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

Regional circulation and its impact on upper ocean variability south of Tasmania
Regional circulation and its impact on upper ocean variability south of Tasmania
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.
Subantarctic Mode Water variability, Antarctic Intermediate Water, Subantarctic Zone, Mesoscale features
0967-0645
2071-2081
Herraiz-Borreguero, Laura
faa962ba-19f8-4cf3-83be-ee4972fdbe9f
Rintoul, Stephen Rich
af574aef-132c-43b5-be4e-a9d12da1602d
Herraiz-Borreguero, Laura
faa962ba-19f8-4cf3-83be-ee4972fdbe9f
Rintoul, Stephen Rich
af574aef-132c-43b5-be4e-a9d12da1602d

Herraiz-Borreguero, Laura and Rintoul, Stephen Rich (2011) Regional circulation and its impact on upper ocean variability south of Tasmania. Deep Sea Research Part II: Topical Studies in Oceanography, 58 (21-22), 2071-2081. (doi:10.1016/j.dsr2.2011.05.022).

Record type: Article

Abstract

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.

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More information

Published date: November 2011
Keywords: Subantarctic Mode Water variability, Antarctic Intermediate Water, Subantarctic Zone, Mesoscale features
Organisations: Physical Oceanography

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Local EPrints ID: 398668
URI: http://eprints.soton.ac.uk/id/eprint/398668
ISSN: 0967-0645
PURE UUID: e83ff22c-f557-45f8-a935-fe2c57d2fdd5

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Date deposited: 28 Jul 2016 16:01
Last modified: 15 Mar 2024 01:38

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Contributors

Author: Laura Herraiz-Borreguero
Author: Stephen Rich Rintoul

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