The intensity and climatic impacts of oceanic overturning are critically shaped by deep-ocean turbulent mixing, which transforms cold waters sinking at high latitudes into warmer, shallower waters. The effectiveness of turbulent mixing in driving this transformation is jointly set by two factors: the intensity of turbulence near topographic boundaries, and the rate at which well-mixed boundary waters are exchanged with the stratified ocean interior. Yet while many near-boundary turbulent processes have been documented, little is known about the mechanisms regulating boundary – interior exchange. Here, we use observations of the turbulent properties of a major outflow of Antarctic Bottom Water (AABW) from the Weddell Sea to identify a previously-unrecognised mechanism of deep-ocean mixing, by which near-boundary turbulence and boundary – interior exchange are concurrently intensified. The observations included high-resolution fine- and microstructure measurements across the AABW flow through the Orkney Passage, and were obtained with ship-deployed instrumentation and the autonomous underwater vehicle Autosub Long Range under the auspices of the U.K. - U.S. DynOPO (Dynamics of the Orkney Passage Outflow) project. The cornerstone of the new mechanism is the generation of submesoscale dynamical instabilities by the flow of deep-ocean waters along a steep topographic boundary. The dynamics and large-scale implications of this mode of mixing will be discussed.
Wednesday 19 September 2018 - 11:00
NOC Southampton - Node Room (074/02) (Waterfront Campus).
Alberto Naveira Garabato