Data from: Shells of the bivalve Astarte moerchi give new evidence of a strong pelagic-benthic coupling shift occurring since the late 1970s in the NOW Polynya

Climate changes in the Arctic may weaken the currently tight pelagic-benthic coupling. In response to decreasing sea ice cover, arctic marine systems are expected to shift from a 'sea-ice algae-benthos' to a 'phytoplankton-zooplankton' dominance. We used mollusk shells as bioarchives and fatty acid trophic markers to estimate the effects of the reduction of sea ice cover on the exported food to the seafloor. Bathyal bivalve Astarte moerchi that lives at 600 m depth in northern Baffin Bay reveals a clear shift in growth variations and Ba/Ca ratios since the late 1970s that we relate to a change in food availability. Fatty acid compositions of tissues show that this species feeds mainly on microalgae exported from the euphotic zone to the seabed. We thus suggest that changes in pelagic-benthic coupling are likely due to either local changes in sea ice dynamics, mediated through bottom-up regulation exerted by sea ice on phytoplankton production or to a mismatch between phytoplankton bloom and zooplankton grazing due to change in their phenology. Both possibilities allow a more regular and increased transfer of food to the seabed.