New Zealand Journal of Marine and Freshwater Research abstracts
Some effects of river discharges and currents on phytoplankton in the
sea off Otago, New Zealand
Graeme J. Haywood
Department of Zoology
University of Otago
P.O. Box 56
Dunedin, New Zealand
email: graemehaywood@clear.net.nz
Abstract Major rivers on the south-eastern coast, South
Island, New Zealand create plumes that are deflected north between the Southland
Current and the coast. Surveys of the continental shelf water mass off the
Otago coast over a 2-year period, May 1996-April 1998, confirmed that when
the Southland Current surfaced it contained less chlorophyll a than
mixed water subject to terrestrial influence, implying that river-borne nutrients
stimulated primary production in the mixed water. The greatest boost occurred
in winter when diatom abundance increased. The band of chlorophyll-rich water
extended through the photic zone and was several kilometres wide suggesting
that riverine influence on marine biomass is substantial. In summer, the
Southland Current often lay beneath oceanic water, with no increase in chlorophyll
a concentration in the overlying water, due possibly to heavy grazing
by zooplankton. In summer 1997-98, seawater temperatures were higher and
phytoplankton biomass lower than in summer 1996-97, consistent with a strong
El Niño event in the Pacific Ocean.
Keywords Clutha; river plume; El Niño
M03001; Online publication date 15 March 2004; Received 6 January 2003;
accepted 9 September 2003
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38:
103-114
0028-8330/04/3801-0103 © The Royal Society of New Zealand 2004
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