The ocean plays an essential role in regulating Earth’s climate; it is also essential for regulating the Earth’s biogeochemical cycles of carbon, nitrogen, and oxygen. Long-term (at the end of this century) changes in ocean biogeochemical cycles will be determined by the pace of anthropogenic emissions and resulting climate change. For the ocean carbon cycle, Earth system models (ESMs) within the 6th Climate Model Intercomparison Project project that while the ocean carbon sink continues to grow with rising emissions, the fraction of emissions that is taken up declines as atmospheric CO2 rises, resulting in a positive carbon–climate feedback. By contrast, near-term (until 2040) changes will be masked by internal climate variability. ESMs in concert with observations are key to constrain the response of ocean biogeochemical cycles to ongoing climate change. Yet, predictive understanding of how ocean biogeochemical cycles would respond to rapid and strong changes in emissions is currently missing. Such knowledge is critical in support of monitoring and verification of political actions for strong and rapid decarbonization. I will talk about recent progress and challenges in our understanding of the long-term and near-term fate of the ocean biogeochemical cycles under changing climate.

How to cite: Ilyina, T.: The changing ocean biogeochemistry in the Earth system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14178, https://doi.org/10.5194/egusphere-egu23-14178, 2023.

How to cite: Vaittinada Ayar, P., Tjiputra, J., Bopp, L., Christian, J., Ilyina, T., Krasting, J., Séférian, R., Tsujino, H., Watanabe, M., and Yool, A.: Response of the ENSO-driven CO2 flux variability in the equatorial Pacific under high-warming scenario, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-958, https://doi.org/10.5194/egusphere-egu23-958, 2023.

The similarity of the average nitrogen-to-phosphorus ratios (N:P) in marine dissolved-inorganic and particulate-organic matter indicates tight links between those pools in the World Ocean. Here we analyse the sensitivity of marine biogeochemistry to variations in phytoplankton N and P subsistence quotas in an optimality-based ecosystem model coupled to the UVic Earth system model. Our results reveal distinct feedbacks between changes in the N and P quotas, N₂ fixation, and denitrification that loosen the coupling between dissolved and particulate N:P.  We demonstrate the importance of particulate N:C and P:C for regulating dissolved N:P on the global scale, with oxygen concentration being an important mediator. Our analysis also reveals a potential interdependence between phytoplankton stoichiometry and global equilibrium climate conditions.

How to cite: Chien, C.-T., Pahlow, M., Schartau, M., Li, N., and Oschlies, A.: Phytoplankton physiology controls global ocean biogeochemistry (and climate), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6639, https://doi.org/10.5194/egusphere-egu23-6639, 2023.

Phytoplankton growth is controlled by environmental drivers such as nutrients and light availability, temperature, and the carbonate system. Thereby, changes in one driver can modify the response towards another driver. These interactive effects are usually not considered in large-scale ocean biogeochemistry models, potentially leading to incomplete projections of future phytoplankton biomass. In the presented work, we first parameterized growth sensitivities to changes in the carbonate system. We then used the results of a meta-analysis on interactive driver effects in published phytoplankton laboratory studies to develop model parameterizations for dual driver interactions (carbonate system versus temperature, carbonate system versus light). The parameterizations were tested in the biogeochemistry and phytoplankton functional type model REcoM under present-day and future conditions. While future phytoplankton biomass decreases by a similar amount with and without driver interactions (5-6%), interactive driver effects become visible on a group-specific level. Once driver interactions are considered, the biomass of diatoms and small phytoplankton decreases by -8.1% and -5.0%, respectively, and the biomass of coccolithophores increases by +33.2% from present-day to future conditions on a global scale. In comparison, the biomass of diatoms, small phytoplankton, and coccolithophores changes by 0.0%, -9.0%, and -10.8%, respectively, in simulations without driver interactions. Hence, projections of the global future phytoplankton community shift towards a larger share of small phytoplankton and coccolithophores and a smaller share of diatoms if interactive driver effects are taken into account. Regionally, the effect of driver interactions is largest in the Southern Ocean, where diatom biomass decreases (-7.5%) instead of increases (+14.5%). In conclusion, our study reveals that model projections of future phytoplankton biomass may miss out important information on the future phytoplankton community composition and group-specific direction of change if driver interactions are not considered.

How to cite: Seifert, M., Nissen, C., Rost, B., Vogt, M., Völker, C., and Hauck, J.: Look ahead! Future projections of phytoplankton communities are altered by interactive effects of environmental drivers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6828, https://doi.org/10.5194/egusphere-egu23-6828, 2023.

Climate change impacts atmospheric properties and circulation at different time scales, ranging from daily to millenial. We specifically assess here the impact of a change in atmospheric synoptic variability (ASV) (0-1 month) on mean upper ocean properties. In a first step, we disentangle the ASV and low frequency part in atmospheric fields originating from a climate change experiment performed by the Kiel Climate Model. In a second step, we use these fields to perform a set of sensitivity experiments to the change in ASV by employing a NEMO-PISCES configuration. We show that a decrease in ASV results in a slowdown of the mean ocean circulation and a global decrease in primary productivity. Our study highlights the need for more precise quantifications of the atmospheric synoptic variability in climate models and observations.

How to cite: Duteil, O. and Park, W.: Future change in atmospheric synoptic variability : impact on ocean circulation and primary productivity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14290, https://doi.org/10.5194/egusphere-egu23-14290, 2023.

Nitrogen (N) plays a central role in marine biogeochemistry by regulating biological productivity, influencing the cycles of carbon, oxygen, and other nutrients, and controlling oceanic emissions of the potent greenhouse gas nitrous oxide (N₂O). Although the marine N cycle consists of multiple chemical species, global biogeochemical models often employ simple parameterizations of N transformations and omit key tracers and processes. Here we present an extended numerical representation of the marine N cycle that includes explicit tracers for nitrate, dinitrogen, nitrous oxide, ammonium, and nitrite. The extended model simulates heterotrophic denitrification, DNRN, DNRA, anammox, and nitrification of ammonium and nitrite and thus allows for a detailed representation of a step-wise reduction of fixed nitrogen in hypoxic zones and oxidation of reduced N-species in oxic waters. The updated biogeochemical model is included in the new global ICOsahedral Non-hydrostatic Ocean model ICON-O developed at the Max Planck Institute for Meteorology. ICON-O features a flexible, triangular grid created by recursively subdividing the original 20 triangles of the icosahedron resulting, in our configuration, in an average resolution of 40 km and 235,403 triangles. We describe the tuning and spin-up of a pre-industrial control simulation and compare model results with global and local estimates to quantify the N cycle (e.g., rates of primary production, N₂ fixation, nitrification, DNRN, DNRA, anammox). We further report results from a historical transient simulation focusing on N dynamics within the oxygen minimum zone of the Eastern Tropical South Pacific.

How to cite: Hülse, D., Six, K., Burt, D., Chegini, F., Ramme, L., and Ilyina, T.: An extended N cycle in the eddy-permitting global ocean model ICON-O, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11625, https://doi.org/10.5194/egusphere-egu23-11625, 2023.

The importance of iron in driving net primary production (NPP) and the biological carbon pump across the Southern Ocean has been explored in numerous studies. However, the potential role for manganese, essential to oxygen production and combating oxidative stress, has not received the same attention despite the noted physiological inter-dependencies between iron-manganese and that both are strongly depleted in Southern Ocean. In the sixth climate model intercomparison project, earth system models (ESMs)  project increasing NPP in the Southern Ocean due to supply of additional iron, while the global trend shows a decline. Similar mechanisms also describe the role of the ocean carbon cycle during the last glacial maximum. However, under increasing iron supply, more manganese is required to fulfil phytoplankton growth, and the neglect of manganese limitation in ESMs can further increase the uncertainty of future NPP in the Southern Ocean under future or past climate change.

Here we use a hierarchy of experiments with the state-of-the-art global ocean biogeochemical model PISCES-QUOTA, including explicit manganese limitation, to explore how the physiological traits govern iron and manganese stress in response to a changing climate. Our results show that manganese is deficient throughout much of the Southern Ocean, but iron is generally the limiting resource. Explicitly representing iron and Mn co-limitation through oxidative stress enhances the extent of manganese deficiency, especially for diatoms. Traits associated with photophysiological adaptation and management of oxidative stress may be unique in Antarctic plankton and are critical in modulating the footprint of both iron and manganese stress and hence the impacts on the carbon cycle in a changing climate. Overall, our results indicate that both iron and manganese are key determinants of the impact of climate change on the Southern Ocean, with a notable role for region-specific adaptive and acclimatory responses that require further constraint.

How to cite: Anugerahanti, P. and Tagliabue, A.: The footprint of iron-manganese limitation of the biological carbon cycle in a changing climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1001, https://doi.org/10.5194/egusphere-egu23-1001, 2023.

Increasing computational power enables Earth System Models (ESMs) to be run at higher resolutions than on conventional grids with spacings of O(100km). The new generation of ESMs running at resolutions of O(5-10km) are able to resolve phenomena such as mesoscale eddies in the ocean and convective storms in the atmosphere. Resolving these features can be a step towards reducing uncertainties in carbon cycle modeling as they directly affect the ocean uptake of anthropogenic carbon (Harrison et al. 2018). However, the spin-up of ocean biogeochemistry in globally high resolution ESMs remains computationally challenging. Traditionally, the spin-up duration of ocean biogeochemical components (e.g., in CMIP5/CMIP6 models) ranges from one hundred to several thousand years to avoid model drifts in the euphotic, mesopelagic and even deeper ocean that has an overturning time of O(1000 years). This long spin-up time is, however, not yet computationally affordable in high resolution ESMs despite recent advances in improving their scalability (Linardakis et al. 2022). Therefore, different spin-up strategies are required and need to be explored.

We here present our strategy to run the HAMburg Ocean Carbon Cycle model (HAMOCC; Ilyina et al. 2013, Jungclaus et al. 2022) in the high resolution ICON-Sapphire ESM (Hohenegger et al. 2022) configuration. We discuss the steps we take from tuning and spin-up of HAMOCC in a cascade of resolutions and configurations: initially in a 40km ocean only setup, subsequently in a 10km ocean-only and eventually a 5km ESM setup. Furthermore, we examine the possibility of replacing interpolated results (used as initialization for the next higher resolution) with available observations (e.g., nutrients, alkalinity, dissolved inorganic carbon) and its consequence on biogeochemical drifts of key tendencies such as CO₂ surface fluxes. Finally, we discuss the scientific questions that can be addressed using this spin-up strategy and its limitations.

References:

Harrison et al. 2018: https://doi.org/10.1002/2017GB005751

Hohenegger et al. 2022: https://doi.org/10.5194/gmd-2022-171

Ilyina, T., et al. 2013: https://doi.org/10.1029/2012MS000178.

Jungclaus et al. 2022: https://doi.org/10.1029/2021MS002813

Linardakis et al. 2022: https://doi.org/10.5194/gmd-2022-214

How to cite: Chegini, F., Casaroli, L., Salinas, M., Nielsen, D., Maerz, J., Mathis, M., Hülse, D., Ramme, L., Li, H., and Ilyina, T.: Spin-up strategy for ocean biogechemistry in a high resolution Earth System Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14222, https://doi.org/10.5194/egusphere-egu23-14222, 2023.

Rare Earth Elements (REE) are among the key tracers in modern chemical oceanography. Yet their budgetary imbalance in the modern ocean has limited our understanding of their marine biogeochemical cycling and their applications as paleo-proxies. The flux of REE across the sediment-water interface appears to be the dominant source of REE to the ocean. Most studies on the marine and sedimentary cycling of REE focus particularly on neodymium (Nd), which has a radiogenic isotope system that helps to constrain its ocean budget. Recently we developed a reactive transport model to study the diagenesis of Nd at a deep sea site on the Oregon margin, which successfully explained the distributions of Nd and its radiogenic isotope in pore water and authigenic sediment, and the diagenetic control of the benthic Nd flux to the ocean. Here we extend this model to include the whole REE series. We show that the transformation and fractionation of REE in sediment can be adequately modelled only via reactions between pore water, authigenic Fe/Mn oxides and phosphates. Using the model result we can scale the sedimentary sources of the rest of the REE elements to that of Nd, providing better constraints on the ocean budgets of all REE.

How to cite: Du, J. and Vance, D.: Modelling the sedimentary source and diagenetic fractionation of Rare Earth Elements in the ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7079, https://doi.org/10.5194/egusphere-egu23-7079, 2023.

How to cite: Cala, B., Sulpis, O., Wolthers, M., and Humphreys, M.: Dissolving better: what can Earth System models learn from 60 years of in situ carbonate mineral dissolution measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8433, https://doi.org/10.5194/egusphere-egu23-8433, 2023.

Although global marine anthropogenic CO₂ inventories have typically highlighted the North Atlantic as being the main feature of interest, southern hemisphere processes also play a key role in the changing marine carbon cycle. The South Subtropical Convergence (SSTC) in the South Atlantic, where low-macronutrient subtropical gyre waters intersect high-macronutrient Antarctic Circumpolar Current waters, is a key location for studying key processes such as the effects of climate change on the biological carbon pump. Here, we present a time series consisting of marine carbonate chemistry measurements from recent expeditions and global marine observations (GLODAPv2.2022 and BGC-ARGO) at 40°S in the Atlantic Ocean. We calculate the rates of change in dissolved inorganic carbon (DIC) and other related variables and use these to disentangle the apparent drivers of DIC change both natural (carbonate pump, C_carb and soft tissue pump, C_soft) and anthropogenic (C_anth). An increase in DIC is observed throughout the water column. The relative contribution of the C_soft and C_anth components to the DIC change varies, however, significantly depending on whether we use nutrients or dissolved oxygen in the analysis. We discuss the causes of this discrepancy, using a water mass analysis to investigate the effect of water mass composition shifts in formation regions, and exploring the impact of reduced oxygenation and increased remineralization in the Southern Ocean, aiming to understand which tracer more accurately represents the changing carbon pump.

How to cite: Delaigue, L., Sulpis, O., Reichart, G.-J., and Humphreys, M. P.: Multidecadal change in natural carbon dynamics at the interface between Atlantic and Southern Ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1394, https://doi.org/10.5194/egusphere-egu23-1394, 2023.

The drawdown of CO₂ via the temperature-dependent weathering of silicate minerals is thought to be one of the key processes acting to maintain Earth’s climate within narrow bounds over geologic time. However, the climatic responsiveness of weathering on multi-million-year timescales is, to our knowledge, yet to be demonstrated. If other factors dominate climate regulation on geologic timsecales, previously unexplored factors may be important in driving long-term carbon cycle changes. Here, we present the first continuous Cenozoic record of the concentration of calcium in seawater ([Ca²⁺_sw]). Our record is based on the Na/Ca of exceptionally well-preserved foraminiferal calcite, a methodology which leverages the extremely long seawater Na⁺ residence time (>40 Myr) to interpret such changes predominantly in terms of [Ca²⁺_sw] fluctuation. We show that a 12 mM decrease in [Ca²⁺_sw] occurred over the last ~50 Ma, with a close correspondence to the timing of atmospheric CO₂ changes, potentially implying a common driver. Using a carbon cycle box model, we demonstrate that, if the relationship between silicate weathering is shallower than commonly assumed, then this change in [Ca²⁺_sw] can mechanistically explain the majority of the Cenozoic CO₂ decrease, via the effect that Ca²⁺ has on CaCO₃ burial rates. Given the recently identified major change in the global sea floor spreading rate, this finding shifts the key driver of long-term climate from the terrestrial to marine realm. Conversely, if there is a steep relationship between silicate weathering and climate, the climatic responsiveness of weathering is such that the system would rebalance before [Ca²⁺_sw] can drive a major CO₂ change. Our results therefore highlight the need to determine whether silicate weathering is responsive to climate change on geologic timescales before the long-term drivers of CO₂ can be determined.

How to cite: Evans, D., Rosenthal, Y., Erez, J., Hauzer, H., Cotton, L., Zhou, X., Nambiar, R., Stassen, P., Pearson, P., Renema, W., Saraswati, P. K., Todd, J., Müller, W., and Affek, H.: The seawater calcium concentration may be a driver of long-term changes in CO2, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16325, https://doi.org/10.5194/egusphere-egu23-16325, 2023.

Levees in modern deep-marine systems have been shown to sequester significant amounts of organic carbon, due largely to their wide expanse and high rates of sedimentation. However, relatively few studies have examined organic carbon sequestration in ancient deep-marine leveed slope channel systems. Examining the distribution of organic material in ancient levee deposits could provide insight into paleoenvironmental conditions and the evolution of ancient ocean and climate systems.

Deep marine levee deposits of the Neoproterozoic Windermere Supergroup are exceptionally well-exposed in the Southern Canadian Cordillera of western Canada, where detailed physical description and stratigraphic logging were combined with total organic carbon (TOC) and X-ray fluorescence (XRF) to evaluate trends in the distribution of organic carbon and elemental composition within a 300 m-thick succession. These geochemical analyses were then used to reconstruct paleoenvironmental conditions such as primary productivity, ocean redox, weathering intensity, and detrital flux. In this succession, TOC ranges from < 0.1% to 4.04% (uncorrected for the effects of greenschist metamorphism). Organic-rich strata, taken to be ≥ 1% TOC, are principally confined to a single 60 m-thick stratigraphic interval, where they typically occur as anomalously thick, mud-rich sandstone turbidites. Organic matter in these beds occurs mostly as micro-scale carbon sorbed onto the surface of clay grains but can also occur as uncommon sand-sized organomineralic aggregates or discrete sand-sized amorphous grains.

In this same interval, trends in elemental data indicate an increase in primary productivity, weathering intensity, and detrital influx, and a decrease in ocean oxygenation levels. These data suggest that intense continental weathering, high terrigenous input, elevated sea level, and relatively low oxygenation conditions all act to enhance organic matter production in shallow marine environments and organic matter accumulation and preservation in the deep marine. However, although all these components contributed to increased organic production, accumulation, and preservation on their own, the results of this study suggest that it is the temporal coincidence of all of them in a “perfect storm” that is required for significant organic carbon enrichment. Additionally, because these strata are Neoproterozoic in age the preserved organic matter is exclusively marine in origin, which then raises the possibility that the conditions described here are unique to deep-sea turbidite systems before the evolution of metazoans or terrestrial plants. 

By studying the geochemical trends of both organic-rich and organic-poor rocks in this ancient outcrop, this study helps to elucidate the role of various paleoenvironmental factors in deep-marine organic matter enrichment throughout geologic time. This will ultimately improve our understanding of the complex interplay of physical, chemical, and biological processes that govern marine sedimentation and their relationship with the carbon cycle and past global climate, particularly in systems that pre-date terrestrial vegetation.

How to cite: Cunningham, C., Ruso, S., and Arnott, W.: Paleoenvironmental Factors Controlling Organic Carbon Sequestration in Neoproterozoic Deep-Marine Levees, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9965, https://doi.org/10.5194/egusphere-egu23-9965, 2023.

Deep-sea oxygen concentrations reflect combined effects of air-sea exchange in high-latitude surface waters, ventilation through ocean circulation and the organic carbon remineralization at depth. Reconstruction of past bottom water oxygen (BWO) concentrations has been challenging due to limitations of each existing BWO proxy whose fidelity may be complicated by diagenetic or depositional factors. Therefore, evaluations on BWO changes with multiple-proxy approach are always preferred. In this study, we exploit the authigenic uranium content on mixed planktonic foraminiferal coatings as a BWO proxy by presenting new foraminiferal U/Ca and U/Mn ratios of the Holocene and last glacial maximum (LGM) sediments from 54 sites throughout the Pacific Ocean, covering a range of modern BWO from 8-210 μmol/kg. As expected, foraminiferal U/Ca and U/Mn are influenced by sedimentation rates and organic carbon fluxes. Nevertheless, we also observe a negative correlation of Holocene U/Ca and U/Mn with BWO, with decreasing sensitivities towards higher BWO, suggesting the control of BWO on foraminiferal U/Ca and U/Mn variations. Based on the comparison of our foraminiferal U/Ca and U/Mn ratios between the Holocene and LGM and existing redox proxy data, we provide new constraints on Equatorial and South Pacific oxygenation changes during the LGM. First, the boundary between better oxygenated upper ocean and less oxygenated deeper ocean in the Eastern Equatorial Pacific was limited to a narrower water depth range between ~0.6 and 0.7 km. Second, our data imply better oxygenation in the upper and bottom waters of the Pacific Ocean and mid-depth deoxygenation, which contrasts with findings in the deep Atlantic and Indian Oceans. After excluding influences from other factors such as sedimentation rates and productivity, our study demonstrates foraminiferal U/Ca and U/Mn provide a useful proxy for BWO reconstruction in the Pacific, thus helping to constrain the glacial-interglacial oceanic carbon cycle.

How to cite: Hu, R.: U/Ca and U/Mn in foraminiferal coatings as a proxy for ocean oxygenation changes: new calibration and constraints on glacial oxygenation changes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15115, https://doi.org/10.5194/egusphere-egu23-15115, 2023.

The most important sulfur sink from a global redox-perspective is diagenetic pyrite produced in marine sediments. The amount and isotopic composition of this pyrite is thought to reflect environmental and physical properties of the ocean. This includes sulfate reduction rate, sulfate concentration, sedimentation rates, organic carbon and reactive iron concentrations and reactivities, porosity of the sediment etc. Our goal is to identify the main drivers that can explain the majority of observed sulfur isotopic composition in pyrite. To this end, we use a diagenetic model and calculate theoretical profiles for organic carbon, reactive iron, and a number of sulfur species and their isotopes in marine sediments. We calibrate our model using 216 sedimentary cores from a wide range of environmental conditions and locations from across the world. The model allows us to calculate burial rates and isotopic composition of pyrite in marine sediments on a global scale as well as infer drivers of the Phanerozoic pyrite d34S record. We show that isotopic composition of pyrite is determined by only three variables: the ratio of sulfate to organic carbon, the ratio of reactive iron to organic carbon, and the porosity. Based on this, we reinterpret Phanerozoic d34S trends as recording a shift in the locus and environmental conditions where pyrite is formed, rather than a change in microbial sulfate reducer fractionation.

How to cite: Mertens, C. and Hemingway, J.: Drivers of Sedimentary Pyrite δ34S Values - at Present and in the Past, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15760, https://doi.org/10.5194/egusphere-egu23-15760, 2023.

Ocean chemistry is dictated by weathering and transporting elements from the land to the ocean and their removal through precipitation and adsorption. While the role of rivers was established many decades ago, other sources of elements such as mid-ocean ridge hydrothermal systems, discharge from forearcs of subduction zones, and submarine groundwater discharge (SGD) have been recognized more recently. SGD may release large amounts of trace metals, nutrients, carbon, and other dissolved species to the coastal ocean. The element fluxes may be comparable to surface water flow due to groundwater interaction with the aquifer sediments and the high ratio between rock and water. To better understand the coastal water budgets, it is crucial to assess all sources and sinks, including SGD. Recent attempts to calculate the dissolved inorganic carbon (DIC) and alkalinity ocean budgets have shown that riverine DIC input and marine carbonate burial cannot be balanced by alkalinity delivered via submarine groundwater. This deficit in the ocean's DIC and alkalinity mass balance may be attributed to insufficient knowledge of the carbonate and alkalinity contributions through SGD, particularly seawater circulation in the aquifer.

The DIC and alkalinity fluxes are influenced by the mechanisms driving groundwater flow in the subsurface (fresh and saline water), affecting the flow paths, residence times, and redox states. Therefore, we expect DIC enrichment or depletion to vary among different environmental settings. Thus, it is unclear if coastal aquifers serve as a source or a sink for DIC, depending on the settings. Our study shows a significant contribution of alkalinity by fresh groundwater discharge and also during long-term seawater circulation in the East Mediterranean coastal aquifer. Even on a relatively short distance like the Israeli Mediterranean coastline (~150 km), we observed differences in alkalinity and DIC derived from the shift in the aquifer's rocks as carbonate amounts drop and sand levels increase from north to south. To comprehensively and globally understand alkalinity fluxes through SGD, we generated an extensive data archive on coastal aquifers worldwide. This data is used to characterize the interactions between groundwater and country rocks depending on the type of rock and how they may impact groundwater alkalinity and DIC. Most of the groundwater samples lie below the 1:1 Alkalinity-DIC ratio line, which may suggest that the major processes affecting the carbonate system contribute more DIC than Alkalinity. Many sandy and carbonate aquifers have a DIC greater than alkalinity, which indicates a significant amount of CO₂ and low pH levels. In contrast, alluvial aquifers have a minor trend, and basaltic aquifers usually have DICs equal to alkalinities (the most common species is bicarbonate). To better understand climate feedback mechanisms, it is crucial to know the ocean's alkalinity buffer system budget and its carbon sources and sinks.

How to cite: Weber, N. and Kiro, Y.: The role of submarine groundwater discharge in the ocean carbon budget, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16545, https://doi.org/10.5194/egusphere-egu23-16545, 2023.