Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesise datasets and methodologies to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (E-FOS) are based on energy and cement production data. Emissions from land-use change (E-LUC) are estimated by bookkeeping models based on land-use data. The global atmospheric CO2 growth rate (G(ATM)) is computed from changes in concentration measured at surface stations. The global net uptake of CO2 by the ocean (S-OCEAN) is estimated with global ocean biogeochemistry models and observation-based fCO(2)-products. The global net uptake of CO2 by the land (S-LAND) is estimated with dynamic global vegetation models. Additional lines of evidence are provided by atmospheric inversions, atmospheric oxygen measurements, ocean interior observation-based estimates, and Earth System Models. This year, we introduced corrections on the E-LUC, S-OCEAN and S-LAND estimates. The sum of all sources and sinks results in the carbon budget imbalance (B-IM), a measure of imperfect data and incomplete understanding of the contemporary carbon cycle. All uncertainties are reported as +/- 1 sigma. For the year 2024, E-FOS increased by 1.1 % relative to 2023, with fossil emissions at 10.3 +/- 0.5 GtC yr(-1) (including the cement carbonation sink, 0.2 GtC yr(-1)), E-LUC was 1.3 +/- 0.7 GtC yr(-1), for total anthropogenic CO2 emissions of 11.6 +/- 0.9 GtC yr(-1) (42.4 +/- 3.2 GtCO(2) yr(-1)). Also, for 2024, G(ATM) was 7.9 +/- 0.2 GtC yr(-1) (3.73 +/- 0.1 ppm yr(-1)), 2.2 GtC above the 2023 growth rate. S-OCEAN was 3.4 +/- 0.4 GtC yr(-1) and S-LAND was 1.9 +/- 1.1 GtC yr(-1), leaving a large negative B-IM (-1.7 GtC yr(-1)), suggesting that the total sink or G(ATM) is strongly overestimated in 2024. The global atmospheric CO2 concentration averaged over 2024 reached 422.8 +/- 0.1 ppm. Preliminary data for 2025 suggest an increase in E-FOS relative to 2024 of +1.0 % (0.2 % to 1.7 %) globally, and atmospheric CO2 concentration increasing by 2.1 ppm reaching 425.6 ppm, 53 % above the pre-industrial level (around 278 ppm in 1750). Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959-2024, with a near-zero overall budget imbalance, although discrepancies of up to around 1 GtC yr(-1) persist for the representation of annual to decadal variability in CO2 fluxes. Comparison of estimates from multiple approaches and observations shows: (1) a persistent large uncertainty in the estimate of land-use change emissions, (2) a low agreement between the different methods on the magnitude of the land CO2 flux in the northern extra-tropics, and (3) a discrepancy between the different methods on the mean ocean sink.

The Surface Ocean CO2 Atlas (SOCAT) is a global scientific community effort to collate and provide additional quality control and standardisation for surface ocean carbon dioxide (CO2) data. Each year the international marine carbon community submit any new measurements collected on research vessels, ships of opportunity, moorings, uncrewed surface vehicles and sailing yachts for inclusion in the annual update of the SOCAT database. The data synthesis effort, which published its first data product in 2011, includes a variety of systems, sampling strategies, maintenance cycles and instrument calibrations. Each in-water CO2 gas measurement is paired, and linked, with a sea surface temperature (SST) measurement. However, the differences in measurement systems means that data pairs from different platforms are representative of differing depths in the ocean, whilst SST measurements can suffer from warming within the observation platform. These complexities can limit the accuracy and precision of any atmosphere-ocean CO2 assessments that use the SOCAT products. Here the SOCATv2025 database with an estimated uncertainty in the fugacity of CO2 in seawater (fCO2 (sw)) of less than 5 µatm is recalculated to a reference temperature at a consistent depth of 0.2 m using the European Space Agency (ESA) Climate Change Initiative (CCI) SST climate data record. This recalculation process of the fCO2 values does not assume isochemical conditions and so temperature driven carbonate speciation is captured. The data pairing is maintained so the resulting dataset is well suited for the analysis of atmosphere-ocean CO2 exchange. The synthesis cruise data and gridded data products, that include both the original and recalculated data, are provided and consistency with the original SOCAT data products and format is confirmed. The importance of robustly accounting for the observed warm bias is demonstrated as removing this signal by recalculation to a climate data record temperature shows a ~0.4 Pg C yr-1 (~12%) increase in the 2024 ocean CO2 sink (3.4 Pg C yr-1). These recalculated data products are needed for annual carbon assessments therefore these will be routinely provided each year following each annual SOCAT dataset release.

In 2023, sea surface temperatures (SSTs) reached record highs, partly due to a strong El Ni & ntilde;o. Based on historical responses to elevated global mean SSTs, oceanic CO2 uptake in 2023 should have increased (-0.11 +/- 0.04 PgC yr-1), driven by reduced outgassing in the tropical Pacific Ocean. However, using observation-based estimates of ocean CO2 fugacity, we show here that the global non-polar ocean absorbed about 10% less CO2 than expected (+0.17 +/- 0.12 PgC yr-1). This weakening was caused by the anomalous outgassing of CO2 in the subtropical and subpolar regions, especially in the Northern Hemisphere, driven primarily by elevated SSTs reducing the solubility of CO2. In most regions, this SST-induced outgassing was mitigated by the depletion of dissolved inorganic carbon in the surface mixed layer. Such negative feedbacks caused an overall muted response of the ocean carbon sink to the record-high SSTs, but this resilience may not persist under long-term warming or more severe SST extremes.

Sea-air exchange of carbon dioxide in the Southern Ocean is strongly seasonal, with ocean uptake in summer, which is partly offset by carbon dioxide outgassing in winter. This seasonal balance can shift due to sea ice conditions, inducing interannual variability in the Southern Ocean carbon sink. A decade (2010-2020) of unique, year-round marine carbonate chemistry observations from the Rothera Time Series (West Antarctic Peninsula) reveals that interannual variability in seawater fugacity of carbon dioxide depends on wintertime processes. Sea ice duration controls ocean stratification, which acts as a gateway to the carbon-rich ocean interior. Consequently, years with persistent sea ice cover and high mean winter stratification absorb, on average, 20% more carbon dioxide than years with less sea ice and weaker stratification in winter. Wintertime marine observations are therefore essential to resolve critical processes and reliably quantify interannual variability of the sea-air carbon dioxide flux in seasonally sea ice-covered regions.

The Weddell Sea has previously been estimated to be a net atmospheric CO2 sink, transporting anthropogenic CO2 to deeper parts of the ocean. However, a paucity of spatial and temporal observational data coverage hinders a complete understanding of its (seasonal and interannual) variability, how it is affected by seasonal sea ice cover, and how it may change with rapidly changing Antarctic sea ice regimes. We provide a status overview of all available partial pressure CO2 (pCO2) observations and estimates in the Weddell Sea, including SOCAT, GLODAP, and SOCCOM float datasets. We identify a particular lack of data on the continental shelves. Floats fill the wintertime-gap by obtaining year-round data, but are restricted to the open ocean and water depths of at least 2000 m. The collated dataset illustrates a seasonal cycle for the Weddell Sea, in which the summertime CO2 uptake can be strong with a mean of -1.2 mol m2 yr-1, but extremely variable (± 2.2 mol m2 yr-1). Some of the summertime CO2 uptake is compensated by wintertime CO2 outgassing, particularly in the northern Weddell Sea where sea ice cover is lowest and wind speeds are high. We use additional reanalysis and observational data-based products to perform a further analysis of differences between subregions within the Weddell Sea. Results show that most regions have a strong seasonal cycle in the sea-air CO2 gradient, with mean amplitudes ranging between 27 µatm (Northern Weddell Sea) and 100 µatm (eastern Peninsula shelf regions). However, wintertime outgassing is largely restricted by sea ice cover in all regions. The central Weddell Sea seems to be a particularly important region for net CO2 uptake, which is partly explained by the timing of wintertime sea ice advance before the surface pCO2 oversaturates with respect to atmospheric CO2. These results imply that the timing of sea ice advance or retreat can have high impact on the net CO2 uptake of the Weddell Sea.

The Southern Ocean (SO) is a critical component of the global carbon cycle, acting as a significant sink for atmospheric carbon dioxide (CO2). Understanding the intricate processes governing CO2 uptake in the SO is paramount for comprehending the global carbon budget and predicting future climate scenarios. Recent observations suggest that changes in SO water masses, driven by climate-induced alterations in temperature and circulation patterns, can significantly impact CO2 uptake. Understanding these feedbacks is crucial for predicting the SO's future role as a carbon sink and its broader implications for climate mitigation efforts. In this work, we determine changes in the water mass composition and their characteristics, including their CO2 content, along the CUSTARD transect (54ºS-59ºS 90ºW) in Subantarctic Pacific waters. The CUSTARD transect crosses a region of formation of mode and intermediate waters. We use an extended Optimum Multiparameter (eOMP) analysis and data from three repeats of the CUSTARD transect in 1993 (expocode 316N19930222; data from GLODAPv2.2023), 2005-2006 (316N20050821 and 316N20060130; from GLODAPv2.2023), and 2019-2020 (74EQ20191202; the CUSTARD cruise). We observe isopycnal heaving in the southern part of the transect from 1993 to 2020. In the upper ocean (neutral density (γn) < 27.2 kg m-3), isopycnal heaving is linked to a temperature decrease of up to -2ºC and a salinity decrease of up to -0.15 between 1993 and 2005, extending to γn < 27.5 kg m-3 in 2019-2020. The physicochemical changes in the upper ocean are linked to changes in the water mass composition, including an increase in the volume of Antarctic Surface Water and Antarctic Intermediate Water and a decrease in the volume of SubAntarctic Mode Water over the 18-year study period. These water mass changes are accompanied by decreases in concentrations of oxygen, dissolved nutrients, and total alkalinity, along with an increase in total dissolved inorganic carbon of up to 40 µmol kg-3 for γn < 27.5 kg m-3 from 1993 to 2019-2020. For 27.5 kg m-3 < γn 28.2 kg m-3), Ross Sea Bottom Water replaces Adélie Bottom Water from 1993 to 2019-2020. The changes in water mass composition observed along the CUSTARD transect indicate circulation variations linked to the Southern Annular Mode (SAM), with a prevalent positive phase since 1995. Positive SAM pahses increase upwelling south of the Antarctic Polar Front and downwelling in the Subantarctic Zone. Due to these circulation changes, the SO’s uptake of atmospheric CO2 decreases during positive SAM phases, which are predicted to intensify with climate change.

The global ocean takes up about a quarter of anthropogenic carbon dioxide emissions, with the Southern Ocean playing a disproportionately large role. This uptake has led to changes in the Southern Ocean's carbonate chemistry, reducing pH through ocean acidification. The Amundsen Sea, West Antarctica, is surrounded by rapidly melting ice shelves, that may be impacting the carbonate balance of this coastal region. Near the Dotson Ice Shelf, we collected the first high-resolution, full-depth pH dataset using a Lab-on-Chip spectrophotometric sensor attached to an autonomous profiling ocean glider. The sensor collected data within 10 km of the Dotson Ice Shelf over a 19-day period in January/February 2022 and captured the variability that results from summertime biogeochemical and physical processes. In the upper 150 m, net primary production dominates variation in pH, producing a maximum pH of 8.34 (on the total hydrogen scale) in front of Dotson Ice Shelf, where chlorophyll fluorescence also peaks. Below 150 m, pH is generally lower, likely as a result of net respiration. The inflow of modified Circumpolar Deep Water near the east side of Dotson Ice Shelf exhibits a slightly elevated pH (0.05 units) compared to surrounding deep waters. The meltwater-laden outflow that exits on the west side of the ice shelf at depths between 300 - 500 m displays a lower pH (0.1 units) relative to the surrounding waters, which shoals and mixes, reducing pH in the overlying surface waters. In the coastal current along Dotson Ice Shelf, an unusual subsurface maximum in pH (0.1 units at 150 m, compared to surrounding waters) is observed and is also associated with increased chlorophyll fluorescence. Possible explanations for the observed features are discussed. These high-resolution findings reveal the potential of pH measurements on an autonomous vehicle for investigating difficult to access regions with glacial melt.

The Arctic Ocean is responsible for around 5-10% of oceanic CO2 uptake, despite the region only accounting for approximately 4% of the world's oceans (Bates & Mathis, 2009). In this study, we investigate the exchange of CO2 between the atmosphere and the ocean in the Arctic Ocean for the period 2000-2017. Our estimates are obtained using the GEOSChem-LETKF inverse model system (Chen et al. 2021), in combination with data from the NOAA surface CO2 monitoring network (ObsPack, Cooperative Global Atmospheric Data Integration Project, 2018). We evaluate the impact of alternative representations of the prior flux distribution for air-sea CO2 fluxes. These include the following datasets: Landschutzer et al. (2016), Rodenbeck et al. (2014), and Watson et al. (2020). We present estimates of the long-term trend, year-to-year fluctuations, and regional and seasonal variability in air-sea CO2 exchange in the Arctic Ocean, with a focus on the region north of 58˚N. The sea ice extent of the regional seas of the Arctic Ocean has an influence on the magnitude and seasonality of the regional air-sea CO2 flux. We also investigate the potential links between changes in sea-ice extent and changes in air-sea CO2 fluxes.

The Arctic Ocean covers only 3 % of the Earth’s surface but contributes 5 - 14 % of the global ocean carbon sink. Sparse and unevenly distributed observations of the partial pressure of CO2 (pCO2) hinder our understanding of the magnitude and the controlling mechanisms of this carbon sink. In order to constrain the magnitude of this flux, we adapt the Self-Organising Map – Feed-Forward neural Network (SOM-FFN) method of Landschützer et al. (2016) to interpolate existing observations and construct a monthly 1 x 1 degree pCO2 product for the Arctic Ocean from 1991 - 2022. We first divide the Arctic Ocean (i.e., the region ≥ 55° N) into five biogeochemical provinces; four obtained from using the SOM method and a fifth for all grid cells with greater than 85 % ice cover. For each province, we then derive non-linear relationships between pCO₂ and predictor variables (i.e., biogeochemical drivers) using the FFN method. The monthly reconstructed Arctic pCO2 product is then evaluated against existing observations of surface ocean pCO2, chiefly from SOCATv2023 and from independent timeseries stations. Our study shows that biogeochemical properties previously selected as predictor variables at the global scale are not well suited to the Arctic Ocean. Limiting the spatial domain from which relationships are derived also improves performance, with less biased p(CO2) values predicted when excluding the Baltic Sea.

The Amundsen Sea polynya hosts intense sea ice formation, but, due to the presence of relatively warm and salty modified Circumpolar Deep Water, the cold, brine-enriched water is not typically dense enough to sink to the deep ocean. A hydrographic survey of the Dotson Ice Shelf region in the Amundsen Sea using two ocean gliders identified and characterised subsurface lenses containing water with temperatures less than −1.70 °C. These lenses, located at depths between 240 to 500 m, were colder, saltier and denser than the overlying Winter Water (WW) layer. The pH of the lenses was 7.99, lower than WW by 0.02 and the dissolved inorganic carbon concentration was higher in the lenses than WW by approximately 10 µmol kg−1. The lenses were associated with a dissolved oxygen concentration greater than surrounding water at the same depth and density due to the cold temperatures increasing O2 solubility. We hypothesise that these lenses are a product of wintertime surface cooling and brine rejection in areas with intense sea ice formation. They may form in shallow regions, potentially around the Martin Peninsula and Bear Island, where intense upper ocean heat loss occurs, and then spill off into the deeper Dotson-Getz Trough to reach their neutrally-buoyant depth. This is supported by wintertime temperature and salinity observations. This study highlights the importance of shallow parts of shelf seas for generating cold dense water masses in the warm sector of Antarctica. These lenses are widespread in the region of the Dotson-Getz Trough and have the potential to sequester carbon deeper than typical in the region, alongside cooling the water impinging on the Dotson ice shelf base.

The Arctic Ocean covers 3 % of the Earth's surface but is estimated to contribute 5-14 % to the global ocean carbon sink. Sparse and unevenly distributed observations complicate our understanding of the size and the controlling mechanisms of this carbon sink. We adopt and advance the two-step neural network approach of Landsch & uuml;tzer et al. (2016, https://doi.org/10.1002/2015gb005359; Self Organizing Map-Feed Forward Network) to improve region-specific reconstructions of the surface ocean partial pressure of carbon dioxide (P(CO2 )) in the Arctic Ocean and subsequently estimate the air-sea CO2 flux. Our study shows that biogeochemical properties previously selected as predictor variables for P(CO2 ) at the global scale are not well suited to the Arctic Ocean and a sensitivity study reveals large differences in the size of the Arctic Ocean carbon sink depending on the choice of air-sea CO2 flux parameterization. This is most acute for those relating to sea ice cover, leading to a difference of up to 25 % (9.2-13.3 Pg C) in the total size of the Arctic Ocean carbon sink over the 32-year duration of the study.

Despite the adoption of the Paris Agreement 10 years ago, carbon dioxide (CO2) emissions from burning fossil fuels continue to increase, pushing atmospheric CO2 levels to 423 ppm in 2024 and driving human-induced warming to 1.36 °C, within years of breaching the 1.5 °C limit1,2. Accurate reporting of anthropogenic and natural CO2 sources and sinks is a prerequisite to tracking the effectiveness of climate policy and detecting carbon-sink responses to climate change. Yet notable mismatches between reported emissions and sinks have so far prevented confident interpretation of their trends and drivers1. Here we present and integrate recent advances in observations and process understanding to address some long-standing issues in global carbon budget estimates. We show that the magnitude of the natural land sink is substantially smaller than previously estimated, whereas net emissions from anthropogenic land-use change are revised upwards1. The ocean sink is 15% larger than the land sink, consistent with recent evidence from oceanic and atmospheric observations3,4. Climate change reduces the efficiency of the sinks, particularly on land, contributing 8.3 ± 1.4 ppm to the atmospheric CO2 increase since 1960. The combined effects of climate change and deforestation have turned Southeast Asian and large parts of South American tropical forests from CO2 sinks to sources. This underscores the need to halt deforestation and limit warming to prevent further loss of carbon stored on land. Improved confidence in assessments of CO2 sources and sinks is fundamental for effective climate policy.

The international and interdisciplinary sea-ice drift expedition "The Multidisciplinary drifting Observatory for the Study of Arctic Climate" (MOSAiC) was conducted from October 2019 to September 2020. The aim of MOSAiC was to study the interconnected physical, chemical, and biological characteristics and processes from the atmosphere to the deep sea of the central Arctic system. The ecosystem team addressed current knowledge gaps and explored unknown biological properties over a complete seasonal cycle focusing on three major research areas: biodiversity, biogeochemical cycles, and linkages to the environment. In addition to the measurements of core properties along a complete seasonal cycle, dedicated projects covered specific processes and habitats, or organisms on higher taxonomic or temporal resolution in specific time windows. A wide range of sampling instruments and approaches, including sea-ice coring, lead sampling with pumps, rosette-based water sampling, plankton nets, remotely operated vehicles, and acoustic buoys, was applied to address the science objectives. Further, a broad range of process-related measurements to address, for example, productivity patterns, seasonal migrations, and diversity shifts, were made both in situ and onboard RV Polarstern. . This article provides a detailed overview of the sampling approaches used to address the three main science objectives. It highlights the core sampling program and provides examples of habitat- or process-specific sampling. The initial results presented include high biological activities in wintertime and the discovery of biological hotspots in underexplored habitats. The unique interconnectivity of the coordinated sampling efforts also revealed insights into cross-disciplinary interactions like the impact of biota on Arctic cloud formation. This overview further presents both lessons learned from conducting such a demanding field campaign and an outlook on spin-off projects to be conducted over the next years.

The Southern Ocean is the primary region for the uptake of anthropogenic carbon dioxide (CO2 ) and is, therefore, crucial for Earth's climate. However, the Southern Ocean CO2 flux estimates reveal substantial uncertainties and lack direct validation. Using seven independent and directly measured air-sea CO2 flux datasets, we identify a 25% stronger CO2 uptake in the Southern Ocean than shipboard dataset-based flux estimates. Accounting for upper ocean temperature gradients and insufficient temporal resolution of flux products can bridge this flux gap. The gas transfer velocity parameterization is not the main reason for the flux disagreement. The profiling float data-based flux products and biogeochemistry models considerably underestimate the observed CO2 uptake, which may be due to the lack of representation of small-scale high-flux events. Our study suggests that the Southern Ocean may take up more CO2 than previously recognized, and that temperature corrections should be considered, and a higher resolution is needed in data-based bulk flux estimates.

In 2023, sea-surface temperatures (SST) reached record highs. Based on historical responses, this SST anomaly would suggest an increased oceanic CO2 uptake (-0.11±0.03 PgC yr-1). In contrast, our observation-based estimates reveal that the global non-polar ocean absorbed about 10% less carbon than expected (+0.16±0.28 PgC yr-1). This weakening occurred despite reduced CO2 outgassing in the tropics associated with El Niño. Hence, the decline in CO2 uptake in 2023 materialised entirely in the extratropics, driven primarily by elevated SSTs in the Northern Hemisphere. Two ocean biogeochemical models demonstrate that in the subtropical North Atlantic the thermally-induced reduction in CO2 uptake was strongly mitigated by the depletion of dissolved inorganic carbon in the surface mixed layer. Such negative feedbacks cause an overall muted response of the ocean carbon sink to the record high SSTs, but this resilience may not persist under long-term warming or more severe SST extremes.

Abstract Observation‐based quantification of ocean carbon dioxide (CO2) uptake relies on synthesis data sets such as the Surface Ocean CO2 ATlas (SOCAT). However, the data collection effort has dramatically declined and the number of annual data sets in SOCATv2023 decreased by ∼35% from 2017 to 2021. This decline has led to a 65% increase (from 0.15 to 0.25 Pg C yr−1) in the standard deviation of seven SOCAT‐based air‐sea CO2 flux estimates. Reducing the availability of the annual data to that in the year 2000 creates substantial bias (50%) in the long‐term flux trend. The annual mean CO2 flux is insensitive to the seasonal skew of the SOCAT data and to the addition of the lower accuracy data set available in SOCAT. Our study highlights the need for sustained data collection and synthesis, to inform the Global Carbon Budget assessment, the UN‐led climate negotiations, and measurement, reporting, and verification of ocean‐based CO2 removal projects.

AbstractThe ocean will ultimately store most of the CO2 emitted to the atmosphere by human activities. Despite its importance, estimates of the 2000−2022 trend in the ocean CO2 sink differ by a factor of two between observation-based products and process-based models. Here we address this discrepancy using a hybrid approach that preserves the consistency of known processes but constrains the outcome using observations. We show that the hybrid approach reproduces the stagnation of the ocean CO2 sink in the 1990s and its reinvigoration in the 2000s suggested by observation-based products and matches their amplitude. It suggests that process-based models underestimate the amplitude of the decadal variability in the ocean CO2 sink, but that observation-based products on average overestimate the decadal trend in the 2010s. The hybrid approach constrains the 2000−2022 trend in the ocean CO2 sink to 0.42 ± 0.06 Pg C yr−1 decade−1, and by inference the total land CO2 sink to 0.28 ± 0.13 Pg C yr−1 decade−1.

North Atlantic Subtropical Mode Water (NASTMW) serves as a major conduit for dissolved carbon to penetrate into the ocean interior by its wintertime outcropping events. Prior research on NASTMW has concentrated on its physical formation and destruction, as well as Lagrangian pathways and timescales of water into and out of NASTMW. In this study, we examine how dissolved inorganic carbon (DIC) concentrations are modified along Lagrangian pathways of NASTMW on subannual timescales. We introduce Lagrangian parcels into a physical-biogeochemical model and release these parcels annually over two decades. For different pathways into, out of, and within NASTMW, we calculate changes in DIC concentrations along the path (ΔDIC), distinguishing contributions from vertical mixing and biogeochemical processes. While the mean ΔD for parcels that persist within NASTMW in one year is relatively small at +6 µmol/L, this masks underlying dynamics: individual parcels undergo interspersed DIC depletion and enrichment, spanning several timescales and magnitudes. The strongest ΔDIC is during subduction of water parcels (+101 µmol/L in one year), followed by transport out of NASTMW due to increases in density in water parcels (+10 µmol/L). Most DIC enrichment and depletion regimes span timescales of weeks, related to phytoplankton blooms. However, mixing and biogeochemical processes often oppose one another at short timescales, so the largest net DIC changes occur at timescales of more than 30 days. Our new Lagrangian approach complements bulk Eulerian approaches, which average out this underlying complexity, and is relevant to other biogeochemical studies, for example on marine carbon dioxide removal.