This session seeks to bring together scientists studying various forms of carbon—organic, inorganic, dissolved, and particulate — to deepen our understanding of how human activities are reshaping the carbon cycle within the LOAC. We welcome research that explores carbon dynamics in the LOAC, particularly about the changes driven by anthropogenic impacts, including but not limited to:
- Characterisation of the carbon flux from land to ocean and the impacts of human activities on that flux
- Quantifying anthropogenic-influenced carbon in inland waters and rivers, estuaries and tidal wetlands, continental shelf waters, and freshwater/coastal/marine sediments.
- Quantification of the ocean carbon sink in coastal waters
- Redistribution of carbon among different carbon forms under anthropogenic perturbations.
- Changes in biogeochemical processes due to natural variability and anthropogenic impacts that influence the LOAC carbon cycle.
- Impacts of carbon dioxide removal interventions on the LOAC carbon cycle.
We strongly encourage contributions using diverse approaches, including cruise-based observations, autonomous platform observations, and machine learning and modeling techniques.
Rivers play a critical role in the global carbon cycle, transporting carbon from land to ocean while emitting significant amounts of CO2 to the atmosphere. Yet, the processes controlling the partitioning of fluvial inorganic carbon (IC) between atmospheric release and downstream transport remain poorly understood due to complex hydrodynamic and biogeochemical interactions.
Building on Budyko’s hydrological framework, we propose a dimensionless approach to uncover the primary controls on IC partitioning. Two key parameters are introduced: (1) the fraction of IC in equilibrium with atmospheric CO2 and (2) the ratio of transport to evasion timescales. Our analysis reveals that water chemistry regulates stable IC transport downstream, while water hydrodynamics dictates the fate of out-of-equilibrium IC. River catchment analyses support the dimensionless framework and highlight different IC dynamics depending on the stream order. Overall, this framework provides a predictive tool for river carbon dynamics, with implications for land-to-ocean fluxes and fluvial emissions.
How to cite: Bertagni, M., Regnier, P., Yan, Y., and Porporato, A.: Dimensionless Controls on the Fate of Fluvial Inorganic Carbon, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11998, https://doi.org/10.5194/egusphere-egu25-11998, 2025.
Dissolved inorganic carbon (DIC) transport along the land-ocean continuum, accounts for ~50% of the lateral carbon fluxes at global scale. One major source of riverine DIC comes from atmospheric carbon dioxide (CO2) uptake by chemical weathering process, which has currently been recognized as a potentially significant contributor of climate mitigation in addition to photosynthesis. However, we still have no clue how much this inorganic carbon sink would end up in the riverine DIC at regional scale and how/whether riverine DIC export has changed over space and time. China with a vast karst area (~1.9 million km2) and higher riverine DIC concentration than the global averaged value (~10mg/L), is particularly one of the largest regions with the big knowledge gap just mentioned. In this study, we compiled a large database of in situ riverine DIC observations (1895 records at 684 observations) in China based on which a machine-learning approach was used to estimate the riverine DIC concentrations (CDIC) and fluxes (FDIC), and evaluate the contribution of chemical weathering to riverine DIC fluxes. Results show that over the period 2001-2018, CDIC in China was on average 22.53 ± 6.62 mg/L with a significant decrease of -0.036 mg C/L/yr (P=0.01) and FDIC was 38.33 ± 9.39 Tg C/yr with little change (0.418 Tg C/yR2, P>0.05). In addition, chemical weathering carbon sink was found to account for ~40% of averaged FDIC at country scale while it can amount up to ~60% of FDIC in the southwest of China. Changes in pH and hydrologic conditions were found to dominate the FDIC across China regardless of whether the basin is chemical weathering dominated or not. GPP, land cover change and soil temperature are also found to contribute substantially to the FDIC in the south of China compared to the north of China.
How to cite: Yan, Y., Wang, X., Ran, L., Regnier, P., Lauerwald, R., Pilesjö, P., and Berggren, M.: Around 40% of riverine DIC export originates from weathering carbon sink in China over the past two decades, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20035, https://doi.org/10.5194/egusphere-egu25-20035, 2025.
Estuarine environments are complex dynamic systems and cornerstone components of the Land-Ocean Aquatic Continuum (LOAC). As such, they play a crucial role in global biogeochemical cycles, acting both as conduits and processors of carbon and nutrients between the terrestrial and oceanic realms of the Earth system. Despite this significance, considerable uncertainties remain associated with the quantification of biogeochemical fluxes within and through estuarine systems. In particular, the interplay between Organic Carbon (OC) degradation and Dissolved Inorganic Carbon (DIC) oversaturation remains poorly constrained in many estuarine systems. Furthermore, global estimates of estuarine CO2 emissions are still derived from limited and heterogeneous observational datasets, highlighting the need for adequate tools to resolve system-specific dynamics for a wide variety of estuarine set-ups.
Reactive Transport Models (RTMs) explicitly simulate both physical and biogeochemical processes controlling these dynamics and can be used to resolve the spatial and temporal gradient of their respective prevalence on net biogeochemical dynamics. Designed to reduce data demands through its one-dimensional structure and generic parameterization, the Carbon-Generic Estuary Model (C-GEM) has emerged as a computationally efficient RTM framework for simulating estuarine biogeochemistry, and has been successfully applied to estuarine systems of diverse morphologies ranging from river to marine dominated. In this work, we present an updated version of C-GEM, designed to answer the growing need for estuarine models capable of addressing the long-term impacts of anthropogenic pressures, climate change, and land-use modifications on carbon cycling, including transient simulations over multi-annual scales, the integration of a module for inorganic carbon dynamics, and improved user-accessibility.
We first demonstrate the applicability of the enhanced C-GEM framework to a range of realistic and idealized estuarine systems, exploring the relationships between hydrodynamic characteristics and biogeochemical functioning. In a second step, we explore the propagation of the inherent uncertainty associated with biogeochemical parameters towards integrated carbon budget diagnostics including CO2 exchange with the atmosphere, primary production or net ecosystem metabolism. A global sensitivity analysis (Morris Screening) is first performed for various estuarine set-ups (i.e. morphologies, residence time…) in order to rank the system-specific importance of biogeochemical parameters in driving integrated carbon budget diagnostics, thereby highlighting which processes are the main drivers of the estuarine carbon dynamics and which parameters may most require fine-tuning to better constrain estuarine budgets. Probability distributions are then built for selected key parameters based on published reference value. Finally, Monte Carlo simulations based on such constrained parameter sampling are used to delineate the resulting uncertainty in integrated estuarine GHG budgets. This analysis is specified for estuarine systems of different morphologies and hydrological regimes, as well as different portions of the estuarine systems, over which certain transport and biogeochemical processes prevail. Besides revealing the shadow zone of global estuarine carbon budgets, characterizing the resulting spread in observable states along estuaries (e.g. nutrients, Org C, ..) also help to identify priority observation efforts that would optimally constrain the overall carbon budget diagnostics.
How to cite: Capet, A., Laruelle, G., Massant, A., Lacroix, G., and Regnier, P.: Exploring Uncertainty and Parameter Sensitivity in Estuarine Carbon Dynamics: A C-GEM Framework Update, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20395, https://doi.org/10.5194/egusphere-egu25-20395, 2025.
Coastal wetlands laterally export a major portion of their fixed atmospheric CO2 to coastal oceans as inorganic carbon via tidal exchange, which is considered as a potential mechanism of blue carbon storage in the ocean due to the long residence time (thousands of years) of inorganic carbon. Such an export from saltmarshes can be evaluated by fluxes of total dissolved inorganic carbon (DIC) and total alkalinity (TA) in tidal creeks. The exported TA should be distinguished from DIC to represent a long-term carbon sink in the ocean, but knowledge of TA exports remains limited due to limited direct measurements. Furthermore, most of the previous estimates of TA exports were based on short-term studies (e.g., over a few tidal cycles at different seasons). However, we find that long-term high-resolution measurements are critical to avoid any biases in these estimates because of their extreme heterogeneity. Herein, we used multi-year, high-frequency measurements to resolve the TA exports from an intertidal saltmarsh, which also enables a comparison to the high-frequency DIC exports. Our study site is located at the Sage Lot Pond (SLP), Massachusetts, USA, where in situ water quality sensors were deployed from 2012 to 2016 and bottle data of TA and DIC were collected over multiple tidal cycles across seasons in the tidal creek. This comprehensive dataset allows us to develop a machine learning algorithm to predict high-frequency TA time series for subsequent calculations of TA exports. We observed that (1) consistent monthly trends in TA exports across years, with a net consumption of 1.0 mol m-2 yr-1 (i.e., TA sink) from October to June and an export of 7.1 mol m-2 yr-1 from July to September; (2) similar annual TA exports averaging 1.9 mol m-2 yr-1 across different years; (3) annual TA exports 16 times less than those of DIC. The finding of the particularly lower TA exports relative to DIC is in contrast with the recent global synthesis and many previous studies. There was a substantial decrease in TA from marsh sediment porewater to the tidal creek, indicating a large TA removal during porewater exchange and transport. We propose several mechanisms to explain such a net TA removal. Firstly, large amounts of aerobic respiration in the tidal creek and surface sediment can remove TA. Secondly, groundwater discharge into the tidal creek likely supplies many reduced compounds (i.e., Mn2+ and Fe2+), which can be oxidized causing a net TA removal. Lastly, sulfate reduction is the primary mechanism for TA production in porewaters, and the resulting S2- may be oxidized prior to the formation and burial of pyrite, decreasing the TA exports. The low TA exports observed here could be collectively driven by these processes at different spatiotemporal scales. These results raise the question, between DIC and TA, which estimated flux may better represent long-term CO2 sink from coastal wetlands. It also generates further interest in studying the fate of wetland exported DIC as it holds the key to credit lateral carbon export as blue carbon.
How to cite: Wang, Z. A., Shangguan, Q., Kuhl, S., Kroeger, K., and Eagle, M.: Variable export and consumption of alkalinity in coastal wetlands: insights from multi-year, high-frequency observations in an intertidal saltmarsh, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20675, https://doi.org/10.5194/egusphere-egu25-20675, 2025.
As an effective tracer for identifying the origin and cycling of carbon in aquatic ecosystems, the distribution pattern of the radiocarbon (Δ14C) of organic carbon (OC) in riverine particles and coastal sediments are essential for understanding the contemporary carbon cycle, but are poorly constrained due to under-sampling. This hinders our understanding of OC transfer and accumulation across the land–ocean continuum worldwide. Machine learning approaches and >3,800 observations have been used to construct a high-spatial resolution global atlas of Δ14C values in river–ocean continuums and show that Δ14C values of river particles and corresponding coastal sediments can be similar or different. Four characteristic OC transfer and accumulation modes are recognized: the old–young mode for systems with low river and high coastal sediment Δ14C values; the young–old and old–old modes for coastal systems with old OC accumulation receiving riverine particles with high and low Δ14C values, respectively; and the young– young mode with young OC for both riverine and coastal deposited particles. Distinguishing these modes and their spatial patterns is critical to furthering our understanding of the global carbon system. Specifically, among coastal areas with high OC contents worldwide, old–old systems are largely neutral to slightly negative to contemporary atmospheric carbon dioxide (CO2) removal, whereas young–old and old–young systems represent CO2 sources and sinks, respectively. These spatial patterns of OC content and isotope composition constrain the local potential for blue carbon solutions.
How to cite: Wang, C., Qiu, Y., Hao, Z., Wang, J., Zhang, C., Middelburg, J., Wang, Y., and Zou, X.: Global patterns of organic carbon transferand accumulation across the land–oceancontinuum constrained by radiocarbon data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2103, https://doi.org/10.5194/egusphere-egu25-2103, 2025.
Increased meltwater from glaciers may drive localized ocean acidification and CO2 uptake, but the carbonate system dynamics in glacially impacted marine environments remains poorly understood. Here we investigate dissolved inorganic carbon (DIC) and total alkalinity (TA) at the land-ocean interface along Iceland’s glacially impacted shelf waters in June 2023. We examine the state and drivers of ocean acidification and air-sea CO2 fluxes. TA in surface shelf waters varied between 1290 and 2340 μmol kg-1 whereas DIC varied between 1460 and 2120 μmol kg-1. The lowest values of both TA and DIC occurred by the outlet of a marine-terminating glacial lagoon. The shelf waters were a net CO2 sink, taking up 2.4±1.4 μmol CO2 m-2 day-1 on average. Aragonite saturation states (ΩAr) ranged between 0.1 - 5.8 (median = 2.4) in surface shelf waters with the majority of stations above 1, the threshold for solid CaCO3 stability. ΩAr<1 were found by the outlets of the marine-terminating glacial lagoon and the largest glacial river. Freshwater inputs such as glacial rivers and groundwater discharging onto the shelf displayed [TA-DIC] values lower than those of the shelf, implying their potential to reduce the buffering capacity of the coastal ocean. The wide range of TA and DIC content of the freshwater endmembers (90-1230 μmol kg-1 TA, 130-1220 μmol kg-1 DIC) makes it challenging to disentangle the contributions of these endmembers to the shelf. Overall, the study improves our understanding of the marine carbonate system across a glacier-ocean continuum, indicating glacial meltwater as a major driver of acidification in these continental shelf waters.
How to cite: Ljungberg, W., Majtényi-Hill, C., Yau, Y. Y. Y., McKenzie, T., Henriksson, L., Ulfsbo, A., and Santos, I.: Glacial meltwater impacts the marine carbonate system and acidification on the continental shelf off Iceland , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11191, https://doi.org/10.5194/egusphere-egu25-11191, 2025.
The ratio of 13C/12C in oceanic dissolved inorganic carbon (δ13C-DIC) is an effective tracer for exploring aquatic carbon cycles influenced by net biological production and respiration, lateral transport from land to ocean, and alongshore ocean currents. Additionally, δ13C-DIC is a valuable tool for estimating anthropogenic CO2 accumulation rates in the ocean. We developed and validated an automated, high-precision (±0.03 ‰) method for ship-based simultaneous analysis of DIC and δ13C-DIC using Cavity Ring-Down Spectroscopy (CRDS). This approach enabled the analysis of over 1,600 discrete seawater samples, along with numerous duplicates and standards, during a 40-day cruise along the North American eastern ocean margin in summer 2022.
Our findings revealed distinct air-sea δ13C disequilibrium due to short water residence times. A clear latitudinal gradient in surface δ13C-DIC distribution was also observed, with highly positive δ13C-DIC values in the northern sub-regions attributed to hotspots of net biological production and very low values in estuaries due to terrestrial inputs. The biological mechanism driven these variations is supported by a strong linear correlation between δ13C-DIC, the biological component of DIC deviation, and O2 supersaturation data. Using a box model, we further examined the interplay of various timescales for biological production, gas exchange (months for CO2 and DIC, years for δ13C-DIC), and water residence time in shaping the distributions of DIC and δ13C-DIC along the ocean margin.
Moreover, we observed a notable decrease in δ13C-DIC over the past 25 years, particularly within the upper ocean mixed layer, with the decline progressively diminishing with depth to approximately 1,500 m. These decadal changes in δ13C-DIC are substantially larger than those of DIC in the context of natural spatial and temporal variability. This pattern underscores the growing influence of anthropogenic carbon in surface and subsurface waters, suggesting δ13C-DIC may serve as a more sensitive indicator than DIC concentration for detecting anthropogenic CO2 accumulation given its more pronounced decadal variability. The characteristic δ13C-DIC signals also help identify carbon sources affecting ocean pH and acidification.
How to cite: Cai, W.-J., Sun, Z., Li, X., Ouyang, Z., Dong, B., Hussain, N., and Atekwana, E.: What Does the Stable Carbon Isotope Ratio (δ13C-DIC) Tell Us About the Coastal Ocean Carbon Cycle Along the North American East Coast?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1861, https://doi.org/10.5194/egusphere-egu25-1861, 2025.
The Spanish Institute of Oceanography (IEO-CSIC) is responsible for monitoring the Spanish coastal waters with ship-based oceanographic time series, the program called IEO Observing System (IEOOS). Although started in the 1990s, only mainly after 2014 CO2 measurements were included in some specific time series. Concretely, in this work we will present ten years of CO2 data in the Iberian upwelling region in the Nortwest of the Iberian penninsula. Here through the combined effort of two time series: (i) the yearly sampled open ocean RADPROF section at 42ºN from Cape Finisterre to the open ocean, and the (ii) coastal time series Radial A Coruña, located in the bay of A Coruña in the Artabro Gulf. This IEO data set shows the relevance of different processes on the CO2 variables dynamics (upwelling/downwelling, benthic processes, river influence) over the acidification trend as a consequence of the global CO2 atmospheric increase. We will combine both open and coastal IEO time series along with other open data available in the region to show case of the land to ocean gradient on the CO2 variables and driving processes in this highly dynamic area.
How to cite: Álvarez, M., García-Ibañez, M., Acerbi, R., Gonzalez-Pola, C., and Nieto-Cid, M.: A decade of CO2 and ancillary data in the Nortwest Upwelling Iberian margin: open to coastal ocean differences, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2019, https://doi.org/10.5194/egusphere-egu25-2019, 2025.
Rivers annually transport ~200 Tg of particulate organic carbon (POC) to the global ocean, of which ~30% is known to be buried in continental-shelf sediments, including deltas. Given that ~35% of riverine POC is considered labile and may undergo remineralization in marine environments, the fate of the remaining “missing” terrestrial POC remains unknown. In this study, we investigated the distribution, fluxes, and fate of terrestrial POC in the northwestern Pacific marginal seas, including the East China Sea shelf and East/Japan Sea. These regions provide an ideal setting to address critical knowledge gaps regarding the fate of terrestrial POC, given substantial terrestrial inputs and extensive shelf areas connected to a semi-enclosed deep sea. Using stable carbon isotope ratios (δ13C) and 234Th tracers, we estimate that ~2.7 Tg C yr-1 of terrestrial POC is transported to the deep sea of the East/Japan Sea, accounting for ~80% of terrestrial POC in these regions. Our results suggest that sediment resuspension on the continental shelf and the refractory nature of terrestrial POC facilitate its effective transport to the deep sea, which serves as its major sink. These findings offer valuable insights into the global carbon cycle across the land-to-ocean continuum.
How to cite: Park, H. and Kim, G.: The fate of terrestrial particulate organic carbon in the northwestern Pacific marginal seas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3413, https://doi.org/10.5194/egusphere-egu25-3413, 2025.
Estuaries are typically net heterotrophic systems and a source of CO2 to the atmosphere, while continental shelves tend to take up CO2 from the atmosphere. Yet the primary production and net ecosystem metabolism (NEM) in these systems are variable, and this has implications for nutrient and carbon processing along the land-sea interface. To resolve this variability in a macrotidal system, high-frequency dissolved oxygen and ancillary biogeochemical data from a research station (equipped with a FerryBox) located at the outflow of a major temperate estuary into a shelf sea, were used to quantify the gross primary production (GPP) and NEM at the land-sea interface. Despite high nutrient concentrations in early and mid-spring in the outer Elbe River estuary in Germany, we find that low GPP rates (155 ± 46 mg C m-2 d-1 in April 2020 and 74 ± 24 mg C m-2 d-1 in March to April 2021) coincided with elevated turbidity (31 ± 9 NTU and 35 ± 7 NTU), suggesting light limitation, which was a function of turbidity and solar irradiance. Only when turbidity decreased (16 ± 5 NTU in 2020 and 19 ± 4 NTU in 2021), did we observe elevated GPP rates in late spring (May), and highest GPP rates in summer (July–August), with seasonal averages of 613 ± 89 mg C m-2 d-1 in 2020 and 558 ± 77 mg C m-2 d-1 in 2021. Primary production in the outer Elbe Estuary waters was most likely not nutrient-limited, since silicate, phosphate and nitrate concentrations exceeded the expected limiting levels of 5 µM Si, 0.5 µM PO43- and 2 µM NO3-. Despite the high nutrient concentrations and estimated GPP rates, the system was in near trophic balance, with seasonal average NEM ranging between -2 ± 49 mg C m-2 d-1 and -149 ± 41 mg C m-2 d-1. The large errors resulted from (weekly to bi-weekly) fluctuations between net heterotrophic and net autotrophic state during the two-year observation period. A significant seasonal decrease in dissolved inorganic carbon (125 – 160 µmol kg-1) from May to September, and in total alkalinity (TA) (116 – 128 µmol kg-1) from December to August, was most likely driven by seasonal high primary production in the upper estuary and upstream regions some 142 km upstream of the outer estuary. This seasonal decrease opposes the previously documented seasonal increase in TA of up to 150 μmol kg-1 in the coastal waters adjacent to the North Sea and to the intertidal flats of the Wadden Sea. This highlights the heterogeneity of carbonate system at the land-sea interface.
How to cite: Rewrie, L., Baschek, B., van Beusekom, J., Körtzinger, A., Petersen, W., Röttgers, R., and Voynova, Y.: Quantifying the impact of primary production and net ecosystem metabolism on carbon and nutrient cycling at the land-sea interface, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10753, https://doi.org/10.5194/egusphere-egu25-10753, 2025.
River and reservoir ecosystems have been considered as hot spots for GHG (greenhouse gas) emissions while their specific hydrological and biogeochemical processes affect GHG concentrations; however, few studies integrated river–reservoir systems to identify the dominant drivers of GHG concentrations and flux changes associated with these systems. In the present study, we examined the seasonal variations in GHG concentrations in the surface water of three river-reservoir systems in the Seine Basin. The levels and seasonal variations of GHG concentrations exhibited distinct patterns among reservoirs, upstream, and downstream rivers. The concentrations of CH4 (methane) in the reservoirs were notably higher than those observed in both upstream and downstream rivers and showed higher values in summer and autumn, which contrasted with CO2 (carbon dioxide) concentrations, while N2O (nitrous oxide) concentrations did not show an obvious seasonal pattern. A high mole ratio of CH4/CO2 was found in these reservoirs, with a value of 0.03 and was more than 30 and 10 times higher than that in the upstream and downstream rivers, respectively. The three river–reservoir systems were oversaturated with GHG during the study period, with the average diffusive fluxes (expressed as CO2eq: CO2 equivalent) of 810 ± 1098 mg CO2eq m–2 d–1, 9920 ± 2413 mg CO2eq m–2 d–1, and 7065 ± 2704 mg CO2eq m–2 d–1 in the reservoirs, upstream and downstream rivers, respectively. CO2 and CH4–CO2 were respectively the dominant contributors to GHG diffusive fluxes in river and reservoir sections, while N2O contributed negligibly to GHG diffusive fluxes in the three river–reservoir systems. Our results showed that GHG concentrations and gas transfer coefficient have varying importance in driving GHG diffusive fluxes among different sections of the river–reservoir systems. In addition, our results also show the combined effect of reservoirs and upstream rivers on the water quality variables and hydrological characteristics of downstream rivers, highlighting the future need for additional investigations of GHG processes in the river–reservoir systems.
How to cite: Yan, X., Thieu, V., and Garnier, J.: Seasonal variation in greenhouse gas concentrations and diffusive fluxes in three river–reservoir systems in the Seine Basin (France), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21899, https://doi.org/10.5194/egusphere-egu25-21899, 2025.
The long-term preservation of organic matter (OM) in the marine environment is crucial for Earth's climate regulation. Clay minerals are commonly believed to shield OC from degradation for millennium scale during its transport from terrestrial to marine environments. However, the complex interactions between clay minerals and OM during this land-ocean transport process and how clay mineral contributes to OM preservation and burial remains unclear. In this study, we examined the radiocarbon signatures of OM in clay fractions (< 2 μm) and the clay mineral compositions in the Eastern China Marginal Sea (ECMS). Our biogeochemical analysis revealed a positive correlation between smectite content and △14C values in clay fractions from sediments transported along different pathways in the ECMS, indicating a strong association between smectite and fresh biomass-OM during sediment transport. Furthermore, our results suggest that intense hydrodynamic conditions may facilitate the continuous adsorption of new produced biomass-OM onto smectite surfaces. We performed molecular dynamics simulations to investigate adsorption mechanism of typical organic molecules on smectite structure surface under different environmental conditions, showing that OM may undergo a continuous desorption-adsorption cycle on smectite surfaces due to change in the binding forms of the mineral-OM assembly during land-ocean transport, which support our geochemical findings. We thus estimated that clay mineral adsorption of biomass onto smectite might generate on the order of approximately 6.6 Tg C yr−1 for OM preservation in marine sediments. We propose that variable smectite inputs to the ocean over geological time could exert a substantial but hitherto unexplored impact on the Earth’s long-term climate evolution.
How to cite: Zhao, S. and Bao, R.: Underestimated organic carbon preservation of marine clay sediments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11813, https://doi.org/10.5194/egusphere-egu25-11813, 2025.
The transport of particulate organic carbon (POC) from land to deep-sea sediments is a key component of the global carbon cycle. However, the magnitude and mechanisms of terrestrial POC transport on continental shelves remain poorly understood due to the complexity of these systems. In this study, we investigated the vertical fluxes and fates of terrestrial versus marine POC using stable carbon isotope ratios (δ13C) and 234Th tracers in the southern coastal region of Korea. The total suspended matter concentrations were highest in the bottom layer, while the POC concentrations were higher in both the surface and bottom layers. Based on δ13C values, terrestrial POC accounted for 29 ± 24% of the total POC, with higher contributions at the innermost stations and in the bottom layer, while the contributions of marine POC were only higher in the surface layer. Based on 234Th-238U disequilibria, residence times of particulate 234Th (10 ± 6 days) were calculated to be significantly longer than those of dissolved 234Th (3.8 ± 2.3 days). Much higher vertical fluxes of terrestrial POC in the deeper layers than in the upper layers suggest that terrestrial POC undergoes multiple cycles of turnover through resuspension before burial, while marine POC undergoes preferential degradation during sinking. Our findings highlight that resuspension processes in coastal margins and the refractory nature of terrestrial POC likely facilitate its long-range transport (> 200 km) to the deep Ulleung Basin of the East/Japan Sea.
How to cite: Kim, G. and Park, H.: Long-range transport of terrestrial particulate organic carbon to the open ocean by sediment resuspension revealed by δ13C and 234Th tracers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3885, https://doi.org/10.5194/egusphere-egu25-3885, 2025.
The land-sea interface is characterized by rapid changes in thermodynamics constants and is influenced by local metabolic processes, watershed characteristics, tidal forcing and anthropogenic pressures. As a result, the aquatic carbonate system parameters are also rapidly changing along salinity gradients. In order to understand this variability and correctly represent it in biogeochemical models, detailed observations must be regularly obtained, and in the SEA-ReCap Project we do this in marginal seas such as the Black Sea or the North Sea. A research cruise was organised in autumn 2024 on the RV Heincke to sample the German exclusive economic zone of the North Sea and three major estuaries draining into the German Bight. Surface seawater pCO2 and pH were measured continuously using a FerryBox system installed on board. Total alkalinity was measured every 15 minutes with an automated sensor, while dissolved inorganic carbon was measured on board from discrete water samples. With all four carbonate system parameters directly observed, the land-ocean continuum can be well characterized. For example, all the dissolved inorganic carbon concentrations converged towards the open North Sea end-member of 2877 ± 4 µmol kg-1, but while the Elbe River estuary measurements decreased with decreasing salinity, to below 1800 µmol kg-1, the Ems and Weser measurements increased with decreasing salinity, exceeding 3100 µmol kg-1 at the most upstream locations sampled. The Elbe freshwater end-member, upstream of our last sampled location, is characterised by high primary production and low dissolved inorganic carbon, while the sampled area of Hamburg and further downstream is a site of remineralisation and dissolved inorganic carbon accumulation. The Ems and Weser Estuaries, on the other hand, are sources of dissolved inorganic carbon and alkalinity through denitrification and fluid mud anaerobic processes, leading to the high concentration freshwater end-members. Additionally, the seawater pCO2 in the open North Sea was 461 ± 4 µatm, while at the lowest salinities sampled in each estuary, the values exceeded 2000 µatm, indicating the dominance of heterotrophy. These results emphasise the large heterogeneity that can arise over small spatial scales and the sometimes contrasting patterns of the carbonate system in nearby estuaries. This has implications for the strength of the buffering capacity of the German Bight and the role of the coastal ocean as a carbon source or sink.
How to cite: Macovei, V., Neumann, A., Sanders, T., Rewrie, L., and Voynova, Y.: Full aquatic carbonate system measurements at the land-ocean interface in the German Bight, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10721, https://doi.org/10.5194/egusphere-egu25-10721, 2025.
Burial of organic carbon in lake sediments is a key process in the global carbon cycle, acting as a permanent sink for both for aquatic and terrestrial carbon. Warming can enhance carbon burial in lakes by promoting prolonged stratification and anoxic conditions. Human activities, particularly land-use changes, have also been shown to significantly influence organic carbon burial rates. Here, we developed a process-based model of particulate organic carbon (POC) burial in lake sediments under the framework of The Inter-Sectoral Impact Model Intercomparison Project (ISIMIP, https://www.isimip.org/), which allows global-scale hind- and forecasting. The model was validated using the time series data of Lake Erken (Sweden). The model includes lake temperature, stratification and mixing dynamics derived from a one-dimensional hydrodynamic lake model. Additionally, it includes oxygen dynamics, accounting for oxygen consumption in both the water-column and sediment. Both aquatic and terrestrial contributions of POC were considered, with inputs from primary production and loading from the catchment. These inputs have three possible fates: export via hydrologic pathways, permanent burial in lake sediments and mineralization to inorganic carbon. Estimates of internal production are from a two-layer process-based model, where phytoplankton growth in the epilimnion was primarily limited by light and nutrients, with temperature influencing these factors. Loss mechanisms include respiration, sinking and loss from the outflow, as well as entrainment from the hypolimnion. Loading from the catchment of sediments, POC and nutrients was formulated as a function of river discharge, land cover and land use. We also developed a new scaling approach to calculate lake-specific river inflows from the ISIMIP gridded hydrological data. The model components (hydrodynamics, oxygen, phytoplankton, river loading) performed well when validated against data from Lake Erken, giving confidence in the modelled carbon burial rate and opening the door to spatially and temporally resolved estimation of carbon burial in global lakes.
How to cite: Ayala, A. I., Pierson, D. C., and Sobek, S.: Modelling the burial of organic carbon in lakes within the ISIMIP framework, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17410, https://doi.org/10.5194/egusphere-egu25-17410, 2025.
Seaweed aquaculture beds (SABs) contribute positively to CO2 removal (CDR) worldwide. Among cultivated seaweed species, Pyropia represents approximately 8% of the global seaweed production and has the capacity to sequester a significant amount of carbon from the surface layer of the coastal ocean. In this study, we evaluated the carbon uptake efficiency of Pyropia SABs by measuring their photosynthetic rate. Pyropia individuals were collected from Pyropia SABs on the south and west coasts of South Korea from December to March (cultivation period) in 2016 to 2019, and the photosynthetic light response curves (P-E curves) were measured. Oxygen-based photosynthesis was converted into carbon-based photosynthetic rates using theoretical photosynthetic quotients. Pyropia thallus consumed an average 37 mg C g-1 d-1, with a high ratio of gross primary production to respiration (5–14). To quantify the carbon uptake potential in the coastal areas of the Korean Peninsula during the cultivation period, we extrapolated the carbon uptake rates using the estimated biomass, total area of Pyropia SABs, and meteorological irradiance data. The highest carbon uptake rate (2143 kilotons [kt] C month–1) was observed in the Southwestern Sea of South Korea in December. Considering all productivity data from the entire cultivation period, approximately 6789 kt C was taken up by the Pyropia SABs. Therefore, our study indicates significant potential for using Pyropia SABs to mitigate climate change by reducing greenhouse gas emissions.
How to cite: Kim, H., Kim, J.-H., Lee, M. H., and Park, C.-U.: The photosynthetic uptake of inorganic carbon from Pyropia seaweed aquaculture beds: Scaling up population-level estimations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10153, https://doi.org/10.5194/egusphere-egu25-10153, 2025.
The global carbon cycle encompasses reservoirs and the dynamic fluxes of carbon within and among them. These reservoirs include the atmosphere, lithosphere, biosphere, and hydrosphere, each contributing to or receiving carbon in spatially and temporally varying ways. Marine sediments represent a critical sink for organic carbon (OC), with coastal and deltaic sediments playing a dominant role in sequestering OC. These sediments receive terrestrial and marine OC in varying proportions along the land-to-ocean continuum, where their preservation is strongly influenced by protective associations with reactive minerals, particularly iron (hydr)oxides and clay minerals. Despite their importance, the combined effects of iron and clay minerals in preferentially stabilizing specific types of OC remain poorly understood, particularly under changing redox conditions. The extent to which these mineral OC associations are formed in-situ within sediments as opposed to pre-depositional formation on land also remains to be determined. To address these knowledge gaps, this study employs dual isotopic (δ13C, Δ14C) and molecular approaches to explore the combined roles of clays and reactive iron in OC stabilization across both temporal and spatial gradients. By analyzing total, iron-associated, clay-associated, and non-soluble residual OC fractions in oxic and anoxic sediment layers along gradients of terrestrial and marine OC inputs, this research will (i) quantify the relative contributions of clays and iron oxides to OC stabilization in surface (0–3 cm) and diagenetically stabilized deep (26–31 cm) sediments and (ii) resolve the preferential preservation of marine versus terrestrial OC within mineral-associated fractions through isotope and biomarker analyses. The findings of this study provide critical insights into the source-to-sink fate of mineral-associated OC in coastal sedimentary systems and elucidate their implications in the global carbon cycle, advancing our understanding of carbon sequestration in dynamic environments.
How to cite: Mirzaei, Y., Blattmann, T., Haghipour, N., Eglinton, T., and Gelinas, Y.: Mineral Influence of a Northern Estuary on the Retention of Aquatic and Land-derived Stabilized Organic Carbon (MINERALS-OC), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12392, https://doi.org/10.5194/egusphere-egu25-12392, 2025.
The ocean is the largest active carbon reservoir on Earth. Transport and burial of the sedimentary carbon affect marine biogeochemical processes and marine carbon cycle on different time scales, and even have an important impact on the global climate change. Distribution, transport and burial of sedimentary carbon in marginal seas are an important part of the global carbon cycle. The east China seas includes the Bohai Sea, Yellow Sea and East China Sea and are characterized by broad shelves. They receive enormous amount of fluvial sediment from the Huanghe and Changjiang rivers and bury abundant sedimentary organic carbon.
Based on the investigated data of China over the past 30 years and collected information, including 5796 stations of organic carbon and other relevant geochemical and sedimentological parameters, we preliminarily compiled a 1:3000000 distribution map of sedimentary organic carbon of the east China seas, elaborated the distribution characteristics, sources and buried flux of sedimentary organic carbon, and discussed the influence of hydrodynamic forces, sediment composition and human activities on it. The results show: (1) TOC contents in the sediments ranges from 0.01 to 2.12% in the east China seas. And there are high values in the mud areas such as the central Bohai Sea, eastern coast of the Shandong Peninsula, central South Yellow Sea, southwest of Jeju Island, old Huanghe River estuary, southeast of the Yellow Sea, and Zhejiang-Fujian coast. (2) δ13C values are from -25.80~-20.00‰ and ~70% of sedimentary organic carbon is marine source. (3) range of Δ14C in the sedimentary organic carbon is -871 ~ -137‰. The age of sedimentary organic carbon is older in the areas of the old Huanghe River estuary, Jiangsu sand ridges, outer shelf of the East China Sea and northeast Taiwan. (4) The burial rates of organic carbon in the mud areas are higher in the east China seas, which reaches maximum value of 68.8 g/m2/yr in the Bohai Sea mud area and is generally low near the old Huanghe River estuary (15.2 g/m2/yr). The burial amount of sedimentary organic carbon is about 8.2 Mt/yr. The distribution and burial of terrigenous organic carbon in the BYES are mainly influenced by the large river inputs and complex marine hydrodynamic environment, while human activities such as dam construction have significantly altered the burial of organic carbon in coastal mud areas.
How to cite: Qiao, S., Shi, X., Wu, B., Yao, Z., Hu, L., Sheng, J., Liu, Y., Liu, S., Wang, K., and Zou, J.: Distribution, source and burial of sedimentary organic carbon in the east China seas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5501, https://doi.org/10.5194/egusphere-egu25-5501, 2025.
