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1. Mapping the global distribution of lead and its isotopes in seawater with explainable machine learning

   https://doi.org/10.5194/essd-17-3679-2025  

   Olivelli, Arianna; Arcucci, Rossella; Rehkämper, Mark; van_de_Flierdt, Tina (January 2025, Earth System Science Data)

   Abstract. Lead (Pb) and its isotopes are powerful tools for studying the pathways of Pb pollution from land to sea and, simultaneously, investigating biogeochemical processes in the ocean. However, the scarcity and sparsity of in situ measurements of Pb concentrations and isotope compositions do not allow for a comprehensive understanding of Pb pollution pathways and biogeochemical cycling on a global scale. Here, we present three machine learning models developed to map seawater Pb concentrations and isotope compositions, leveraging the global GEOTRACES dataset as well as historical data. The models use climatologies of oceanographic and atmospheric variables as features from which to predict Pb concentrations, 206Pb/207Pb, and 208Pb/207Pb. Using SHapley Additive exPlanations (SHAP), we found that seawater temperature, atmospheric dust, atmospheric black carbon, and salinity are the most important features for predicting Pb concentrations. Dissolved oxygen concentration, salinity, temperature, and atmospheric dust are the most important features for predicting 206Pb/207Pb, atmospheric black carbon and dust, seawater temperature, and surface chlorophyll a for 208Pb/207Pb. In line with observations, our model outputs show that (i) the surface Indian Ocean has the highest levels of pollution, (ii) pollution from previous decades is sinking in the North Atlantic and Pacific oceans, and (iii) waters characterised by highly anthropogenic Pb isotope fingerprints are spreading from the Southern Ocean throughout the Southern Hemisphere at intermediate depths. By analysing the uncertainty associated with our maps, we identified the Southern Ocean as the key area to prioritise in future sampling campaigns. Our datasets, models, and their outputs, in the forms of Pb concentrations, 206Pb/207Pb climatologies, and 208Pb/207Pb climatologies, are made freely available to the community by Olivelli et al. (2024a; https://doi.org/10.5281/zenodo.14261154) and Olivelli (2025; https://doi.org/10.5281/zenodo.15355008). 

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2. OSU-UVic hosing run with LGM initial conditions (LGM Full)

   https://doi.org/10.5281/zenodo.14231977  

   Schmittner, Andreas (November 2024, Zenodo)

   This directory contains model code, input, output, and scripts from a hosing (freshwater forcing in the North Atlantic) simulation with the OSU-UVic climate model (version 2.9.10) to investigate the effect of changes in the Atlantic Meridional Overturning Circulation (AMOC) on carbon and carbon-13 components in the ocean as described in Schmittner and Boling (2025) and Schmittner (2025). Model code is in the code/ subdirectory. Model input data is in the data/ subdirectory and in the control.in and mk.in files. Model output data is in the tavg*nc and tsi*nc files. Ferret scripts used to produce the figures are in the ferret/ subdirectory. A more detailed description about the OSU-UVic climate model is available at https://github.com/OSU-CEOAS-Schmittner/UVic2.9 and https://doi.org/10.5281/zenodo.11224826. Andreas Schmittner (andreas.schmittner@oregonstate.edu) References: Schmittner, A. and M. Boling (2025) Impact of Atlantic Meridional Overturning Circulation Collapse on Carbon Components in the Ocean, Global Biogeochemical Cycles, 39, e2025GB008526 doi: 10.1029/2025GB008526. Schmittner, A. (2025) Impact of Atlantic Meridional Overturning Circulation Collapse on Carbon-13 Components in the Ocean, Global Biogeochemical Cycles, 39, e2025GB008527 doi: 10.1029/2025GB008527. 

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3. Harmonization of global surface ocean pCO2 mapped products and their flux calculations; an improved estimate of the ocean carbon sink

   https://doi.org/10.5194/essd-2021-16  

   Fay, A. R.; Gregor, L.; Landschützer, P.; McKinley, G. A.; Gruber, N.; Gehlen, M.; Iida, Y.; Laruelle, G. G.; Rödenbeck, C.; Zeng, J.: (December 2021, Earth system science data)

   Elger, Kirsten; Carlson, David; Klump, Jens; Peng, Ge (Ed.)

   Air-sea flux of carbon dioxide (CO2) is a critical component of the global carbon cycle and the climate system with the ocean removing about a quarter of the CO2 emitted into the atmosphere by human activities over the last decade. A common approach to estimate this net flux of CO2 across the air-sea interface is the use of surface ocean CO2 observations and the computation of the flux through a bulk parameterization approach. Yet, the details for how this is done in order to arrive at a global ocean CO2 uptake estimate varies greatly, unnecessarily enhancing the uncertainties. Here we reduce some of these uncertainties by harmonizing an ensemble of products that interpolate surface ocean CO2 bservations to near global coverage. We propose a common methodology to fill in missing areas in the products and to calculate fluxes and present a new estimate of the net flux. The ensemble data product, SeaFlux (Gregor & Fay (2021), doi.org/10.5281/zenodo.4133802, https://github.com/luke-gregor/SeaFlux), accounts for the diversity of the underlying mapping methodologies. Utilizing six 30 global observation-based mapping products (CMEMS-FFNN, CSIR-ML6, JENA-MLS, JMA-MLR, MPI-SOMFFN, NIESFNN), the SeaFlux ensemble approach adjusts for methodological inconsistencies in flux calculations that can result in an average error of 15% in global mean flux estimates. We address differences in spatial coverage of the surface ocean CO2 between the mapping products which ultimately yields an increase in CO2 uptake of up to 19% for some products. Fluxes are calculated using three wind products (CCMPv2, ERA5, and JRA55). Application of an appropriately scaled gas exchange 35 coefficient has a greater impact on the resulting flux than solely the choice of wind product. With these adjustments, we derive an improved ensemble of surface ocean pCO2 and air-sea carbon flux estimates. The SeaFlux ensemble suggests a global mean uptake of CO2 from the atmosphere of 1.92 +/- 0.35 PgC yr-1. This work aims to support the community effort to perform model-data intercomparisons which will help to identify missing fluxes as we strive to close the global carbon budget. 

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4. Autonomous seawater <i>p</i>CO₂ and pH time series from 40 surface buoys and the emergence of anthropogenic trends

   https://doi.org/10.5194/essd-11-421-2019  

   Sutton, Adrienne J.; Feely, Richard A.; Maenner-Jones, Stacy; Musielwicz, Sylvia; Osborne, John; Dietrich, Colin; Monacci, Natalie; Cross, Jessica; Bott, Randy; Kozyr, Alex; et al (January 2019, Earth System Science Data)

   Abstract. Ship-based time series, some now approaching over 3 decades long, are critical climate records that have dramatically improved our ability to characterize natural and anthropogenic drivers of ocean carbon dioxide (CO2) uptake and biogeochemical processes. Advancements in autonomous marine carbon sensors and technologies over the last 2 decades have led to the expansion of observations at fixed time series sites, thereby improving the capability of characterizing sub-seasonal variability in the ocean. Here, we present a data product of 40 individual autonomous moored surface ocean pCO2 (partial pressure of CO2) time series established between 2004 and 2013, 17 also include autonomous pH measurements. These time series characterize a wide range of surface ocean carbonate conditions in different oceanic (17 sites), coastal (13 sites), and coral reef (10 sites) regimes. A time of trend emergence (ToE) methodology applied to the time series that exhibit well-constrained daily to interannual variability and an estimate of decadal variability indicates that the length of sustained observations necessary to detect statistically significant anthropogenic trends varies by marine environment. The ToE estimates for seawater pCO2 and pH range from 8 to 15 years at the open ocean sites, 16 to 41 years at the coastal sites, and 9 to 22 years at the coral reef sites. Only two open ocean pCO2 time series, Woods Hole Oceanographic Institution Hawaii Ocean Time-series Station (WHOTS) in the subtropical North Pacific and Stratus in the South Pacific gyre, have been deployed longer than the estimated trend detection time and, for these, deseasoned monthly means show estimated anthropogenic trends of 1.9±0.3 and 1.6±0.3 µatm yr−1, respectively. In the future, it is possible that updates to this product will allow for the estimation of anthropogenic trends at more sites; however, the product currently provides a valuable tool in an accessible format for evaluating climatology and natural variability of surface ocean carbonate chemistry in a variety of regions. Data are available at https://doi.org/10.7289/V5DB8043 and https://www.nodc.noaa.gov/ocads/oceans/Moorings/ndp097.html (Sutton et al., 2018). 

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5. Global Carbon Budget 2025

   https://doi.org/10.5194/essd-18-3211-2026  

   Friedlingstein, Pierre; O'Sullivan, Michael; Jones, Matthew W; Andrew, Robbie M; Bakker, Dorothee_C E; Hauck, Judith; Landschützer, Peter; Le_Quéré, Corinne; Li, Hongmei; Luijkx, Ingrid T; et al (January 2026, Earth System Science Data)

   Abstract. 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 (EFOS) are based on energy and cement production data. Emissions from land-use change (ELUC) are estimated by bookkeeping models based on land-use data. The global atmospheric CO2 growth rate (GATM) is computed from changes in concentration measured at surface stations. The global net uptake of CO2 by the ocean (SOCEAN) is estimated with global ocean biogeochemistry models and observation-based fCO2-products. The global net uptake of CO2 by the land (SLAND) 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 ELUC, SOCEAN and SLAND estimates. The sum of all sources and sinks results in the carbon budget imbalance (BIM), a measure of imperfect data and incomplete understanding of the contemporary carbon cycle. All uncertainties are reported as ± 1σ. For the year 2024, EFOS 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), ELUC 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 GtCO2 yr−1). Also, for 2024, GATM was 7.9 ± 0.2 GtC yr−1 (3.73 ± 0.1 ppm yr−1), 2.2 GtC above the 2023 growth rate. SOCEAN was 3.4 ± 0.4 GtC yr−1 and SLAND was 1.9 ± 1.1 GtC yr−1, leaving a large negative BIM (−1.7 GtC yr−1), suggesting that the total sink or GATM 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 EFOS 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. This living data update documents changes in methods and datasets applied to this most-recent global carbon budget as well as evolving community understanding of the global carbon cycle. The data presented in this work are available at https://doi.org/10.18160/GCP-2025 (Friedlingstein et al., 2025c). 

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