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Water mass changes in the North and South Pacific Oceans between the 1960s and 1985-94

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Wong, APS (1999) Water mass changes in the North and South Pacific Oceans between the 1960s and 1985-94. PhD thesis, University of Tasmania.

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Abstract

Comparisons have been made along five modern hydrographic sections against
historical hydro graphic data to investigate water mass changes in the North and
South Pacific oceans. The five modern hydrographic sections were sampled in
the decade 1985-94, while the historical data were mostly from the late 1960s.
Below the seasonal mixed layer, statistically significant temporal differences in
temperature and salinity have been detected in the water masses that occur in
the top 2000 dbar of the water column. These differences in water mass properties
are assumed to result from sea surface changes at the formation regions.
Of all the water mass changes, the most spatially coherent ones come from
the shallow salinity maxima of North Pacific Subtropical Water (NPSTW) and
South Pacific Subtropical Water (SPSTW), and the intermediate salinity minima
of North Pacific Intermediate Water (NPIW) and Antarctic Intermediate Water
(AAIW). The two shallow salinity maxima, NPSTW and SPSTW, have shown
signs of salinity increase, while the two intermediate salinity minima, NPIW and
AAIW, have become fresher and, except along l 7°S, have become warmer. Since
NPSTW and SPSTW originate under the high evaporative cells of the subtropical
North and South Pacific, and NPIW and AAIW acquire their properties near
the polar gyres, these changes in the ocean interior imply an increase in net
evaporation over the mid-latitudes, and an increase in net precipitation over the
high-latitudes in both hemispheres. Together these results imply a strengthening
of the hydrological cycle over the North and South Pacific oceans.
Outputs from a coupled climate model show that under increasing atmospheric
C02 , the model ocean responds with a warming of the water column in the top
300 dbar. Superimposed on this background warming trend is a decrease in salinity
in the two intermediate salinity minima of the Pacific (NPIW and AAIW), and
corresponds to near-surface freshening where their respective isopycnals outcrop.
Hence the freshening signature that has been detected in NPIW and AAIW from
observational data is qualitatively consistent with this climate model's response
to increasing C02 • However, natural variability cannot be discarded as a possible
cause for the observed changes.
The steric sea level change for the area in the Pacific between 60°N and 31.5°S
over the roughly 20-year study period is estimated to be a rise of 0.85 mm/yr.
This is larger than that estimated by numerical models, and so demonstrates
the usefulness of observational studies such as this in testing the effectiveness of
numerical models in simulating the natural variability of the climate system.

Item Type: Thesis (PhD)
Keywords: Water masses, Water masses, Oceanography, Oceanography, Ocean-atmosphere interaction, Ocean-atmosphere interaction
Copyright Holders: The Author
Copyright Information:

Copyright 1999 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, 1999. Includes bibliographical references

Date Deposited: 04 Feb 2015 23:26
Last Modified: 11 Mar 2016 05:55
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