OS3.2 | Carbon Cycle Impacts and Feedbacks on Ocean Biogeochemistry
Carbon Cycle Impacts and Feedbacks on Ocean Biogeochemistry
Including Fridtjof Nansen Medal Lecture
Co-organized by BG4
Convener: Richard Sanders | Co-conveners: Mebrahtu Weldeghebriel, Yael Kiro, Netta Shalev, Michael A. St. John
Orals
| Wed, 17 Apr, 08:30–12:30 (CEST)
 
Room L3
Posters on site
| Attendance Wed, 17 Apr, 16:15–18:00 (CEST) | Display Wed, 17 Apr, 14:00–18:00
 
Hall X4
Posters virtual
| Attendance Wed, 17 Apr, 14:00–15:45 (CEST) | Display Wed, 17 Apr, 08:30–18:00
 
vHall X5
Orals |
Wed, 08:30
Wed, 16:15
Wed, 14:00
Understanding the carbon cycle and ocean biogeochemistry, and how they relate to each other, is important for our understanding of the Earth’s environment in the past, present, and future. This session will discuss these interactions through different timescales and processes, from the ‘short-term’ biological pump to the ‘long-term’ burial in marine carbonates.
The ocean biological pump stores enough CO2 in the ocean interior to keep atmospheric pCO2 200ppm lower than it would otherwise be, with the depth at which this storage occurs being a key determinant of the size of this effect. This storage results from the surface production and interior respiration of organic matter, however, the transfer between surface and interior, and hence the depth at which remineralization occurs is driven by a wide array of processes including sinking, active fluxes, packaging of material by grazing, egestion and likely affected by plankton community composition and temperature. Understanding the relative importance of these processes is key to predicting the response of ocean biological C storage to climate change and human exploitation. The current intensification of human exploitation impacts on the ocean coupled with climate change is driving multiple projects (e.g. Ocean ICU, BioCarbon, Apero and Exports) to address these issues with the general objective of better predicting the evolution of future ocean C storage.
Ocean chemistry is linked to both short- and long-term C cycles via alkalinity input, saturation of carbonate minerals, and transfer of organic and inorganic C from the surface to the deep ocean. The sources and sinks of different elements and isotopes dictate their concentrations and isotope ratios in the ocean. Weathering and transport in rivers and reactions at mid-ocean ridges are major sources of elements to the ocean, while reactions with seafloor basalt, precipitation, scavenging, and adsorption onto particles are major sinks. These processes have also an important role in the C cycle. For example, silicate weathering removes CO2 and volcanism provides CO2 to the atmosphere over the long-term, and elements, such as Fe and Cd, are scavenged by the biological pump. Thus, studying oceanic geochemical budgets constrained by multiple isotope systems (e.g., δ11B, δ26Mg, δ30Si, δ88/86Sr) and concentrations (e.g., Fe, Sr, Ba, Li, S), and their variation over time, provides a useful tool in constraining the carbon cycle.

Orals: Wed, 17 Apr | Room L3

Chairpersons: Netta Shalev, Mebrahtu Weldeghebriel, Yael Kiro
08:30–08:35
08:35–08:45
|
EGU24-19534
|
On-site presentation
Lennart de Nooijer, Laura Pacho Sampedro, Daniel Francois, Szabina Karancz, and Gert-Jan Reichart

Many foraminifera form shells made of calcium carbonate. The elemental and isotopic composition of these shells varies greatly from inorganically precipitated calcites, suggesting a strong biological control on the process of CaCO3 precipitation. Moreover, this composition differs, sometimes greatly, between species, which may indicate that the controls on calcite chemistry is not fixed among all species. For paleoceanographic application, a better grip on this inter-species variability in calcite chemistry is necessary. Here we present the latest insights in environmental controls on element incorporation, biomineralization mechanisms and evolutionary patterns in biomineralization. An integrated understanding of foraminiferal calcification will also allow predicting their response to changes in marine inorganic carbon chemistry (e.g. ocean acidification), which in turn, is necessary to assess the contribution of changes in foraminiferal calcification rates to (surface) marine inorganic carbon cycling.

How to cite: de Nooijer, L., Pacho Sampedro, L., Francois, D., Karancz, S., and Reichart, G.-J.: Foraminiferal biomineralization: mechanisms, calcite chemistry and evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19534, https://doi.org/10.5194/egusphere-egu24-19534, 2024.

08:45–08:55
|
EGU24-19571
|
ECS
|
On-site presentation
Szabina Karancz, Joji Uchikawa, Lennart J. de Nooijer, Mariëtte Wolthers, Kyle Conner, Corinne Hite, Geert-Jan A. Brummer, Julie Lattaud, Negar Haghipour, Yair Rosenthal, Richard E. Zeebe, Shiv Sharma, and Gert-Jan Reichart

Sulfur over calcium ratio (S/Ca) in foraminiferal calcite has been suggested as a potential tool to reconstruct seawater carbonate ion concentration ([CO32-]). The approach of using sulfur incorporation as a proxy for the carbon system was based on benthic foraminiferal controlled growth experiments, which suggested that foraminifera incorporate more sulfur when there is less [CO32-] available in the seawater. With sulfate ([SO42-]) being proposed to be the dominant form in which sulfur is incorporated in the calcium carbonate of the foraminiferal shells, S/Ca would provide an independent parameter for the reconstruction of seawater inorganic carbon chemistry. To further explore the potential of this proxy, we used five planktonic foraminiferal species collected from the field. S/Ca values in planktonic foraminifera collected from core-top sediments that span a large range of growth conditions (temperature, salinity, [CO32-] and [HCO3-]) reveal an opposite trend with [CO32-] compared to the results from the benthic foraminifera culture experiments. Moreover, we found an additional effect of incorporation of Mg on S/Ca ratios, or a combined effect on both. Using the ratio of S to Mg overcomes this issue and S/Mg ratios correlate with [CO32-]. Still, these correlations are likely affected by multiple parameters and/or incorporation pathways other than only SO42- as suggested by our inorganic calcite growth experiments. Results of this study suggest a critical evaluation of the use of foraminiferal S/Ca, considering the aqueous species involved during uptake and potentially combining other elements that may share controls.

How to cite: Karancz, S., Uchikawa, J., de Nooijer, L. J., Wolthers, M., Conner, K., Hite, C., Brummer, G.-J. A., Lattaud, J., Haghipour, N., Rosenthal, Y., Zeebe, R. E., Sharma, S., and Reichart, G.-J.: Sulfur incorporation in (foraminiferal) calcite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19571, https://doi.org/10.5194/egusphere-egu24-19571, 2024.

08:55–09:05
|
EGU24-7103
|
On-site presentation
Juraj Farkas, Yuexiao Shao, Luke Mosley, Jonathan Tyler, John Tibby, and Anton Eisenhauer

Ocean water yields an integrated global signal of geological and biological processes operating on our planet, which in turn control the marine C cycle, oceanic alkalinity budget and atmospheric CO2 levels. Therefore, reconstructing the chemical and isotope composition of seawater and/or coastal waters through time represents one of the main research objectives of earth system evolution studies.

Here we present stable and radiogenic Sr isotope variations (δ88/86Sr and 87Sr/86Sr) measured in waters and carbonates from modern and Holocene coastal marine system in South Australia (Coorong Lagoon/Murray River Estuary) that is connected to the Southern Ocean, thus exhibiting large gradients in water chemistry, salinity and carbonate saturation (Mosley et al. 2023; Shao et al. 2021). The studied hydrological system shows a large salinity range from brackish (<20 psu) to normal marine (~35 psu) and hypersaline (~110 psu), with the salinity changes being tightly linked to DIC and Alkalinity, and thus CaCO3 saturation state (SI values) of local waters, calculated via PHREEQC. The primary research aim was to assess how spatial and temporal changes in salinity, carbonate chemistry and CaCO3 saturation (dissolution vs precipitation of carbonates), monitored throughout the year (in spring, summer, fall and winter), impact the Sr isotope composition in the present-day coastal marine system. Such knowledge is, in turn, important for a better calibration and assessment of the δ88/86Sr proxy for paleo-oceanographic and environmental applications including past marine alkalinisation/acidification events and/or paleo-salinity reconstructions (Farkas et al. 2024; Shao, 2022).

Importantly, our results from seasonal sampling and monitoring showed that the δ88/86Sr in waters is positively correlated with their SI values (carbonate saturation) and salinity, with the heaviest or most positively fractionated stable Sr isotope signatures of +0.48 ± 0.03‰ (thus above ‘normal seawater’ of +0.39 ‰) measured in summer season (hot and dry period) in hypersaline (>70 psu) and oversaturated (SI ~1) waters. In contrast, the isotopically light and systematically lower stable Sr isotope signatures (< 0.35‰) are documented in brackish waters that are also undersaturated with respect to CaCO3 minerals (SI < 0). Overall, these results point to the primary control of carbonate dissolution versus precipitation phenomena, and thus CaCO3 saturation, on the δ88/86Sr proxy in the modern coastal marine system.

Finally, we will also illustrate how a coupled δ88/86Sr and 87Sr/86Sr approach can be applied for paleo-salinity reconstructions of the coastal marine systems, such as the Coorong Lagoon, based on the Sr isotope analysis of recent and fossil carbonate archives (bivalve shells) recovered from local sediment cores (Shao, 2022). Briefly, available results and geochemical modeling of the Sr isotope data from Holocene fossil shells suggest that over the last ~2400 years the Coorong Lagoon become progressively more evaporitic, exhibiting a temporal shift from a purported brackish paleo-lagoon to the present-day hypersaline carbonate producing system.   

 

References

Farkas et al. (2024) Treatise on Geochemistry, Third Edition. Elsevier (Book Chapter 00086)

Mosley et al. (2023) Marine Pollution Bulletin, 188, 1-16.  

Shao (2022) PhD Thesis, University of Adelaide 

Shao et al. (2021) GCA, 293, 461-476.  

How to cite: Farkas, J., Shao, Y., Mosley, L., Tyler, J., Tibby, J., and Eisenhauer, A.: Calibrating stable Sr isotope proxy for paleo-oceanographic studies: Insights from δ88/86Sr variability in modern and Holocene coastal marine system in South Australia , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7103, https://doi.org/10.5194/egusphere-egu24-7103, 2024.

09:05–09:25
|
EGU24-13608
|
ECS
|
solicited
|
Highlight
|
On-site presentation
Hana Jurikova, Robert Bodnar, Oscar Branson, Matthew Dumont, David Evans, Fernando Gázquez, Yana Kirichenko, Boaz Lazar, Mao-Chang Liang, Tim Lowenstein, Eszter Sendula, Claudia Voigt, Chen Xu, Xinyuan Zheng, and James Rae

The chemical history of seawater provides key information on Earth’s geologic processes and is fundamental for robust CO2 reconstructions. The knowledge of the secular evolution of the oceanic boron isotope budget is particularly important for CO2 reconstruction from boron isotopes. The boron isotope composition of seawater (δ11Bsw) is homogeneous, but varies on multi-million year time scales, given its residence time of approximately 10 million years. To date, the secular evolution of the oceanic boron isotope budget has been difficult to constrain, posing a major uncertainty for boron-based pH and CO2 reconstructions from Earth’s geologic past and critically limiting our understanding of the global biogeochemical cycling of this important element through time. Evaporitic minerals bearing fluid inclusions – and halites in particular – have provided important insights on past variations in major and minor ion composition, and present a highly appealing archive for reconstructing δ11Bsw (as well as other isotopic systems) given their direct origin from seawater. However, the interpretation of their signatures is not straightforward due to the possibility of fractionation during evaporation, crystallisation, and local biogeochemical interactions. Here we present data illuminating the evolution of boron isotopes and various other elements during evaporite formation from laboratory experiments and natural modern evaporitic settings across the globe, accompanied by new analytical developments for high-precision single fluid inclusion measurement using laser ablation. These data enable us to critically evaluate the evaporite archive, paving an avenue to robust seawater and CO2 reconstructions from Earth’s geological past.

How to cite: Jurikova, H., Bodnar, R., Branson, O., Dumont, M., Evans, D., Gázquez, F., Kirichenko, Y., Lazar, B., Liang, M.-C., Lowenstein, T., Sendula, E., Voigt, C., Xu, C., Zheng, X., and Rae, J.: Ocean chemistry archived in modern evaporites: implications for robust seawater and CO2 reconstructions from Earth’s past, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13608, https://doi.org/10.5194/egusphere-egu24-13608, 2024.

09:25–09:35
|
EGU24-4178
|
On-site presentation
Wei-Li Hong, Xiaole Sun, Tzu-Hao Huang, and Marta Torres

Despite the growing recognition of in-situ silicate alteration (dissolution and formation) in marine sediments, its global significance and controlling factors are still poorly understood. By compiling information from scientific ocean drilling programs and applying numerical modelling, we aim to 1) provide constraints on the environmental parameters of silicate dissolution in marine sediments, 2) identify silicate phases responsible for the hyper porewater alkalinity (>56 meq/L) commonly observed from productive continental margin sediments, and 3) investigate the interplay between silicate dissolution, clay formation, and carbonate authigenesis as well as their effect on marine carbon cycling. 

Through numerical modelling, we show that alkaline conditions resulting from combined iron and sulfate reduction favour formation of smectite group clay minerals, while the acidic conditions arising from organic matter fermentation promote dissolution of saponite and several mica-group silicates. This result resonates with previous observations of reverse weathering (i.e. clay formation) in shallow iron- and/or sulfate reducing sediments, while silicate weathering (i.e. silicate dissolution) has been reported deeper in methanogenic sediment columns. 

Using pore fluid composition data, we show that marine silicate weathering is primarily driven by dissolution of K- and Mg-containing silicate minerals. Especially, higher-than-seawater Mg concentrations were observed in almost all sites that have hyper alkalinity and the weathering process contribute more than one-third of the measured alkalinity. No apparent difference was observed for porewater Ca concentrations when comparing sites with and without hyper alkalinity, which hints for complicated feedbacks through authigenic carbonate formation. 

The global dataset analysed revealed that sites with high alkalinity correspond to locations with a medium distance from shore. While such a pattern cannot be easily explained by supply of organic matter nor by silicate phases alone, we interpret this observation to be the result of sediment maturity. Our inference is further strengthened by observations of higher alkalinity at sites with greater thermal history within the methanogenesis zone, a factor that measures how much time and temperature a sediment parcel has experienced under subsurface conditions. Collectively, we conclude that substantial dissolution of marine silicate phases occurs when the sediments have been transported some distance offshore and buried below sulfate reduction zone for a prolonged period and/or experience sufficiently high geothermal heating.

We simulated alteration of silicate and carbonate phases within a complete early diagenetic sequence to understand how dissolved carbon is converted to alkalinity under variable organic matter degradation rates. We show that authigenic carbonate formation is effective in control downcore DIC/alkalinity level with a moderate organic matter degradation rate. Only a very limited amount of carbonic acid produced by reverse weathering can diffuse away from sediments. Under a scenario with fast organic matter fermentation, dissolution of silicates (such as phlogopite) becomes the only buffer for porewater pH that converts most of the dissolved inorganic carbon produced from organic matter fermentation to carbonate alkalinity. Consequently, marine weathering sustained by silicate mineral dissolution increases the alkalinity production by as much as 16%, with most of the alkalinity leaking to surface oxic sediments instead of being sequestrated as carbonate minerals. 

How to cite: Hong, W.-L., Sun, X., Huang, T.-H., and Torres, M.: The role of marine silicate alteration in regulating carbon cycling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4178, https://doi.org/10.5194/egusphere-egu24-4178, 2024.

09:35–09:45
|
EGU24-18309
|
ECS
|
On-site presentation
Ethan Petrou, Luke Bridgestock, Gideon M. Henderson, Yu-Te Hsieh, Germain Bayon, and Nolwenn Lemaitre

Global warming has the potential to release large quantities of methane (CH4) from marine sediments, representing a positive carbon cycle-climate feedback [1]. Unambiguous evidence of this feedback in the geological record will improve understanding of the potential risk it poses for exacerbating anthropogenic global warming. For example, climate driven sedimentary CH4 release is one of the hypothesized mechanisms for the onset of the Paleocene-Eocene Thermal Maximum (PETM) [2]. Increased sedimentary barium (Ba) burial rates have been interpreted as evidence of this mechanism [2,3], but these records are also sensitive to other processes [4]. Stable Ba isotope variations are a new geochemical tool that may improve interpretations of such records, potentially leading to clearer geological insights into the significance of this carbon cycle-climate feedback.

This study aims to determine (1) the flux and isotope composition of Ba across the sediment-water interface associated with seafloor CH4 venting and (2) the significance of these fluxes for the marine Ba inventory. To achieve this, Ba concentration and isotope data is presented for seawater samples at different altitudes above the seafloor (1m to 60m) collected across the Regab pockmark, a methane cold seep offshore Congo. Samples were collected with a remotely operated vehicle, providing a high resolution of sample collection within the benthic boundary layer, spanning areas of varying CH4 venting fluxes.

The measured Ba isotope values from all sites possess δ138/134Ba values +0.20 to +0.40 ‰ and [Ba] values 80.0 – 90.6 nmol kg-1, which are typical of ambient seawater from this depth range. Furthermore, no difference in dissolved Ba isotopes or Ba concentrations with altitude at each location is observed and there is no significant difference in seawater [Ba] and Ba isotope composition between locations featuring different dissolved seawater CH4 concentrations.

These results are interpreted to show that there is no resolvable difference in the [Ba] vs. δ138/134Ba relationship over the pockmark, and any Ba fluxes are too small to resolve in a circulating water column. This likely reflects the quantitative removal of pore water Ba by barite precipitation within the upper sediments, preventing significant Ba release to the water column.

The findings indicate CH4 seeps do not seem to significantly impact either the dissolved Ba concentration or isotope composition of the ocean, and consequently makes the use of sedimentary Ba concentration and isotope records as a tracer of past CH4 release events questionable. These insights suggest caution should be held when developing Ba isotopes as a novel tracer of past large-scale seafloor methane release i.e. PETM sediments. The study also provides insights on the influence of methane seep environments on Ba isotopes and the factors governing the stable isotope distribution of Ba in both modern and ancient sediments and oceans.

 

Reference:

[1] James et al., (2017), Limnology and Oceanography, 61, S283-S299

[2] Dickens et al., (2003), GSA Special Paper, 369, 11-23

[3] Frieling et al., (2019), Palaeoceanography and paleoclimatology, 34, 546-566

[4] Bridgestock et al., (2019), Earth and Planetary Science Letters, 510, 53-63

How to cite: Petrou, E., Bridgestock, L., Henderson, G. M., Hsieh, Y.-T., Bayon, G., and Lemaitre, N.: Examining the utility of barium isotopes as a tracer of large-scale seafloor methane venting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18309, https://doi.org/10.5194/egusphere-egu24-18309, 2024.

09:45–09:55
|
EGU24-16921
|
On-site presentation
Leopoldo D. Pena, Sara Campderrós, Ester García-Solsona, Eduardo Paredes-Paredes, Jaime Frigola, César Nicolás Rodríguez-Díaz, Arturo Lucas, Eva Calvo, Carles Pelejero, and Isabel Cacho

The North Atlantic Ocean plays a critical role in the global circulation system, regulating the penetration of surface waters into the deep ocean, but also in key ocean biochemical cycles (e.g. carbon, oxygen, nutrients). Meridional heat and salt transport (i.e. buoyancy) drive the formation of different water masses and their circulation pathways. A relatively unknown but important element controlling the net meridional export of heat, salt and other chemical species into the North Atlantic is the Mediterranean Outflow Water (MOW): the salt injector. In this work, we present the first high resolution systematic study of traditional (T, S, Nutrients) and novel (Nd isotopes, alkalinity, pH) geochemical parameters of MOW waters from its source area at the Strait of Gibraltar up to the northern Iberian margin (Cantabric Sea). During the TRANSMOW cruise in spring 2021, over 500 seawater samples were collected along the main MOW pathway following its northward flow. A comprehensive suite of geochemical parameters including εNd, alkalinity, pH and preformed nutrients were analyzed for these samples. We show that MOW can be ‘traced’ unequivocally using εNd as a conservative tracer, a feature that opens a new set of possibilities to better estimate the contribution of MOW export to higher latitudes in the North Atlantic Ocean. Other parameters directly linked to the carbon cycle (alkalinity and pH) are also controlling the distinctive chemical properties of the Mediterranean waters.. One of the key advantages of these geochemical tracers is that they allow to better quantify export and mixing rates of MOW with North Atlantic waters. Using statistical tools such as the Optimum Multi-Parameter Analysis (OMPA) on an array of conservative tracers we have quantified mixing rates and exports between different water masses. These results will be fundamental to better constrain paleoreconstructions in the sedimentary record using different proxies such as Nd and B isotopes (for water mass distribution and pH), B/Ca ratios (for seawater carbonate ion saturation) and even new experimental proxies such as Na/Ca (for salinity).

How to cite: Pena, L. D., Campderrós, S., García-Solsona, E., Paredes-Paredes, E., Frigola, J., Rodríguez-Díaz, C. N., Lucas, A., Calvo, E., Pelejero, C., and Cacho, I.: Geochemical characterization of Mediterranean Outflow Waters in the modern ocean: Nd isotopes, carbon cycle and new export constraints, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16921, https://doi.org/10.5194/egusphere-egu24-16921, 2024.

09:55–10:05
|
EGU24-16877
|
ECS
|
On-site presentation
Markus Adloff, Ashley Dinauer, Charlotte Laufkötter, Frerk Pöppelmeier, Aurich Jeltsch-Thömmes, and Joos Fortunat

We present a novel mechanistic representation of both organic and inorganic marine particles within the Bern3D Earth system model of intermediate complexity, which is based on the columnar particle flux model MSPACMAM. This new approach moves away from the assumption of globally and temporally invariant sinking profiles. Instead, the new scheme calculates sinking speeds and remineralisation and dissolution rates based on local temperature, density, and seawater chemistry. When combined with an improved representation of dynamic iron release and scavenging, this scheme introduces new dynamic feedbacks in the response of the biological pump to climate and circulation changes in the Bern3D model. Particle remineralisation and dissolution rates are now functions of temperature, oxygenation, saturation state, and sinking speed. The sinking rate is in turn modulated by changes in export production (amount and composition) as well as the viscosity of seawater. In addition to light and macronutrients, export production is affected by iron availability, which is depending on the rate of iron removal through scavenging and iron release from decaying particles and sediments, both processes that depend on organic particle fluxes and local oxygen concentrations. We demonstrate the non-linear interactions between these new dependencies in transient and steady-state simulations of various climatic boundary conditions. The newly introduced particle concentrations sensitive to changes in temperature and density result in shallower carbonate dissolution and deeper organic particle remineralisation in the Southern Ocean under full glacial conditions. In idealized scenarios of anthropogenic climate change, there is a smaller decline of export production but faster oxygen depletion than with the old static particle decay scheme. In addition, organic particle fluxes affect sedimentary iron release, which can lead to a positive feedback on export production if the released iron reaches the surface ocean.

How to cite: Adloff, M., Dinauer, A., Laufkötter, C., Pöppelmeier, F., Jeltsch-Thömmes, A., and Fortunat, J.: Impacts of dynamically simulated biogenic particles and iron on the marine carbon cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16877, https://doi.org/10.5194/egusphere-egu24-16877, 2024.

10:05–10:15
|
EGU24-9768
|
ECS
|
On-site presentation
Olivier Sulpis, Perrine Chaurand, Anne Kruijt, Ben Cala, Katja TCA Peijnenburg, Robin van Dijk, Daniëlle van der Burg, and Matthew Humphreys

Part of the carbon taken up by the ocean is transformed into biogenic particulate matter, that eventually leaves the surface ocean, settling toward the seafloor. Planktonic organisms secreting a calcium carbonate (CaCO3) shell occupy a key, but ambivalent role in this scheme. First, the precipitation of their shell generates CO2, thereby reducing the ocean CO2 sink, while the sinking of their shell constitutes a direct export of carbon to the deep ocean. Meanwhile, the dissolution of their shells generates alkalinity, which in turn boosts the capacity of seawater to take up more CO2 from the atmosphere.

 

CaCO3 is present in the ocean under two main mineral forms: calcite (relatively stable) and aragonite (relatively soluble). Aragonite, produced in today’s oceans mostly by pteropods, a group of pelagic snails, has a very poorly understood role in the marine carbon cycle, and key questions remain unanswered: what controls their soft parts degradation and shell dissolution in the upper kilometer of the water column? How do both processes interact?

 

During the BEYΩND expedition that took place in March 2023 across the Southern Atlantic, we sampled pteropods using a multinet at 5 different depth ranges in the upper kilometer. Retrieved pteropods were representative of different life stages (adults, juveniles), some still well preserved, some dead with various stages of decomposition. Individuals were then preserved into ethanol, and later scanned with a micrometric resolution using microtomography. From the scans, the post-mortem degradation of the different body parts can be appreciated, shell micro-ornamentations can be seen, and possibly gut contents, which may influence dissolution and degradation processes. From the collected scans, a reactive transport model is then applied to predict in 3D the rates at which both organic matter degradation and aragonite dissolution occur, as well as how they interact.

How to cite: Sulpis, O., Chaurand, P., Kruijt, A., Cala, B., Peijnenburg, K. T., van Dijk, R., van der Burg, D., and Humphreys, M.: Post-mortem pteropod degradation in the Southern Atlantic twilight zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9768, https://doi.org/10.5194/egusphere-egu24-9768, 2024.

Coffee break
Chairpersons: Richard Sanders, Michael A. St. John
10:45–10:50
10:50–11:00
|
EGU24-12166
|
ECS
|
On-site presentation
Nicola Wiseman, J. Keith Moore, and Adam C. Martiny

Phytoplankton acclimate to increased nutrient stress by decreasing their cellular quotas (nutrient:carbon ratios). Reducing cellular quotas reduces the export efficiency of the limiting nutrient, helping sustain biological productivity. Here we present a version of the Community Earth System Model with phytoplankton group specific, fully variable C:N:P:Fe:Si ratios constrained by field observations of particulate organic matter stoichiometry and individual cell spectroscopy. We compare the results of a steady-state fully fixed stoichiometry model to the fully variable model and find that using a fixed Redfield stoichiometry leads to a decrease of 1PgC/yr carbon export, increase of 18 ppm atmospheric CO2, decrease of 55 TgN/yr nitrogen fixation, and decrease of 27/yr TgN nitrogen fixation. We also investigate the impacts of variable nutrient acquisition on global patterns of nutrient limitation and find that the weaker ability of phytoplankton to acclimate to N stress by lowering their cellular quotas relative to other nutrients pushes marine ecosystems towards nitrogen limitation. Only when the nutrient supply ratios are highly skewed, exceeding the ability of the phytoplankton to acclimate, do other nutrients become growth-limiting, as with iron in the High Nitrate, Low Chlorophyll (HNLC) regions. We show that in the oligotrophic gyres, variable plankton stoichiometry, given sufficient time, pushes the marine ecosystems towards co-limitation, as non-limiting nutrients are more efficiently drawn down and exported (higher cellular quotas), relative to the growth-limiting nutrient (lower cellular quotas).

How to cite: Wiseman, N., Moore, J. K., and Martiny, A. C.: Phytoplankton variable elemental composition modifies the marine biological pump and largely determines the global patterns of nutrient limitation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12166, https://doi.org/10.5194/egusphere-egu24-12166, 2024.

11:00–11:10
|
EGU24-723
|
ECS
|
On-site presentation
Fabio Berzaghi, Jerome Pinti, Olivier Aumont, Olivier Maury, and Mary Wisz

Marine organisms, from plankton to fish, provide a wealth of ecosystem services, including carbon sequestration in a process known as the ocean’s biological carbon pump (BCP). The BCP brings carbon from the atmosphere to the ocean depths where it is stored for decades to centuries. Although parts of the ocean’s BCP are under threat from human activities,  BCP carbon sequestration rarely features as an objective in efforts to protect ocean spaces. Moreover, although BCP carbon sequestration services could support discussions of conservation and climate finance,  its economic value has yet to be estimated in space and time.

Biogeochemical modeling and mapping efforts have grown in recent years, and emerging results could potentially help to fill in important spatially explicit and economic knowledge gaps that could inform the protection of the BCP. We developed a new metric to map and quantify the global ocean’s BCP long-term carbon sequestration and computed its value on a potential carbon market. We show the  global spatial patterns and valuation in relation to geopolitical and management boundaries, and highlight options for governance and management. Our results highlight potential opportunities for preserving the climate services of the BCP both nationally and in areas beyond national jurisdiction , and can be used to inform discussions about marine protected areas, environmental impact assessment, and conservation finance.

How to cite: Berzaghi, F., Pinti, J., Aumont, O., Maury, O., and Wisz, M.: Distribution and valuation of the biological carbon pump and its carbon sequestration:  Implications for international area-based management and climate finance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-723, https://doi.org/10.5194/egusphere-egu24-723, 2024.

11:10–11:20
|
EGU24-4985
|
ECS
|
On-site presentation
Yibin Huang and Fei Chai

The North Pacific (>20°N) stands out as a significant carbon sink, contributing to approximately 25% of the global oceanic CO2 uptake and absorbing around 0.5 Pg C yr-1 from the atmosphere. Despite the well-established importance of the biological carbon pump in maintaining this regional carbon sink, our current understanding of the strength and efficiency of the biological pump in this vast region remains incomplete. Historical studies have primarily relied on extrapolations from a limited number of observations.

In this study, we utilize data from 85 BGC-floats, covering over 160 annual cycles, to constrain essential fluxes relevant to the biological pump in the North Pacific, including net primary production, the export of distinct biogenic carbon, and air-sea CO2 flux. Furthermore, we combine the output from a well-constrained regional ecosystem model (ROMS-CoSiNE-Iron Model) to gain mechanistic insights into how the food-web dynamics drive the strength and efficiency of the biological carbon pump across different ecosystems.

Overall, our study offers an integrated perspective on the North Pacific biological pump by leveraging high-resolution observations from the BGC-float array and simulation from an improved ecosystem model.

How to cite: Huang, Y. and Chai, F.: Integrated Perspective of the Biological Pump in the North Pacific: Synergy from BGC-Float Observations and Ecosystem Model Simulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4985, https://doi.org/10.5194/egusphere-egu24-4985, 2024.

11:20–11:30
|
EGU24-12043
|
ECS
|
On-site presentation
Jack Williams, Sari Giering, Chelsey Baker, Hannah East, Benoit Espinola, Fred Le Moigne, Maria Villa, Katsiaryna Pabortsava, Sabena Blackbird, Corinne Pebody, Kevin Saw, Mark Moore, Stephanie Henson, Richard Sanders, and Adrian Martin

Diatoms, a ubiquitous group of phytoplankton, account for approximately 40% of particulate organic carbon (POC) exported via the ocean biological carbon pump, which modulates atmospheric CO2. Diatoms are represented in global biogeochemical models as effective vectors for sinking POC, with their large size and dense skeletons made of biogenic Silica (BSi) thought to allow rapid transfer of organic carbon to the ocean interior. However, we observe this not to be the case across large parts of the Southern Ocean mesopelagic zone. Here we present direct flux measurements from different sectors of the Southern Ocean demonstrating that silica and carbon cycles in the Southern Ocean mesopelagic are strongly decoupled, with a weak mechanistic link between BSi and POC fluxes. By combining Marine Snow Catcher flux measurements, in-situ pump, and CTD particulate data, we show that for a large part of the productive season, diatoms do not represent efficient vectors of sinking POC through the mesopelagic, yet POC is still efficiently transferred to depth. We suggest that processes influencing flux attenuation differ between the upper mesopelagic and deep ocean, with rapid BSi flux attenuation in the upper mesopelagic caused by elevated rates of BSi remineralization or negation of biomineral ballast effects by particle processes such as buoyancy regulation or fragmentation. Biomineral ballast may yet play an important role in shaping the efficiency of sinking POC transfer in the deep ocean. More broadly, these results highlight the need to understand the nuanced role this key taxon plays in transferring carbon through the mesopelagic, a region that is highly vulnerable to climate change effects and key in shaping the efficiency of downward carbon transport. As diatoms appear to be inefficient at delivering carbon to the deep ocean, projected losses in the strength of the Southern Ocean BCP due to shifts in phytoplankton community composition to smaller size classes may be less than previously predicted.

How to cite: Williams, J., Giering, S., Baker, C., East, H., Espinola, B., Le Moigne, F., Villa, M., Pabortsava, K., Blackbird, S., Pebody, C., Saw, K., Moore, M., Henson, S., Sanders, R., and Martin, A.: Reassessing the role of diatoms in carbon transfer through the Southern Ocean Twilight Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12043, https://doi.org/10.5194/egusphere-egu24-12043, 2024.

11:30–11:40
|
EGU24-9848
|
On-site presentation
Angela Landolfi, Ivy Frenger, Karin Kvale, Christopher J. Somes, Andreas Oschlies, Wanxuan Yao, and Wolfgang Koeve

The marine biological carbon pump (BCP) stores carbon in the ocean interior, isolating it from exchange with the atmosphere and thereby coregulating atmospheric carbon dioxide (CO2). As the BCP commonly is equated with the flux of organic material to the ocean interior, termed “export flux,” a change in export flux is perceived to directly impact atmospheric CO2, and thus climate. Here, we recap how this perception contrasts with current understanding of the BCP, emphasizing the lack of a direct relationship between global export flux and atmospheric CO2. We argue for the use of the storage of carbon of biological origin in the ocean interior as a diagnostic that directly relates to atmospheric CO2, as a way forward to quantify the changes in the BCP in a changing climate. The diagnostic is conveniently applicable to both climate model data and increasingly available observational data. It can explain a seemingly paradoxical response under anthropogenic climate change: Despite a decrease in export flux, the BCP intensifies due to a longer reemergence time of biogenically stored carbon back to the ocean surface and thereby provides a negative feedback to increasing atmospheric CO2. This feedback is notably small compared with anthropogenic CO2 emissions and other carbon-climate feedbacks. A comprehensive view of the BCP's impact on atmospheric CO2, is a prerequisite for assessing the effectiveness of marine CO2 removal approaches mediated by biology.

How to cite: Landolfi, A., Frenger, I., Kvale, K., Somes, C. J., Oschlies, A., Yao, W., and Koeve, W.: Misconceptions of the marine biological carbon pump in a changing climate: Thinking outside the “export” box, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9848, https://doi.org/10.5194/egusphere-egu24-9848, 2024.

11:40–11:50
|
EGU24-13592
|
Virtual presentation
Eun Young Kwon, John Dunne, and Kitack Lee

Calcifying organisms produce calcium carbonate (CaCO3) shells and skeletons. When they die, biogenic CaCO3 is vertically exported from the euphotic zone and dissolves throughout the water column and in sediments. The alkalinity generated from this process can influence the ocean’s buffer capacity for absorbing atmospheric CO2. However, the magnitude and driver of surface CaCO3 export and subsequent dissolution in the ocean’s interior – a process called the carbonate pump – are highly uncertain. We present key drivers of pelagic CaCO3 dissolution constrained by an inverse ocean biogeochemistry model combined with multiple observation databases. Within the upper twilight zone (shallower than 300 m), we found a tight association between particulate organic carbon remineralization rates and the CaCO3 dissolution efficiency (the fraction by which the surface exported CaCO3 dissolves), which is further supported by the observed particle flux and concentration data. In the deep ocean (deeper than 300 m), dissolution of CaCO3 is primarily driven by conventional thermodynamics of CaCO3 solubility with reduced fluxes of CaCO3 burial to marine sediments beneath more corrosive North Pacific deep waters. Shallow CaCO3 dissolution, shown to be sensitive to ocean export production, can increase the neutralizing capacity for respired CO2 by up to 6% in low-latitude thermocline waters. Without shallow dissolution, the ocean might lose 20% more CO2 to the atmosphere through the low-latitude upwelling regions – the world’s largest area of CO2 outgassing in the contemporary climate. Our work identifies a previously overlooked sensitivity of oceanic CO2 uptake to the biological pump. We suggest that Earth system models need to include the respiration driven CaCO3 dissolution processes for a better projection of future oceanic carbon sink.

How to cite: Kwon, E. Y., Dunne, J., and Lee, K.: Present-day global patterns of the ocean carbonate pump and the key drivers of CaCO3 dissolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13592, https://doi.org/10.5194/egusphere-egu24-13592, 2024.

11:50–12:00
|
EGU24-7805
|
ECS
|
On-site presentation
Jiaying Li, Zhifei Liu, Baozhi Lin, Yulong Zhao, Xiaodong Zhang, Junyuan Cao, Jingwen Zhang, Hongzhe Song, Thomas Blattmann, Negar Haghipour, and Timothy Eglinton

Zooplankton fecal pellets constitute a major component of passively sinking particles in the ocean. The sinking of zooplankton fecal pellets provides an efficient vehicle for the transfer and sequestration of particulate organic carbon in the deep sea, which has been widely reported in different ocean regions. However, most existing studies focus on the sinking flux of fecal pellets within the upper ocean, while the lower mesopelagic and bathypelagic zones are rarely investigated. Here, we report the spatiotemporal flux variation of zooplankton fecal pellets collected by two sediment traps deployed in mesopelagic and bathypelagic zones (500 m and 2190 m, respectively) of the southern South China Sea from June 2020 to May 2023. The average fecal pellet numerical flux is 3.21*104and 4.64*104 pellets m-2 d-1 at 500 m and 2190 m, respectively, corresponding to an average fecal pellet carbon flux from 0.43 to 0.84 mg C m-2 d-1 at these two depths. Fecal pellet fluxes display distinct seasonal patterns due to the control of the East Asian monsoon system, with higher fluxes in winter and spring, and lower fluxes in summer and autumn. Higher fecal pellet fluxes combining with the presence of extra-large pellets are found in bathypelagic zone, which is attributed primarily to in-situ reworking and repackaging of sinking particulate matter by deep-dwelling zooplankton communities, as well as lateral inputs from adjacent high productive continental coasts and shelves. We compare our results with global deep-sea (>500 m) fecal pellet flux data reported from different sediment-trap stations with distinct marine primary productivity and zooplankton biomass. Furthermore, we will report on the state of our progress on carbon isotope analysis (13C, 14C) for disentangling the source-to-sink dynamics of fecal pellets and its role in the deep-sea carbon export and sequestration.

How to cite: Li, J., Liu, Z., Lin, B., Zhao, Y., Zhang, X., Cao, J., Zhang, J., Song, H., Blattmann, T., Haghipour, N., and Eglinton, T.: Zooplankton Fecal Pellet Flux and Carbon Export in the Deep South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7805, https://doi.org/10.5194/egusphere-egu24-7805, 2024.

12:00–12:30
|
EGU24-2879
|
solicited
|
Highlight
|
Fridtjof Nansen Medal Lecture
|
On-site presentation
|
Stephanie Henson

The biological carbon pump is a series of processes that transfers organic carbon from the surface ocean into the deep ocean.  Without it, atmospheric CO2 levels would be ~ 50 % higher than pre-industrial levels.  Despite its importance, we currently struggle to understand how the strength and efficiency of the biological carbon pump varies temporally and spatially.  This makes it difficult to observe, and therefore model the pump, so our knowledge of how this important component of the global carbon cycle might respond to climate change is poor.  In this talk I’ll present recent progress on using autonomous vehicles to quantify variability in the biological carbon pump, discuss the current limitations in our understanding of the pump, and the implications of those knowledge gaps for robust modelling of the current and future pump. 

How to cite: Henson, S.: Future trends and climate feedbacks of the biological carbon pump, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2879, https://doi.org/10.5194/egusphere-egu24-2879, 2024.

Posters on site: Wed, 17 Apr, 16:15–18:00 | Hall X4

Display time: Wed, 17 Apr, 14:00–Wed, 17 Apr, 18:00
Chairpersons: Richard Sanders, Netta Shalev, Mebrahtu Weldeghebriel
X4.33
|
EGU24-13908
|
ECS
Mebrahtu Weldeghebriel, Tim Lowenstein, and John Higgins

Secular variations in the major ion chemistry and isotopic composition of seawater on multimillion-year time scales over the Phanerozoic are well documented, but the causes of these changes are debated. δ7Li and 87Sr/86Sr are widely utilized to interpret the driving mechanisms of secular changes in seawater chemistry, the tectonic history of the Earth and the link between paleo-ocean chemistry and the carbon cycle. These interpretations and models, however, are based on (1) few quantitative data on strontium concentration [Sr]SW in seawater calculated from the Sr/Ca ratios of marine carbonates and (2) the assumption that the Li concentration [Li]sw of seawater has been similar to modern [Li]sw. But those assumptions, if inaccurate, could undermine the validity of modeling results. The marine strontium and lithium cycles through time could be better reconstructed using coupled marine records of [Sr]SW, 87Sr/86Sr, [Li]sw and δ7Li. [Sr]SW and [Li]sw in ancient seawater would be particularly useful for examining which global processes, continental weathering or global volcanicity at seafloor hydrothermal systems and subduction zones, exerted the dominant control on the changes in seawater chemistry. Recent analytical advances using combined cryo-SEM-EDS and laser ablation ICP-MS now allow quantitative measurement of [Sr]FI and [Li]FI in fluid inclusions in halite. [Sr]SW and [Li]sw, reconstructed from chemical analyses of >1,000 fluid inclusions in more than 100 halite samples with marine 87Sr/86Sr values, varied seven-ten-fold and oscillated twice between high- and low-Sr and Li concentrations over the past 550 million years, in rhythm with Ca-rich and SO4-poor paleoseawater intervals, calcite-aragonite seas, supercontinent breakup, dispersal, and assembly cycles, greenhouse–icehouse climates, and modeled atmospheric pCO2. These data enable us to better constrain the Sr and Li cycle, and offer new insights into geochemical modeling of Phanerozoic seawater chemistry using multiple isotope systems and seawater concentrations. 

How to cite: Weldeghebriel, M., Lowenstein, T., and Higgins, J.: Variability in strontium and lithium composition of ancient seawater from fluid inclusions in halite—implications for reconstructing drivers of seawater secular variability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13908, https://doi.org/10.5194/egusphere-egu24-13908, 2024.

X4.34
|
EGU24-6440
|
ECS
Neeraja Baburaj, Alexander Dickson, and Hannah Elms

Organic carbon burial plays an important role in the global carbon cycle, and changes in the magnitude of such carbon burial have the potential to impact the global climate. Recent studies have shown that stable cadmium isotopes (δ114/110Cd) have potential as a tracer for marine organic carbon burial. However, the input and output fluxes and isotopic fractionation behaviour of Cd in the marine system are currently insufficiently constrained for robust application as a paleo-proxy. For example, while the main input flux of Cd to the oceans is from rivers, the isotopic behaviour of Cd during its passage through estuarine mixing zones is poorly understood.

In this study we will present Cd concentration and isotopic measurements of waters spanning a salinity gradient of 34–1 PSU and bedload sediments collected from the Milford Haven estuary in Pembrokeshire, western Wales, The aim is to test the conservative behaviour of Cd in the estuarine mixing zone, to constrain the composition of Cd from weathering in a shale and sandstone dominated catchment, and to investigate the fractionation of Cd during catchment weathering. These data will help in better understanding the riverine input flux of cadmium into the oceans, and the marine cadmium budget.

How to cite: Baburaj, N., Dickson, A., and Elms, H.: Investigating the fractionation behaviour and mass balance of cadmium isotopes during continental weathering and marine burial., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6440, https://doi.org/10.5194/egusphere-egu24-6440, 2024.

X4.35
|
EGU24-12937
Netta Shalev, Stefano Lugli, Vinicio Manzi, Christoph Leitner, Yining Li, and Yana Kirichenko

Records of the stable-Sr isotope composition of past seawater, δ88/86Srsw, have recently been demonstrated to be good proxies for the evolution of the marine ‘carbonate factory’, the ultimate sink of carbon from the ocean-atmosphere system [e.g., 1-3]. Nevertheless, these records are incomplete, and they generally do not overlap in age. Thus, despite their proven significance, these records have not been validated by data from any independent archives. The Ca-sulfate minerals, gypsum (CaSO4∙2H2O), and its burial transformation product, anhydrite (CaSO4), are relatively abundant in ancient evaporitic sequences and they contain Sr in typically high concentrations of 1000-2000 ppm. In a previous study, we show that gypsum is always 88Sr-enriched relative to its precipitating solution by around 0.2‰ and that it is possible to detect significant variations in past δ88/86Srsw (≥0.1‰) from ancient gypsum/anhydrite samples from the geological record.

Here, we study Phanerozoic Ca-sulfate samples of four different ages: Ordovician, Triassic, Cretaceous, and Messinian. Preliminary δ88/86Sr results are in the range of 0.29 – 0.67‰. Most of the results cluster between the calculated gypsum composition expected for the two known extreme cases of seawater δ88/86Sr values inferred from Ca-carbonate archives: the high- δ88/86Sr Precambrian seawater [3], and Late Permian seawater - the Phanerozoic minimum [2]. Thus, our preliminary Phanerozoic data are generally in accordance with the suggestion that the long-term Precambrian seawater δ88/86Sr is higher than the Phanerozoic long-term background [3]. Furthermore, our preliminary data point to significant seawater δ88/86Sr variations during the Phanerozoic, with lower values in the Ordovician and Triassic relative to Cretaceous and Messinian samples. Such variations may suggest major changes in the ‘carbonate factory’ in the ocean between the Triassic and Cretaceous. It is further suggested that such variations in the mineralogy and/or flux of marine carbonates may result from evolutionary changes in marine calcifiers.

 

[1] Paytan et al. (2021) A 35-million-year record of seawater stable Sr isotopes reveals a fluctuating global carbon cycle. Science 371(6536), 1346-1350.

[2] Vollstaedt et al. (2014) The Phanerozoic δ88/86Sr record of seawater: New constraints on past changes in oceanic carbonate fluxes. Geochim. Cosmochim. Acta 128, 249–265.

[3] Wang et al. (2023) The evolution of the marine carbonate factory. Nature, 1-5.

[4] Kirichenko et al. (n.d.), First Insights into Strontium Isotope Fractionation in Gypsum and Its Geochemical Implications. Under review in Geochim. Cosmochim. Acta.

How to cite: Shalev, N., Lugli, S., Manzi, V., Leitner, C., Li, Y., and Kirichenko, Y.: Reconstructing past seawater δ88/86Sr from calcium-sulfates (gypsum and anhydrite), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12937, https://doi.org/10.5194/egusphere-egu24-12937, 2024.

X4.36
|
EGU24-3289
|
ECS
|
Tzu-Hao Huang, Xiaole Sun, Ji-Hoon Kim, Chris Mark, and Wei-Li Hong

Marine silicate alteration is a combined process of lithogenic silicate (LSi) dissolution (known as marine silicate weathering) and secondary clay neoformation (known as reverse weathering). Both processes have been shown to affect long-term C cycling. Yet, the net CO2 consumption and production due to marine silicate alteration have not been studied thoroughly. Factors such as silicate types and rates are crucial in determining the fate of CO2 in the marine subsurface. In this study, we aimed to constrain silicate types of marine silicate alterations and their rates by measuring Si isotopic signatures of porewater and different silicate phases (including LSi, biogenic silica (BSi) and amorphous secondary Si phase (ASSi)) and modelling downcore profiles from two drill cores retrieved from the Ulleung Basin, where up to 130 mM of alkalinity has been documented as a result of fast marine silicate weathering. A decrease in porewater dissolved Si (DSi) concentration and an increase in porewater δ30Si (δ30Sipw) value indicate the formation of ASSi in the shallow subsurface (0 to 9 meter below seafloor (mbsf)). Below the sulfate-methane transition zone (9 to 32 mbsf), an increase in DSi concentrations and a decrease in δ30Sipw values were attributed to the LSi dissolution releasing lighter Si isotopes into porewater. Such a dissolving LSi phase is likely a mica-group silicate, as suggested by the elemental content of the separated solid phase and porewater. This finding is supported by reactive transport simulation, which indicates that mica, vermiculite and albite are able to dissolve and release Mg, K and Na into porewater. Precipitation of smectite group silicates consumes Mg and K in the pore fluids at rates lower than the overall silicate dissolution rates. The dissolving mica-group silicate (and albite) neutralises CO2 produced through organic matter fermentation and increases porewater alkalinity, which is 60 times higher than the seawater value. By further conducting model sensitivity tests using various organic matter degradation rates, we found that the alkalinity concentrations contributing by dissolved Mg and K concentrations are majorly affected by changes in smectite group formation rates while mica and vermiculite dissolution rates remain constant. The decreased contribution of mica-like silicate dissolution and the increased contribution of BSi dissolution with sediment depth from 32 to 218 mbsf are indicated by increased DSi concentration, increased δ30Sipw values and rate results output by modelling.

How to cite: Huang, T.-H., Sun, X., Kim, J.-H., Mark, C., and Hong, W.-L.: Extremely high alkalinity due to dissolution of mica-group silicate in the pelagic sediments of the Ulleung Basin (East Sea): stable Si isotopes evidence and reactive transport modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3289, https://doi.org/10.5194/egusphere-egu24-3289, 2024.

X4.37
|
EGU24-13298
|
ECS
|
Faranak Dalvand, Adriana Dutkiewicz, R. Dietmar Müller, Nicky M. Wright, and Ben R. Mather

The Pacific Ocean, the largest ocean basin, plays a critical role in the global carbon cycle, where a massive quantity of deep-sea sediment is sequestered on the seafloor and ultimately transferred into the mantle through its extensive subduction zones. However, the fluxes of carbonate carbon to the seafloor, and the volume stored and subducted in the Pacific remains relatively unknown over the Cenozoic. Here we estimate the carbonate carbon flux to the Pacific seafloor since the early Cenozoic by modelling the evolution of the carbonate compensation depth (CCD), defined as the water depth where carbonate supply from the surface equals its dissolution at depth. This results in a lack of carbonate sediments below the CCD. Except for the eastern equatorial region, the CCD is poorly constrained or unknown in other regions of the Pacific. Given the regional and latitudinal variations in oceanographic parameters affecting carbonate sedimentation (e.g., water chemistry, surface productivity) across the Pacific basin, the Cenozoic CCD is modelled for six regions of the western and eastern North Pacific, western tropical Pacific, eastern equatorial Pacific, and western and eastern South Pacific. We utilize 110 deep-sea drill sites from DSDP, ODP and IODP expeditions to reconstruct the paleo-water depth through time at each location using pyBacktrack software. We carry out a linear reduced major-axis regression of the carbonate accumulation rate (CAR) versus paleo-water depth to compute the CCD in 0.5 My time intervals, incorporating dynamic topography and eustatic sea-level in our computations. We find that the CCD has fluctuated over the Cenozoic by ~1–1.2 km and shows distinct variabilities within the six regions of the Pacific. For example, a relatively shallow CCD (~2.8–4 km) across the western North and eastern South Pacific versus a deep CCD (~4–4.7 km) in the eastern equatorial region, and highly fluctuating western tropical CCD over the late Cenozoic, suggest substantial latitude-longitude control on the carbonate flux. The results indicate that the total carbonate carbon flux is primarily dominated by the eastern equatorial region between the early Oligocene and the middle Miocene (to maximum 55 Mt C/yr), due to enhanced nutrient concentration and higher primary productivity rate, as reflected by a deeper CCD. This contrasts with minimal carbonate carbon flux in the eastern and western North Pacific ranging between 0 and 5 Mt C/yr over the Cenozoic. Additionally, the Pacific total carbonate carbon mass has experienced a modest rise from the early Eocene (55 Ma) to the early Oligocene at ~34 Ma (from 3000 to 3500 Mt), followed by a gradual increase, reaching 4400 Mt at the present day. This recorded progressive rise since the early Oligocene coincides with the initiation of the Antarctic ice-sheet growth and intensified continental silicate weathering and alkalinity input to the oceans. Our new modelling of the CCD to assess the evolution of the Pacific deep-sea carbonate carbon reservoir during the Cenozoic improves constraints on deep carbon computations in the context of the global carbon cycle. 

How to cite: Dalvand, F., Dutkiewicz, A., Müller, R. D., M. Wright, N., and R. Mather, B.: Carbonate Compensation Depth and Carbonate Carbon Flux in the Pacific Ocean over the Cenozoic , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13298, https://doi.org/10.5194/egusphere-egu24-13298, 2024.

X4.38
|
EGU24-19681
|
ECS
Carbon cycling and environmental transitions: insights from sediment core analyses in sepetiba bay mangrove
(withdrawn after no-show)
Valleria Vieira Pereira, Claudia Hamacher, Antonio Tadeu dos Reis, Cassia Oliveira Farias, Michelle Passos Araújo, Mário Luis Gomes Soares, Sonia Barbosa dos Santos, Filipe de Oliveira Chaves, Cleverson Guizan Silva, Ana Clara Coimbra Abreu, and Ioanna Bouloubassi
X4.39
|
EGU24-4351
Bangqin Huang, Chao Xu, and Yibin Huang

The biological carbon pump (BCP) is a key mechanism sustaining ocean carbon sequestration and thus significantly influences atmospheric CO2 concentration. However, most of the key processes of the BCP, particularly in the twilight zone, remain poorly constrained. In this study, we use multiple approaches to constrain the key BCP processes throughout the water column in the South China Sea (SCS), including carbon export, remineralization and sequestration. Firstly, we calculated the small particulate organic carbon (POC) flux exported via the mixed layer pump (MLP) by biogeochemical profiling floats (BGC-float), which are typically ignored in low-latitude regions. We further combined three independent approaches, including BGC-float observation, in vivo reduction of the tetrazolium salt by the cellular electron transport system (in vivo INT), and the synthesis of prokaryotic respiration (PR) determined by radiolabeled leucine incorporation and zooplankton respiration (ZR) empirically estimated from the biomass (PR+ZR), to constrained the twilight zone remineralization (TZR) in the SCS. To reconcile methodological discrepancies, we estimated the possible range of carbon supply by integrating comprehensive carbon sources, including sinking POC flux, dissolved organic carbon input, lateral transport, dark carbon fixation, and active carbon transport by zooplankton migration. We find the in vivo INT approach may overestimate the TZR, while the TZR measured by BGC-float and PR+ZR approaches can be balanced with the total carbon sources. Finally, we further calculate the time-series POC flux at 1000 m by using the optical sediment trap equipped on the BGC-float, which indicates the real carbon sequestration flux and can be isolated from the atmosphere at the time scale of centuries to millennia. Our study provides new insights of the BCP and highlights the importance of inter-disciplinary and integrative process studies for constraining biogeochemical processes.

How to cite: Huang, B., Xu, C., and Huang, Y.: Observing the biological carbon pump of the twilight zone in the South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4351, https://doi.org/10.5194/egusphere-egu24-4351, 2024.

X4.40
|
EGU24-4833
Ruigang Ma, Chuanlian Liu, and Xiaobo Jin

The oceanic carbonate cycle plays a crucial role in buffering anthopogenic CO2 emmision by regulating the total alkalinity (TA) and dissolved inorganic carbon (DIC) in the seawater. There is a growing interest in comprehending the role of biogenic calcification, the carbonate (counter) pump. The Early Miocene glaciation is thought to be triggered by the declining pCO2 potentially through a threshold effect of ~400 ppm (Greenop et al., 2019), a level we are approaching today. The mechanism(s) behind the long-term pCO2 decline during this period is still an open question, with little discussion on fluctuations in the carbonate burial. We estimated the changes in volume and flux of pelagic carbonate, specifically using coccoliths (calcite scales produced by coccolithophores). Our investigation spanned the transition from the Paleogene to the Neogene (~27-20 Ma), using marine calcareous nannofossil ooze retrieved from the IODP Site U1501 and U1505 located in the western tropical Pacific Ocean. The circular-polarized light microscope is used to measure the thickness (and volume) of the coccolith crystals. Integrating the linear sedimentation rates, we estimated that coccolith carbonate burial varied between 2-8×104 mol·yr-1·km-2. Our result aligns with the modeled alkalinity removal through pelagic carbonate burial (van der Ploeg et al., 2019). Moreover, scanning electron microscope (SEM) observations revealed calcite carbonate dissolution effects in the water column, with ~5-30% of coccolith carbonate dissolving during sinking, releasing additional alkalinity to the sea-water. A negative correlation between Ks and bulk TOC suggests that the organic and inorganic carbon burial were decoupled during the studied period. While further constraints are needed to improve our estimation (e.g., considering assemblage changes in coccolith and planktonic foraminifera), we tentatively conclude that the decline in carbonate production together with the increased dissolution weakened the carbonate pump. As a result, enhanced buffering capacity of the ocean likely played a role in the drawdown of pCO2 from the Late Oligocene to the Early Miocene.

How to cite: Ma, R., Liu, C., and Jin, X.: Decreased carbonate pump during the Oligocene-Miocene Transition: Regulating the oceanic buffering capacity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4833, https://doi.org/10.5194/egusphere-egu24-4833, 2024.

X4.41
|
EGU24-6054
|
Highlight
Richard Sanders, Sarah Giering, Stephanie Henson, Adrian Martin, Elaine McDonagh, Ingrid Wiedmann, and Andrew Yool

Ocean biological processes, principally the surface production, sinking and interior conversion of organic carbon to CO2 store enough carbon in the ocean interior to keep atmospheric CO2 concentration substantially lower than it would otherwise be. The size of this effect is linked to the depth at which sinking organic matter is remineralised in the ocean, with a deeper mineralisation causing a greater storage. Two prominent hypotheses regarding the control over the depth at which sinking material is lost are Temperature and Ecosystem Structure, specifically the proportion of diatoms in the surface community. These are both theoretically valid (temperature controls respiration, diatoms control density) and have some support in the literature, however to date have been considered in isolation. In this paper we firstly compute the strength of these effects in isolation from simple theory and show that they produce relationships consistent with existing literature thus suggesting that both factors may play a role. We use these relationships to produce an equation linking mineralisation depth, parameterised as remineralisation length scale, to community structure and temperature, thus uniting the two factors. An analysis of this equation suggests that community structure exerts a stronger control over remineralisation length scale than does temperature.

How to cite: Sanders, R., Giering, S., Henson, S., Martin, A., McDonagh, E., Wiedmann, I., and Yool, A.: Temperature vs ecosystem structure control over remineralisation length scale of sinking particles in the Global Ocean , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6054, https://doi.org/10.5194/egusphere-egu24-6054, 2024.

X4.42
|
EGU24-19416
|
ECS
Damien Couespel, Jerry Tjiputra, Siv Kari Lauvset, and Nadine Goris

The biological carbon pump (BCP) stores a large quantity of carbon in the deep ocean and is a major contributor to the surface to depth gradient in dissolved inorganic carbon. Without the BCP, the atmospheric CO2 concentration would be higher by about 200 ppm. Thus, the BCP is a key component of the global carbon cycle, and yet its future evolution is highly uncertain. In model simulations, changes in the BCP are often estimated using the Apparent Oxygen Utilisation (AOU) that measures the difference between the in-situ oxygen content and the saturated oxygen content. With a changing climate, AOU can vary because of changes in ocean circulation or changes in remineralization. Here, we combine AOU with water mass ideal age to take apart changes in the BCP due to circulation change and to remineralization change. We will apply our analysis to a set of Earth System Models under different global warming scenarios. We will determine the sensitivity of these drivers to different level of climate change and investigate the spatio-temporal variability and magnitude of the projected BCP changes. This analysis may help to trace models uncertainty in future BCP change back to ocean physic and marine biogeochemistry. 

How to cite: Couespel, D., Tjiputra, J., Lauvset, S. K., and Goris, N.: Projections and drivers of future changes in biological pump as inferred from apparent oxygen utilizations , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19416, https://doi.org/10.5194/egusphere-egu24-19416, 2024.

X4.43
|
EGU24-5933
|
ECS
Aaron Naidoo-Bagwell, Fanny Monteiro, Andre Visser, and Stephanie Henson

The export efficiency of the biological carbon pump depends on a multitude of processes that can affect the sinking speed of particulate organic matter (POC). The uncertainty surrounding factors that promote particle aggregation (e.g. through transparent exopolymer particles – TEP), remineralization (e.g. via microbes) and zooplankton consumption and fragmentation (e.g. coprophagy) has led to inconsistent estimates and future predictions for global export flux amongst earth system models. Two of the most unaccounted-for and least understood processes for constraining these simulations of POC flux are fragmentation and diel vertical migration (DVM) by zooplankton, with the majority of CMIP6 model omitting these from their frameworks. Fragmentation rates can be physically-mediated (e.g. turbulent shear) or biologically-mediated (e.g. “sloppy feeding” by zooplankton) and drive remineralization and thus flux attenuation. Another zooplankton activity, DVM, also contributes to export flux. the resulting export flux. DVM, where organisms nocturnally migrate to surface waters to feed and descend during the day, has great implications for biogeochemical fluxes of nutrients and provides a mechanism for POC to bypass potential transformation via fecal pellet production at depth. Here, we use a 1-dimensional particle model (SISSOMA) that includes mechanistic descriptions of key particle transformation processes (aggregation, remineralization, fragmentation etc.) to explore the potential consequences of fragmentation and DVM. SISSOMA enables study into the formation and fate of particles in the mixed layer, producing particle size distributions of the flux exported. Through sensitivity tests on the drivers of fragmentation rates, fed by Underwater Vision Profiler (UVP) and Biogeochemical-Argo floats observations, we can determine what drives particle size distribution and ultimately carbon export. We apply a DVM component to SISSOMA, driven by ecological observations of migrating zooplankton (e.g. EcoTaxa) to investigate the extent to which this process contributes to export flux and its particle size composition. We implore future modelling and observationally-based studies related to constraining the biological pump to consider these processes when designing their research.

How to cite: Naidoo-Bagwell, A., Monteiro, F., Visser, A., and Henson, S.: A mechanistic reproduction of particle transformation via fragmentation and diel vertical migration , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5933, https://doi.org/10.5194/egusphere-egu24-5933, 2024.

X4.44
|
EGU24-6276
Xinyang Wang

The vast and rugged seafloor, densely populated with unique topographic characteristics such as seamounts, serves as hotspots for ocean deep-sea biodiversity and fisheries resources. For oligotrophic regions covering more than a quarter of the global ocean, such unique topography regions are ecological oases within the oceanic desert. However, research on these ecological hotspots remains scarce, particularly in understanding the mechanisms behind the formation of these ecological oases. We selected a shallow seamount in a typical oligotrophic region as a case study and conducted comprehensive on-site physical, chemical, and biological observations, revealing its coupled temporal and spatial response characteristics. By comparing observations from multiple 24-hour time-series stations at different locations on the seamount, we uncovered the differential response characteristics between the upstream and downstream sides induced by the seamount topography. Based on this, we elucidated the efficient organic matter production and export processes on the seamount, attempting to propose a mechanism for the formation of seamount ecological oases.

How to cite: Wang, X.: Seamounts Generate Efficient Biological Carbon Pump Processes to Nourish the Twilight Ecosystem, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6276, https://doi.org/10.5194/egusphere-egu24-6276, 2024.

X4.45
|
EGU24-7112
|
ECS
Junhyeong Seo, Intae Kim, Hyunmi Lee, and Suk Hyun Kim

We investigated the export flux of particulate organic carbon (POC) using 234Th as a tracer in the western Indian Ocean along 60°E and 67°E transects in 2017 and 2018. The Seychelles-Chagos Thermocline Ridge (SCTR), where production is relatively high due to nutrient replenishment by upwelling of subsurface water, was observed at 3°S – 12°S in 2017 and 4°S – 13°S both 60°E and 67°E in 2018. POC fluxes in 2017 showed no differences between the SCTR and non-SCTR regions. However, in 2018, the POC fluxes in the SCTR regions (8.52 ± 7.89 mmol Cm–2 d–1) were one order of magnitude higher than those observed in the non-SCTR regions (0.63 ± 0.07 mmol C m–2 d–1), which appeared to be related to the strong upwelling of subsurface water. These POC fluxes were comparable to those observed under bloom conditions, and thus, are important for estimating the efficiency of carbon sequestration in the ocean.

How to cite: Seo, J., Kim, I., Lee, H., and Kim, S. H.: POC export fluxes across the Seychelles-Chargos Thermocline Ridge in the western Indian Ocean based on 234Th as a tracer, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7112, https://doi.org/10.5194/egusphere-egu24-7112, 2024.

X4.46
|
EGU24-18479
|
ECS
Beatriz González-González, María Villa-Alfageme, Unai Abascal-Ruiz, and Santiago-José Hurtado-Bermúdez

Quantifying the ocean carbon export and sequestration is essential to understand not only the marine carbon cycle but also the impact of the biological pump (BP) on global carbon cycle. The BP includes the different mechanisms by which atmospheric carbon is transferred from the surface to the deep ocean in a process started by the carbon synthetization of phytoplankton and followed by the formation and sinking of the marine snow, enabling the storage of carbon for long periods of time. Particulate organic carbon (POC) downward flux is a key and necessary parameter to characterize the BP and the ocean carbon cycle models.

In order to estimate POC flux, radioactive pairs (238U-234Th or 210Pb-210Po) disequilibrium and sediment traps are robust and accurate methods; however, they generally present low spatial-temporal resolution. In situ optical observations have shown a big potential to generate a wide database of POC fluxes.

Artificial intelligence (AI) and machine learning (ML) algorithms have already shown their potential in the last years to improve the estimations of oceanic POC concentration. It can be obtained as a satellite-derived product using colour remote sensing data, as POC is correlated with optical properties and water components (suspended particulate matter and chlorophyll-a). In contrast, ML have just only recently started to be used to evaluate POC export fluxes, partly because the lack of consistent and extensive datasets combining POC fluxes and ancillary parameters.

Here, we review the state of art of the use of ML techniques for POC concentration predictions as the cornerstone for estimations of POC export fluxes. The potential of ML methodologies to generate global reconstructions of particle fluxes in the ocean, using the current available POC flux databases, will be discussed and described. We will finally include general guidelines to analyse POC export evaluations using ML and comprehensive databases.

How to cite: González-González, B., Villa-Alfageme, M., Abascal-Ruiz, U., and Hurtado-Bermúdez, S.-J.: Developing machine learning algorithms to quantify carbon export fluxes in the ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18479, https://doi.org/10.5194/egusphere-egu24-18479, 2024.

X4.47
|
EGU24-22422
|
ECS
Charlotte Schnepper, Rut Pedrosa-Pamies, Maureen Conte, Nicolas Gruber, Negar Haghipour, and Timothy Ian Eglinton

The imprint of bomb radiocarbon on sinking particulate organic carbon (PO¹⁴C) intercepted by sediment traps, together with flux and elemental data, provides information about the origin and dynamics of oceanic particles (Hwang et al., 2010). Of particular interest is the question of the degree to which sinking POC in the deep ocean stems from overlying primary production, i.e., vertical supply via the biological pump, versus other processes such as advection and subsequent aggregation of resuspended sedimentary carbon originating from continental margins and other distal sources (Conte et al., 2019). In this context, natural abundance variations in 14C serves as a useful tracer given contrasting signatures recently fixed and pre-aged carbon sources. To quantify the seasonal to inter-annual variability in sinking PO¹⁴C, we have analyzed sediment trap samples from the Oceanic Flux Program (OFP) in the Sargasso Sea, a deep ocean time-series which has examined the particle flux and its composition at 500, 1500 and 3200 m water depths since 1978.

Radiocarbon measurements of POC of all OFP samples spanning September 2012 to December 2015 reveal seasonal and subseasonal variations in sinking PO¹⁴C with an amplitude in Δ¹⁴C values of ca. 100 ‰. This variability in Δ¹⁴C values is inversely linearly correlated with the proportion of lithogenic material to POC (LM:POC; r2=4.2, p <0.01). This relationship suggests that POC with high Δ¹⁴C values and a low LM:POC ratio reflect the supply of particles that sink vertically via the biological pump. Conversely, lower Δ¹⁴C values and high LM:POC ratios indicate laterally transported materials originating from resuspended sediments containing pre-aged organic carbon. Significant deviations from the linear regression (p <0.01) correlate with δ13C values, indicating an increased state of POC remineralization that is independent of Δ¹⁴C variations attributable to particle provenance.  

Over the 3.3 year period of observation, POΔ¹⁴C decreased by ca. 26 %, exceeding the expected annual decline (~6 ‰) based on reconstructed surface DI14C. This decline potentially could be linked to different source(s) of laterally supplied aged organic carbon associated with lithogenic material and/or a shift in the POΔ¹⁴C of the overlying flux (e.g.  from reduction in particle sinking speeds, enhanced decomposition, increased incorporation of aged suspended particles and/or dissolved organic carbon into the sinking flux). On-going work extending the OFP time-series will examine these multiyear trends and assess potential variability in the balance between vertically exported and laterally supplied POC to the deep ocean flux in the deep Sargasso Sea, enabling a better understanding of the underlying processes which control POC dynamics. 

How to cite: Schnepper, C., Pedrosa-Pamies, R., Conte, M., Gruber, N., Haghipour, N., and Eglinton, T. I.: Temporal variations of sinking particulate organic radiocarbon in the deep Sargasso Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22422, https://doi.org/10.5194/egusphere-egu24-22422, 2024.

X4.48
|
EGU24-913
|
ECS
Joelle Habib, Lars Stemman, Pierre Climent, Alexandre Accardo, Alberto Baudena, Franz Philip Tuchen, Peter Brandt, and Rainer Kiko

The equatorial upwelling system is characterized by a strong seasonal cycle with relatively cold sea surface temperature (SST) and enhanced primary production in the “cold tongue region” of the eastern basin during boreal summer. During the boreal summer of 2021, the equatorial Atlantic witnessed its most intense warm event since the beginning of satellite observations, which is assumed to have a direct impact on the carbon cycle. Here we use data from a BGC Argo float, deployed in the equatorial upwelling region in order to investigate the production peaks of marine particles during two distinct periods: the decay period of the anomalous weak cold tongue and the period of secondary cooling in boreal winter. In situ images of plankton and particles and physical and biogeochemical data provided by the Underwater Vision Profiler 6 (UVP6) and various sensors mounted on the float were analyzed in conjunction with satellite data (sea surface height, SST, ocean color). The float covered the period between 13 July 2021 and 23 March 2022 drifting eastward from 23-7.4°W along the equator and conducting 2000 m profiles every three days. Our data revealed the occurrence of two blooms with high surface chlorophyll concentrations accompanied by the presence of two carbon export events reaching at least 2000 m depth. Both events exhibited high carbon flux at the mixed layer with a flux of 106±5 mgC.m-2d-1 during the first event compared to 122±17 mgC.m-2d-1 during the second while flux between both events remained below 89 mgC.m-2d-1. However, a distinction in the vertical extent of these events was recorded as there was a slightly higher flux at 2000 m for the winter boreal, 30% higher, suggesting a difference between the carbon attenuation flux export associated with the primary upwelling season with the one observed during the secondary cooling period in the boreal winter. The characterization of the morphology of detritus using in situ imaging and clustering method revealed the presence of five different morpho-types with different sinking properties. Two primary classifications—large and small dense aggregates—emerged as the predominant exported detritus to depths while porous aggregates were more concentrated in the surface layer. Our study revealed a dynamic interaction between various layers, involving carbon production in the surface layer, succeeded by its subsequent export to deeper layers. Finally, this study offers new insights into particle dynamics and the morphology of sinking particles within the equatorial region.

How to cite: Habib, J., Stemman, L., Climent, P., Accardo, A., Baudena, A., Tuchen, F. P., Brandt, P., and Kiko, R.: Dynamics and morphology of sinking particles in the equatorial Atlantic during the 2021 Atlantic Nino, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-913, https://doi.org/10.5194/egusphere-egu24-913, 2024.

X4.49
|
EGU24-10926
|
ECS
Visualizing the Biological Carbon Pump: carbon export and attenuation in the North Atlantic using Underwater Vision Profilers.
(withdrawn)
Elena Ceballos-Romero, Clarissa Karthäuser, and Ken Buesseler

Posters virtual: Wed, 17 Apr, 14:00–15:45 | vHall X5

Display time: Wed, 17 Apr, 08:30–Wed, 17 Apr, 18:00
Chairpersons: Yael Kiro, Mebrahtu Weldeghebriel
vX5.28
|
EGU24-12853
|
ECS
Maricarmen Igarza, Michelle Graco, Mohammed Boussafir, Abdelfettah Sifeddine, Jorge Valdés, and Dimitri Gutiérrez

Phytoplankton production represents the ultimate source of organic matter in the ocean; thus, the study of organic compounds can give us information related to organic matter (OM) origin and transformations. Usually less than 1% of the OM produced in the ocean surface reaches the seafloor, although in highly productive regions nearly 10% can be buried and subjected to further degradation. The Peruvian upwelling system is among the most productive marine ecosystems in the world ocean, with high primary production sustained mainly in a year-round upwelling. Along the Peruvian continental margin, variations in primary production, bottom dissolved oxygen, and depth influence OM accumulation and preservation, and thus determine the existence of different depositional environments. Previous geochemical and palaeoceanographic studies have shown that the best records of well-preserved OM are found towards the central area of the Peruvian continental margin, between 12°S and 14°S. Therefore, the study of organic compounds, particularly lipids, deposited in surface sediments could give us information regarding early diagenetic processes related to OM degradation/preservation. The objective of this study was to characterize both the solvent extractable OM fraction (i.e. free lipids) and the insoluble OM fraction (i.e. protokerogen) in order to elucidate possible preservation mechanisms involved in OM accumulation. A total of 14 surface sediment samples from different locations between 12°S and 14°S were analyzed by means of gas chromatography mass spectrometry. Organic compounds such as short-chain and long-chain alkanes and fatty acids were quantified in the solvent-extractable OM fraction, which allowed the calculation of a pristane/phytane index and a carbon preference index. In the insoluble OM fraction, alkanes and fatty acids were also quantified together with dithiophene and benzothiophene compounds and organic sulfur heterocompounds. Overall, our results allowed a detailed geochemical molecular characterization of the OM deposited in surface sediments beneath one of the most productive areas of the Peruvian coast. The differences observed in both the n-alkane and fatty acids distribution between the solvent-extractable OM fraction and the insoluble OM fraction, together with the quantification of sulfur compounds in the insoluble fraction, suggests that complex diagenetic processes occur in surface sediments. An important part of the freshly-produced OM in the highly productive surface waters off central Peru reaches the seafloor and undergoes preservation mechanisms mainly related to natural sulfurization and selective preservation, tightly coupled to the reduced conditions that characterize surface sediments in the area.

How to cite: Igarza, M., Graco, M., Boussafir, M., Sifeddine, A., Valdés, J., and Gutiérrez, D.: Molecular characterization of the sedimentary organic matter deposited off central Peru (12 – 14ºS): first insights into preservation processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12853, https://doi.org/10.5194/egusphere-egu24-12853, 2024.