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A critical question regarding the organic carbon cycle in the Arctic Ocean is whether the decline in ice extent and thickness and the associated increase in solar irradiance in the upper ocean will result in increased primary production and particulate organic carbon (POC) export. To assess spatial and temporal variability in POC export, under-ice export fluxes were measured with short-term sediment traps in the northern Laptev Sea in July-August-September 1995, north of the Fram Strait in July 1997, and in the Central Arctic in August-September 2012. Sediment traps were deployed at 2-5 m and 20-25 m under ice for periods ranging from 8.5 to 71 h. In addition to POC fluxes, total particulate matter, chlorophyll a, biogenic particulate silica, phytoplankton, and zooplankton fecal pellet fluxes were measured to evaluate the amount and composition of the material exported in the upper Arctic Ocean. Whereas elevated export fluxes observed on and near the Laptev Sea shelf were likely the combined result of high primary production, resuspension, and release of particulate matter from melting ice, low export fluxes above the central basins despite increased light availability during the record minimum ice extent of 2012 suggest that POC export was limited by nutrient supply during summer. These results suggest that the ongoing decline in ice cover affects export fluxes differently on Arctic shelves and over the deep Arctic Ocean and that POC export is likely to remain low above the central basins unless additional nutrients are supplied to surface waters.

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The composition of sea ice communities in the Ross Sea region was examined during the autumn to winter transition and during the summer. The biomass of autotrophs and heterotrophs in autumn reached maximum values of 709 and 167 mg C m , respectively. During the autumn-winter cruise, most of the biomass was found within ice floes as interior and bottom layer communities. During summer, surface-layer slush communities occurred throughout the ice-covered regions. The biomass was highly variable throughout the study regions during both cruises. Diatoms dominated the autotrophic biomass; however, autotrophic dinoflagellates and autotrophic flagellates contributed significantly to the community make-up. Among heterotrophs, ciliates predominated during both cruises, followed by heterotrophic flagellates and heterotrophic dinoflagellates. Similarity analysis, based on the biomass composition of major groups, showed consistency between and within cruises, with most samples > 70% similar. The autumn to winter samples (all from within floes) showed higher similarity clusters that could be related to changing compositions of diatoms, ciliates, and autotrophic dinoflagellates. Most variable were some summer surface slush samples, where samples dominated by Phaeocystis, Pyramimonas, Gymnodinium, and the ciliate Gymnozoum formed outlying clusters. The dynamics of ice biota may be determined by relatively few taxa that are persistently found within the ice floes. Surface blooms may develop either from a biota within the ice or from opportunistic forms from the water column that are introduced during flooding events. Thus, these assemblages may show considerably more variability in composition than those that develop within the underlying ice. KEY WORDS: Sea ice community · Antarctic · ProtistsResale or republication not permitted without written consent of the publisher