Variation and Assimilation of Arctic Riverine Sestonin the Pelagic Food Web of the Mackenzie River Delta and Beaufort Sea Transition Zone

On-going shifts in the arctic climate and landscape have the potential to increase terrestrial particulate organic matter (POM) transported to the Mackenzie delta and coastal Beaufort shelf. If increased terrestrial/freshwater material exports to the coastal zone can be assimilated by the pelagic food web, then this represents a new pool of carbon for the regional food web and could result in a shift in the nature of carbon supporting pelagic productivity. Analysis of the δ¹³C of POM from the riverine, estuarine, and marine (shelf) zones of the Mackenzie delta shows that the signatures of terrestrial/freshwater carbon does extend onto the shelf, although it diminishes with distance from the Mackenzie River. δ¹³C values of calanoid copepods, mysid shrimp, and two species of Amphipods varied depending on their environment (river, estuary, or marine) and local POM δ¹³C signature. From this, we conclude that exported terrestrial POM can be a subsidy for portions of both the estuarine and marine pelagic food web. However because the response of consumer δ¹³C depended on both species and location, we also conclude that the response to increased riverine POM will be different for estuarine versus marine biota. The implication is that increases in exported terrestrial carbon represent a significant potential shift in coastal pelagic ecosystem structure and function.