Climatic and biological forcing of the vertical flux of biogenic particles under seasonal Arctic sea ice

Ice algae, phytoplankton, zooplankton and the vertical fluxes of chloropigments and particulate organic carbon (POC) were monitored from May to June/July of 1992, 1994 and 1995 under the ice of Barrow Strait (Canadian Arctic Archipelago), Large interannual differences in the timing, magnitude and nature of vertical fluxes were driven by meteorological events that controlled snow cover and by differences in zooplankton assemblages. In 1992, ice algae released from the ice matrix were intensely recycled by the exceptionally abundant calanoid Pseudocalanus acuspes, The persistent snow cover delayed the phytoplankton bloom until after the ice break-up in July. Ice algae were abruptly released and sank rapidly to depth following early rain in late May 1994 and a heat-wave in early June 1995. In both years, the early removal of snow triggered an under-ice phytoplankton bloom and strong downward fluxes of POC and chloropigments (13.7 gC m(-2), 381 mg chloropigments m(-2) in 1994), In the absence of nutrient limitation, under-ice fluxes represented a net addition to the annual flux of POC. The analysis of local climate from 1950 to 1995 suggests that strong and early under-ice fluxes of biogenic carbon in spring may become more frequent under the climatic conditions anticipated by general circulation models.