Plankton community respiration in Bransfield Strait (Antarctic Ocean) during austral spring

Community respiration (R) was determined in Bransfield Straitfrom oxygen changes in water samples incubated in borosilicatebottles maintained at in situ temperature. The respiratory electrontransport system (ETS) activity of seawater communities wasalso measured from the same samples. Both data sets were relatedby the regression equation: log R (mg O₂ m^–3 day^–1)=0.462+0.730xlogETS activity mg O₂ m^–3 day^–1) (r=0.80, n=23). Fromthis equation and 37 ETS activity depth profiles, we calculatedthe integrated (0–100 m) community respiration as beingin the range 1.2–4.5 g O₂ m^–2 day^–1 (mean=2.2).These values do not differ significantly from other publishedresults for the Arctic and Antarctic Oceans. Assuming a respiratoryquotient of unity, the areal respiration ranges between 0.45and 1.69 g C m^–2 day^–1 (mean=0.8). This would representan important sink for the primary production reported for BransStrait. The spatial distribution of community respiration showedhigher values associated with the warmer and phytoplankton-richwaters outflowing from Gerlache Strait into Bransfield Strait,and with the front that separates Bellingshausen Sea watersfrom Weddell Sea waters. We suggest that this pattern of distributionmay be related to the transport of organic matter by the BransfieldCurrent along the front.     

The relationship between community respiration and ETS activity in the ocean

We have studied the relationship between community respiration(R) and enzymatic activity of the electron transport system(ETS) in upper ocean microbial communities (<225 µm)from different oceanic regions. In all except one of the regions,R and ETS were significantly positive correlated. This supportsthe hypothesis that ETS can be widely used to estimate planktonrespiration in natural marine communities (Packard, T.T., Adv.Aquat Microbiol, 3,207–261, 1985). A regression equationwas obtained between all the R and ETS data studied, to deriverespiration from ETS activity. This equation yields a mean errorin the prediction of ±34%, similar to the errors obtainedapplying the equations at each area, but lower than the errorobtained when using the mean R:ETS ratio to determine respiration(±45%). Our results suggest that the use of the ETS-Ralgorithm, along with measurements of ETS activity in seawater,facilitates the estimation of seawater respiratory oxygen consumptionon the mesoscale. This means that by using this approach onecould extend our knowledge of oceanic respiration over largetemporal and spatial scales, and begin to use respiration, notonly productivity, in addressing carbon balance problems inthe upper ocean.