Pigment analysis of phytoplankton during a subarctic spring bloom: xanthophyll cycling

Abstract

The objective in this study of the spring bloom in Auke Bay, Alaska, was to determine if light-dependent xanthophyll cycling can be used to estimate the rate of vertical mixing in a subarctic environment. This was done by measuring the concentration of the xanthophylls diadinoxanthin (DD) and diatoxanthin (DT) in phytoplankton samples collected from different depths and different times of the day and in samples incubated in situ. We sampled throughout the photic zone weekly from 16 March until 9 May 1989. Pigments typical diatom assemblages (e.g., Chl a and c, fucoxanthin, DT, DD, and ß-carotene) were found throughout the sampling period. In situ incubations between dawn and early afternoon showed large differences in xanthophyll composition between incubated samples and those from the water column. Differences between samples collected in early morning and early afternoon were also found, as well as between samples collected at different depths. However, the technique was not found satisfactory to describe mixing events in this environment. Other factors besides light seemed to affect the concentrations of the xanthophyls, DT and DD. These findings cast doubt on the ability of DT: DD ratios to infer the vertical mixing history of field assemblages.