The perennially ice-covered Central Arctic is changing rapidly due to extensive sea-ice retreat and the loss of multiyear ice. The thinning of the ice allows more light to reach the water column enhancing productivity. These changes in the under ice ecosystem can lead to under-ice phytoplankton blooms which may increase grazing and carbon export. However, our knowledge of the interactions between sea ice, sub-ice and under-ice communities is still poor, especially in high latitudes. A key limitation is observations of the undisturbed under-ice flora and fauna. To address this gap in observations, the Nereid Under Ice remotely operated vehicle (NUI) was developed, equipped with thin optical fibre and acoustic navigation to explore under-ice environments at distances up to 20 km away from research vessels from which it is deployed. This vehicle can accommodate various interdisciplinary payloads including HD video cameras, CTD and biological sensor packages including chlorophyll fluorometers, CDOM optical sensors and optical nitrate sensors. Research capabilities of NUI were tested during the RV Polarstern PS86 expedition to the Aurora Vent field, at 83ºN 6°W north-east of Greenland. From 12 to 30 July 2014 the evolution of a phytoplankton bloom below 2m thick multiyear ice was followed. Video footage obtained with NUI directly below the ice showed the development of algal mats at the bottom of the ice floe and a succession of zooplankton blooms presumably causing a decline of the phytoplankton bloom. Polar copepods, ctenophores and appendicularia could be identified forming dense biomasses underneath the ice. From NUI’s chlorophyll, CDOM and nitrate profiles, steep gradients of high biogeochemical activity were detected in the mixed layer (upper 6-15 m), which could not be observed by the ship-deployed CTD. These structures were identified as layers of sinking particles with different optical characteristics. This poster summarizes the advantages of robotic observations over classical ship-based sampling for the study of under ice communities. In vivo observations of phyto- and zooplankton communities are needed to better assess the impacts of changing sea-ice conditions on under ice organisms
