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Temporal and vertical variability in photosynthesis in the North Pacific Subtropical Gyre
Author(s) -
Corno Guido,
Letelier Ricardo M.,
Abbott Mark R.,
Karl David M.
Publication year - 2008
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2008.53.4.1252
Subject(s) - ocean gyre , photosynthesis , chlorophyll a , subtropics , chlorophyll fluorescence , mixed layer , chlorophyll , deep chlorophyll maximum , photic zone , nutrient , photosynthetic capacity , surface layer , biology , photosystem ii , environmental science , oceanography , botany , atmospheric sciences , phytoplankton , chemistry , layer (electronics) , geology , ecology , organic chemistry
In situ fast‐repetition‐rate fluorometric (FRRF) surveys were conducted in the North Pacific Subtropical Gyre (NPSG) at Station ALOHA (Sta. ALOHA, 22°459N, 158°009W), from September 2002 to December 2004, to assess temporal and vertical photosynthetic variability in relation to environmental conditions. The nighttime potential photosynthetic efficiency of the photoautotrophic microbial assemblage (given as the ratio of variable to maximal fluorescence, F V :F M ) was low in the mixed layer and increased with depth. High F V :F M values were observed at and below the deep chlorophyll maximum layer (DCML); some values approached the theoretical maximum for prokaryotes grown under nutrient‐replete conditions in the laboratory (0.60). In contrast, the absorption cross section of photosystem II ( ςPSII ) was high at the surface and decreased with depth; minima (1,000 A° 2 quanta ‐1 ) occurred around the DCML. These vertical patterns suggest photosynthetic stress conditions in surface photoautotrophic populations. No significant seasonal cycles were found for F V :F M , but surface ςPSII values peaked in winter and decreased during summer, suggesting that seasonal variations in light availability may influence the observed ςPSII variability. A significant correlation was found among surface F V :F M , ςPSII , and the distance from the mixed‐layer depth (MLD) to the top of the nutricline. Neither nutrient nor light variations were significantly related to F V :F M and ςPSII in the DCML. Within this layer, F V :F M variability was positively and negatively related to concentrations of chlorophyll b and zeaxanthin, respectively. Our results suggest that, at Sta. ALOHA, surface photosynthesis takes place under chronic nutrient limitation, while higher photosynthetic efficiency in the lower euphotic zone appears to be sensitive to community‐structure changes.