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during upwelling off the Biochemical indicators of N utilization by phytoplankton Washington coast
Author(s) -
Dortch Quay,
Postel James R.
Publication year - 1989
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.1989.34.4.0758
Subject(s) - upwelling , phytoplankton , oceanography , photic zone , nitrate , environmental science , benthic zone , hydrography , biomass (ecology) , ammonium , chlorophyll a , nutrient , water column , chlorophyll , transect , biology , ecology , geology , chemistry , botany , organic chemistry
The manner in which N utilization by phytoplankton responds to persistent upwelling was examined along the Washington coast. Biochemical indicators of N deficiency, source of N supporting growth, and relative phototrophic and heterotrophic biomass, as well as time‐courses of 1 5 N and 14 C uptake, nutrient and chlorophyll concentrations, and routine hydrography were measured from 11 to 24 June 1982 from a ship which completed a transect perpendicular to the coast every 1–3 d and a second ship which followed drogues deployed at the upwelling source. From 11 to 12 June a spatial separation was observed between increased nutrients and high chlorophyll. The lag was probably due to the need of phytoplankton to adapt both N and C utilization to higher light. Despite a very N‐depleted euphotic zone, N deficiency was only apparent quite far offshore. Later (15–23 June), extraordinarily high phytoplankton biomass developed nearshore. It was N sufficient, highly productive, and fueled by both nitrate and ammonium. Most was located in a pronounced, metabolically active, subsurface chlorophyll maximum. Although benthic and water‐column regeneration of ammonium and diffusion of nitrate across the steep nutracline are probably important, there was also evidence of sporadic nitrate supply which correlated with slight changes in the wind. Nitrate pumping into an already N‐sufficient, fully shifted‐up phytoplankton population during weak upwelling may result in maximal phytoplankton response to upwelling.