In situ oxygen microelectrode measurements of bottom-ice algal production in McMurdo Sound, Antarctica

Abstract

In-situ estimates of fast-ice algal productivity at Cape Evans, McMurdo Sound, in 1999 were lower than at the same site in previous years. Under-ice irradiance was between 0 and 8 μmol photons m-2 s-1; the ice was between 1.9 and 2.0 m thick and the algal biomass averaged 150 mg chl a m-2, although values as high as 378 mg chl a m-2 were recorded. Production on 11 and 12 November was between 0.053 and 1.474 mg C m-2 h1. When the data from 11 November were fitted to a hyperbolic tangent function, a multilinear regression gave estimates for P max of 0.571 nmol 02 cm-2 s-1, an αof 0.167 nmol 02 cm-2 s-1 μmol-1 photons m-2 s-1 and an Ek of 3.419 μmol photons m-2 s-1. A P max of 2.674 nmol 02 cm-2 s-1 an α of 0.275 nmol 02 cm-2 s-1 μmol-1 photons m-2 s-1, r of 0.305 nmol 02 cm-2 s-1 and an E k of 9.724 μmol-1 photons m-2 s-1 were estimated from the 12 November data. The sea-ice algal community was principally comprised of Nitzschia stellata, Entomoneis kjellmanii and Berkeleya adeliensis. Other taxa present included N. lecointei, Fragilariopsis spp., Navicula glaciei, Pleurosigma spp. and Amphora spp. Variations in the method for estimating the thickness of the diffusive boundary layer were not found to significantly affect the measurements of oxygen flux. However, the inability to accurately measure fine-scale variations in biomass is thought to contribute to the scatter of the P versus E data.