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 μmol kg <sup> −1 </sup> d <sup> −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‐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 > 1.5 to < 0.5 μg L <sup> −1 </sup> , with 75–85% of total chlorophyll a in the < 5μm size fraction. Particulate matter composition, with mean ratios of particulate organic carbon:chlorophyll <em> a </em> > 200 and particulate organic nitrogerr.chlorophyll <em> a </em> > 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±5 mmol C m <sup> −2 </sup> d <sup> −1 </sup> ( <em> n </em> = 3) while dark respiration rates, estimated from dark bottle incubations, were approximately ‐ 40±3 mmol C m <sup> −2 </sup> d <sup> −1 </sup> . Net community production rates (6±6 mmol C m <sup> −2 </sup> d <sup> −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 (−51±8 mmol C m <sup> −2 </sup> d <sup> −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 language | American English |
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Journal | Journal of Geophysical Research |
Volume | 105 |
DOIs | |
State | Published - Mar 15 2000 |
Disciplines
- Life Sciences
- Marine Biology