Lagrangian pathways for sub-Antarctic Mode Water (SAMW) formation and carbon uptake

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• Bieito Fernandez Castro (University of Southampton)
• Thursday 11 May 2023, 15:00-16:00
• BAS Seminar Room 330b; https://ukri.zoom.us/j/91474458573.

If you have a question about this talk, please contact Dr Michael Haigh.

Sub-Antarctic Mode Waters (SAMW), forming in the deep winter mixed layers in the Sub-Antarctic Zone to the north of the Antarctic Circumpolar Current (ACC), connect the ocean thermocline with the atmosphere, contributing to ocean carbon and heat uptake and transporting high-latitude nutrients northward, to fuel primary production at lower and northern latitudes. The important climatic role of SAMW is controlled by the rate of fluid subduction from the deep winter mixed layers and the the mixed layer properties at the end of winter. These concentrations depend on a range of processes, both physical and biogeochemical, whose relative contributions are very poorly understood. With a Lagrangian particle-tracking experiment in a data-assimilative coupled physico-biogeochemical model of the Southern Ocean (B-SOSE), we assessed the origin of the waters leading to SAMW formation and the physico- and biogeochemical transformations occurring along their pathways. Our results revealed two main pathways for SAMW formation: a “classical” pathway originating from the upwelling of Circumpolar Deep Waters south of the ACC and a subtropical pathway with waters accessing the ACC at the intersection with the subtropical western boundary currents. The two pathways are characterised by contrasting transit times, degree of ventilation and range of processes controlling the final SAMW properties. The number particles joining each pathway was also different between the Indian and Pacific SAMW varieties. These findings have implications for our understanding of the Southern Ocean overturning circulation and its role on the sequestration of heat, nutrients and carbon dioxide.

This talk is part of the British Antarctic Survey - Polar Oceans seminar series series.

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