The Changing Arctic Ocean Seafloor (ChAOS) project aims to better understand how changes in the Arctic Ocean sea ice cover and water mass distribution will affect biological and biogeochemical processes at the seabed. The seafloor is by no means a merely passive receiver of everything that settles through the overlying water column – it is rather a highly dynamic environment that hosts a wide variety of biota, and plays a crucial role in carbon and nutrient cycling and burial. ChAOS will focus its research activities on the central and northern Barents Sea, a part of the Arctic shelf system that is strongly affected by modern climate change, and of interest to the hydrocarbon and fisheries industries. With a multi-disciplinary team of around 20 scientists from eight UK research institutions, and in collaboration with various international partners, ChAOS will analyse the chemical composition of the seafloor deposits and its pore waters, will assess the diversity and activity of biota from the micro- to macroscale, will expose intact pieces of the seafloor to laboratory conditions representing potential future change scenarios, and will compile all data into a modelling framework to provide a predictive tool of how the Arctic Ocean seafloor of the future might look like. The project involves three research expeditions to the Barents Sea onboard the RRS James Clark Ross, and will build close links with other projects studying the biology and biogeochemistry of the overlying water column.