New Zealand Journal of Marine and Freshwater Research abstracts

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Size-fractionated phytoplankton standing stocks and primary production during austral winter and spring 1993 in the Subtropical Convergence region near New Zealand

J. M. BRADFORD-GRIEVE¹
F. H. CHANG¹
M. GALL²
S. PICKMERE³
F. RICHARDS²

1National Institute of Water & Atmospheric
Research Ltd (NIWA)
P.O. Box 14 901, Kilbirnie
Wellington, New Zealand

2NIWA
P. O. Box 8602, Riccarton
Christchurch, New Zealand

3NIWA
P. O. Box 11 115, Hillcrest
Hamilton, New Zealand

Abstract  Size-fractionated phytoplankton standing stocks and potential primary production (PPP) off the west and east coasts of South Island, New Zealand, were evaluated in austral winter and spring 1993. These are the first size-fractionated primary production data to be reported from the southern Subtropical Convergence (STC) and in oceanic New Zealand waters. Picophytoplankton (< 2 um) formed > 30% of integrated chlorophyll a and daily PPP in most water types and seasons, except when the 20-200 um size class dominated in west coast waters in spring and in the STC in winter and spring. In subtropical and STC waters, PPP was 30% higher than at similar latitudes in the North Atlantic Ocean. Interpretation of whether or not there was accumulation of chlorophyll a in the various water types and seasons depends on microzooplankton grazing, because mesozooplankton grazing and the proportion of chlorophyllous particulate matter sinking out of the upper water column was low. In the STC in spring, phytoplankton growth was slowing down (potential doubling times were at most 1.01 per day at 10 m and PPP per unit biomass was lower than in water masses to the north and south), probably because of decreasing concentrations of dissolved reactive silica. A sedimentation event of diatoms is postulated to have occurred in the STC soon after our spring sampling dates. The balance between algal growth and loss factors in the south-west Pacific depends on the unique combination of physical and chemical environmental conditions experienced there. The implications of the distribution of phytoplankton biomass and primary production by size-fraction for carbon export is discussed.

Keywords  chlorophyll a; potential primary production; size-fractionated; south-west Pacific Ocean; Subtropical Convergence; winter; spring; dissolved inorganic nutrients

New Zealand Journal of Marine and Freshwater Research, 1997, Vol. 31: 201-224

0028-8330/97/3102-0201 $7.00/0 (c) The Royal Society of New Zealand 1997

PDF file of entire paper: medium quality (1770K); (scanned from paper original: notes about this process)

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