Abstract
The fate of mesoscale eddy kinetic energy represents a large source of uncertainty in the global ocean energy budget. Satellite altimetry suggests that mesoscale eddies vanish at ocean western boundaries. However, the fate of the eddies’ kinetic energy remains poorly known. Here we show that the generation of small-scale turbulence as eddy flow impinges on the steep and corrugated slope of an ocean western boundary plays a dominant role in the regional decay of mesoscale eddy kinetic energy. We compare altimetry-based estimates of mesoscale eddy kinetic energy decline with measurements of turbulent dissipation. Mesoscale eddies are found to decay at a rate of 0.016 ± 0.012 GW and 0.023 ± 0.017 GW for anticyclonic and cyclonic eddies, respectively, similar to the observed turbulent dissipation rate of 0.020 ± 0.011 GW. This demonstrates that a major direct transfer of mesoscale eddy kinetic energy to small, dissipative scales can be effectively triggered by the eddies’ interaction with the western boundary topography.
Highlights
The fate of mesoscale eddy kinetic energy represents a large source of uncertainty in the global ocean energy budget
One potentially major mechanism for mesoscale eddy dissipation was highlighted by Zhai et al.[10], who showed that the western boundaries of ocean basins act as sinks of mesoscale eddy kinetic energy as detected by satellite altimetry
We have shown that the decay of mesoscale eddy kinetic energy in a region offshore of the Bahamian islands, typical of the western boundary of the North A tlantic[10], is driven predominantly by the dissipative action of small-scale turbulence, which is generated by the impingement of eddy flows onto the boundary’s steep and rough topographic slope
Summary
The fate of mesoscale eddy kinetic energy represents a large source of uncertainty in the global ocean energy budget. The observations were acquired under the auspices of the MeRMEED (Mechanisms Responsible for Mesoscale Eddy Energy Dissipation) project, and included vessel- and mooring-mounted acoustic Doppler current profiler (ADCP) measurements of eddy flows and vertical microstructure profiler- (VMP) based estimates of the turbulent energy dissipation rate across each eddy’s shoreward edge (see Methods) This data set revealed elevated levels of turbulent dissipation above the topographic slope that were especially high for anticyclonic eddies[16] and occurred in association with a host of eddy-topography interaction processes[16,17]. A rigorous test of this hypothesis requires that a quantitative assessment of the energetics of the boundary-impinging eddies be performed To conduct this assessment, we compare the rate of decay in the energy of mesoscale eddies entering the MeRMEED study domain with the rate of energy dissipation by small-scale turbulence linked to the eddies’ interaction with the local topographic slope. Eddy kinetic energy decay rates are estimated using satellite altimetric
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