Production and retention of biogenic matter in the southeast Beaufort Sea during 2003–2004: insights from annual vertical particle fluxes of organic carbon and biogenic silica

Abstract

Regional variability in the annual fluxes of particulate organic carbon (POC) and biogenic silica (Si) at the periphery of the Mackenzie Shelf (Beaufort Sea) was investigated using eight long-term sediment traps moored at ~100-m depth. Relatively high autochthonous POC and Si fluxes were recorded in the Mackenzie Trough (4.1 and 8.9 g m−2 year−1 respectively) and off Cape Bathurst (6.6 and 79 g m−2 year−1), two areas where upwelling events are frequently observed. Diatomaceous new production was minimum on the mid-slope of the Mackenzie Shelf (2.8 g C m−2 year−1), moderate in the Mackenzie Trough (14.5 g C m−2 year−1), and highest off Cape Bathurst (128.7 g C m−2 year−1). High annual autochthonous POC flux corresponded to high diatom production. Among sites, the vertical attenuation of the POC flux increased with diatomaceous new production. Hence, the retention of autochthonous POC in the surface layer (<100 m) was highest (95%) at the highly productive site off Cape Bathurst, intermediate (72%) in the moderately productive Mackenzie Trough, and low (4%) at the unproductive mid-slope of the shelf. Our results indicate that, on Arctic shelves, upwelling and the production of diatoms increase the fraction of the POC which is retained in the surface layer and diverted to the pelagic food web. In the relatively unproductive waters of the Arctic Ocean, biological hot spots such as the one identified off Cape Bathurst where the food web promotes retention rather than vertical export could be disproportionately important as feeding grounds for higher trophic levels.