Articles | Volume 22, issue 1
https://doi.org/10.5194/os-22-209-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Special issue:
https://doi.org/10.5194/os-22-209-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Observations of tracer ventilation in the Cape Basin, Agulhas Current Retroflection
Renske Koets
CORRESPONDING AUTHOR
Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden
Sebastiaan Swart
Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden
Department of Oceanography, University of Cape Town, Rondebosch, South Africa
Kathleen Donohue
Graduate School of Oceanography, University of Rhode Island, Narragansett, USA
Marcel du Plessis
Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden
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We introduce TS-Cast, a novel deep neural network that reconstructs subsurface thermohaline structures from satellite observations (ADT, SST, and SSS). Validated against independent time-series data, TS-Cast achieves RMSE < 1 °C and < 0.1 psu in the upper 500 m of the Kuroshio Extension, comparable or surpassing data-assimilated numerical models. Critically, we demonstrate that the physical limitations of the input satellite data fundamentally constrain the model's predictive skill.
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In the Sea of Oman, mode waters form at the surface in winter and are trapped beneath a warmer surface layer in spring, linking the surface ocean and the oxygen minimum zone. Using data from ocean gliders, our study examines how this layer evolves. Changes occur along layers of equal density, with brief episodes of vertical mixing, enhanced by eddies. Glider data reveal more variability than monthly means, showing the need for sustained glider observations to understand future ecosystem impacts.
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Mode water is formed annually and sits between the warm surface water and deeper older waters. In the Arabian Sea, it plays a crucial role in regulating ocean heat and oxygen variability by acting as a doorway between the surface and deeper waters. Using observations and models, we show that its formation is primarily driven by atmospheric forcing, though ocean currents, eddies, and biological heating also influence its life cycle. This water mass contributes up to 40 % of the region's oxygen content.
Kirtana Naëck, Jacqueline Boutin, Sebastiaan Swart, Marcel du Plessis, Liliane Merlivat, Laurence Beaumont, Antonio Lourenco, Francesco d'Ovidio, Louise Rousselet, Brian Ward, and Jean-Baptiste Sallée
Biogeosciences, 22, 1947–1968, https://doi.org/10.5194/bg-22-1947-2025, https://doi.org/10.5194/bg-22-1947-2025, 2025
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In summer 2022, a CARbon Interface OCean Atmosphere (CARIOCA) drifting buoy observed an anomalously strong ocean carbon sink in the subpolar Southern Ocean associated with large plumes of chlorophyll a. Lagrangian backward trajectories indicate that these waters originated from the sea ice edge in spring 2021. Our study highlights the northward migration of the CO2 sink associated with early sea ice retreat.
Blandine Jacob, Bastien Y. Queste, and Marcel D. du Plessis
Ocean Sci., 21, 359–379, https://doi.org/10.5194/os-21-359-2025, https://doi.org/10.5194/os-21-359-2025, 2025
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Few observations exist in the Amundsen Sea. Consequently, studies rely on reanalysis (e.g., ERA5) to investigate how the atmosphere affects ocean variability (e.g., sea-ice formation and melt). We use data collected along ice shelves to show that cold, dry air blowing from Antarctica triggers large ocean heat loss, which is underestimated by ERA5. We then use an ocean model to show that this bias has an important impact on the ocean, with implications for sea-ice forecasts.
Ria Oelerich, Karen J. Heywood, Gillian M. Damerell, Marcel du Plessis, Louise C. Biddle, and Sebastiaan Swart
Ocean Sci., 19, 1465–1482, https://doi.org/10.5194/os-19-1465-2023, https://doi.org/10.5194/os-19-1465-2023, 2023
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At the southern boundary of the Antarctic Circumpolar Current, relatively warm waters encounter the colder waters surrounding Antarctica. Observations from underwater vehicles and altimetry show that medium-sized cold-core eddies influence the southern boundary's barrier properties by strengthening the slopes of constant density lines across it and amplifying its associated jet. As a result, the ability of exchanging properties, such as heat, across the southern boundary is reduced.
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Short summary
The Cape Basin is a dynamic region where warm, salty Indian Ocean waters meet cooler Atlantic waters. Mixing between these waters drives ventilation, the transport of surface waters to deeper layers in the ocean. Using high-resolution observations from an autonomous Seaglider combined with satellite altimetry we provide new evidence on how small-scale ocean dynamics contribute to ventilation in the Cape Basin, with broader implications on ocean circulation.
The Cape Basin is a dynamic region where warm, salty Indian Ocean waters meet cooler Atlantic...
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