Plankton Community Composition, Production, and Respiration in Relation to Dissolved Inorganic Carbon on the West Florida Shelf, April 1996

Gary L. Hitchcock, Gabriel A. Vargo, Mary-Lynn L. Dickson

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Abstract

<p> In April 1996 the Florida Shelf Lagrangian Experiment examined dissolved inorganic carbon (DIC) dynamics on the West Florida Shelf. DIC concentrations increased over 2 weeks at an average rate of 1 &mu;mol kg <sup> &minus;1 </sup> d <sup> &minus;1 </sup> in a patch of the intentionally released tracers sulfur hexafluoride (SF <sub> 6 </sub> ) and helium 3 ( <sup> 3 </sup> He). Approximately 20% of the increase was due to air&hyphen;sea exchange with the remaining 80% attributed to plankton respiration [ <em> Wanninkhof et al. </em> , 1997]. Here we present particulate matter concentrations, phytoplankton production, and community respiration rates from the tracer patch that suggest that heterotrophs dominated the community after the termination of a spring bloom. During the experiment, chlorophyll a and phaeopigment concentrations declined from &gt; 1.5 to &lt; 0.5 &mu;g L <sup> &minus;1 </sup> , with 75&ndash;85% of total chlorophyll a in the &lt; 5&mu;m size fraction. Particulate matter composition, with mean ratios of particulate organic carbon:chlorophyll <em> a </em> &gt; 200 and particulate organic nitrogerr.chlorophyll <em> a </em> &gt; 100, suggests that phytoplankton were a minor component of the plankton biomass. Rates of daily gross primary production estimated by the H <sub> 2 </sub> <sup> 18 </sup> O method averaged 69&plusmn;5 mmol C m <sup> &minus;2 </sup> d <sup> &minus;1 </sup> ( <em> n </em> = 3) while dark respiration rates, estimated from dark bottle incubations, were approximately &hyphen; 40&plusmn;3 mmol C m <sup> &minus;2 </sup> d <sup> &minus;1 </sup> . Net community production rates (6&plusmn;6 mmol C m <sup> &minus;2 </sup> d <sup> &minus;1 </sup> ) were much lower than respiration rates. Thus respiration rates nearly balanced phytoplankton production. Light respiration rates were estimated from gross production minus net community production (&minus;51&plusmn;8 mmol C m <sup> &minus;2 </sup> d <sup> &minus;1 </sup> ) and exceeded dark respiration. Plankton community respiration rates, corrected for autotrophic carbon fixation, were more than sufficient to account for the observed increase of DIC within the tracer patch.</p>
Original languageAmerican English
JournalJournal of Geophysical Research
Volume105
DOIs
StatePublished - Mar 15 2000

Disciplines

  • Life Sciences
  • Marine Biology

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