Photoadaptive response during the development of a coustal Antarctic diatom bloom and relationship to water column stability

Abstract

The raio of the xanthophylll pigments diadinoxanthin and diatoxanthin to chlorophyll a [(DD+DT}:Chl a] was used as a photoadaptive index during the development of a large Antarctic diatom bloom. This index was found to track fluctuations in the incident solar irradiance and the in situ light field over a 3 order magnitude change in the water column biomass. Depth profiles of the (DD+DT}:Chl a ratio showed that the upper mixed layer, assessed by physical data, was in fact stable over the course of the month. Diel experiments conducted over the same period showed a delayed (5–8 h) response of the DD+DT pool to the instantaneous Qpar (400–700 nm) irradiance. These time series results illustrate the potential use of xanthophyll pigmnents in assessing phytoplankton light histories and the degree of water column stability.