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The circulation of the Southern Ocean and the adjacent ocean basins determined by inverse methods

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Sloyan, Bernadette M (1997) The circulation of the Southern Ocean and the adjacent ocean basins determined by inverse methods. PhD thesis, University of Tasmania.

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Abstract

Inverse methods which conserve mass, heat and salt are applied to high
resolution hydrographic data in the Southern Ocean and adjacent ocean basins.
Dianeutral fluxes are incorporated into the inverse model by including a
separate dianeutral flux unknown for each property. Further model development
includes the addition of air-sea forcing (wind stress, air-sea heat flux and
freshwater flux). The inverse model is then used to test different circulation
hypotheses, including the estimated size of the heat loss over the Weddell Sea
and the strength of the Malvinas Current.
The accuracy of inverse methods are tested using the Fine Resolution
Antarctic Model. This shows that the lateral and dianeutral fluxes are well
determined by inverse methods and that the "true" effective diffusion across
neutral surfaces in the inverse model can be much larger, and in some cases of
opposite sign, to the explicit diffusion in the numerical model when layers
outcrop or undercrop. The latter results has implications for how diffusivity
estimates obtained from inverse models should be interpreted. In the initial inverse model the Antarctic Circumpolar Current transport
varies from 133±2x106m3s-1 at Drake Passage to 148±4.5 south of Australia.,
There is a -15±8x106m3s-1 southward transport through the Indian Ocean and
a similar sized northward transport into the Pacific Ocean at 32°S. The addition
of air-sea fluxes results in a 5x106m3s-1 decrease in the southward, eastward
and northward transport in the Indian ocean, south of Australia and across
32°S in the Pacific. The imposition of a large northward Malvinas Current
(60x 106m3 s-1 ), adjacent to the South American coast maintains a similar
eastward transport at Drake Passage, south of Africa and south of Australia.
The southward and northward transport through the Indian Ocean and across
32°S in the Pacific is decreased further to -8.3±5.lx106m3s-1 and
8.8±14.2x 106m3 s-1 , respectively.
By including air-sea forcing and interior dianeutral fluxes, the water mass
production and modification that occurs in the regions defined by the
hydrographic sections, can be quantified. In the Indian Ocean sector, the
1
Agulhas Current transports warm Indonesian throughflow thermocline water
into the Southern Ocean. The thermocline water (10x106m3 s-1 ) is transferred
to SAMW by air-sea (cooling and evaporation) processes and interior dianeutral
fluxes. As the SAMW moves eastward with the ACC, Antarctic surfaces water
(16x106m3 s-1 ) is converted to SAMW across the Polar Front Zone resulting in
progressive cooling and freshening of SAMW. 10x106m3s-1 of the locally
produced SAMW in the Southern Ocean Indian exits the region northward
across 32°S ventilating the subtropical gyre, while the remaining 15x106m3s-1
moves eastward with the ACC into the Southern Ocean Pacific sector. In the
Southern Ocean Pacific sector 11x106m3 s-1 of SAMW is transferred into
thermocline water by air-sea fluxes and exported northward in the Pacific
Ocean across 32°S. This circulation path of thermocline water between the
Indian and Pacific Oceans describes the Indonesian throughflow as a
circum-Australia feature.
North Atlantic Deep Water (20x106m3 s-1 ) moves southward across 15°S
in the Atlantic and is the major source of Lower Circumpolar Deep Water.
Lower Circumpolar Deep Water salinity and oxygen maxima are eroded during
the eastward progression of the Antarctic Circumpolar Current. Strong deep
overturning circulation are found in the Indian (26x106m3 s-1 ) and Pacific
(30x106m3s-1 ) Oceans. The northward transport of Antarctic Bottom Water
and Circumpolar Deep Water into the Indian and Pacific Oceans is essentially
balanced by the return of slightly less dense, low oxygen Indian and Pacific
Deep water. The southward inflow of Indian and Pacific deep water to the
Southern Ocean results in the formation of Upper Circumpolar Deep Water.
The eastward flow of Antarctic Bottom Water, by the Antarctic
Circumpolar Current, into the Southern Ocean Pacific sector is not sufficient to
balance the northward export of Antarctic Bottom Water into the Pacific Ocean
across 32°S. This implies there are sources of Antarctic Bottom Water within
the Southern Ocean Pacific sector.
The circulation results in a meridional heat flux at 30°S of -0.51 PW. The
southward heat flux is dominated by a large southward heat flux in the Indian
Ocean (-0.94±0.18 PW), a northward heat flux in the Atlantic (0.34±0.13 PW)
and a small northward heat flux in the Pacific (0.09±0.26 PW).

Item Type: Thesis (PhD)
Keywords: Ocean circulation
Copyright Holders: The Author
Copyright Information:

Copyright 1997 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1998. Includes bibliographical references

Date Deposited: 03 Feb 2015 03:22
Last Modified: 11 Mar 2016 05:55
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