Influence of terrestrial organic matter in marine food webs of the Beaufort Sea shelf and slope

Forecasted increases in terrestrial organic matter (OMterr) inputs to the Arctic Beaufort Sea necessitate a better understanding of the proportional contribution of this potential food source to the trophic structure of marine communities. This study investigated the relative ecological importance of OMterr across the Beaufort Sea shelf and slope by examining differences in community trophic structure concurrent with variation in terrestrial versus marine organic matter influence. Oxygen stable isotope ratios (delta O-18) of surface water confirmed the widespread influence of Canada's Mackenzie River plume across the Beaufort Sea. Carbon stable isotope ratios (delta C-13) of pelagic particulate organic matter (pPOM) and marine consumers indicated a significant decrease in OMterr presence and utilization by consumers with increasing distance from the Mackenzie River outflow. Food web length, based on the nitrogen stable isotope ratios (delta N-15) of marine consumers, was greater closer to the Mackenzie River outflow both in shelf and slope locations, due to relatively higher delta N-15 values of pelagic and benthic primary consumers. Strong microbial processing of OMterr in the eastern regions of the Beaufort Sea is inferred based on a trophic gap between assumed end members and lower trophic consumers. A greater proportion of relative epifaunal biomass occupying higher trophic levels suggests that OMterr as a basal food source can provide substantial energetic support for higher marine trophic levels. These findings challenge the current conception of low terrestrial matter usage in the Arctic marine food web, and indicate the need for a more specific understanding of energy transfer through the OMterr-associated microbial loop.