Phytoplankton photosynthetic pigments in the Ross Sea: Patterns and relationships among functional groups

Phytoplankton assemblages of the Ross Sea are generally dominated by two functional groups: diatoms and haptophytes (Phaeocystis antarctica). Within this “normal” pattern of dominance, there is a substantial amount of temporal (over months, seasons and years) and spatial variability. Such variability has a significant impact on several biogeochemical cycles, such as the carbon and sulfur cycles, at the regional and global scales. We compiled all available accessory pigment data for the southern Ross Sea as a means to quantify the prevalence and dominance of each group, and generated a seasonal “climatology” of assemblage composition. The climatological pattern of phytoplankton pigments shows that haptophytes normally grow and accumulate early in the season, and largely in the southern Ross Sea polynya. Diatoms reach a biomass maximum later, and reach most extensive concentrations closer to the coast of Victoria Land. While the pattern of spring growth of P. antarctica followed by an increase in diatom abundance is found frequently, deviations from that pattern were observed. Two periods – November, 2006 and January, 2004 – illustrated that variations of up to one order of magnitude can occur relative to the climatology. These deviations may provide insights into the dominant control mechanisms of the two functional groups.