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Tracer stirring and variability in the Antarctic Circumpolar Current near the Southwest Indian Ridge
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  • Dhruv Balwada,
  • Alison Gray,
  • Lilian A. Dove,
  • Andrew F. Thompson
Dhruv Balwada
Columbia University

Corresponding Author:dhruvbalwada@gmail.com

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Alison Gray
University of Washington
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Lilian A. Dove
California Institute of Technology
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Andrew F. Thompson
California Institute of Technology
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Oceanic macroturbulence is efficient at stirring and transporting tracers. The dynamical properties of this stirring can be characterized by statistically quantifying tracer structures. Here, we characterize the macroscale (1-100 km) tracer structures observed by two Seagliders downstream of the Southwest Indian Ridge (SWIR) in the Antarctic Circumpolar Current (ACC). These are some of the first glider observations in an energetic standing meander of the ACC, regions associated with enhanced ventilation. The small-scale density variance in the mixed layer (ML) was relatively enhanced near the surface and base of the ML, while being muted in the middle, suggesting the formation mechanism to be associated to ML instabilities and eddies. In addition, ML density fronts were formed by comparable contributions from temperature and salinity gradients, suggesting the dominant role of stirring, over air-sea interactions, in their formation and sustainability. In the interior, along-isopycnal spectra and structure functions of spice indicated that there is relatively lower variance at smaller scales than would be expected based on non-local stirring, suggesting that flows smaller than the deformation radius play a role in the cascade of tracers to small scales. These interior spice anomalies spanned across isopycnals, and were found to be about 3-5 times flatter than the aspect ratio that would be expected for O(1) Burger number flows like interior QG dynamics, suggesting the ratio of vertical shear to horizontal strain is greater than $N/f$. This further supports that small-scale flows, with high-mode vertical structures, stir tracers and impact tracer distributions.
08 Mar 2023Submitted to ESS Open Archive
09 Mar 2023Published in ESS Open Archive