Reduced efficiency of pelagic-benthic coupling in the Arctic deep sea during lower ice cover.

Pelagic-benthic coupling describes the connection between surface-water production and seafloor habitats via energy, nutrient and mass exchange. Massive ice loss and warming in the poorly studied Arctic Chukchi Borderland are hypothesized to affect this coupling. The strength of pelagic-benthic coupling was compared between 2 years varying in climate settings, 2005 and 2016, based on δ13C and δ15N stable isotopes of food-web end-members and pelagic and deep-sea benthic consumers. Considerably higher isotopic niche overlap and generally shorter isotopic distance were found between pelagic and benthic food web components in 2005 than in 2016, suggesting weaker coupling in the latter, low-ice year. δ15N values indicated more refractory food consumed by benthos in 2016 and fresher food reaching the seafloor in 2005. Higher δ13C values of zooplankton indirectly suggested a higher contribution of ice algae in 2005 than 2016. The difference in pelagic-benthic coupling between these years is consistent with higher energy retention within the pelagic system, perhaps due to strong stratification in the Amerasian Basin in the recent decade. Weaker coupling to the benthos can be expected to continue with ice loss in the study area, perhaps reducing benthic biomass and remineralization capacity; monitoring of the area is needed to confirm this prediction.