Longitudinal variation in zooplankton δ13C through the Northwest Passage: inference for incorporation of sea-ice POM into pelagic foodwebs

Abstract

Previous research has demonstrated a west-to-east decrease in zooplankton δ¹³C along the Alaskan coast. We extended the transect into the Canadian Arctic archipelago through the Northwest Passage in order to investigate whether this longitudinal gradient persists eastward. Contrary to the previous observations, zooplankton δ¹³C was found to be essentially invariate, despite a sampling survey length double that of the earlier studies. This resulted from zooplankton at the coldest and ice-bound stations being found to be enriched in ¹³C relative to what would be expected from the ambient water temperatures and calculated [CO₂aq]. We suggest that this was due to the assimilation of ice POM which, as has been demonstrated for other forms of benthic algae, is enriched in ¹³C due to restraints on boundary layer diffusion. The present results therefore support other traditional, non-isotope research in suggesting that ice-bound polar foodwebs may be examples of aquatic systems where there is a functional energy connectivity between the attached and openwater environments.