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Antarctic Intermediate Water Circulation and Variability in a Coupled Climate Model

Antarctic Intermediate Water Circulation and Variability in a Coupled Climate Model The variability of Antarctic Intermediate Water (AAIW) in a long-term natural integration of a coupled climate model is examined. The mean state of the climate model includes a realistic representation of AAIW, which appears centered on the σσ θθ == 27.2 kg m −−3 density surface (hereinafter σσ 27.2 ) both in observations and the model. An assessment of ventilation rates on the σσ 27.2 surface suggests that this particular climate model forms AAIW in a mostly circumpolar fashion, with a significant contribution from Antarctic Surface Water. This motivates the assessment of oceanic variability along this core AAIW isopycnal surface. Complex empirical orthogonal function analyses decompose the variability into three dominant modes showing circumpolar patterns of zonal wavenumber-1, -2, and -3 on the σσ 27.2 density surface. The modes contain eastward-propagating signals at interannual to centennial time scales. Mechanisms forcing this variability are investigated using heat and salt budget analyses at the wintertime outcrop of the σσ 27.2 surface. Such an approach ignores the mechanism of AAIW variability sourced by Subantarctic Mode Water variations, which has been examined previously and is, for the most part, beyond the present study. Variability in meltwater rates and atmospheric heat and freshwater fluxes are found to dominate the intermediate water variability at the outcrop region. In contrast, northward Ekman transport of heat and salt plays a significant but localized role in AAIW temperature––salinity variability. There is also an important contribution from the Antarctic Circumpolar Current to the variability at the outcrop region via zonal transport of heat and salt. While the magnitude of AAIW natural variability can be large near the outcrop of the salinity minimum layer, recent observations of cooling and freshening at depth are suggested to be beyond that of the unperturbed system. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Physical Oceanography American Meteorological Society

Antarctic Intermediate Water Circulation and Variability in a Coupled Climate Model

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References (60)

Publisher
American Meteorological Society
Copyright
Copyright © 2002 American Meteorological Society
ISSN
1520-0485
DOI
10.1175/1520-0485(2004)034<2160:AIWCAV>2.0.CO;2
Publisher site
See Article on Publisher Site

Abstract

The variability of Antarctic Intermediate Water (AAIW) in a long-term natural integration of a coupled climate model is examined. The mean state of the climate model includes a realistic representation of AAIW, which appears centered on the σσ θθ == 27.2 kg m −−3 density surface (hereinafter σσ 27.2 ) both in observations and the model. An assessment of ventilation rates on the σσ 27.2 surface suggests that this particular climate model forms AAIW in a mostly circumpolar fashion, with a significant contribution from Antarctic Surface Water. This motivates the assessment of oceanic variability along this core AAIW isopycnal surface. Complex empirical orthogonal function analyses decompose the variability into three dominant modes showing circumpolar patterns of zonal wavenumber-1, -2, and -3 on the σσ 27.2 density surface. The modes contain eastward-propagating signals at interannual to centennial time scales. Mechanisms forcing this variability are investigated using heat and salt budget analyses at the wintertime outcrop of the σσ 27.2 surface. Such an approach ignores the mechanism of AAIW variability sourced by Subantarctic Mode Water variations, which has been examined previously and is, for the most part, beyond the present study. Variability in meltwater rates and atmospheric heat and freshwater fluxes are found to dominate the intermediate water variability at the outcrop region. In contrast, northward Ekman transport of heat and salt plays a significant but localized role in AAIW temperature––salinity variability. There is also an important contribution from the Antarctic Circumpolar Current to the variability at the outcrop region via zonal transport of heat and salt. While the magnitude of AAIW natural variability can be large near the outcrop of the salinity minimum layer, recent observations of cooling and freshening at depth are suggested to be beyond that of the unperturbed system.

Journal

Journal of Physical Oceanography – American Meteorological Society

Published: Oct 22, 2002

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