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Mesoscale variability in nitrogen uptake rates and the f ‐ratio during a coastal phytoplankton bloom
Author(s) -
Vézina Main F.
Publication year - 1994
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.1994.39.4.0854
Subject(s) - photic zone , phytoplankton , mesoscale meteorology , bloom , biogeochemical cycle , sink (geography) , environmental science , stratification (seeds) , new production , nitrate , oceanography , algal bloom , spatial variability , biological pump , atmospheric sciences , nitrogen , flux (metallurgy) , carbon flux , nutrient , ecology , ecosystem , environmental chemistry , chemistry , geology , biology , botany , mathematics , seed dormancy , germination , cartography , statistics , organic chemistry , dormancy , geography
The proportion of the biological nitrogen demand met by nitrate ( f ‐ratio) is a strong candidate for a biogeochemical parameter to relate primary production to the oceanic organic carbon flux, the latter being a potential global carbon sink. There is a controversy over whether f can be related to spatial and temporal variations in NO 3 − concentration for the purposes of estimating carbon fluxes. I report measurements of NO 3 − and NH 4 + uptake rates and of the f ‐ratio taken during a coastal phytoplankton bloom and address the problem of mesoscale f ‐ratio variability. The results reveal two distinct behaviors of the f ‐ratio depending on light level: at the 50% level, f is nonlinearly related to ambient NO 3 − concentration; at the 10 and 1% light levels, f is not related to NO 3 concentration but is instead related to variations in the stratification in the NO 3 − profile. There seems to be a “two‐track” biological system in the euphotic zone: a shallow food web that quickly incorporates new NO 3 − supplies and a deep food web that responds more slowly to a varying supply. New production tends to be higher near the surface than deeper, which is opposite the vertical structure generally proposed for NO 3 − ‐limited systems. The implication is that NO 3 − ‐based algorithms to predict f may not work over the full three‐dimensional NO 3 − field.