Photosynthetic characteristics and estimated growth rates indicate grazing is the proximate control of primary production in the equatorial Pacific
作者:
John J. Cullen,
Marlon R. Lewis,
Curtiss O. Davis,
Richard T. Barber,
期刊:
Journal of Geophysical Research: Oceans
(WILEY Available online 1992)
卷期:
Volume 97,
issue C1
页码: 639-654
ISSN:0148-0227
年代: 1992
DOI:10.1029/91JC01320
数据来源: WILEY
摘要:
Macronutrients persist in the surface layer of the equatorial Pacific Ocean because the production of phytoplankton is limited; the nature of this limitation has yet to be resolved. Measurements of photosynthesis as a function of irradiance (P‐I) provide information on the control of primary productivity, a question of great biogeochemical importance. Accordingly, P‐I was measured in the equatorial Pacific along 150°W, during February‐March 1988. Diel variability of P‐I showed a pattern consistent with nocturnal vertical mixing in the upper 20 m followed by diurnal stratification, causing photoinhibition near the surface at midday. Otherwise, the distribution of photosynthetic parameters with depth and the stability of P‐I during simulated in situ incubations over 2 days demonstrated that photoadaptation was nearly complete at the time of sampling: photoadaptation had not been effectively countered by upwelling or vertical mixing. Measurements of P‐I and chlorophyll during manipulations of trace elements showed that simple precautions to minimize contamination were sufficient to obtain valid rate measurements and that the specific growth rates of phytoplankton were fairly high in situ, a minimum of 0.6 d−1. Diel variability of beam attenuation also indicated high specific growth rates of phytoplankton and a strong coupling of production with grazing. It appears that grazing is the proximate control on the standing crop of phytoplankton. Nonetheless, the supply of a trace nutrient such as iron might ultimately regulate productivity by influencing species composition and food
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