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Seasonal variability in the phytoplankton community of the North Pacific Subtropical Gyre
Author(s) -
Winn Christopher D.,
Campbell Lisa,
Christian James R.,
Letelier Ricardo M.,
Hebel Dale V.,
Dore John E.,
Fujieki Lance,
Karl David M.
Publication year - 1995
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/95gb02149
Subject(s) - photic zone , ocean gyre , phytoplankton , water column , oceanography , chlorophyll a , environmental science , biomass (ecology) , deep chlorophyll maximum , mixed layer , chlorophyll , chlorophyll fluorescence , subtropics , biology , geology , botany , ecology , nutrient
Time series measurements of in situ fluorescence, extracted particulate chlorophyll a , primary productivity, extracted adenosine 5′‐triphosphate, and fluorescence per cell, as measured by flow cytometry, demonstrate seasonal cycles in fluorescence and chlorophyll concentrations in the North Pacific Subtropical Gyre (22° 45′N, 158° 00′W). Two opposing cycles are evident. In the upper euphotic zone (0–50 m), chlorophyll a concentrations increase in winter, with a maximum in December, and decrease each summer, with a minimum in June or July. In contrast, chlorophyll a concentrations in the lower euphotic zone (100–175 m) increase in spring, with a maximum in May, and decline in fall, with a minimum in October or November. The winter increase in chlorophyll a concentration in the upper 50 m of the water column appears to be a consequence of photoadaptation in response to decreased average mixed‐layer light intensity rather than a change in phytoplankton biomass. In the lower euphotic zone, however, the seasonal cycle in pigment concentration does reflect a change in the rate of primary production and in phytoplankton biomass as a consequence of increased light intensity in summer. These observations have important implications for phytoplankton dynamics in the subtropical oceans and for remote sensing of phytoplankton biomass.