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Prochlorococcus contributes to new production in the Sargasso Sea deep chlorophyll maximum
Author(s) -
Casey John R.,
Lomas Michael W.,
Mandecki Joanna,
Walker Donald E.
Publication year - 2007
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2006gl028725
Subject(s) - prochlorococcus , biogeochemical cycle , biogeochemistry , sargasso sea , population , biology , oceanography , ecophysiology , ecology , synechococcus , botany , cyanobacteria , photosynthesis , genetics , bacteria , geology , demography , sociology
Prochlorococcus is ubiquitous in tropical oceans, but its biogeochemical role is not well constrained. For example, cultured Prochlorococcus clones do not grow on NO 3 − , but these cultured clones may only represent 10–15% of the natural population variance resulting in a biased biogeochemical role. We report NO 3 − , NO 2 − , NH 4 + and urea uptake rates for flow‐cytometrically sorted Sargasso Sea Prochlorococcus populations. Reduced nitrogen substrates accounted for most, 90–95%, of the measured nitrogen uptake, but these populations also directly assimilate a significant fraction of NO 3 − , 5–10%; a finding in stark contrast to conclusions drawn from culture studies. The observed population‐specific NO 3 − uptake rates compare favorably with both net Prochlorococcus population growth rates and diapycnal NO 3 − fluxes. We hypothesize that while reduced nitrogen supports overall high growth rates, balancing high grazing mortality, the net seasonal Prochlorococcus population growth is supported by NO 3 − assimilation and that Prochlorococcus contributes to new production in the oligotrophic ocean.