Fluxes and composition of siliceous phytoplankton particles in year-round sediment trap materials from Bransfield Strait, Antarctica

Abstract

Fluxes, abundance and species composition of siliceous phytoplankton in sediment trap materials were measured in the Bransfield Strait, Antarctica. Traps were deployed at two sites in central (KAST 1) and eastern Bransfield Strait (KAST 2) during December 1999 to December 2000. The assemblages of siliceous phytoplankton in the surface water near South Shetland Islands were measured at 54 stations from 9 to 19 January, 2001. These analyses and comparison to assemblages of siliceous phytoplankton in surface water provide information concerning the influence succession, and deposited floral assemblage. There was a significant settling of siliceous phytoplankton into the trap during the austral summer in eastern and central Bransfield Strait (>5 X 109 valves m-2 day-2 and >2 X 109 valves m-2 day-2, respectively). The estimated flux of siliceous phytoplankton into the trap shows a considerable seasonal variation. At KAST 1, the flux was the highest in late February (3.2 X 1010 valves m-2 day-1) and decreased abruptly toward March. The abundant species was Minidiscus chilensis during January and changed to Thalassiosira spp. in February. During winter (March through August), the abundant species were Fragilariopsis spp. and Chaetoceros spore. At KAST 2, the flux was the highest in mid-January (7.5 X 109 valves m-2 day-1) and decreased toward February. The abundant specie was M. chilensis in January. The mean abundance of siliceous phytoplankton was 3.2 X 105 cells l-1 in the surface water near South Shetland Island. M. chilensis and Thalassiosira spp. were also abundant species in surface water during January, accounting for 51% of total siliceous phytoplankton. The concentration of M. chilensis in the surface water was the highest in the north of South Shetland Island (1.6 X 106 cells l-1) , whereas Thalassiosira spp. was abundant in the eastern Bransfield Strait Region. According to the abundance and species composition in the trap material, the abundance of siliceous p