Export fluxes of biogenic matter in the presence and absence of seasonal sea ice cover in the Chukchi Sea |
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| Authors: | Catherine Lalande Jacqueline M Grebmeier Paul Wassmann Lee W Cooper Mikhail V Flint Valentina M Sergeeva |
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| Institution: | 1. Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN, 37932, USA;2. Norwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway;3. Shirshov Institute of Oceanology, Russian Academy of Sciences, Nakhimovsky Prospect 36, Moscow, 117997, Russia;4. Institute of Marine Science, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, P.O. Box 757220, Fairbanks, AK, 99775, USA |
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| Abstract: | Drifting sediment traps were deployed at 9 stations in May-June (ice-covered conditions) and July-August (ice-free conditions) 2004 in the Chukchi Sea to investigate the variability in export fluxes of biogenic matter in the presence and absence of sea ice cover. Measurements of chlorophyll-a (Chl-a), particulate organic carbon (POC), particulate nitrogen (PN), phytoplankton, zooplankton fecal pellets, and the stable carbon isotope composition (δ13C) of the sinking material were performed along Barrow Canyon (BC) and a parallel shelf-to-basin transect from East Hanna Shoal (EHS) to the Canada Basin. POC export fluxes were similarly high in the presence (378±106 mg C m−2 d−1) and in the absence of ice cover (442±203 mg C m−2 d−1) at the BC stations, while fluxes were significantly higher in the absence (129±98 mg C m−2 d−1) than in the presence of ice cover (44±29 mg C m−2 d−1) at the EHS stations. The C/N ratios and δ13C values of sinking organic particles indicated that POC export fluxes on the Chukchi continental shelf were mostly composed of freshly produced labile material, except at the EHS stations under ice cover where the exported matter was mostly composed of refractory material probably advected into the EHS region. Chl-a fluxes were higher under ice cover than in ice-free water, however, relatively low daily loss rates of Chl-a and similar phytoplankton carbon fluxes in ice-covered and ice-free water suggest the retention of phytoplankton in the upper water column. An increase in fecal pellet carbon fluxes in ice-free water reflected higher grazing pressure in the absence of ice cover. Elevated daily loss rates of POC at the BC stations confirmed other indications that Barrow Canyon is an important area of carbon export to the basin and/or benthos. These results support the conclusion that there are large spatial and temporal variations in export fluxes of biogenic matter on the Chukchi continental shelf, although export fluxes may be similar in the presence and in the absence of ice cover in highly productive regions. |
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| Keywords: | Arctic Ocean Chukchi Sea Sediment traps Export flux Particulate organic carbon Ice cover |
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