Tobias Ehmen

Southern Ocean primary productivity is often limited by the availability of the essential micronutrient iron (Fe), and sediment-derived fluxes of Fe from the Antarctic shelf have been linked with hotspots of productivity. Glacial meltwater along the West Antarctic Peninsula delivers significant volumes of Fe-rich glacially weathered material to shelf surface sediments. Measured acoustic doppler current profiler and acoustic backscatter turbidity data indicate ongoing resuspension of sediment in the coastal region. Onboard mesocosm experiments simulated resuspension of oxic sediments, rich in highly reactive Fe (2–9 mg g ⁻¹ ), in the nearshore glaciated West Antarctic Peninsula across King George Island, Anvers Island, and Adelaide Island. These experiments produced a high sustained bottom water enrichment in dissolved Fe of ∼ 4–12 nM over the 48 h experiment duration. Our observations support a dissolved Fe flux to the water column of 0.18–4.0 µmol m ⁻² d ⁻¹ by resuspension within the glaciated fjords, demonstrating that resuspension of reactive oxic nearshore sediments is a key source of dissolved and reactive particulate Fe to Antarctic shelf waters, the export of which could potentially supply bioavailable Fe to Fe-limited Southern Ocean waters.

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their partitioning among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, supporting 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. 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 2025, EFOS increased by 1.2% relative to 2024, with fossil emissions at 10.5 ± 0.5 GtC yr-1 (including the cement carbonation sink, 0.2 GtC yr-1), ELUC was 1.2 ± 0.7 GtC yr-1, for total anthropogenic CO2 emissions of 11.7 ± 0.9 GtC yr-1 (42.8 ± 3.2 GtCO2 yr-1). Also, for 2025, GATM was 4.4 ± 0.2 GtC yr-1 (2.06 ± 0.1 ppm yr-1), 3.6 GtC lower than the record high 2024 growth rate. SOCEAN was 3.2 ± 0.7 GtC yr-1 and SLAND was 3.6 ± 0.9 GtC yr-1, with a small BIM (0.5 GtC yr-1). The global atmospheric CO2 concentration averaged over 2025 reached 425.6 ± 0.1 ppm. Preliminary data for 2026 suggest a decrease in EFOS relative to 2025 of 0.40% (–1.5% to +0.6%) globally, and atmospheric CO2 concentration increasing by 2.2 ppm reaching 427.7 ppm, 54% 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 1959–2025, with a small positive overall budget imbalance, (0.6 GtC yr-1 averaged over the period 1959–2025), 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 estimates on the magnitude of the land CO2 flux, particularly in the northern extra-tropics, and (3) a discrepancy between the different estimates on the mean ocean sink and its trend. 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-2026 (Friedlingstein et al., 2026b).

The Eurasian Basin Transect 2026 cruise (EBT2026; ID 2026007011) was conducted 23 July–10 September 2026. Its geographical coverage included the Nansen and Amundsen Basins, the adjacent Lomonosov Ridge and Southeastern Makarov Basin, including the full width of the Transpolar Drift current. Throughout the cruise, a comprehensive set of physical, chemical, and biological observations was collected from multiple components of the Arctic system, including the atmosphere, ocean, sea ice, and sea floor.

The oceans mitigate climate change by absorbing 25–30 % of anthropogenic carbon emissions. Decadal variability in the ocean carbon sink has been suggested by pCO₂-based reconstructions of the ocean uptake, but these variations are less apparent in reconstructions based on global ocean biogeochemistry models (GOBMs) which also predict a slower increase in the ocean sink over the period from 2000 to 2015, raising concerns about our ability to accurately project future changes. An independent method to study the uptake uses interior observations to calculate how dissolved inorganic carbon (DIC) is changing. To address the sparsity of interior data, machine learning techniques have been applied, but as yet, global, full-depth reconstructions of the complete inventory of DIC have not been produced. Here we develop such a full-depth reconstruction, from the 1990s to 2019, using "ResNet-DIC", a deep neural network trained on GLODAPv2.2023 observations. Atmospheric CO₂, location, temperature, and salinity from EN4 analysis are used as predictors. Our method shows good predictive power when validated using independent data sets and model subsampling experiments. We diagnose the total oceanic DIC pool as 37,508 ± 274 Pg C in 2019 with an average rate of increase of 2.64 ± 0.13 Pg C/year over the whole time period. The global change in the DIC inventory exhibits pronounced peaks in decadal variability, especially in the early 2000s, driven primarily by intermediate waters at depths of 300–1000 m, particularly in the Atlantic, Indian, and Southern Oceans, and to a lesser extent in the Pacific. The accumulation rate of DIC increases steadily from the mid-2000s.

The oceans mitigate climate change by absorbing 25–30 % of anthropogenic carbon emissions. Decadal variability in the ocean carbon sink has been suggested by pCO₂-based reconstructions of the ocean uptake, but these variations are less apparent in reconstructions based on global ocean biogeochemistry models (GOBMs) which also predict a slower increase in the ocean sink over the period from 2000 to 2015, raising concerns about our ability to accurately project future changes. An independent method to study the uptake uses interior observations to calculate how dissolved inorganic carbon (DIC) is changing. To address the sparsity of interior data, machine learning techniques have been applied, but as yet, global, full-depth reconstructions of the complete inventory of DIC have not been produced. Here we develop such a full-depth reconstruction, from the 1990s to 2019, using "ResNet-DIC", a deep neural network trained on GLODAPv2.2023 observations. Atmospheric CO₂, location, temperature, and salinity from EN4 analysis are used as predictors. Our method shows good predictive power when validated using independent data sets and model subsampling experiments. We diagnose the total oceanic DIC pool as 37,508 ± 274 Pg C in 2019 with an average rate of increase of 2.64 ± 0.13 Pg C/year over the whole time period. The global change in the DIC inventory exhibits pronounced peaks in decadal variability, especially in the early 2000s, driven primarily by intermediate waters at depths of 300–1000 m, particularly in the Atlantic, Indian, and Southern Oceans, and to a lesser extent in the Pacific. The accumulation rate of DIC increases steadily from the mid-2000s.

The oceans mitigate climate change by absorbing 25–30 % of anthropogenic carbon emissions. Decadal variability in the ocean carbon sink has been suggested by pCO2-based reconstructions of the ocean uptake, but these variations are less apparent in reconstructions based on global ocean biogeochemistry models (GOBMs) which also predict a slower increase in the ocean sink over the period from 2000 to 2015, raising concerns about our ability to accurately project future changes. An independent method to study the uptake uses interior observations to calculate how dissolved inorganic carbon (DIC) is changing. To address the sparsity of interior data, machine learning techniques have been applied, but as yet, global, full-depth reconstructions of the complete inventory of DIC have not been produced. Here we develop such a full-depth reconstruction, from the 1990s to 2019, using "ResNet-DIC", a deep neural network trained on GLODAPv2.2023 observations. Atmospheric CO2, location, temperature, and salinity from EN4 analysis are used as predictors. Our method shows good predictive power when validated using independent data sets and model subsampling experiments. We diagnose the total oceanic DIC pool as 37,508 ± 274 Pg C in 2019 with an average rate of increase of 2.64 ± 0.13 Pg C/year over the whole time period. The global change in the DIC inventory exhibits pronounced peaks in decadal variability, especially in the early 2000s, driven primarily by intermediate waters at depths of 300–1000 m, particularly in the Atlantic, Indian, and Southern Oceans, and to a lesser extent in the Pacific. The accumulation rate of DIC increases steadily from the mid-2000s.

Southern Ocean primary productivity is often limited by the availability of the essential micronutrient iron (Fe), and sediment-derived fluxes of Fe from the Antarctic shelf have been linked with hotspots of productivity. Glacial meltwater along the West Antarctic Peninsula delivers significant volumes of Fe-rich glacially weathered material to shelf surface sediments. The mechanisms that supply a bioavailable flux of Fe from shelf sediments are not well understood. This study simulated the resuspension of oxic sediments in the nearshore glaciated West Antarctic Peninsula across King George Island, Anvers Island, and Adelaide Island. Glaciomarine surface sediments were rich in highly reactive Fe (2 – 9 mg Fe g^-1), and onboard mesocosm resuspensions produced a sustained bottom water enrichment in dissolved Fe of 4 – 12 nM over the 48 h experiment duration. Additional acoustic doppler current profiler and acoustic backscatter turbidity data indicate ongoing resuspension of sediment in the region. Our observations support a flux of highly reactive Fe of 5–20 µmol cm^-2 per sediment by resuspension within the glaciated fjords studied, exceeding recent outer shelf estimates of 0.7 µmol cm^-2. Reactive oxic nearshore sediments therefore represent an important supply of colloidal and reactive particulate Fe to the Antarctic shelf water column, the export of which can potentially supply bioavailable Fe to Fe-limited Southern Ocean waters.

Southern Ocean primary productivity is often limited by the availability of the essential micronutrient iron (Fe), and sediment-derived fluxes of Fe from the Antarctic shelf have been linked with hotspots of productivity. Glacial meltwater along the West Antarctic Peninsula delivers significant volumes of Fe-rich glacially weathered material to shelf surface sediments. The mechanisms that supply a bioavailable flux of Fe from shelf sediments are not well understood. This study simulated the resuspension of oxic sediments in the nearshore glaciated West Antarctic Peninsula across King George Island, Anvers Island, and Adelaide Island. Glaciomarine surface sediments were rich in highly reactive Fe (2 – 9 mg Fe g^-1), and onboard mesocosm resuspensions produced a sustained bottom water enrichment in dissolved Fe of 4 – 12 nM over the 48 h experiment duration. Additional acoustic doppler current profiler and acoustic backscatter turbidity data indicate ongoing resuspension of sediment in the region. Our observations support a flux of highly reactive Fe of 5–20 µmol cm^-2 per sediment by resuspension within the glaciated fjords studied, exceeding recent outer shelf estimates of 0.7 µmol cm^-2. Reactive oxic nearshore sediments therefore represent an important supply of colloidal and reactive particulate Fe to the Antarctic shelf water column, the export of which can potentially supply bioavailable Fe to Fe-limited Southern Ocean waters.

Southern Ocean primary productivity is often limited by the availability of the essential micronutrient iron (Fe), and sediment-derived fluxes of Fe from the Antarctic shelf have been linked with hotspots of productivity. Glacial meltwater along the West Antarctic Peninsula delivers significant volumes of Fe-rich glacially weathered material to shelf surface sediments. The mechanisms that supply a bioavailable flux of Fe from shelf sediments are not well understood. This study simulated the resuspension of oxic sediments in the nearshore glaciated West Antarctic Peninsula across King George Island, Anvers Island, and Adelaide Island. Glaciomarine surface sediments were rich in highly reactive Fe (2 – 9 mg Fe g^-1), and onboard mesocosm resuspensions produced a sustained bottom water enrichment in dissolved Fe of 4 – 12 nM over the 48 h experiment duration. Additional acoustic doppler current profiler and acoustic backscatter turbidity data indicate ongoing resuspension of sediment in the region. Our observations support a flux of highly reactive Fe of 5–20 µmol cm^-2 per sediment by resuspension within the glaciated fjords studied, exceeding recent outer shelf estimates of 0.7 µmol cm^-2. Reactive oxic nearshore sediments therefore represent an important supply of colloidal and reactive particulate Fe to the Antarctic shelf water column, the export of which can potentially supply bioavailable Fe to Fe-limited Southern Ocean waters.