Pathways of boundary mixing in the Antarctic Circumpolar Current revealed by a tracer release experiment.

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• Marie-Jose Messias, University of Exeter
• Wednesday 23 May 2018, 11:00-12:00
• British Antarctic Survey, Innovation Centre, Seminar Room 1.

If you have a question about this talk, please contact Dr Emma Boland.

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Diapycnal mixing (across density surfaces) is a key process in the Antarctic Circumpolar Current (ACC) said to control a third of the upward transport of deep water towards the surface of the ocean overturning in the Southern Ocean. To shed light on the on going debate of pathways to mixing in the Southern Ocean, we present here the spatiotemporal patterns of the mixing inferred from a tracer released at mid-depth upstream of the topographic threshold of Drake Passage. The magnitude and distributions of the mixing intensification are fund to be robust, linked to flow velocity and topography: most notably, a double intensification in the jets cores and a two order of magnitude intensification from O(2×10-5) m2 s-1 above the smooth seafloor of the eastern Pacific, O(2×10-4) m2 s-1 where the tracer lies at 2-km depth above the abyssal complex topography, to O(2×10-3) m2 s-1 where the tracer encounters sloping topography along the ACC northern boundary (within Sub-Antarctic Front) and in the Falkland Through. The evidence of intense near-boundary mixing suggest that diapycnal mixing in the ACC is intrinsically 3-dimensional, i.e. water gets mixed mostly near isopycnal incrops and the products of boundary mixing distributed away from the boundary along sloping isopycnals. In that context, we compare the vertical displacement of the tracer along sloping topography with its displacement in a region of different dynamics (i.e Polar Front). The tracer in the PF appears to have migrated towards higher density, giving a diapycnal downwelling O(0.025kg/m3).

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

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