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Regional circulation and its impact on upper ocean variability south of Tasmania

journal contribution
posted on 2023-05-17, 10:41 authored by Laura Herraiz-BorregueroLaura Herraiz-Borreguero, Stephen Rintoul
Ocean colour images of the Subantarctic Zone (SAZ) south of Tasmania show a higher biomass in the east than in the west. To identify the main features of the regional circulation and the physical drivers of the east/west contrast, we used World Ocean Circulation Experiment hydrographic sections SR3 and P11S (west and east of Tasmania, respectively), Argo float profiles and trajectories, and high resolution climatology. The East Australian Current and the Tasman Outflow are the mechanisms driving the variability in the eastern Subantarctic Zone. This region has a weak flow and an enhanced input of subtropical waters through eddies, interleaving and a subsurface salinity maximum intruding from the north to south. In the western Subantarctic Zone, the regional circulation is dominated by a northwestward circulation and a deep reaching anticyclonic recirculation. The South Tasman Rise acts as a barrier, inhibiting exchange between waters southeast and southwest of Tasmania. The regional circulation and mixing processes result in the strong contrast in water properties between the eastern and western Subantarctic Zone: cooler and fresher in the west and warmer and saltier in the east. The Subantarctic Mode Water (SAMW) pycnostad is more prominent in the west, with a local variety of SAMW associated with the anticyclonic recirculation west of the South Tasman Rise. Antarctic Intermediate Water (AAIW) formed in the southeastern Pacific and southwestern Atlantic Oceans meet in the SAZ south of Tasmania. Cool, fresh, and well-ventilated AAIW is found in the west and southeast SAZ. Relatively warm, salty and low oxygen AAIW enters the SAZ from the Tasman Sea, after having traversed the Pacific Ocean subtropical gyre. Enhanced input of subtropical water high in micronutrients (such as iron) in the east likely supports the higher surface biomass observed there. The physical processes responsible for maintaining the east/west contrast south of Tasmania (e.g. regional circulation, eddies and intrusions) are likely to drive variability in physical and biogeochemical properties of SAMW, AAIW, and the Subantarctic Zone elsewhere in the Southern Ocean.

History

Publication title

Deep-Sea Research. Part 2: Topical Studies in Oceanography

Volume

58

Issue

21-22

Pagination

2071-2081

ISSN

0967-0645

Department/School

Institute for Marine and Antarctic Studies

Publisher

Pergamon-Elsevier Science Ltd

Place of publication

The Boulevard, Langford Lane, Kidlington, Oxford, England, Ox5 1Gb

Rights statement

The definitive version is available at http://www.sciencedirect.com

Repository Status

  • Restricted

Socio-economic Objectives

Antarctic and Southern Ocean oceanic processes

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