Observations of a diapycnal shortcut to adiabatic upwelling of Antarctic Circumpolar Deep Water

• Published in: Geophysical Research Letters
• Main Authors: Mead Silvester, J., Lenn, Yueng-Djern, Polton, Jeff A., Rippeth, Tom P., Morales Maqueda, M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2014
• Subjects: Antarctic; Southern Ocean; The Antarctic; Antarctic Peninsula; Drake Passage; Elephant Island; Antarc*
• Online Access: http://nora.nerc.ac.uk/id/eprint/508796/; https://nora.nerc.ac.uk/id/eprint/508796/1/grl52261_MeadSilvester.pdf; https://doi.org/10.1002/2014GL061538

In the Southern Ocean, small-scale turbulence causes diapycnal mixing which influences important water mass transformations, in turn impacting large-scale ocean transports such as the Meridional Overturning Circulation (MOC), a key controller of Earth'sclimate. We present direct observations of mixing over the Antarctic continental slope between water masses that are part of the Southern Ocean MOC. A 12-hour time-series of microstructure turbulence measurements, hydrography and velocity observations off Elephant Island, north of the Antarctic Peninsula, reveals two concurrent bursts of elevated dissipation of O(10–6Wkg–1, resulting in heat fluxes ~10 times higher than basin-integrated Drake Passage estimates. This occurs across the boundary between adjacent adiabatic upwelling and downwelling overturning cells. Ray tracing and topography show mixing between 300-400 m consistent with the breaking of locally-generated internal tidal waves. Since similar conditions extend to much of the Antarctic continental slope where these water masses outcrop, their transformation may contribute significantly to upwelling.