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Abrupt transitions in submesoscale structure in Southern Drake Passage: Glider observations and model results

Artikel i vetenskaplig tidskrift
Författare Giuliana Viglione
Andrew Thompson
Mar Flexas
Janet Sprintall
Sebastiaan Swart
Publicerad i Journal of Physical Oceanography
Volym 48
Nummer/häfte 9
Sidor 2011-2027
ISSN 0022-3670
Publiceringsår 2018
Publicerad vid Institutionen för marina vetenskaper
Sidor 2011-2027
Språk en
Länkar https://doi.org/10.1175/JPO-D-17-01...
Ämnesord Antarctica; Atmosphere-ocean interaction; Instability; Potential vorticity; Mixed layer; Oceanic mixed layer
Ämneskategorier Oceanografi

Sammanfattning

Enhanced vertical velocities associated with submesoscale motions may rapidly modify mixed layer depths and increase exchange between the mixed layer and the ocean interior. These dynamics are of particular importance in the Southern Ocean, where the ventilation of many density classes occurs. Here we present results from an observational field program in southern Drake Passage, a region preconditioned for submesoscale instability owing to its strong mesoscale eddy field, persistent fronts, strong down-front winds, and weak vertical stratification. Two gliders sampled from December 2014 through March 2015 upstream and downstream of the Shackleton Fracture Zone (SFZ). The acquired time series of mixed layer depths and buoyancy gradients enabled calculations of potential vorticity and classifications of submesoscale instabilities. The regions flanking the SFZ displayed remarkably different characteristics despite similar surface forcing. Mixed layer depths were nearly twice as deep, and horizontal buoyancy gradients were larger downstream of the SFZ. Upstream of the SFZ, submesoscale variability was confined to the edges of topographically steered fronts, whereas downstream these motions were more broadly distributed. Comparisons to a one-dimensional (1D) mixing model demonstrate the role of submesoscale instabilities in generating mixed layer variance. Numerical output from a submesoscale-resolving simulation indicates that submesoscale instabilities are crucial for correctly reproducing upper-ocean stratification. These results show that bathymetry can play a key role in generating dynamically distinct submesoscale characteristics over short spatial scales and that submesoscale motions can be locally active during summer months.

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