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Physical oceanographic controls on phytoplankton distribution in the Banda Sea and Western Australian region

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Moore, Thomas Surman 2007 , 'Physical oceanographic controls on phytoplankton distribution in the Banda Sea and Western Australian region', PhD thesis, University of Tasmania.

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Abstract

Marine phytoplankton rely on nutrients and light to survive and grow. By controlling
the supply of nutrients and by moving phytoplankton around the upper ocean, ocean
physics play a critical role in influencing the distribution of phytoplankton. The
physical processes that influence phytoplankton distribution act over a wide range of
temporal and spatial scales. Using in-situ, and remotely-sensed measurements, this
thesis investigates the relationship between ocean physics and phytoplankton
distributions in the Banda Sea and off the coast of Western Australia, over a range of
scales including synoptic mesoscale eddies, seasonal monsoons, climatological
features and ENSO impacts.
In the Banda Sea, the distribution of chlorophyll-a is used as an indicator to describe
the biophysical response of the Banda Sea to the seasonal winds of the southeast
monsoon. The in-situ and remotely sensed data support the idea that phytoplankton
respond to upwelling driven by the southeast monsoon (June - September). In-situ
physical data from the BIOP98 cruise suggest an upwelling signal, and analysis of
phytoplankton pigments indicates a community dominated by diatoms to the east and
a more oligotrophic community to the west; further supporting the idea of an
upwelling response. Satellite observations reveal a strong seasonal signal and an east
west gradient in chlorophyll-a, indicating monsoon driven upwelling on the eastern
side of the basin. Remotely sensed observations of chlorophyll-a during the 1997
1998 El Nino suggest that the distribution of chlorophyll-a in the Banda Sea is
modulated by ENSO, most likely through changes to the thermocline depth and wind
regime.
South of the Indonesian Archipelago, the waters off central Western Australia (WA)
are unique in terms of their biological and physical oceanographic character.
Unusually for an eastern boundary current, the Leeuwin flows poleward and
contributes to prevailing downwelling conditions along the WA coast. Significant
spatial and temporal variability in phytoplankton distribution exists and a key regional
feature of the phytoplankton variability is a seasonal peak in chlorophyll-a in the
winter May-July period on the central WA shelf. To test the hypothesis that this
seasonal cycle is related to nutrient inputs, this thesis attempts to address several
potential sources: (1) upwelling from off-shelf; (2) rainfall and associated runoff;
(3) Leeuwin Current transport; ( 4) shall owing and/or mixing of the nutricline; and
(5) benthic supply. Nutrient inputs from Leeuwin Current transport and coastal runoff
appear to be most important, although sparse data prevent a definite conclusion.
Phytoplankton distribution off central WA also displays persistent mesoscale features.
Both satellite and in-situ estimates of surface chlorophyll-a suggest low
phytoplankton concentrations in cyclonic ("upwelling") eddies and high
concentrations in anti-cyclonic ("downwelling") eddies. The anti-cyclonic eddies
entrain regionally high chlorophyll-a shelf waters and then export this material
offshore as· these eddies propagate westward. The formation of these anti-cyclonic
eddies occurs at two preferred zones along the central WA shelf, near 29°S and
between 31° and 33°S, and their formation and movement offshore controls the mixed
layer distribution of phytoplankton in the open ocean off the central WA coast during
the May-October period.

Item Type: Thesis - PhD
Authors/Creators:Moore, Thomas Surman
Keywords: Marine phytoplankton, Ocean currents, Marine phytoplankton, Ocean currents, Chlorophyll
Copyright Holders: The Author
Copyright Information:

Copyright 2007 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:

Available for library use only and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2007. Includes bibliographical references

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