The aims were to quantify the release of the carbon species total alkalinity (TA) and dissolved inorganic carbon (DIC) along the Elbe estuary, and to estimate the contribution of aerobe and anaerobe metabolic processes. Therefore, we used water samples collected continuously during a cruise in June 2019, to measure TA and DIC, and the stable isotopes of nitrate. We applied mass balances, to characterize the metabolic activity and detect their effect on the carbon species

The Elbe estuary could be subdivided into two parts: 1) an outer marine driven part, which is dominated by conservative mixing, also visible in higher TA than DIC values, and 2) an inner fresh water part in which metabolic processes play an important role.

We found a strong increase in TA and DIC (several hundred µmol kg-1) in the Hamburg port area, with higher DIC than TA values. We unraveled the water column impacts of nitrification and denitrification on TA and DIC by analyzing the stable isotopes δ15N-NO3- and δ18O-NO3-, and identified water column nitrification as a dominant pelagic process in the port of Hamburg and in the fresh water part further downstream. Because nitrification cannot explain the significant increase of TA and DIC in the port region, anaerobic processes such as denitrification in the sediment also appear to play an important role.


How to cite: Norbisrath, M., Hansen, J., Dähnke, K., Sanders, T., van Beusekom, J. E. E., and Thomas, H.: Metabolic alkalinity release from the Elbe estuary to the North Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8648,, 2021.

Elise Olson, Nina Nemcek, and Susan Allen

We have developed a coupled physical-biological model representing plankton and nutrient dynamics of the Strait of Georgia, a fjord-like semi-enclosed coastal sea on the west coast of Canada. The nutrient-phytoplankton-zooplankton-detritus (NPZD)-type biological model is based on nitrogen uptake and remineralization with a coupled silicon cycle and includes both diatom and non-siliceous phytoplankton functional groups. The Strait of Georgia exhibits an estuarine circulation driven by input from the Fraser River as well as many smaller rivers and streams. It has high levels of dissolved silica (can be >50 μM even at the surface). Silicon-replete conditions shape key characteristics of the local ecosystem, which include heavily silicified glass sponge reefs as well as frequent diatom and occasional silicoflagellate blooms. We therefore consider the ability of the model to match observed silicon levels an indicator of the fidelity of its representation of local biogeochemistry. Silicon in the model may be in the form of dissolved silica, living diatoms, or particulate biogenic silica, and model diatom growth may be limited by nitrogen, light, or dissolved silica availability. We will discuss the challenges involved in accurately representing important drivers of the regional silicon cycle. These include accurately capturing the division of primary productivity between diatoms and non-siliceous phytoplankton functional groups, as well as uncertainties in the magnitude of terrestrial inputs and sediment fluxes. We will show how evaluating the model functional groups by comparison with phytoplankton community composition determined by high performance liquid chromatography (HPLC) has informed our interpretation of model results and provided direction for efforts at improving model performance. We will discuss the impact of targeted adjustments to model parameters on the model silicon cycle in light of comparisons to observations.

How to cite: Olson, E., Nemcek, N., and Allen, S.: Observations Inform Improvements in Model Silicon Cycling in a Semi-enclosed Coastal Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10502,, 2021.

Aude Flamand, Gwénaëlle Chaillou, Lauren Kipp, and Dustin Whalen

Global warming increases the thawing rate of the permafrost in high northern latitudes. The Arctic soil organic carbon accounts for over 50% of global soil carbon which is roughly twice the amount present in the atmosphere. An increasing amount of the newly mobilized old organic carbon, and its associated compounds, originating from permafrost thaw, is expected to be delivered to the Arctic Ocean by rivers and groundwater discharges all along the Arctic coastline. Absorbance and fluorescence spectroscopy can be used to identify a specific optical signature of permafrost-derived solutes with the objective of studying their transport and transformation to coastal waters. Emission-excitation spectra (EEMs) from three sampling sites along the coastal area of the delta were assessed and parallel factor analysis (PARAFAC) was used to identify three different components characterizing the origin and the nature of the organic carbon present in various types of samples (massive ice, groundwater, seawater and water samples on top/bottom of slumps). This study suggests that the carbon originating from the thawing of the permafrost could indeed be traced along the coastal area of the Delta.

How to cite: Flamand, A., Chaillou, G., Kipp, L., and Whalen, D.: Characterization of an optical signature of the DOM of the coastal permafrost in the Mackenzie delta, by PARAFAC analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16506,, 2021.

Fabrice Lacroix, Tatiana Ilyina, Moritz Mathis, Goulven Gildas Laruelle, and Pierre Regnier

Past century increases in terrigenous N and P inputs to the ocean due to industrialization, agricultural practices and wastewater have been reported to have dramatic consequences for ecosystems in various coastal regions. Yet, the impacts of increased nutrient inputs through river transports and atmospheric deposition on the coastal and open ocean carbon cycle have yet to be quantitatively investigated at the global scale. To address this gap of knowledge, we enhanced the ocean biogeochemical model HAMOCC at a horizontal resolution of around 0.4° in order to improve the representation of temporal changes of riverine fluxes and of coastal ocean dynamics in the model. Through a series of simulations with differing model forcings, we isolated individual effects arising from (1) increasing atmospheric CO2 levels, (2) a changing physical climate and (3) alterations in oceanic inputs of terrigenous P and N inputs, all over the 1905 to 2010 period. Our results indicate a strong response of the coastal ocean ecosystem to increased terrestrial nutrient inputs, which induce the global coastal Net Primary Production (NPP) to increase by 14% over the simulation time span. This eutrophication signal is, furthermore, partly exported to the open ocean, which undergoes an increase in NPP of 1.75 Pg C yr-1, or 4 % in relative terms, in the simulations, owing to the cross-shelf export of 33-46% of the anthropogenic P and N inputs to the coastal ocean. As a whole, increased P and N inputs lead to an overall global ocean NPP rise of around 2.15 Pg C yr-1, or 5% (combined coastal and open ocean). This net increase attributed to land-ocean couplings exceeds the simulated global oceanic NPP decrease of 4 % associated with stronger upper ocean thermal stratification over the time span, a feedback that been under stronger scrutiny in published literature. Our results suggest that increased riverine nutrient concentrations due to anthropogenic activities may also have substantial impacts for ecosystems in the open ocean, in contrary to what was assumed until now, although this is dependent on the rate of transfer of the nutrients from the coastal to the open ocean.

How to cite: Lacroix, F., Ilyina, T., Mathis, M., Laruelle, G. G., and Regnier, P.: Past century increases of terrestrial nutrient inputs impact both the coastal and open ocean carbon cycle, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9419,, 2021.

Jacob Noble, Alix Cage, Olivia Beavers, Bradley Sparks, Mark Furze, and James Scourse

Shelf seas account for around 10-30% of ocean productivity, 30-50% of inorganic carbon burial and up to 80% of organic carbon storage (Sharples et al., 2019); as such, shelf-sea sediments are a potential store of carbon and could play an important role in the ‘blue’ carbon cycle, and thus global climate. UK shelf-sea hydrography is dominated by seasonal stratification which drives productivity; however, stratification evolved with sea-level and tidal dynamic changes over the Holocene epoch on the UK shelf, and thus carbon stores will have changed over time. These shallow marine environments are typically seen as erosional environments and have therefore been somewhat overlooked in terms of palaeoenvironments with only a few studies from the UK continental shelf (e.g. Austin and Scourse, 1997). Here we use a core collected from the Celtic Deep, on the UK shelf, to explore environmental change, and the evolution of stratification in this setting and the potential role it plays in the global carbon cycle.

JC106-052PC, a 7.5m long marine sediment core, was recovered in 2018 at a water-depth of 116 m from the Celtic Deep (a relatively deep trough in the Celtic Sea between Britain and Ireland) as part of the BRITICE project. A radiocarbon date of 10,435 ±127 years cal BP at 4.1m suggests the core covers the Holocene epoch and preceding deglacial period. Preliminary multiproxy data from this expanded archive (ITRAX XRF, organic content, benthic foraminifera assemblages) points to changing environmental conditions and productivity potentially reflecting the evolution of seasonal stratification in the Celtic Sea over the Holocene. Work currently focuses on increasing the resolution of the benthic foraminifera record of JC106-052PC, extending the record into the deglacial period, and applying a benthic foraminifera transfer function approach to estimate sea-surface temperature of the Celtic Sea during the Holocene and deglacial period.  

This study aims to increase our understanding of the shelf-sea dynamics and productivity of the Celtic Sea over the last deglacial to Holocene period. By elucidating the response of the Celtic Sea to changing sea level and oceanographic conditions, and its capacity to act as a carbon store, we can better understand the role of other shelf environments, potentially benefiting global studies of palaeoclimate and future climate change. 

How to cite: Noble, J., Cage, A., Beavers, O., Sparks, B., Furze, M., and Scourse, J.: The palaeoceanographic history of the Celtic Sea since the last deglaciation and its potential for carbon storage, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9689,, 2021.

Vlad Macovei, Yoana Voynova, Holger Brix, and Wilhelm Petersen

Surface seawater carbon dioxide partial pressure (pCO2) in the North Sea, a large temperate shelf sea, was measured between 2014 and 2018 using FerryBox-integrated membrane sensors on ships of opportunity. The use of commercial vessels ensured a high spatio-temporal resolution, with data available year-round in areas belonging to all the stratification regime types found in the North Sea. Average annual cycles revealed a dominant biological control on pCO2 variability, with thermal effects modulating its amplitude. In the regions of freshwater influence, the biogeochemical characteristics of the riverine end-member also influenced the pCO2 measured near shore. Deseasonalized winter trends of seawater pCO2 were positive (ranging from 4.4 ± 2.0 µatm yr-1 to 8.4 ± 2.9 µatm yr-1 depending on the region), while the trends calculated including all deseasonalized monthly averages were even higher (ranging from 9.7 ± 2.8 µatm yr-1 to 12.2 ± 1.4 µatm yr-1). All these trends were stronger than the atmospheric pCO2 trend. Consequently, during our study period, the southern North Sea became a stronger source and the northern North Sea became a weaker sink for atmospheric carbon with implications for the Northwestern European Shelf carbon uptake capacity.

How to cite: Macovei, V., Voynova, Y., Brix, H., and Petersen, W.: Recent FerryBox observations reveal a strong increase in surface seawater pCO2 in the North Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5692,, 2021.

Chantal Mears, Helmuth Thomas, and Hendrik Wolschke

The North Sea’s location has made it an object of oceanographic study for over 150 years. But within the more recent past, this shelf sea with its strong continental shelf pump system has captivated science’s attention for a different reason: artificial ocean alkalinization (AOA). Through the enhancement of metabolic pathways or the addition of dissolved alkaline minerals into the ocean to draw down atmospheric CO2, AOA seems to offer a compelling option to mitigate climate change. But without judicious thought, human interaction could come at great cost. Alkalinity plays an integral role within a system’s biogeochemistry, and disruptions may result in large scale changes to small scale environments. But, within the North Sea, an extremely effective tracer of total alkalinity has been found, 228Ra. This isotope along with 226Ra, comprise the two long-lived isotopes of the Radium Quartet with half-lives of 1600yrs and 5.8yrs, respectively. As naturally occurring, sediment-derived radioisotopes, 228Ra and 226Ra have the potential to map the water-mass composition, the distribution patterns, and the associated timescales from shelf-sediment interaction to the open ocean. Furthermore, providing a possible method to shed light on the North Sea’s water-mass distributions, changing alkalinity patterns, and the potential effects of AOA. Over the course of this study, we will identify the basin’s key water-mass patterns and end members through the use of 226Ra and 228Ra, complemented by hydrological and carbonate parameters collected from the North Sea during the summers of 2018 and 2019 aboard the German research vessel Heincke. By employing inverse modelling techniques, we will investigate how AOA can cause changes on both a local and potentially global scale.

How to cite: Mears, C., Thomas, H., and Wolschke, H.: 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 2021, online, 19–30 Apr 2021, EGU21-8232,, 2021.

Bryce Van Dam, Pierre Polsenaere, Aylin Barreras-Apodaca, Christian Lopes, Zulia Sanchez-Mejia, Tatsuki Tokoro, Tomohiro Kuwae, Lucia Gutiérrez Loza, Anna Rutgersson, James Fourqurean, and Helmuth Thomas

Coastal vegetated habitats like seagrass meadows can mitigate anthropogenic carbon emissions by sequestering CO2 as “blue carbon” (BC). Already, some coastal ecosystems are actively managed to enhance BC storage, with associated BC stocks included in national greenhouse gas inventories. However, the extent to which BC burial fluxes are enhanced or counteracted by other carbon fluxes, especially air-water CO2 flux (FCO2) remains poorly understood. To this end, we synthesized all available direct FCO2 measurements over seagrass meadows made using a common method (atmospheric Eddy Covariance), across a globally-representative range of ecotypes. Of the four sites with seasonal data coverage, two were net CO2 sources, with average FCO2 equivalent to 44 - 115% of the global average BC burial rate. At the remaining sites, net CO2 uptake was 101 - 888% of average BC burial. A wavelet coherence analysis demonstrates that FCO2 was most strongly related to physical factors like temperature, wind, and tides. In particular, tidal forcing appears to shape global-scale patterns in FCO2, likely due to a complex suite of drivers including: lateral carbon exchange, bottom-driven turbulence, and pore-water pumping. Lastly, sea-surface drag coefficients were always greater than prediction for the open ocean, supporting a universal enhancement of gas-transfer in shallow coastal waters. Our study points to the need for a more comprehensive approach to BC assessments, considering not only organic carbon storage, but also air-water COexchange, and its complex biogeochemical and physical drivers.

How to cite: Van Dam, B., Polsenaere, P., Barreras-Apodaca, A., Lopes, C., Sanchez-Mejia, Z., Tokoro, T., Kuwae, T., Gutiérrez Loza, L., Rutgersson, A., Fourqurean, J., and Thomas, H.: Global trends in air-water CO2 exchange over seagrass meadows revealed by atmospheric Eddy Covariance, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2283,, 2021.

Peisheng Huang, Naomi S. Wells, Bradley D. Eyre, Daniel Paraska, and Matthew R. Hipsey

Coastal waters are typically productive aquatic ecosystems and play an important role in the global greenhouse gas (GHG) budget. However, the uncertainty in the estimation of GHG emission from estuaries remains large due to significant variability in GHG concentrations in time and space. This study aimed to provide a more accurate estimation of GHG emissions from sub-tropical estuaries by validating and analyzing results from a 3D hydrodynamic-biogeochemical model used to capture the temporal and spatial dynamics of the major GHG (CO2 CH4, and N2O). The model was applied to the Brisbane, Maroochy, and Noosa Estuary in Queensland, Australia, representing systems under high, median, and low human impacts, and was validated with datasets from long-term monitoring stations and field campaigns along the freshwater-marine continuum. Distinct spatial heterogeneity of GHG distribution was found with the upstream acting as a hotspot for emission to the atmosphere, despite this area occupying a relatively small portion of the rivers. Seasonal variations of pCO2 at the surface were driven mostly by the changes in water temperature and DIC concentrations, while strong diurnal variation was also found, driven by the changes related to tidal forcing. All GHG showed distinct signatures in the three rivers, related to trophic statues and hydrology. The model allowed us to approximate the fraction of incoming carbon and nitrogen that was lost to the atmosphere as GHG emissions, which is a step towards improving regional and national GHG budgets. A link of the biogeochemical model to a parameter optimization software PEST is being used to assist in uncertainty analysis from the model outputs.

How to cite: Huang, P., Wells, N. S., Eyre, B. D., Paraska, D., and Hipsey, M. R.: Insights of greenhouse gases (CO2, CH4 and N2O) dynamics in sub-tropical estuaries from a coupled hydrodynamic-biogeochemical estuarine model , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14382,, 2021.

Tereza Jarnikova, Debby Ianson, Susan E. Allen, Andrew E. Shao, and Elise M. Olson

Coastal regions are typically characterized by considerable physical variability that in turn leads to dramatic variability in coastal carbonate chemistry.  Recent shipboard and mooring-based observations have shown large spatial and temporal variations of carbonate chemistry parameters, including air-sea CO2 flux and aragonite saturation state, in one prominent coastal region in the Northeast Pacific Ocean - the Salish Sea. The range of the observed variability in the regional carbonate system is significantly larger than the global anthropogenic change, complicating the detection of secular carbon trends. Simultaneously, sparse observations limit understanding of the carbonate balance as a whole. Here, we use a highly resolved coastal model, SalishSeaCast, to characterize the drivers of the carbonate chemistry balance of the Salish Sea, with an emphasis on air-sea CO2 flux and aragonite saturation state. We then investigate the impact of a relatively modest increase in anthropogenic carbon in this region in the context of the governing physical and biological dynamics of the system. We examine the striking effects of the anthropogenic change to date on the inorganic carbon balance of the system, highlighting impacts on the aragonite saturation state of the system and its buffering capacity, as well as suggesting some bounds for the regional air-sea and lateral carbon fluxes. We then use the GLODAP dataset of global coastal carbon observations to consider our results in the context of other regions of the Pacific Rim and the global coastal ocean. 

How to cite: Jarnikova, T., Ianson, D., Allen, S. E., Shao, A. E., and Olson, E. M.: The Impact of a Modest Anthropogenic Carbon Increase on the Carbonate Chemistry Balance of a Temperate Fjord System, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13862,, 2021.

Tainan Fonseca, Roberta Bittencourt Peixoto, Luana Pinho, Leticia Cotrim da Cunha, Ricardo Pollery, and Humberto Marotta

Eutrophication in coastal waters caused by non-treated urban discharges has been considered one of the most important effects of global change. At tropical latitudes, nutrient dynamics may be especially intense due to increased metabolic responses supported by high temperatures and solar incidence throughout the year. In addition, short-term variations, such as in rainfall and the tidal regime, may determine important changes in nutrient concentrations and the subsequent trophic status of coastal waters, which are still neglected especially during nocturnal periods due to common logistical constraints. Here, we assessed 24-h variations of water quality during the winter season in a tropical eutrophic bay that receives large inputs of nutrients from non-treated urban effluents (Guanabara Bay, RJ, Brazil). We measured concentrations of dissolved forms of nutrients (nitrate, nitrite, N-ammoniacal, phosphate, and silicate) and carbon (DOC), and oxygen (DO) associated with temperature, salinity, and pH in surface waters each 2h over two daily cycles (July and August 2018). Water samples for nutrients and DOC were preserved for later analysis, while other variables were measured in the field. A biomonitoring system with a submersible pump was used to collect surface coastal waters without bubbling, and along a 70 m pipe from the beach to the field lab. In turn, meteorological data were obtained from a city weather station located ~6 Km from the sampling area. The monthly accumulated precipitation with respect to the 24-h cycle in July was ~70% lower than in August (58 and 16 mm, respectively), although only that in July has showed a rainfall event during the sampling period. As a result, average DOC and N-ammoniacal concentrations in surface waters were ~50% lower, while nitrate, silicate and DO concentrations ~56, 164 and 50 % higher, respectively, during the 24-h cycle in August compared to July. Also, waters were slightly more basic and less saltier in August, contrasting with similar average values of phosphate concentrations and temperature between both sampling periods. Finally, DO concentrations indicated an intense metabolism, varying from a peak of supersaturation with high solar incidence to net autotrophy (2 pm) to undersaturation values as a proxy of net heterotrophy after the nocturnal period (6 am). In conclusion, this short-term study showed that higher monthly accumulated precipitation may dilute high DOC and N-ammoniacal concentrations in coastal aquatic ecosystems undergoing anthropogenic eutrophication. On the other hand, silicate and nitrate concentrations might be related to higher runoff inputs from the watershed. The event of precipitation in July also confirmed a drastic increase in nitrate concentrations, likely due to inputs from the watershed. Therefore, our findings reveal the complexity of accumulated and immediate effects of rainfall on nutrient levels in tropical coastal waters, which  highlight the importance of biomonitoring studies specially in urban areas.

How to cite: Fonseca, T., Bittencourt Peixoto, R., Pinho, L., Cotrim da Cunha, L., Pollery, R., and Marotta, H.: Short-term changes of anthropogenic eutrophication with precipitation in tropical coastal waters (Guanabara Bay, Rio de Janeiro, Brazil), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14046,, 2021.

Guy Munhoven

SolveSAPHE, the Solver Suite for Alkalinity-PH Equations (Munhoven, 2013, DOI:10.5194/gmd-6-1367-2013), hereafter SolveSAPHE v.1, was the first carbonate chemistry speciation package that was able to securely and reliably calculate pH for any physically meaningful pair of total alkalinity (AlkT) and dissolved inorganic carbon (CT) values. We have now revised and extended the solution approach developed for SolveSAPHE v.1 so that AlkT & CO2, AlkT & HCO3 and AlkT & CO3 problems can be processed as well.

The mathematical analysis of the modified alkalinity-pH equations reveals that the AlkT & CO2 and AlkT & HCO3 problems have one and only one positive root for any physically sensible pair of data (i.e., such that, resp., [CO2] > 0 and [HCO3] > 0). For AlkT & CO3 the situation is completely different: there are pairs of data values for which there is no solution, others for which there is one and still others for which there are two. Similarly to its predecessor, the new SolveSAPHE-r2 offers automatic root bracketing and efficient initialisation schemes for the iterative solvers. The AlkT & CO3 problem is furthermore autonomously and completely characterised: for any given pair of data values, the number of solutions is determined and non-overlapping bracketing intervals are calculated.

The numerical solution of the alkalinity-pH equations for the three new pairs is far more difficult than for the AlkT & CT pair. The Newton-Raphson and the secant based solvers from SolveSAPHE v.1 had to be reworked in depth to reliably process the three additional data input pairs. The AlkT & CO2 pair is computationally the most demanding. With the Newton-Raphson based solver, it takes about five times as long to solve as the companion AlkT & CT pair, while AlkT & CO32– requires about four times as much time. All in all, the secant based solver offers the best performances. It outperforms the Newton-Raphson based one by up to a factor of four and leads to equation residuals that are up to seven orders of magnitude lower. For carbonate speciation problems posed by AlkT and either one of [CO2], [HCO3] or [CO32–] the secant based routine from SolveSAPHE-r2 is clearly the method of choice; for calculations with AlkT & CT, the SolveSAPHE v.1 solvers will perform better, due to the mathematically favourable characteristics of the alkalinity-pH equation for that pair.

How to cite: Munhoven, G.: SolveSAPHE-r2: a new versatile 4x4 engine for carbonate system pH calculations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9477,, 2021.