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Calanoid copepods dominate mesozooplankton biomass in the Arctic Ocean. Variations in C content, C:N ratio and stable isotope composition (δ13C, δ15N) of Calanus hyperboreus, Calanus glacialis and Metridia longa collected from January to August 2008 in the southeast Beaufort Sea provided insights into their metabolism, feeding and reproduction. Seasonal differences in the C–prosome length relationships and C:N ratios were driven by distinct spawning strategies and changes in lipid content. Relatively high copepod biomass over the study period (2.6–9.7 g C m−2) corresponded to favorable growth conditions in 2007–2008. The mean 15N enrichment of copepods (+2.8–4.7‰) relative to particulate organic nitrogen values recorded at the ice bottom and at the chlorophyll maximum indicated a primarily herbivorous diet. In all species, δ13C and δ15N decreased markedly in April, reflecting the feeding onset on ice algae, but a rapid transition to feeding on phytoplankton occurred as a pelagic bloom was triggered by the early ice melt in May. A second decline in the δ13C and δ15N of copepods was recorded in June–July, coincident with a second increase in phytoplankton production. The two isotope depletion events in copepods were both followed by a return to high values and an increase in their C:N as a consequence of previous C fixation and nitrate limitation in phytoplankton and the likely formation of body reserves/tissue. Our results illustrate that Arctic calanoids respond quickly to any increase in primary production and can cope with changes in its nature and timing. [ABSTRACT FROM AUTHOR]

Abstract: Surface concentrations and vertical fluxes of particulate organic carbon (POC) were assessed in the Amundsen Gulf (southeastern Beaufort Sea, Arctic Ocean) over the years 2004 to 2006 by using ocean color remote-sensing imagery and sequential sediment traps moored over the ca. 400m isobath. Environmental conditions (sea ice, wind) and oceanographic variables (temperature, salinity, fluorescence and currents) were investigated to explain the variability of POC data. Annual downward POC fluxes in 2004, 2005 and 2006 cumulated, respectively, to 3.3, 4.2 and 6.0gCm−2 yr−1 at ∼100m depth, and to 1.3, 2.2 and 3.3gCm−2 yr−1 at ∼210m depth. The fraction of settling POC attributable to autochthonous processes occurring at or next to ice break-up was estimated to be 75–84% of the 100m annual fluxes and to be 61–75% of the 210m fluxes. Over the three ice-reduced seasons, distinct scenarios between ice conditions, surface POC pools and vertical POC export at 100m were identified: (1) in 2004, despite a normal ice break-up, a weak primary production was measured and low vertical fluxes were collected as old ice moved across the region; (2) in 2005, a lengthened ice-free period allowed an extended season of surface POC production near-shore, while an intermediate increase of vertical fluxes was recorded offshore; and (3) in 2006, a late ice melt gave rise to a pulsed ice edge bloom and to large vertical fluxes also associated with extra ice-flushed material. Linear regressions of vertical POC fluxes against satellite-derived surface POC concentrations suggested that the pelagic POC retention in the upper 100m of the Amundsen Gulf ranged from ca. 70% to 90% depending on the timing of ice cover melt. Regardless of the inter-annual variability, the estimated fraction of the surface POC reservoir reaching the 210m water depth was reduced to ∼5%. Therefore, as the Arctic Ocean warms up, our results support the expectation that the increasing extent of the seasonal ice zone will promote the POC pathways that benefit pelagic webs rather than benthic communities. [Copyright &y& Elsevier]

Abstract: The ongoing regression of sea ice cover is expected to significantly affect the fate of organic carbon over the Arctic continental shelves. Long-term moored sediment traps were deployed in 2005–2006 in the Beaufort Sea, Northern Baffin Bay and the Laptev Sea to compare the annual variability of POC fluxes and to evaluate the factors regulating the annual cycle of carbon export over these continental shelves. Annual POC fluxes at 200m ranged from 1.6 to 5.9gCm−2 yr−1 with the highest export in Northern Baffin Bay and the lowest export over the Mackenzie Shelf in the Beaufort Sea. Each annual cycle exhibited an increase in POC export a few weeks before, during, or immediately following sea ice melt, but showed different patterns over the remainder of the cycle. Enhanced primary production, discharge of the Lena River, and resuspension events contributed to periods of elevated POC export over the Laptev Sea slope. High POC fluxes in Northern Baffin Bay reflected periods of elevated primary production in the North Water polynya. In the Beaufort Sea sediment resuspension contributed to most of the large export events. Our results suggest that the outer shelf of the Laptev Sea will likely sustain the largest increase in POC export in the next few years due to the large reduction in ice cover and the possible increase in the Lena River discharge. The large differences in forcing among the regions investigated reinforce the importance of monitoring POC fluxes in the different oceanographic regimes that characterize the Arctic shelves to assess the response of the Arctic Ocean carbon cycle to interannual variability and climate change. [Copyright &y& Elsevier]

Abstract: To investigate the mechanisms underlying the transport of particles from the shelf to the deep basin, sediment traps and oceanographic sensors were moored from October 2003 to August 2004 over the 300- and 500-m isobaths on the slope of the Mackenzie Shelf (Beaufort Sea, Arctic Ocean). Seasonal variations in the magnitude and nature of the vertical particulate organic carbon (POC) fluxes were related to sea-ice thermodynamics on the shelf and local circulation. From October to April, distinct increases in the POC flux coincided with the resuspension and advection of shelf bottom particles by thermohaline convection, windstorms, and/or current surges and inversions. Once resuspended and incorporated into the Benthic Nepheloid Layer (BNL), particles of shelf origin were transported over the slope by the isopycnal intrusion of the BNL into the Polar-Mixed Layer off-shelf. Offshore transport of the resuspended particles allowed them to settle over the slope. The resulting vertical POC flux at the shelf-basin boundary amounted to 1.0 g C m−2 y−1 or 58% of the annual POC flux over the 300-m isobath. Consistent with the resuspension of shelf sediments, POC fluxes in fall/winter were characterized by a high terrigenous fraction (25–60%), the dominance of small flagellate cells, and increasingly degraded fecal pellets with time. In late May–early June, a short-duration POC flux maximum characterized by high POC:PON ratio and more positive δ 13C resulted from the direct sinking of ice algae and transparent exopolymeric matter flushed from melting sea-ice. In July, a last sedimentation event coincided with the retreat of the sea-ice cover, phytoplankton production from a subsurface bloom, and the sinking of the intact fecal pellets of large herbivorous copepods and appendicularians. Our results confirm the importance of sea-ice thermodynamics and BNL resuspension in promoting the transfer of POC from the shelf to the deep basin in fall/winter. The actual contribution of the summer biological production to the shelf–basin flux of POC remains uncertain. [Copyright &y& Elsevier]