Benthic Soft-bottom Communities and Ecosystem Functions on the Northeast Greenland Shelf

Benthic communities regulate numerous ecosystem processes and rely almost exclusively on the sinking of organic matter from the pelagic. In association with climate change the Arctic sea ice is shrinking, glacial discharge is increasing and Arctic marine ecosystems are expected to become more Atlantic in character. For the last 20 years, these environmental changes were observed for the Northeast Greenland (NEG) shelf and might have altered benthic community structures and their function in this region. In September/October 2017, soft-bottom communities were sampled and oxygen consumption was measured ex situ over time at 13 stations on the NEG shelf. Sediment granulometry and porosity, pigment concentrations and porewater chemistry (DIC, nutrients, sulfate, chloride) were assessed to characterize the habitat. It was found that macrofauna communities did not separate among regions, while foraminifera communities (>500 mm) and polychaeta did distinguish the northern Westwind Trough from the southern Norske Trough and the 79N Glacier. Benthic pigment concentration was the most important predictor for the community structure. Total abundance and biomass of macrofauna, single cell abundances, porewater DIC and ammonia concentrations were highest in the Westwind Trough compared to all other regions, which suggests the highest benthic productivity in theWestwind Trough. Overall benthic pigment concentrations were up to sevenfold lower compared to the 1990s, accompanied by a fivefold lower total abundance of macrofauna. The present study confirms previous reports about a strong pelagic-benthic coupling on the NEG shelf which might have weakened since the 1990s, suggesting that this is a result of higher zooplankton grazing. Longer ice-free periods and higher inflow of warm AtlanticWater on the NEG shelf might have led to favourable conditions for zooplankton of Atlantic origin, increasing pelagic mineralization that would finally lead to a reduction in the amount of organic matter reaching the sea floor