Sinking export of particulate organic material from the euphotic zone in the eastern Beaufort Sea

This paper presents an extensive spatial and temporal study of the sinking export of particulate organic material below the euphotic zone in the eastern Beaufort Sea. Free-drifting short-term particle interceptor traps were deployed, generally at 50 m, during fall 2002 and 2003, and summer 2004. The different regions of the sampling area, i.e. the Amundsen Gulf and the Mackenzie shelf and slope, showed similar ranges in the sinking export of chlorophyll a (chl a) and particulate organic carbon (POC) in fall, while regional differences were observed in summer. The 2 regions showed a general decreasing trend in sinking fluxes towards fall. The highest chl a and POC sinking fluxes during this study were therefore recorded during summer (3.6 and 258 mg m(-2) d(-1), respectively). A high retention of suspended biomass was observed throughout this study, i.e. low daily loss rates of suspended chl a and POC (both averaging ca. 1% d(-1)) were observed. Still, the POC sinking export accounted for, on average, half of the particulate primary production throughout this study. Zooplankton, primarily copepods, played an important role in the sinking export of particulate organic material, particularly in the Amundsen Gulf. A cluster-based analysis of the sinking protist cell assemblage revealed a seasonal succession that prevailed over spatial and interannual differences between the stations sampled in the eastern Beaufort Sea. Flagellates dominated throughout the study area, while diatoms, dominated by Fragilariopsis cylindrus, showed a decreasing contribution to the sinking protist cell assemblage towards fall. The presence of the sea ice related pennate diatoms Nitzschia frigida and Navicula vanhoeffenii in the material collected during summer reflected an input of organic material from sea ice. Results from particle interceptor traps deployed at a station in Franklin Bay during ice-covered and ice-free conditions showed the importance of taking into account under-ice sinking fluxes (up to 115 mg C m(-2) d(-1) for POC) for sinking export estimates on Arctic shelves.