Title

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

Document Type

Article

Publication Date

3-15-2000

Digital Object Identifier (DOI)

dx.doi.org/10.1029/1998JC000293

Abstract

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(-1) d(-1) in a patch of the intentionally released tracers 3 (He-3). Approximately 20% of the increase was due to sulfur hexafluoride (SF6) and helium air-sea exchange with the remaining 80% attributed to plankton respiration [Wanninkhof et al., 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 mu g L-1, with 75-85% of total chlorophyll a in the < 5 mu m size fraction. Particulate matter composition, with mean ratios of particulate organic carbon:chlorophyll a > 200 and particulate organic nitrogen:chlorophyll a > 100, suggests that phytoplankton were a minor component of the plankton biomass. Rates of daily gross primary production estimated by the (H2O)-O-18 method averaged 69 +/- 5 mmol C m(-2) d(-1) (n = 3) while dark respiration rates, estimated from dark bottle incubations, were approximately, proximately - 40 +/- 3 mmol C m(-2) d(-1). Net community production rates (6 +/- 6 mmol C m(-2) d(-1)) 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(-2) d(-1)) 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.

Citation / Publisher Attribution

Journal of Geophysical Research - Oceans, v. 105, no. C3, p. 6579-6589.