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OS3.8

Marine biogeochemical cycles regulate air-sea CO2 exchanges and oceanic carbon sequestration that, ultimately, controls the Earth’s climate. Key actors of these cycles are marine particulate and dissolved organic matter (OM) whose comprehension of the dynamics is one of the most pressing issue in marine science. However, marine biogeochemical cycles are impacted by anthropogenic pollution and there is an urgent need of quantifying sources and fluxes of the contaminants to the marine environment as well as to analyse and understand their possible effects on marine ecosystems and human health.
This session opens to in-field, laboratory and biogeochemical modelling studies that can help to understand where we are and what future directions must be taken to get insights into organic matter and pollutants cycle. The mechanisms of OM production, removal and accumulation, and correlation with optical properties are far from being unravelled. Limited knowledge exists on the impact of phytoplankton metabolism and environmental conditions on OM production as well as on the mechanisms determining its biological lability.
We would like to share the current research on how the multiple sources of anthropogenic pollution impact marine biogeochemical cycles, such as pollutant leaching from plastics and direct contamination of the water by contaminated rivers, aerosols, or submarine groundwater. In this session we aim at discussing mechanisms driving OM dynamics, transfer of pollutants through the marine trophic web, the effects of climate change on OM and pollutants cycle as well as scenarios of mitigation and adaptation to mercury and POP’s pollution.
We encourage submissions dealing with in-situ and space-based observational studies about OM dynamics, at the global as well as at the regional scale Inter-disciplinary studies are strongly encouraged. The session welcomes direct measurements of contaminant fluxes, isotopic or other approaches to tracing contamination, modelling, experimental incubations with contaminants, mesocosm studies and toxicity assessments, with particular attention to Hg and POP (persistent organic pollutants) cycles in the estuarine, coastal and ocean environments.
Thanks to this session we aim to gather together experts in physical, biogeochemical, optical and satellite oceanography. Other compartments of the earth system, and related societal, ecosystem and human health impact studies are welcome as well.

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Convener: Emanuele Organelli | Co-conveners: Donata Melaku Canu, Camille RichonECSECS, Chiara Santinelli, Lars-Eric Heimburger, Paolo Lazzari
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| Wed, 06 May, 08:30–10:15 (CEST)

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Chat time: Wednesday, 6 May 2020, 08:30–10:15

Chairperson: Emanuele Organelli, Donata Melaku Canu, Camille Richon, Chiara Santinelli, Paolo Lazzari
D2635 |
EGU2020-10736
| Highlight
| OS Division Outstanding ECS Lecture
Frederic Le Moigne

The oceanic biological carbon pump (BCP) regulates the Earth carbon cycle by transporting part of the photosynthetically fixed CO2 into the deep ocean. Suppressing this mechanism would result in an important increase of atmospheric CO2 level. The BCP occurs mainly in the form of organic carbon particles (POC) sinking out the surface ocean. Various types of particles are produced in surface ocean. They all differ in production, sinking and decomposition rates, vertically and horizontally. The amount of POC transported to depths via these various export pathways as well as their decomposition pathways all have different ecological origins and therefore may response differently to climate change. Here I will briefly review some of the processes driving both particle export out of the euphotic zone (0-100m) as well as particles transport within the mesopelagic zone (100-1000m). In the early 2000s, strong correlations between POC and mineral (calcite an opal) fluxes observed in the deep ocean have inspired the inclusion of “ballast effect” parameterizations in carbon cycle models. These relationships were first considered as being universal. However global analysis of POC and mineral ballast fluxes showed that mineral ballasting is important in regions like the high-latitude North Atlantic but that in most places (some of which efficiently exporting) the unballasted fraction often dominates the export flux. In such regions, we later on showed that zooplankton-mediated export (presence of faecal pellets) and surface microbial abundance were important drivers of the efficiency of particles export. Similar trends were found globally by including bacteria and zooplankton abundances to a global reanalysis of the global variations of the POC export efficiency. This implies that the whole ecosystem structure, rather than just the phytoplankton community, is important in setting the strength of the biological carbon pump. Further down in the water column (mesopelagic zone), processes impacting the transport of particles are less clear. Sinking particles experience a number of biotic and abiotic transformations during their descent. These includes solubilization, remineralisation, fragmentation, ingestion/active transport, break down among others. While some potential factors such as O2 concentration and temperature have been proposed as powerful controls, globally evidences are often inconsistent. Current challenges related to the role of particles consumption by zooplankton and fishes as well as the role of particles attached prokaryotes (bacteria and archaea) in setting the efficiency of the carbon transport in the mesopelagic zone will be discussed.

D2636 |
EGU2020-19041
Lea Oeljeschlaeger, Nils Hintz, Jutta Niggemann, Oliver Wurl, and Thorsten Dittmar

The sea surface microlayer (SML) is the boundary layer at the ocean and atmosphere interface and plays a crucial role in air-sea gas exchange processes and global climate. It is enriched in dissolved organic matter (DOM) compared to the underlying water, but the chemical composition of this material has been insufficiently studied. For improved understanding of the exchange processes it is of utmost importance knowing the molecular composition of the SML. Studying the microlayer is very challenging due to its thinness and strong influence of external forces as wind, UV light and atmospheric deposition on the chemical and microbial composition. The complex and dynamic nature of the microlayer and the enrichment of hydrophobic substances led to the assumption that we find unique chemical composition and distinct compound groups. SML samples of the Indo-Pacific Ocean from R/V Falkor cruise FK161010 (October 2016) were studied with respect to molecular composition of DOM. We analyzed solid-phase extracted DOM with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The results were compared to the underlying water (ULW, 1m depth). We found similar molecular DOM composition in the ULW, whereas microlayer extracts were more variable and diverse. This can be related to the influence of changing weather conditions during the cruise on the SML. To reveal molecular changes without interfering external forces, a 5-week indoor mesocosm experiment with induced marine phytoplankton blooms was conducted. A modified solid-phase extraction approach was used to chemically fractionate the microlayer DOM prior to molecular analysis. Our experiment showed that the DOM enrichment in the SML is linked to different phytoplankton communities. In addition, it revealed that depending on the predominant community the DOM concentration can be even depleted in the SML compared to the ULW. Based on the outcome of our field and laboratory studies we conclude that molecular level analysis of surface microlayers is essential to understand the chemical diversity of this highly dynamic boundary layer.

D2637 |
EGU2020-12621
Chia-Ying Chuang, Francois Guillemette, Jennifer Harfmann, Karl Kaiser, Robert Spencer, Brian Bergamaschi, and Peter Hernes

The San Francisco Bay Estuary (SFBE) together with the Sacramento–San Joaquin River Delta is the second largest estuary in the United States and represents a highly dynamic ecosystem. From 2014 to 2016, we conducted three transects across a salinity gradient to investigate the roles of sources, hydrologic and seasonal changes on the DOM composition. Sampling started with a riverine endmember, through a vast area of marshes, wetlands, to the Golden Gate, the largest estuary in western North America. The winter transect at its maximum discharge allowed the study of DOM dynamics largely in the absence of photodegradation processes and low levels of algal production; the summer transect captured significant photodegradation and algal production; the spring transect revealed the signal of stored DOM from the snowmelt cold water flows. Multiple studies indicated that algal primary production alone cannot support the SFBE foodweb, and the wetlands could also serve to reduce DOM loadings coming off of the delta.  Hence, other sources of organic matter must be considered, including autochthonous and allochthonous DOM. Terrestrial DOM export in SFBE were revealed by dissolved lignin dynamics. Optical proxies (UV-vis and fluorescence) were also used to study the photochemical and biological transformations of DOM.

D2638 |
EGU2020-4496
Luca Polimene, Sevrine Sailley, Darren Clark, and Susan Kimmance

Circa 624 gigatons of carbon are locked in the ocean as dissolved organic matter (DOM), an amount comparable with the entire CO2 content of the extant atmosphere. This DOM is operationally defined as refractory, meaning that it is resistant to bacterial degradation and persists in the ocean for millennia. Refractory DOM is considered primarily a residual product of heterotrophic bacterial activity after the bacterial consumption of more labile (i.e. easily degradable) DOM produced by marine autotrophs through photosynthesis. The process through which bacteria form refractory-DOM is termed the ‘Microbial Carbon Pump’ (MCP). Abiotic degradation (e.g. photo-degradation) is thought to balance refractory DOM production, thus maintaining its current pool in steady state. However, recent studies suggest that changes in surface ocean inorganic nutrient availability, due to climate change related increases in thermal stratification, could modify MCP activity, increasing refractory-DOM production with respect to its consumption. Marine bacteria thus have the potential to mitigate increases in atmospheric CO2 by shunting more photosynthesised carbon into refractory-DOM. This hypothesis can only be tested by including the MCP in numerical models used for climate prediction. However, the lack of mechanistic understanding of the process (due, in turn, to the lack of experimental data) has hitherto prevented the development of adequate model formulations. In this talk, I will discuss the potential (and limitations) of existing process models to simulate (at least partially) the MCP and highlight future research directions (and related challenges) to develop new model formulations describing this process.

D2639 |
EGU2020-8929
Cécile Dupouy, Farid Juillot, Hugues Lemonnier, Marie Bessard, Leocadie Jamet, Laura Boher, and Stephane Mounier

Dissolved organic matter (DOM) is ubiquitous in the environment. Its composition and properties depend on water type (freshwater, estuarine, brackish, marine) and are influenced by the geological nature (ultramafic, volcano-sedimentary, metamorphic) and occupancy (mangrove, forest, agriculture, urbanized) of the upstream catchment. Due to its capacity  to form complexes with dissolved trace metals, DOM can render them hardly available to living organisms, and thus limit their toxicity. Considering its capacity to be transported on large distances, DOM can significantly contribute to the dispersal of trace metals in aquatic ecosystems. In this study, we used 3D fluorescence spectroscopy to characterize the actual nature of FDOM (a fraction of DOM that shows specific fluorescence properties) across estuaries downstream of two contrasted catchments (ultramafic vs. volcano-sedimentary) in New Caledonia. In a first step, Excitation-Emission Matrix (EEM) were obtained on 0.2 µm filtered water samples and a parallel factor analysis (PARAFAC) allowed to identify the different FDOM components in the two catchments. These data indicated a dramatic decrease of all components as a function of increasing salinity, with a threshold value around 25 g/L whatever the catchment. This trend is considered to reflect an aggregation-flocculation behavior of FDOM across the salinity gradient of the studied estuaries. In a second step, fluorescence quenching experiments emphasized the complexing capacity of the different components toward dissolved Ni. FDOM might thus play a significant role on Ni dispersal in aquatic ecosystems through the formation of FDOM-Ni complexes. However, this dispersal capacity might be hampered in estuaries due to the suspected aggregation-flocculation behavior of FDOM across the salinity gradient. Rather than the geological setting of the upstream catchment, salinity appears thus as the major driver of Ni dynamics across estuaries through FDOM-Ni complexes.

D2640 |
EGU2020-7342
Ana Gabriela Bonelli, Hubert Loisel, Vincent Vantrepotte, Daniel Jorge, Antoine Mangin, and Julien Demaria

The Dissolved Organic Carbon (DOC) represents the largest pool of organic carbon and the most active carbon compartment in the ocean. Describing the spatio-temporal dynamics of the oceanic DOC in response to variation in the physical of biological forcings is therefore crucial for better understanding the global carbon cycle. The DOC distribution and its temporal dynamics is however currently not well known.

In the recent years several works have demonstrated the possibility to assess from space the DOC distribution in the coastal ocean thanks to direct relationships between DOC and the optical properties of colored dissolved organic matter (CDOM). Such CDOM-DOC relationships are not applicable for the open ocean water due making more complex the DOC estimation from space in the latter environments. Here we present first results documenting an alternative method for estimating DOC from satellite imagery which rely on the use of a neural network which combines different physical and biogeochemical input variables (SST, SSS, PAR, aCDOM and Chl-a).

D2641 |
EGU2020-10101
Jakob J. Stamnes, Ciren Nima, Børge Hamre, Øyvind Frette, Yi-Chun Chen, Kai Sørensen, Marit Norli, Daren Lu, Qiangguo Xing, Dennis Muyiimbwa, Taddeo Ssenyyonga, Knut Stamnes, and Svein Rune Erga

We present absorption properties of colored dissolved organic matter (CDOM) sampled in six different water bodies along extreme altitudinal, latitudinal, and trophic state gradients. Three sites are in Norway: the mesotrophic Lysefjord (LF), Samnangerfjord (SF), and Røst Coastal Water (RCW); two sites are in China: the oligotrophic Lake Namtso (LN) and the eutrophic Bohai Sea (BS); and one site is in Uganda: the eutrophic Lake Victoria (LV).

 

The site locations ranged from equatorial to subarctic regions, and they included water types from oligotrophic to eutrophic and altitudes from 0 m to 4700 m. The mean CDOM absorption coefficients at 440 nm [aCDOM(440)] and 320 nm [aCDOM(320)] varied in the ranges 0.063–0.35 m-1 and 0.34–2.28 m-1, respectively, with highest values in LV, Uganda and the lowest in the high-altitude LN, Tibet.

 

The mean spectral slopes S280-500 and S350-500 were found to vary in the ranges of 0.017–0.032 nm-1 and 0.013–0.015 nm-1, respectively. The highest mean value for S280-500 as well as the lowest mean value for S350-500 were found in LN. Scatter plots of S280-500 versus aCDOM(440) and aCDOM(320) values ranges revealed a close connection between RCW, LF, and SF on one side, and BS and LV on the other side.

 

CDOM seems to originate from terrestrial sources in LF, SF, BS, and LV, while RCW is characterized by autochthonous-oceanic CDOM, and LN by autochthonous CDOM. Photobleaching of CDOM is prominent in LN, demonstrated by absorption towards lower wavelengths in the UV spectrum. We conclude that high altitudes, implying high levels of UV radiation and oligotrophic water conditions are most important for making a significant change in CDOM absorption properties.

Considering all study sites, we find a strong negative linear relationship between the base-10 logarithm of aCDOM(440) and the spectral slope S280-500, and also between the base-10 logarithm of aCDOM(320) and the spectral slope S280-500.

D2642 |
EGU2020-21916
Anh Pham and Takamitsu Ito

Phytoplankton growth in the Indian Ocean is generally limited by macronutrients (nitrogen: N and phosphorus: P) in the north and by micronutrient (iron: Fe) in the south. Increasing anthropogenic atmospheric deposition of N and dissolved Fe (dFe) into the ocean can thus lead to significant responses from marine ecosystems in this ocean basin. Previous modeling studies investigated the impacts of anthropogenic nutrient deposition on the ocean, but their results are uncertain due to incomplete representations of Fe cycling. We use a state-of-the-art ocean ecosystem and Fe cycling model to evaluate the transient responses of ocean productivity and carbon uptake in the Indian Ocean, focusing on the centennial time scale. The model incorporates all major external sources and represents a complicated internal cycling process of Fe, thus showing significant improvements in reproducing observations. Sensitivity simulations show that after a century of anthropogenic deposition, increased dFe stimulates diatoms productivity in the southern Indian Ocean poleward of 50⁰S and the southeastern tropics. Diatoms production weakens in the south of the Arabian Sea due to the P limitation, and diatoms are outcompeted there by coccolithophores and picoplankton, which have a lower P demand. These changes in diatoms and coccolithophores productions alter the balance between the organic and carbonate pumps in the Indian Ocean, increasing the carbon uptake in the south of 50⁰S and the southeastern tropics while decreasing it in the Arabian Sea. Our results reveal the important role of ecosystem dynamics in controlling the sensitivity of carbon fluxes in the Indian Ocean under the impact of anthropogenic nutrient deposition over a centennial timescale.

D2643 |
EGU2020-20458
Anna Sobek, Inna Nybom, Hans Peter Arp, Naiara Berrojalbiz, Nathan Charlton, Mari Forsell, Dorothea Gilbert, Gisela Horlitz, and Janneke van Grimbergen

Persistent organic pollutants (POPs) are ubiquitously present in the aquatic environment. They are hydrophobic substances that sorb to organic carbon (OC), and thus their environmental fate is closely linked to OC fluxes and pools. In this project, we test the hypothesis that future changes in the OC cycle can influence POP flux from air to sediment and reduce the POP sink in Baltic Sea sediments. The hypothesis relies on the assumption that the OC sorption capacity is affected by the relative contribution of terrestrial OC as well as the trophic status (oligotrophic versus eutrophic) of the area. Four different coastal sites were sampled, to capture different carbon regimes in terms of nutrient status and level of terrestrial OC influence. Concentrations of POPs were analysed along high-resolution sediment porewater- bottom water interface profiles, in total sediment, suspended matter collected in sediment traps and plankton, in the water column and in air. Stable carbon isotope signatures (δ13C) showed that the sites are different in terms of the influence of terrestrial organic matter, and the sites differ in nutrient conditions.

Preliminary results demonstrate that in general, sediments (three sites analysed) act as a source of PAHs to overlying water, whereas sediment and water more often are in equilibrium for PCBs, although there are variations for individual compounds. At the high nutrient-low terrestrial site, which was sampled at two different seasons, both air and water concentrations were higher for PAHs and PCBs in the autumn compared to the summer, indicating the importance of air as source of these contaminants to the water column. Accordingly, air seems an important source of PAHs to the water column in the low terrestrial-low nutrient site, as concentrations in the water column are increasing towards the water surface, whereas this was not observed for PCBs at the same site. Preliminary results from two contrasting sites in the Gulf of Finland, both with high nutrient levels but with different relative contribution of terrestrial OC, demonstrate higher total sediment concentrations of PAHs in the sediment with more marine OC, which was not observed as clearly for PCBs. Data from the water column indicate that marine OC is more efficient in sorbing POPs as air and water concentrations were similar at both sites, even though the OC vertical export at the high terrestrial site was more than double compared to the low terrestrial site. The full data set, will allow for further evaluation of hypotheses on the links between OC cycling and contaminant fate in the Baltic Sea.

D2644 |
EGU2020-6183
Feiyue Wang and Kang Wang

A subsurface enrichment of methylmercury (MeHg) has been observed at shallow depths (~100–300 m) in several regions of the Arctic Ocean. The spatial distribution of this subsurface seawater MeHg has been suggested to be responsible for the spatial variability in mercury concentrations of marine animals in the Canadian Arctic. The origin of the sub-surface MeHg in seawater, however, remains a subject of debate. In most other ocean basins, seawater MeHg typically peaks at deeper depths with a much lower dissolved oxygen content, and is thought to be produced in situ and in association with organic matter remineralization. In contrast, our water mass analysis suggests that MeHg enrichment in the shallow, well-oxygenated waters in the Canadian Arctic bears a signature that is most consistent with long-range transport of the Upper Halocline Pacific Water (UHW). Our results further show that seawater MeHg concentrations exhibit a significant correlation with a denitrification tracer, N*, and that the MeHg-to-N* slope decreases progressively from west to east across the Canadian Arctic. The negative N* values in the Canadian Arctic are known to have originated from denitrification in the productive Chukchi Sea shelf sediments, where anaerobic mercury methylation could also be favored. As MeHg- and N*-carrying UHW advects eastwards toward the Canadian Arctic, MeHg is progressively lost through demethylation, resulting in the observed decreasing trend in the MeHg-to-N* slope. The long-distance transport implies that the half-life of MeHg in Arctic seawater below the euphotic zone must be much longer than previously reported. This is supported by a critical literature review, which casts doubt on mercury methylation and demethylation rates previously determined from a seawater incubation approach due to unexplainable methylation and demethylation at time zero and poor fitting of the experimental data to first-order kinetics. Our results thus call for a better understanding of productive shelf sediments as potential MeHg “hotspots” in the Arctic and more reliable measurements of mercury methylation and demethlyation rates in the ocean.

D2645 |
EGU2020-19646
Sofi Jonsson, Johannes West, and Van Liem Nguyen

Dimethylmercury (DMeHg), a highly toxic form of mercury (Hg), appears as a dissolved gas in marine waters as well as some terrestrial environments. Although DMeHg does not reach concentrations in natural environments that are of direct concern for human and wildlife health, it has been suggested that DMeHg could play a role in controlling the amount of monomethylmercury (MMeHg) available. As MMeHg bioaccumulates in aquatic food webs to concentrations of concern, it links the occurrence of DMeHg in marine systems with the negative consequences of Hg pollution for human and wildlife health. Our understanding of the biogeochemical cycle of DMeHg is however scant. The potential for adsorption of DMeHg onto natural particles has so far not been addressed. This, despite the fact that adsorption is recognised to be an important process controlling the distribution of other chemical forms of Hg in the environment, including ionic forms of inorganic divalent Hg and monomethylmercury as well as gaseous elemental Hg.  

Here, we will present the data from the first adsorption experiments with dimethylmercury using model compounds (including FeS-minerals) as well as natural sediments and soils. For FeS(s), DMeHg readily adsorbed onto the mineral surface reaching equilibrium within 1-2 h. Observed partitioning between the solid and aqueous phase for FeS were also close to observed partitioning of e.g. MMeHg. Preliminary data also suggests DMeHg to readily adsorb onto natural particles, including sediments and soils.

D2646 |
EGU2020-13828
Joel Knœry, Bastien Thomas, Christophe Brach-Papa, Nicolas Briant, Sandrine Bruzac, Tiphaine Chouvelon, Sylvette Crochet, pauline Le Monier, Emmanuel Ponzevera, and Teddy Sireau

We have examined the distribution and spectiation mercury and trace metals under contrasted season, river flow conditions and tidal amplitudes with a series of  cruises taking place between 2012 and 2015. Our laboratory had alredy undertaken a similar study in the early 1990's. The latest data acquisition efforts are an opportunity to examine the changes that occurred within that time span for mercury and its species, and to discuss the causes of the observed changes. In particular, we will replace the  observations in the perspectives of environmental regulation, and of field and laboratory practices observed for environmental chemical characterization.

Early 1980's estuarine transects show total dissolved Hg levels near 5nM in the Loire river (Frenet, 1981). In the early 1990's, a careful and detailed study shows estuarine levels between 1 and 6pM (Coquery, 1994) with a strong dependency on the hydrological regime. New results confirm the riverine clevels in the low pM range. Concentrations decrease progressively during mixing with seawater and the oceanic end-member concentrations are near 0.5pM. Monitoring of mercury levels and speciation in the Loire river and the upper reaches of the estuary show that these Hg levels and species fluctuate with water flow and areal flooding upstream, AND on the history of that hydrological regime.

D2647 |
EGU2020-14875
Johannes Bieser, Ute Daewel, and Corinna Schrum

Five decades of Hg science have shown the tremendous complexity of the global Hg cycle. Yet, the pathways that lead from anthropogenic Hg emissions to MeHg exposure through sea food are not fully comprehended. Moreover, the observed amount of MeHg in fish exhibits a large temporal and spatial variability that we cannot predict yet. A key issue is that fully speciated Hg measurements in the ocean are difficult to perform and thus we will never be able to achieve a comprehensive spatial and temporal coverage.

Therefore, we need complex modeling tools that allow us to fill the gaps in the observations and to predict future changes in the system under changing external drivers (emissions, climate change, ecosystem changes). Numerical models have a long history in Hg research, but so far have virtually only addressed inorganic Hg cycling in atmosphere and oceans.

Here we present a novel 3d-hydrodynamic mercury modeling framework based on fully coupled compartmental models including atmosphere, ocean, and ecosystem. The generalized high resolution model has been set up for European shelf seas and was used to model the transition zone from estuaries to the open ocean. Based on this model we present our findings on intra- and inter-annual dynamics and variability of mercury speciation and distribution in a coastal ocean. Moreover, we present the first results on the dynamics of mercury bio-accumulation from a fully coupled marine ecosystem model. Most importantly, the model is able to reproduce the large variability in methylmercury accumulation in higher trophic levels.

D2648 |
EGU2020-1695
Peipei Wu, Emily Zakem, Stephanie Dutkiewicz, and Yanxu Zhang

Methylmercury is greatly bioconcentrated and biomagnified in marine plankton ecosystems, and these communities form the basis of marine food webs. Therefore, evaluating the potential exposure of methylmercury to higher trophic levels, including humans, requires a better understanding of its distribution in the ocean and the factors that control its biomagnification. In this study, a coupled physical/ecological model was used to simulate the trophic transfer of monomethylmercury (MMHg) in a marine plankton ecosystem. The model includes phytoplankton, a microbial community, herbivorous zooplankton (HZ), and carnivorous zooplankton (CZ). The model captured both shorter food chains in oligotrophic regions, with small HZ feeding on small phytoplankton, and longer chains in higher nutrient conditions, with larger HZ feeding on larger phytoplankton and larger CZ feeding on larger HZ. In the model, trophic dilution occurred in the food webs that involved small zooplankton, as the grazing fluxes of small zooplankton were insufficient to accumulate more MMHg in themselves than in their prey. The model suggested that biomagnification was more prominent in large zooplankton and that the microbial community played an important role in the trophic transfer of MMHg. Sensitivity analyses showed that with increasing body size, the sensitivity of the trophic magnification ratio to grazing, mortality rates, and food assimilation efficiency (AEC) increased, while the sensitivity to excretion rates decreased. More predation or a longer zooplankton lifespan may lead to more prominent biomagnification, especially for large species. Because lower AEC resulted in more predation, modeled ratios of MMHg concentrations between large CZ and HZ doubled when the AEC decreased from 40% to 10%. This suggested that the biomagnification of large zooplankton was particularly sensitive to food assimilation efficiency.

D2649 |
EGU2020-669
Giancarlo Bachi, Elisabetta Morelli, Margherita Gonnelli, Raffaella Casotti, Stefano Vestri, Valter Evangelista, Cecilia Balestra, and Chiara Santinelli

Phytoplankton is the primary source of Dissolved Organic Matter (DOM) to the oceans. DOM is mainly released by extracellular exudation and used by heterotrophic prokaryotes to synthesise biomass and recycle inorganic nutrients. DOM released by phytoplankton is mainly composed by carbohydrates, proteins and lipids that are thought to be labile and by humic substances that are thought to be recalcitrant and thus resistant to bacterial degradation. There are a lot of uncertainties regarding the biological lability of exudates and the role of DOM released by phytoplankton in the marine carbon cycle. In this study, cultures of the diatom P. tricornutum were produced under axenic conditions and Dissolved Organic Carbon (DOC) concentration, Excitation-Emission matrices (EEMs) and cell density were measured with time in order to follow the release of DOM during the different growth phases. Exudates were then inoculated with a marine microbial community for 24 days, DOC removal and FDOM transformation were followed with time in the exudates and in the permeate (< 3k Da; Low Molecular Weight, LMW) and retentate (> 3k Da; High Molecular Weight, HMW) fractions. Heterotrophic prokaryotes abundance was also followed during the incubations. Our results show that ~75% of the total DOC pool was LMW. After 24 days, 28% of the initial DOC pool was removed. Fluorescence indicate high lability of protein-like molecules and degradation of bigger proteins into smaller peptides before their removal. The production of humic-like and flavin-like substances was also observed.

 

D2650 |
EGU2020-19058
Vincenzo Vellucci, Melek Golbol, and David Antoine

Typical measurements of the absorption coefficient of the chromophoric fraction of dissolved organic carbon (CDOM) are performed on filtered seawaters samples. Though samples could be stored in the dark at 4° for up to 6 months, it is preferable to analyse them within 24 hours from collection as variation of absorption might occur depending on the nature of the sample, and to minimize the effect of possible contamination.

As it is not always practical to analyse samples on board, techniques have been proposed to measure the CDOM with in situ deployed reflective tube absorption meters (i.e. SeaBird ac-9 and ac-s). These techniques allow time effective measurements of CDOM at high vertical resolution. However the typical path-length of the cavity containing the water sample is of 0.25 m, i.e. one eighth of most common protocols used in laboratory analyses, thus limiting the accuracy of the measurements at lower signals.

Integrating cavity absorption meters (ICAM) represent an alternative to reflective tube absorption meters. They have been primarily developed to reduce the effect of scattering of particulate onto absorption measurements. Nonetheless this technique presents also the advantage to increase the effective optical path-length of the light beam due to multiple reflections into the reflecting cavity (up to 2 m for a 10 cm sphere diameter). This peculiarity make ICAM suitable for applications with lower signal such as open ocean case I waters.

Here we present some advances toward the definition of a protocol for the use of a hyperspectral integrating cavity sphere (Hobilabs a-sphere) for the in situ measurement of CDOM. In particular we address aspects related to cleaning, blank measurements, water flow into the cavity and pressure and we present data from the BOUSSOLE bio-optical time series (NW Mediterranean Sea).

D2651 |
EGU2020-20832
Jeonghyun Kim, Yeseul Kim, Tae-Hoon Kim, Sung Eun Park, Dong-Jin Kang, and TaeKeun Rho

The hydrological properties (temperature, salinity, pH, and dissolved oxygen), dissolved organic carbon (DOC) and nitrogen (DON), and optical absorption and fluorescence signals were measured in Jeju Island, Korea, during 2016–2018, especially in potential point-sources (e.g. coastal aquafarms, a sewage treatment facility, and coastal artesian springs). The water samples were filtered through 0.2 μm polycarbonate syringe filters. The optical analysis was conducted using a spectrophotometer (Aqualog, Horiba, USA). Absorbance spectra were converted into the absorption coefficient, and fluorescence intensities were conducted by the parallel factor analysis (PARAFAC) model. The fluorescent components were compared with previous studies through the web-based OpenFluor database.

The absorption coefficient at 350 nm ranged from 0.05 to 7.63 m −1, and it was up to 150 times higher near the point-sources than in the normal coastal ocean. In addition, a350 was observed to be exponentially increased as the reduced distance from the aquafarm outlet. Similarly, the concentration of DOC was 89 ± 29 μM near the point-sources and 78 ± 13 μM in the normal coastal area. They were also observed to be high fluorescence near the point-sources. Principal component analysis (PCA) was applied to illustrate the relationship among the five PARAFAC components, DOC, DON, a350, and fluorescence indexes (HIX, BIX, FI, TC ratio, and RI). The PCA results separated allochthonous, terrestrial components from autochthonous, microbial components, as explained 71.3% of the variance in the data. Based on the HIX (1.26 – 55.70) and BIX (0.52 – 2.87) values in this study, the organic matter around the coastal Jeju Island seem to be highly affected by the coastal groundwater. Here, we used multiple optical properties of organic matter near the coastal area to identify the key factor contributing its distribution and water qualities and to determine the significant influence of the point-sources.

D2652 |
EGU2020-18207
Simona Retelletti Brogi, Marta Furia, Giancarlo Bachi, Vanessa Cardin, Giuseppe Civitarese, Bruno Tiribilli, Toste Tanhua, Massimo Vassalli, and Chiara Santinelli

The Mediterranean Sea (Med Sea) can be considered as a natural laboratory for the study of dissolved organic matter (DOM) dynamics. Despite its small size, it is characterized by the same physical processes and dissolved organic carbon (DOC) concentration and distribution as the global ocean. The Med Sea deep water DOC pool is however older than the Atlantic one and differences in the microbial loop and in DOM dynamics have been observed between the eastern (EMED) and western (WMED) basins. Fluorescence is a fast, cheap and highly sensitive tool to study DOM dynamics, it can therefor give useful information about the main processes affecting DOM distribution.

The main aims of this study were: (i) to investigate DOM dynamics in both Med Sea basins, in relation to the physical processes (e.g. vertical stratification, irradiation); and (ii) to validate the use of a new fluorescence sensor, developed in the framework of the SENSOR project (POR FESR, Tuscany Region), for the rapid, in-situ measurements of open-sea fluorescent DOM (FDOM). DOM dynamics was investigated by measuring dissolved organic carbon (DOC) and the fluorescence of FDOM. Samples were collected from surface to bottom in 26 stations during the trans-Mediterranean cruise “MSM72”, carried out on board the R/V MARIA S.MERIAN (Institut für Meereskunde der Universität Hamburg). The stations cover both the EMED and the WMED, from Gibraltar to the Crete Island.

Six fluorescent components were identified by applying the parallel factorial analysis (PARAFAC) to the measured excitation-emission matrices (EEMs). Two components were identified as marine humic-like, two as terrestrial humic-like, one as protein-like and one as polycyclic aromatic hydrocarbon-like (PAH-like).

Temperature and salinity increased moving from the WMED to the EMED. A surface minimum in salinity, was observed in the WMED, indicating the occurrence of the Atlantic Water (AW), whereas the presence of the Levantine Intermediate Water (LIW) was observed south of Crete. The vertical distribution of both DOC and humic-like FDOM was strongly affected by the water masses circulation and water column stratification. In the upper 200 m, DOC markedly increased from 50 to 80 μM moving eastward, likewise the protein-like component dominates the upper layer and increased moving from Gibraltar to Crete. In contrast, the humic-like components showed a minimum in the surface layer, and a decreasing moving eastward, probably due to photobleaching. The PAH-like component showed its maximum in correspondence with the areas characterized by intensive naval traffic. The accumulation of DOC, observed in the EMED, could be explained by a change in DOM quality, supported by the differences in FDOM.

In 2 selected stations, the fluorescence of humic-like and protein-like compounds was also measured along the water column by using the new fluorescence sensor and compared with PARAFAC results, in order to evaluate its performance for open sea waters.

D2653 |
EGU2020-10870
Carla Morais, Benjamin Oursel, Francisco Edouardo Gontijo Guimaraes, Debora Marcondes Bastos Pereira Milori, and Stéphane Mounier

The sediments are complex and heterogeneous environments, thus, besides determining the concentration of potentially toxic metals present in sediments, it is necessary to understand the sediment's ability to accumulate or release contaminants, because many biogeochemical processes are involved, influencing the fate of these metals. The main modes of dispersion, which can lead to remobilization of contaminants are (i) early diagenesis, (ii) natural or anthropogenic resuspension of the sediment and (iii) the diffusive flow at the water-sediment interface. In this context, it is important to understand in how sedimentary organic matter (SedOM) acts in the retention and remobilization of metals, what environmental risks and how climate change influences the flow of rivers and causes remobilization of sedimentation, resulting in the release of these metals. As a result, it will be possible to evaluate if SedOM is a danger or protection against contaminants. In this work were used 69 samples collected at different depths at 3 points on the Tietê river, at 3 points on the Piracicaba river and at one point in the confluence region. The samples were freeze-dried, crushed, and sieved through a 100 mesh sieve. Two SedOM extraction methods were conducted in this work: NaOH extraction and deionized water extraction. Approximately 1.0 g of each sediment was placed in polypropylene flasks with 45.0 mL of 0.1 mol L-1 NaOH and 45.0 mL of deionized water, and then shaken for 24 h in an overhead shakerat 10 rpm. Then the samples were centrifuged at 3,000 g for 10 min and filtered over a 0.45 μm syringe filters. To study the fluorescence mode in EEM, 1.0 mL of each diluted with same absorbance sample was placed in quartz cells with 1.0 mL of 0.3 mol L-1 HEPES and 1.5 mL of 0.1 mol L-1 NaClO4. The fluorescence spectra were acquired in scan speed of 2,400 nm min-1 from 250 to 700 nm in emission and from 200 to 500 nm in excitation. The steps and slits of emission and excitation were fixed at 5 nm, and the detector voltage was 700 V. EEM data were processed using the method of Parallel Factor Analysis to determine the contribution of each component using homemade PROGMEEF software. SedOM samples extracted with NaOH and deionized water from Tietê and Piracicaba rivers presented COre CONsistency DIAgnostic of 83.3% with the contribution of four components or fluorophores. According the components obtained by PARAFAC, the component 2 is noise and it was excluded. The emission wavelength of fluorophore 1 is approximately 450 nm, fluorophore 3 is 550 nm and fluorophore 4 is 400 nm. Therefore, the fluorophore 4 refers to OM fresher, simpler and less humidified. Whereas fluorophore 3 refers to OM older, more complex and more humidified, that is, it is from the terrestrial environments. According to data obtained by EEM and treated with PARAFAC was possible to determine the presence of three fluorophores and the complexity of their structure.

D2654 |
EGU2020-11065
Amonda El Houssainy, Gaël Durrieu, Huy Duc Dang, Cédric Garnier, and Stéphane Mounier

Dissolved organic matter (DOM) is a complex continuum of molecular species and plays an important role in biogeochemical processes in the aquatic ecosystem, waters and sediments (Aiken et al., 2011; Bolan et al., 2011; Burdige et al., 2004; Chen and Hur, 2015; Fu et al., 2006; Jiang et al., 2018; Stedmon et al., 2003). Once settled into marine sediments, organic matter undergoes biogeochemical transformations (Chen and Hur, 2015). These biogeochemical conditions are dependent on different parameters such as redox condition and microbial activities controlling its dynamics. Studies on pore water organic matter (PW-OM) and extracted organic matter (EOM) give understanding on the fate of sedimentary organic matter. Several studies (Burdige, 2001; Burdige et al., 2004; Chen and Hur, 2015; Dang et al., 2014; Hur et al., 2014; Murphy et al., 2008; Stedmon et al., 2003; Stedmon and Bro, 2008) have used Excitation Emission Matrices of fluorescence coupled to PARAFAC and UV-Vis spectroscopy to characterize DOM among several technics. As it is rapid and gives information on the dynamics, the aromatic structure and even the degree of humification of DOM. Toulon bay is a semi-enclosed bay located in the N-W basin of the Mediterranean Sea and in the S-E of the French coast. This bay is exposed to numerous pollution sources. The origins of organic matter in the bay is the input of two urbanized rivers (Las and Eygoutier), aquaculture, treated sewage outlets and planktonic activities (Boge et al., 2006; Nicolau et al., 2012). Sediment cores and column seawaters were collected at four points in the bay in front of Las River. Each core was sliced within a 2cm resolution under inert atmosphere (N2). Then, pore water was retrieved and filtered (0.2 µm) and solid fraction was freeze-dried, 2mm sieved, crushed. DOC and nutrients concentrations in water samples and total carbon, organic carbon (POC) and total nitrogen were measured on solid. Extraction with alkaline solution was performed and extracted organic carbon and extracted nitrogen were measured. 3D fluorescence measurements were done for all samples from 200 to 800 nm for both excitation and emission. The results showed that the degradation of OM was more intense in front of Las River than outside of the bay. Pore water and extracted OM are influenced by fresh biomass input and the latter is strongly humified. Pore water OM in the superficial layers of sediments comes from autochthonous origin and less humified with a weak aromaticity. However, in deep layers, it shows a terrestrial origin, a regain of aromaticity and an important humic character based on HIX index. Moreover, it is controlled by the production and degradation of nutrients and POC. Extracted OM derives from terrestrial origin and is strongly humified based on HIX index. The state of FDOM in superficial sediments is different from the one in deep sediments because of the reducing environment. There is a contradiction of FDOM fate/behavior between the dissolved and solid phase in deep sediments because the production of FDOM isn’t from the POC pool.

D2655 |
EGU2020-9059
ruili Li

Denitrifier communities differ in mangrove wetlands across China

Ruili Li*, Sijie Wu, Minwei Chai, Xiaoxue Shen, Lingyun Yu

Key Laboratory for Heavy Metal Pollution Control and Reutilization, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, Guangdong, PR China

*Corresponding author. E-mail address: liruili@pkusz.edu.cn

Abstract:

Denitrification plays an important role in the removal of nitrogen from coastal wetlands. However, knowledge regarding the dynamics of denitrifier communities in mangrove wetlands is limited, and the corresponding influential factors lack quantitative analysis. To explore the geographical variations in the nosZ-denitrifier community and the underlying influential factors, surface sediments in mangrove forest and adjacent mudflat were collected from six mangrove wetlands across China, including high-latitude Yunxiao (YX) and Futian (FT) mangroves, middle-latitude Fangchenggang (FCG), Zhanjiang (ZJ) and Dongzhaigang (DZG) mangroves, and low-latitude Dongfang (DF) mangrove. The nosZ gene abundance in mangrove sediments varied from 1.60×105–1.17×106 copies g-1 dry sediment, with a higher density in Avicennia marina forest than the mudflat. Denitrifier community richness and diversity increased with decreasing latitude based on the Chao1 richness and Shannon diversity index, with the highest diversity being observed in the DF mangrove. The denitrifier communities could be classified into three groups including low-latitude DF mangrove, middle-latitude FCG, ZJ and DZG mangroves, and high-latitude YX and FT mangroves based on HCA and PCA analysis. The nosZ OTUs could be divided into seven distinct clusters with different proportionality characteristics among mangroves. Environmental factors (TN, TOC, and salinity) could collectively shape denitrifier communities in mangrove sediments.

D2656 |
EGU2020-12861
| Highlight
Katharina Seelmann, Tobias Steinhoff, and Arne Körtzinger

The observation and documentation of the marine carbon cycle is of utmost importance because of probable future changes such as ocean acidification, warming or deoxygenation. Over decades, ship-based observatories (Ships of Opportunity – SOOP) equipped with sensors measuring the CO2 partial pressure (pCO2) in the surface seawater form the backbone of the global ocean carbon observation system. However, one severe shortcoming of the current carbon-SOOP observatory is the fact that it mostly only measures pCO2 which is required to calculate the net air-sea CO2 flux. Full insight into the marine CO2 system for important aspects such as net biological production, ocean acidification, and marine calcification requires the measurement of two out of the four measurable variables of the marine CO2 system which are pCO2, total alkalinity (AT), dissolved inorganic carbon (CT) and pH. The so far common workaround is the calculation of AT from sea surface temperature and sea surface salinity using established parameterizations. Unfortunately, this procedure leads to high uncertainties and is particularly prone to regional bias. Therefore, autonomous AT measurements are necessary. Our study describes the implementation of a novel autonomous analyzer for seawater AT, the CONTROS HydroFIA® TA system (Kongsberg Maritime Contros GmbH, Kiel, Germany) on a North Atlantic SOOP line based on the merchant vessel M/V Atlantic Sail (Atlantic Container Line). The first main part of this work deals with the installation of the analyzer, for which several circumstances must be taken into account: 1) The system’s typical drift behavior, 2) stabilization measurements and cleaning procedures, and 3) the waste handling. We present our installation in detail and how we handle the named issues. Another major problem during automated long-term campaigns is the provision of sufficient reference seawater for regular quality assurance measurements and subsequent drift correction. We tested ten different container types and materials with minimum 5L volume (e.g. gas sampling bags) for their suitability as long-term seawater storage. As a result, only one gas sampling bag based on polyvinylidene fluoride (PVDF) featured the high-quality requirements and was chosen as reference seawater storage. The second main part focusses on the measured sea surface AT data from the first four unattended measurement campaigns. In order to prove the success of the installation, we compared the measurements with 1) discrete samples (taken manually only during the first two transits), and 2) calculated AT values based on established parameterization. The gained results show very promising consistency between the measured values and the AT range and variability of the monitored region. We conclude that the implementation of the CONTROS HydroFIA® TA system on a SOOP line was successful and brings ocean carbon observations to a new level.

D2657 |
EGU2020-478
Gisela Horlitz, Stefano Bonaglia, Igor Eulaers, Ronnie N. Glud, and Anna Sobek

The biogeochemistry of deep-sea trenches is strongly influenced by their V-shape topography and tectonic position in the ocean, leading to a focusing effect of sediment and organic matter into the trench centre. Recent findings showed elevated mineralization rates in trench sediments, suggesting both high carbon turnover and organic matter degradation rates. As persistent organic pollutants (POPs) favourably partition to organic matter, deep-sea trenches act as a sink for these substances. Composition, source and age of the organic matter have been shown to have a significant influence on contaminant dynamics in sediment from more shallow regions. Also, the trophic status of marine systems plays a significant role in transport of POPs from air to water and to sediment. However, knowledge about organic pollutants in deep-sea environments is scarce. In the present study, sediment samples from two deep-sea trenches with different trophic states and deposition regimes are analysed for POPs with a wide range of physicochemical properties. Concentrations will be compared between the semi-eutrophic Atacama and the oligotrophic Kermadec Trench. Sampling of sediment cores was performed at the slope, abyssal plain and trench at Atacama (depth between 2,500 and 8,000m) and at the abyssal plain and trench at Kermadec (depth of 6,000 and 9,600m). The total organic carbon content largely varied between 0.3 and 2.1% at different sites at the Atacama Trench, while values were more homogeneous at the Kermadec Trench (around 0.3%). Preliminary results from the Atacama samples demonstrate concentrations of PCBs at the pg g-1 dw level, and indicate highest concentrations to occur at the highest depth in the trench. Low sedimentation- and high mineralization rates in the trench centre, as well as the funnel-effect from the topology may explain these differences.

D2658 |
EGU2020-1159
Murugan Ramasamy, Suresh Babu, and Reji Srinivas

Submarine groundwater discharge (SGD) is a possible source for nutrients and anthropogenic pollutants that flow from the land to the ocean. The coastal zone of southwest (SW) India is capped with Tertiary sandstone-limestone-clay intercalations, Quaternary sediments, and laterites up to 600 m thickness above bedrock, which are considered as productive aquifer belts. The signatures of freshwater discharge to sea are not entirely vivid on the SW coast of India due to different constraints on investigation techniques and coastal dynamics. Hence, an onshore and offshore sampling and monitoring were carried out from Kanyakumari to Mangalore (∼640 km) along the SW coast of India to understand the groundwater discharge from the coastal aquifer system. The combined techniques used make it possible to identify groundwater outflows using satellite thermal infrared images to monitor physico-chemical anomalies in the sea (from 7 October – 5 November 2019 onboard the Sakar Kanya research vessel). Surface-to-bottom CTD (conductivity, temperature, depth) profiling and sampling of radium and nutrients were performed during fieldwork. The conventional water balance method and radium isotopic analyses were used to quantify the SGD. The findings of the water balance method show that the average of all fresh SGD is 790 m3/y/m with a minimum of 72 m3/y/m and a maximum of 2070 m3/y/m exported by SW coast to the sea. Regional precipitation patterns and coastal drainage geometry control local variation in fresh SGD. Nutrient concentrations have apparently followed conservative and non-concentrative mixing between fresh, high nutrient groundwater and saline, low-nutrient seawater at coastal ocean sites. Further investigations are in progress for flux estimation using radium isotopes in offshore and deployment of seepage meters in specific known areas along the shore.

D2659 |
EGU2020-10016
Yun-Hsuan Ho, Jie Yinn Lee, and Chia-Ying Chuang

Progress has been made towards optimizing extracting dissolved organic matter (DOM) using a styrene-divinylbenzene copolymer (PPL) sorbent, which is a widely used solid phase extraction (SPE) method to separate DOM from different aquatic samples. To establish the suitable extraction conditions, the effects of critical SPE variables such as loading mass, concentration, flow rate, as well as the extraction selectivity of the PPL sorbent have been systematically studied. Tens liters of water samples were collected from various aquatic environments, including headwater, downstream river water, coastal seawater, surface seawater from open ocean, seawater from open ocean at the depth of fluorescence maximum, and deep ocean water. 5g-Bond Elut PPL columns were used and the extraction kinetics of DOM were monitored liter-by-liter while extraction. Fluorescence spectrum were decomposed into their underlying chemical components resolved by PARAllel FACtor analysis (PARAFAC). Extraction selectivity of the PPL sorbent among different types of waters was verified through those fluorescence excitation emission matrices (EEMs) and chromophoric dissolved organic matter (CDOM) measurements.

D2660 |
EGU2020-11163
Marc Cerdà-Domènech, Jaime Frigola, Anna Sanchez-Vidal, and Miquel Canals

X-ray fluorescence core scanners (XRF-CS) allow rapid, non-destructive and continuous high-resolution analyses of the elemental composition of sediment cores. Since XRF-CS analyses are usually performed in fresh untreated materials, elemental intensities can be affected by the physical properties of the sediment (e.g. pore water content, grain size, sediment irregularities and changes in matrix) and the selected excitation parameters. Accordingly, the records of the measured elemental intensity cannot be considered quantitative. Nonetheless, these data can be converted to quantitative data through a linear regression approach using a relatively small number of discrete samples analyzed by techniques providing absolute concentrations. Such conversion constitutes a powerful tool to determine pollution levels in sediments at very high resolution. However, a precise characterization of the errors associated with the linear function is required to evaluate the quality of the calibrated element concentrations.

Here we present a novel calibration of high-resolution XRF-CS for Ti, Mn, Fe, Zn, Pb and As measured in heavily contaminated marine deposits. Three widely applied regression methods have been tested to determine the best linear function for XRF data conversion, which are: the ordinary least-squares (OLS) method, which does not consider the standard error in any variable (x and y), the weighted ordinary least-squares (WOLS) method, which considers the weighted standard error of the vertical variable (y), and the weighted least-squares (WLS) method, which incorporates the standard error in both x and y variables.

The results, derived from the analysis of metal-polluted sediments from offshore Portmán Bay and Barcelona, in the Mediterranean Sea off Spain, demonstrate that the applied calibration procedure improves the quality of the linear regression for any of the three regression methods (OLS, WOLS, and WLS), thus increasing correlation coefficients, which are higher than r2=0.94, and reducing data deviation from the linear function. Nonetheless, the WLS appears as the best regression method to minimize errors in the calibrated element concentrations. Our results open the door to use calibrated XRF-CS data to evaluate marine sediment pollution according to the sediment quality guidelines (SQG) with errors lower than 0.4% to 2% for Fe, 1% to 7% for Zn, 3 to 14% for Pb, and 5% to 16% for Mn, which highlight the robustness of the calibration procedure here presented. Our study incorporates and evaluates for the first time the analytical and statistical errors of XRF-CS data calibration, and evidences that the errors of the calibrated element concentrations must be properly assessed in future calibration efforts.

D2661 |
EGU2020-22062
Elena Mikheeva, Johannes Bieser, and Corinna Schrum

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) that have a long residence time in the marine environment. Due to processes of biomagnification in food chains, their presence in aquatic matrices is especially harmful for living organisms (incl. humans). The process of photolysis in the upper layers of the water column leads to a decreasing concentrations of higher chlorinated congeners (HCC) and increases the concentration of lower chlorinated congeners via the process of HCC declorination. This impacts the environmental fate of pollutants (e.g. sedimentation, accumulation, air-sea exchange), especially in coastal areas. Additionally, depending on the pollutant, degradation products can be even more harmful than the originally emitted species.

To estimate the environmental fate of the chosen contaminants in the marine ecosystems, a Framework for Aquatic Biogeochemical Models (FABM) has been implemented into a high-resolution numerical model. The first results of modeling PCBs concentrations will be presented for 1d simulations including factors such as light penetration, mixing, remineralisation and resuspension and the biological pump. This study aims to compare results for different regions and regimes with different conditions.

D2662 |
EGU2020-5545
Ginevra Rosati, Cosimo Solidoro, and Donata Melaku Canu

The Venice Lagoon (Mediterranean Sea) is a shallow coastal lagoon that have been subjected to several anthropogenic pressures, including significant Hg loadings from industrial activities. Inorganic Hg is methylated to neurotoxic MeHg in lagoon water and sediment, posing the ecosystem wealth at risk.

Here, we use a biogeochemical model to investigate the long-term dynamics of Hg species in the Venice Lagoon from the pre-industrial period to the post-industrial period (1900-2100), also taking into account environmental changes occurred in the lagoon such as eutrophication, and the increase of sediment resuspension driven by manila clam harvesting.

Time-variable Hg emissions from industries were estimated from available information about industrial production and technology-dependent emissions factors, while Hg loading species from other sources (river, atmospheric deposition, urban wastes) where estimated through downscaling from global studies, using observations from previous field studies (1970 - 2010) as constraints. The impacts of future trends of Hg atmospheric deposition are explored through scenario analysis. 

Modeled Hg species are in a satisfactory agreement with the available observations. In the current postindustrial phase, HgT in the lagoon waters comes mostly from sediments, while MeHg comes primarily from the watershed.

We estimate in ∼56 kg y-1 the HgT export for 2019 to the Adriatic Sea, which includes ∼0.13 kg y-1 of MeHg. Both Hg and MeHg concentrations are decreasing since outputs slightly exceed inputs. The analysis of Hg and MeHg reservoirs and fluxes reveals the impacts of the changes in environmental conditions on Hg fluxes. On the one hand, eutrophication has enhanced sediment deposition to the seabed, causing a maximum in sediment Hg concentrations when Hg inputs were already declining; on the other hand, the enhanced sediment resuspension due to clam harvesting led to increased Hg fluxes from the sediment to the water, also causing a redistribution of Hg from the central lagoon to the northern and southern areas, as reported by observational studies. These results emphasize the importance of adopting an ecosystem approach when investigating Hg dynamics, considering the different uses of the ecosystem.

D2663 |
EGU2020-2246
Zhe Hao, Chenglong Wang, and Xinqing Zou

In this study, we analyzed the distribution and bioaccumulation of six heavy metals (Cu, Pb, Zn, Cr, Cd, Hg) in marine organisms from China’s Hainan and Zhoushan coastal regions. Across all marine organism samples, as well as sediment and seawater samples, Zn and Hg ranked highest and lowest in concentration, respectively. Heavy metal distributions in the marine organisms varied by region and species; concentrations were higher (except for Zn) in Zhoushan than in Hainan and in crab than in fish. A marine organism’s ability to digest and eliminate heavy metals (bioaccumulation ability), based on bioaccumulation factors, was significantly higher for heavy metals in seawater than in sediment; higher sediment background values may explain the higher heavy metal concentrations in crab. In general, a marine organism’s bioaccumulation ability was higher for Cu and Zn and lower for Pb in China.

D2664 |
EGU2020-9204
| Highlight
Vlado Cuculić, Neven Cukrov, Irena Radić Rossi, and Željko Kwokal

Near the Gnalić islet at the southeast entrance of the Pašman Channel, Croatian Eastern Adriatic there is one of the most important "post-medieval shipwreck known". In November 1583 during sailing popular sea route from Venice (Italy) to Constantinople (Istanbul, Turkey) Venetian merchantman “Gagliana Grossa” with capacity of 1200 Venetian barrels (700 tonnes) and length of 40 meters sank at this site, two nautical miles of the town of Biograd na Moru. A very varied ship's cargo consisted of large quantities of semi finished and finished products manufactured in various part of Europe. However, the ship also carried raw materials such as tin, brass, white lead and especially mercury in various forms: elemental mercury, ore cinnabar (HgS), and vermillion powder (HgS opaque red pigment). Elemental sulfur found in the cargo also indicates possibility of its use in the production of vermillion by chemical coupling of Hg and S. It is assumed that the mercury was meant for medical (elemental Hg), cosmetic and painting (vermillion) purposes. The ship with the full cargo sank at twenty-five meters of depth and wreck was discovered in 1967, while first detailed and systematic sampling and measurements of mercury at a sinking site and its vicinity began in 2013. Seawater sampling was performed eight times in six years (2013-2019). Individual samples were taken by scuba diving at eight positions 1 to 1.5 m above excavating area (60x20 m) as well as in vicinity and on the sea surface above the site. Measurements of mercury species (total, reactive and dissolved gaseous) were performed 24 hours after sampling using CVAAS method.

The Gnalić shipwreck is located in the Middle Adriatic coastal waters. According to the "A long-term survey (1984-2017) of the spatial and temporal trends of the total mercury in seawater of the Adriatic Sea" (Kwokal and Cuculić, in preparation) the mean concentration of total mercury based on over 600 samples is 1.4 ng L-1 for the Middle Adriatic and 1.6 ng L-1 for the coastal water.

During archaeological activities on the excavation site all three measured mercury species, total, reactive and dissolved gaseous appeared in concentrations up to three orders of magnitude higher in comparison with the averages found in the Middle Adriatic seawater.

There is a difference between the results obtained during recovering of the artefacts, cleaning of the hull at the shipwreck site and during the idle state when workspace is conserved. Nevertheless, with no activity on the site, concentrations of mercury species are more than one order of magnitude higher compared to surrounding pristine environment. Data indicates the need of removal of all forms of mercury, especially elemental (roughly estimated 500-1000 kg) from the seabed in order to stop damaging impact on seawater and sediment, consequently on marine life.

D2665 |
EGU2020-21887
| Highlight
Kathleen Gosnell, Aaron Beck, and Eric Achterberg

The Second World War (WWII) resulted in many humanitarian, cultural and environmental impacts throughout Europe and the world. During WWII anti-aircraft ammunition was used extensively in the Baltic Sea region, and the legacy of WWII munitions are present throughout the area. For example, up to 1.5 million anti-aircraft grenades were shot down in a 10 km2 region along the Dänisch-Nienhof (DN) training center of northern Germany near Kiel. Anti-aircraft grenades contain toxic explosive chemicals such as trinitrotoluene (TNT) and mercury fulminate. It has been estimated that the detonation of WWII bombs released up to 2 tons of mercury (Hg) species into the coastal environment of Germany in the surrounding Kiel area. The DN and greater Kiel Bay (KB) region additionally have non-detonated and partial bombs which could also yield a critical source of Hg to the area. Until now very little research has been done into how much of this Hg might be stored in the sediment, or moving through the waters and food chains of the region.

Water, sediment and plankton samples were collected from around DN and KB in order to quantify and investigate potential impacts and magnitudes of Hg contamination from munition sites and bombs. These Hg levels are compared to available TNT values, and other potential munition-sourced pollutants. Water samples were collected using ‘trace metal clean’ techniques at surface and depth for each station. Plankton samples were gathered at each water station using a vertically towed net in order to assess Hg in the lower food chain. While sediment samples were carefully collected from stations surrounding the KB bomb dumps. These results provide an initial assessment into how much of an impact Hg sourced from anti-aircraft munitions might have on the environment and food chain health within the southern Baltic and KB region.