Phytoplankton pigment distributions and associated fluxes in the Bellingshausen Sea during the austral spring 1992

Abstract

Pigment distribution patterns were investigated in the marginal ice zone of the Bellingshausen Sea and across the Drake Passage during the austral spring of November/December 1992. Elevated chlorophyll a (chl a) and fucoxanthin levels were observed at the Sub-Antarctic and Polar Fronts in the Drake Passage and at the Southern Polar Front in the Bellingshausen Sea. Investigations at 5 stations along 85°W in the Bellingshausen Sea between 70.3°S and 67.5°S revealed high concentrations of chl a (up to 24 000 ng l −1 ice melt) and fucoxanthin in hard pack ice samples and very low levels of pigments in the underlying water column (<100 ng l −1). At two ice melt stations, pigment concentrations in the ice were considerably lower and chl a in the upper mixed layer ranged from 120–250 ng l −1, with increased levels of hexanoyloxyfucoxanthin and chlorophyll b (chl b). In open water, the high chl a band at the Southern Polar Front (up to 2400 ng l −1) was associated with elevated fucoxanthin concentrations. Integrated concentrations, pigment ratios and a conversion of accessory pigments to chl a equivalents indicated that diatoms (fucoxanthin) were the most important group in the ice (>70%), although prymnesiophytes (hexanoyloxyfucoxanthin) and green algae (chl b) were present in smaller proportions. Diatoms dominated at the open water stations (>60%) and were prominent in the water column under the pack ice (52–61%). However, at the ice melt stations, prymnesiophytes (40–45%), green algae (11–13%) and, to a lesser extent, cryptophytes (4–6%; alloxanthin) collectively contributed more to the chl a biomass than the diatoms (37–42%). Budgeting the proportions of chloropigments indicated an increase in chlorophyllide a and phaeopigments from the ice to the northern open water stations, with chlorophyllide a being prominent in the upper water column and in the ice. Export fluxes of phytoplankton–carbon and phytodetritus in the upper 100 m were estimated from chloropigment inventories and residence times of 210 Po radionuclide reported by Shimmield et al. (1995) [Shimmield, G.B., Ritchie, G., Fileman, T.W., 1995. The impact of marginal zone processes on the distribution of 210 Pb , 210 Po and 234 Th and implications for new production in the Bellingshausen Sea Antarctica. Deep-Sea Res. II, 42 (1995) 1313–1335], revealing very low fluxes at the ice stations and up to 29 mg phyto-C m −2 day −1 at the open water high chlorophyll locality.