Abstract
AbstractQuantifying and understanding the processes driving turbulent mixing around Antarctica are 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. The 12 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.
Highlights
Ice shelves in the West Antarctic sector are experiencing the greatest mass loss anywhere in Antarctica, with basal melt rates of up to ∼5 m yr−1 (Rignot et al, 2013)
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
The ridge, provides sustained heat to the base of the thermocline, which can be released into overlying waters during the bay-wide, thermocline-focused dissipation events. This highlights the role of ridges, which are widespread across the West Antarctic Peninsula, in the regional heat budget
Summary
Ice shelves in the West Antarctic sector are experiencing the greatest mass loss anywhere in Antarctica, with basal melt rates of up to ∼5 m yr−1 (Rignot et al, 2013). Winds can influence the WAP heat budget by driving Ekman upwelling/downwelling at the coast: if the orientation of the winds is in the alongshore direction, Ekman transport will drive water toward or away from the coast (Mitchum & Clarlymake, 1986) This process is thought to be significant within Ryder Bay, where wind-induced oscillations of the water column's hydrographic structure are observed (Wallace et al, 2008), causing vertical migration of the interface between CDW and the overlying cold Winter Water (WW).
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