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Antarctic Circumpolar Current transport through Drake Passage: What can we learn from comparing high-resolution model results to observations?
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  • Xiaobiao Xu,
  • Eric P. Chassignet,
  • Yvonne Firing,
  • Kathleen Donohue,
  • Eric Chassignet,
  • Yvonne Firing
Xiaobiao Xu
Florida State University, Florida State University, Florida State University

Corresponding Author:[email protected]

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Eric P. Chassignet
Florida State University
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Yvonne Firing
National Oceanography Centre
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Kathleen Donohue
University of Rhode Island, University of Rhode Island, University of Rhode Island
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Eric Chassignet
Florida State University, Florida State University
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Yvonne Firing
National Oceanography Centre, National Oceanography Centre
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Abstract

Uncertainty exists in the time-mean total transport of the Antarctic Circumpolar Current (ACC), the world’s strongest ocean current. The two most recent observational programs in Drake Passage, DRAKE and cDrake, yielded transports of 141 and 173.3 Sv, respectively. In this paper, we use a realistic 1/12 global ocean simulation to interpret these observational estimates and reconcile their differences. We first show that the modeled ACC transport in the upper 1000 m is in excellent agreement with repeat shipboard acoustic Doppler current profiler (SADCP) transects and that the exponentially decaying transport profile in the model is consistent with the profile derived from repeat hydrographic data. By further comparing the model results to the cDrake and DRAKE observations, we argue that the modeled 157.3 Sv transport, i.e. approximately the average of the cDrake and DRAKE estimates, is actually representative of the time-mean ACC transport through the Drake Passage. The cDrake experiment overestimated the barotropic contribution in part because the array undersampled the deep recirculation southwest of the Shackleton Fracture Zone, whereas the surface geostrophic currents used in the DRAKE estimate yielded a weaker near-surface transport than implied by the SADCP data. We also find that the modeled baroclinic and barotropic transports are not correlated, thus monitoring either baroclinic or barotropic transport alone may be insufficient to assess the temporal variability of the total ACC transport.
Jul 2020Published in Journal of Geophysical Research: Oceans volume 125 issue 7. 10.1029/2020JC016365