Rates and mechanisms of turbulent mixing in a coastal embayment of the West Antarctic Peninsula

Quantifying and understanding the processes driving turbulent mixing around Antarctica is key to closing the Southern Ocean’s heat budget, an essential component of the global climate system. In 2016, a glider deployed in Ryder Bay, West Antarctic Peninsula, collected hydrographic and microstructure data, obtaining some of the first direct measurements of turbulent kinetic energy dissipation off West Antarctica. Elevated dissipation O(10−8) W kg−1 is found above a topographic ridge separating the 520 m‐deep bay, where values are O(10−10) W kg−1, from a deep fjord of the continental shelf, suggesting the ridge is important in driving upward mixing of warm Circumpolar Deep Water. Twelve glider transects reveal significant temporal variability in hydrographic and dissipation conditions. Mooring‐based current and nearby meteorological data are used to attribute thermocline shoaling (deepening) to Ekman upwelling (downwelling) at Ryder Bay’s southern boundary, driven by ∼ 3‐day‐long south‐westward (north‐westward) wind events. Anticyclonic winds generated near‐inertial shear in the bay’s upper layers, causing elevated bay‐wide shear and dissipation ∼ 1.7 days later. High dissipation over the ridge appears to be controlled hydraulically, being co‐located (and moving) with steeply sloping isopycnals. These are observed in ∼ 60% of the transects, with a corresponding mean upward heat flux of ∼ 2.4 W m−2. The ridge therefore provides sustained heat to the base of the thermocline, which can be released into overlying waters during the bay‐wide, thermocline‐focused dissipation events (mean heat flux of ∼ 1.3 W m−2). This highlights the role of ridges, which are widespread across the West Antarctic Peninsula, in the regional heat budget.

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