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All exchanges between the open ocean and the Antarctic continental shelf must cross the Antarctic Slope Current (ASC). Previous studies indicate that these exchanges are strongly influenced by mesoscale and tidal variability, yet the mechanisms responsible for setting the ASC’s transport and structure have received relatively little attention. In this study the roles of winds, eddies, and tides in accelerating the ASC are investigated using a global ocean–sea ice simulation with very high resolution (1/48° grid spacing). It is found that the circulation along the continental slope is accelerated both by surface stresses, ultimately sourced from the easterly winds, and by mesoscale eddy vorticity fluxes. At the continental shelf break, the ASC exhibits a narrow (~30–50 km), swift (>0.2 m s−1) jet, consistent with in situ observations. In this jet the surface stress is substantially reduced, and may even vanish or be directed eastward, because the ocean surface speed matches or exceeds that of the sea ice. The shelfbreak jet is shown to be accelerated by tidal momentum advection, consistent with the phenomenon of tidal rectification. Consequently, the shoreward Ekman transport vanishes and thus the mean overturning circulation that steepens the Antarctic Slope Front (ASF) is primarily due to tidal acceleration. These findings imply that the circulation and mean overturning of the ASC are not only determined by near-Antarctic winds, but also depend crucially on sea ice cover, regionally-dependent mesoscale eddy activity over the continental slope, and the amplitude of tidal flows across the continental shelf break.
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Shelfbreak Jet Structure and Variability off New Jersey Using Ship of Opportunity Data From the CMV Oleander
Abstract Repeat measurements of velocity and temperature profiles from the Container Motor Vessel (CMV) Oleander provide an unprecedented look into the variability on the New Jersey Shelf and upper continental slope. Here 1362 acoustic Doppler current profiler (ADCP) velocity sections collected between 1994 and 2018 are analyzed in both Eulerian and stream coordinate reference frames to characterize the mean structure of the Shelfbreak Jet, as well as its seasonal to decadal variability. The Eulerian mean Shelfbreak Jet has a maximum jet velocity of 0.12 m s−1. The maximum jet velocity peaks in April and May and reaches its minimum in July and August. In a stream coordinate framework, the jet is only identified in 61% of transects, and the mean stream coordinate Shelfbreak Jet has a maximum jet velocity of 0.32 m s−1. Evidence is found that Warm Core Rings, originating from the Gulf Stream arriving in the Slope Sea adjacent to the New Jersey Shelf, shift the Shelfbreak Jet onshore of its mean position or entirely shutdown the Shelfbreak Jet's flow. At interannual timescales, variability in the Shelfbreak Jet velocity is correlated with the temperature on the New Jersey Shelf 2 months later. When considered in a stream coordinate framework, Shelfbreak Jet have decreased over the time period considered in the study.
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- Award ID(s):
- 1924041
- PAR ID:
- 10444987
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 125
- Issue:
- 9
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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