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Turbulence and cross-slope transport off Antarctica and California


Onshore penetration of oceanic water across the Antarctic continental slope (ACS) plays a major role in global sea level rise by delivering heat to the Antarctic marginal seas, thus contributing to the basal melting of ice shelves. We show that the time-mean and eddy components of the onshore Heat Transport (HT) around the Antarctic Continental Margin (ACM) in a global 0.1° coupled ocean-sea ice model add up to O(20 TW) in the annual average. The contributions from eddy advection, eddy stirring, and mean flow advection to the total onshore HT vary regionally. The time-mean component governs the seasonal variability of the total HT and largely cancels the eddy component. We examine the depth-integrated vorticity balance of this simulation to gain further insigth into the dynamics of these processes. Maps of the time-averaged depth-integrated vorticity budget terms and time series of the spatially-averaged, depth-integrated vorticity budget terms reveal that the flow in the Amundsen, Bellingshausen and Weddell Seas and in the western portion of East Antarctica, is closer to an approximate Topographic Sverdrup Balance compared to other segments of the ACM. This suggests that the surface-stress curl, imparted by the wind and the sea ice, has the potential to contribute to the meridional, approximately cross-slope, transport to a greater extent in some segments of the ACM than others.

In the second part of this thesis, we describe the observed spatio-temporal variability and vertical structure of turbulent Reynolds stresses in a stratified mid-latitude inner-shelf with an energetic internal wave climate. We link the Reynolds stresses to different physical processes, namely internal bores, mid-water shear instabilities within vertical shear events related to wind-driven subtidal along-shelf currents; and non-turbulent stresses related to incoming Nonlinear Internal Wave (NLIW) trains. Among other conclusions, the results highlight that internal bores and shoaling NLIWs may also be important dynamical players in other inner-shelves with energetic internal waves. In the mesoscale, simulations and an along-isobath survey suggest that the balanced-to-unbalanced transition along the 50 m isobath is at 12-22 km, and that baroclinic instability of the subtidal along-shelf flow is a plausible explanation for the cross-shelf structure of the transition scale.

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