Gilles Reverdin

Data of seawater stable isotopologs in the quality-controlled database from the isotopic platform facility at LOCEAN (hereafter “CISE-LOCEAN”) provide an unprecedented sampling of the surface Atlantic Ocean and the southwest Indian Ocean. This investigation of δ ¹⁸ O, δ ² H and deuterium excess (d-excess) in surface sea water for 20 subregions indicates a large variability of the regional regression lines with salinity for δ ¹⁸ O and δ ² H. Weakest slopes are found near the equator, and increase towards higher latitudes, but also to a lesser extent in the western Atlantic compared with the eastern Atlantic in the tropics and subtropics. These regressions often explain a large share of the variability in the data (40 % to 70 %), except for d-excess at high latitudes and δ ¹⁸ O, δ ² H near the equator. The data are sufficient to extract a rather small seasonal variability in these relationships and an average seasonal cycle in some regions of the North Atlantic subpolar gyre, with signals probably related to changes in the input of sea ice melt and depleted water of Arctic origin. A significant correlation between observed seasonal cycles in δ ¹⁸ O, δ ² H, and d-excess and that of salinity is found in the central equatorial Atlantic. These seasonal cycles change between the vicinity of the equator and the region to its north, which is associated with the seasonal shift of the Inter-tropical Convergence Zone and with the seasonality of the equatorial upwelling. Elsewhere, the seasonal signal usually does not emerge from the noise. An independent over 7-years long time series of nearly monthly surface sampling at the BATS site near Bermuda (31°50 ^′ N, 64°10 ^′ W) also indicates a rather well-defined seasonal cycle of surface salinity, δ ¹⁸ O, δ ² H and d-excess. Its interannual variability in δ ¹⁸ O does not appear closely related to the one in salinity.

Data of stable isotopologs of water in the quality-controlled CISE-LOCEAN database provide an unprecedented sampling of the surface Atlantic Ocean and the southwest Indian Ocean. This investigation of δ¹⁸O, δ²H and deuterium excess (d-excess) in surface sea water indicates large variability of the regional regression lines with salinity as a function of latitude for δ¹⁸O and δ²H, with weakest slopes near equator, but also to a lesser extent with weaker slopes in the western Atlantic compared with the eastern Atlantic at low and mid-latitudes. These regressions often explain a large share of the variability in the data (40 to 70 %), except for d-excess at the higher latitudes and δ¹⁸O, δ²H near the equator. The data are sufficient to extract a seasonal variability in these relationships and an average seasonal cycle in some regions of the North Atlantic subpolar gyre with signals probably related to changes in the input of heavier sea ice melt and depleted water of Arctic origin. A seasonal cycle is also found in the central equatorial Atlantic with the strong contrast between the vicinity of the equator and the region to its north, associated with the seasonal shift of the precipitation belt and with the seasonality of the equatorial upwelling. In those regions there is also some evidence in seasonal variability of the d-excess that is not currently explained. Elsewhere, the seasonal signal usually does not come out of the noise. A 7–8 years long time series of nearly monthly surface sampling at the BATS site near Bermuda (31°50’ N, 64°10’ W) also indicates a rather well-defined seasonal cycle of SSS, δ¹⁸O, δ²H and deuterium excess. There is also some indication of interannual variability, which might not be closely related to salinity.

Data of stable isotopologs of water in the quality-controlled CISE-LOCEAN database provide an unprecedented sampling of the surface Atlantic Ocean and the southwest Indian Ocean. This investigation of δ¹⁸O, δ²H and deuterium excess (d-excess) in surface sea water indicates large variability of the regional regression lines with salinity as a function of latitude for δ¹⁸O and δ²H, with weakest slopes near equator, but also to a lesser extent with weaker slopes in the western Atlantic compared with the eastern Atlantic at low and mid-latitudes. These regressions often explain a large share of the variability in the data (40 to 70 %), except for d-excess at the higher latitudes and δ¹⁸O, δ²H near the equator. The data are sufficient to extract a seasonal variability in these relationships and an average seasonal cycle in some regions of the North Atlantic subpolar gyre with signals probably related to changes in the input of heavier sea ice melt and depleted water of Arctic origin. A seasonal cycle is also found in the central equatorial Atlantic with the strong contrast between the vicinity of the equator and the region to its north, associated with the seasonal shift of the precipitation belt and with the seasonality of the equatorial upwelling. In those regions there is also some evidence in seasonal variability of the d-excess that is not currently explained. Elsewhere, the seasonal signal usually does not come out of the noise. A 7–8 years long time series of nearly monthly surface sampling at the BATS site near Bermuda (31°50’ N, 64°10’ W) also indicates a rather well-defined seasonal cycle of SSS, δ¹⁸O, δ²H and deuterium excess. There is also some indication of interannual variability, which might not be closely related to salinity.

Ocean acidification is expected to be particularly severe in Antarctic continental shelves due to enhanced anthropogenic carbon uptake in cold waters in response to rising atmospheric CO₂, sea-ice retreat, freshening and climate-change feedbacks. Models suggest that undersaturated conditions with respect to aragonite (Ωar), a major form of calcium carbonate formed by marine species, could be reached as soon as 2052 for austral winter. Here we present new ocean carbonate system observations from cruises conducted since 2010 in the Adélie Land coastal region in East Antarctica, along with data from a BCG-Argo float and results from a neural network model for the period 1985–2025. The region is a permanent CO₂ sink and was most pronounced since 2006. The CO₂ sink leads to a positive increase of surface water total CO₂ concentrations (C_T) (+0.44 ± 0.01 µmol.kg^-1.yr^-1) and to a progressive decrease of pH (-0.013 per decade) and Ωar (-0.035 per decade) for the winter season. The lowest surface Ωar of 1.2 was observed in winter 2024 from the float data, a critical limit for some marine species such as pteropod. A projection of the C_T concentrations in the future, based on observed anthropogenic CO₂ concentrations and emissions scenarios, suggests that aragonite saturation state (Ωar = 1) will occur in surface waters as soon as 2055 in the Adélie Land region, which is part of a larger area of East Antarctica proposed as a Marine Protected Area by the Commission for the Conservation of Antarctic Marine Living Resources since the early 2010s.

Ocean acidification is expected to be particularly severe in Antarctic continental shelves due to enhanced anthropogenic carbon uptake in cold waters in response to rising atmospheric CO₂, sea-ice retreat, freshening and climate-change feedbacks. Models suggest that undersaturated conditions with respect to aragonite (Ωar), a major form of calcium carbonate formed by marine species, could be reached as soon as 2052 for austral winter. Here we present new ocean carbonate system observations from cruises conducted since 2010 in the Adélie Land coastal region in East Antarctica, along with data from a BCG-Argo float and results from a neural network model for the period 1985–2025. The region is a permanent CO₂ sink and was most pronounced since 2006. The CO₂ sink leads to a positive increase of surface water total CO₂ concentrations (C_T) (+0.44 ± 0.01 µmol.kg^-1.yr^-1) and to a progressive decrease of pH (-0.013 per decade) and Ωar (-0.035 per decade) for the winter season. The lowest surface Ωar of 1.2 was observed in winter 2024 from the float data, a critical limit for some marine species such as pteropod. A projection of the C_T concentrations in the future, based on observed anthropogenic CO₂ concentrations and emissions scenarios, suggests that aragonite saturation state (Ωar = 1) will occur in surface waters as soon as 2055 in the Adélie Land region, which is part of a larger area of East Antarctica proposed as a Marine Protected Area by the Commission for the Conservation of Antarctic Marine Living Resources since the early 2010s.

Data of stable isotopologs of water in the quality-controlled CISE-LOCEAN database provide an unprecedented sampling of the surface Atlantic Ocean and the southwest Indian Ocean. This investigation of δ¹⁸O, δ²H and deuterium excess (d-excess) in surface sea water indicates large variability of the regional regression lines with salinity as a function of latitude for δ¹⁸O and δ²H, with weakest slopes near equator, but also to a lesser extent with weaker slopes in the western Atlantic compared with the eastern Atlantic at low and mid-latitudes. These regressions often explain a large share of the variability in the data (40 to 70 %), except for d-excess at the higher latitudes and δ¹⁸O, δ²H near the equator. The data are sufficient to extract a seasonal variability in these relationships and an average seasonal cycle in some regions of the North Atlantic subpolar gyre with signals probably related to changes in the input of heavier sea ice melt and depleted water of Arctic origin. A seasonal cycle is also found in the central equatorial Atlantic with the strong contrast between the vicinity of the equator and the region to its north, associated with the seasonal shift of the precipitation belt and with the seasonality of the equatorial upwelling. In those regions there is also some evidence in seasonal variability of the d-excess that is not currently explained. Elsewhere, the seasonal signal usually does not come out of the noise. A 7–8 years long time series of nearly monthly surface sampling at the BATS site near Bermuda (31°50’ N, 64°10’ W) also indicates a rather well-defined seasonal cycle of SSS, δ¹⁸O, δ²H and deuterium excess. There is also some indication of interannual variability, which might not be closely related to salinity.

Ocean acidification is expected to be particularly severe in Antarctic continental shelves due to enhanced anthropogenic carbon uptake in cold waters in response to rising atmospheric CO₂, sea-ice retreat, freshening and climate-change feedbacks. Models suggest that undersaturated conditions with respect to aragonite (Ωar), a major form of calcium carbonate formed by marine species, could be reached as soon as 2052 for austral winter. Here we present new ocean carbonate system observations from cruises conducted since 2010 in the Adélie Land coastal region in East Antarctica, along with data from a BCG-Argo float and results from a neural network model for the period 1985–2025. The region is a permanent CO₂ sink and was most pronounced since 2006. The CO₂ sink leads to a positive increase of surface water total CO₂ concentrations (C_T) (+0.44 ± 0.01 µmol.kg^-1.yr^-1) and to a progressive decrease of pH (-0.013 per decade) and Ωar (-0.035 per decade) for the winter season. The lowest surface Ωar of 1.2 was observed in winter 2024 from the float data, a critical limit for some marine species such as pteropod. A projection of the C_T concentrations in the future, based on observed anthropogenic CO₂ concentrations and emissions scenarios, suggests that aragonite saturation state (Ωar = 1) will occur in surface waters as soon as 2055 in the Adélie Land region, which is part of a larger area of East Antarctica proposed as a Marine Protected Area by the Commission for the Conservation of Antarctic Marine Living Resources since the early 2010s.

Ocean acidification is expected to be particularly severe in Antarctic continental shelves due to enhanced anthropogenic carbon uptake in cold waters in response to rising atmospheric CO₂, sea-ice retreat, freshening and climate-change feedbacks. Models suggest that undersaturated conditions with respect to aragonite (Ωar), a major form of calcium carbonate formed by marine species, could be reached as soon as 2052 for austral winter. Here we present new ocean carbonate system observations from cruises conducted since 2010 in the Adélie Land coastal region in East Antarctica, along with data from a BCG-Argo float and results from a neural network model for the period 1985–2025. The region is a permanent CO₂ sink and was most pronounced since 2006. The CO₂ sink leads to a positive increase of surface water total CO₂ concentrations (C_T) (+0.44 ± 0.01 µmol.kg^-1.yr^-1) and to a progressive decrease of pH (-0.013 per decade) and Ωar (-0.035 per decade) for the winter season. The lowest surface Ωar of 1.2 was observed in winter 2024 from the float data, a critical limit for some marine species such as pteropod. A projection of the C_T concentrations in the future, based on observed anthropogenic CO₂ concentrations and emissions scenarios, suggests that aragonite saturation state (Ωar = 1) will occur in surface waters as soon as 2055 in the Adélie Land region, which is part of a larger area of East Antarctica proposed as a Marine Protected Area by the Commission for the Conservation of Antarctic Marine Living Resources since the early 2010s.

Data of stable isotopologs of water in the quality-controlled CISE-LOCEAN database provide an unprecedented sampling of the surface Atlantic Ocean and the southwest Indian Ocean. This investigation of δ¹⁸O, δ²H and deuterium excess (d-excess) in surface sea water indicates large variability of the regional regression lines with salinity as a function of latitude for δ¹⁸O and δ²H, with weakest slopes near equator, but also to a lesser extent with weaker slopes in the western Atlantic compared with the eastern Atlantic at low and mid-latitudes. These regressions often explain a large share of the variability in the data (40 to 70 %), except for d-excess at the higher latitudes and δ¹⁸O, δ²H near the equator. The data are sufficient to extract a seasonal variability in these relationships and an average seasonal cycle in some regions of the North Atlantic subpolar gyre with signals probably related to changes in the input of heavier sea ice melt and depleted water of Arctic origin. A seasonal cycle is also found in the central equatorial Atlantic with the strong contrast between the vicinity of the equator and the region to its north, associated with the seasonal shift of the precipitation belt and with the seasonality of the equatorial upwelling. In those regions there is also some evidence in seasonal variability of the d-excess that is not currently explained. Elsewhere, the seasonal signal usually does not come out of the noise. A 7–8 years long time series of nearly monthly surface sampling at the BATS site near Bermuda (31°50’ N, 64°10’ W) also indicates a rather well-defined seasonal cycle of SSS, δ¹⁸O, δ²H and deuterium excess. There is also some indication of interannual variability, which might not be closely related to salinity.