Observed bottom warming in the East Siberian Sea driven by the intensified vertical mixing

Abstract. The East Siberian Sea has the broadest continental shelf on Earth and nearly 80 % of the subsea permafrost worldwide. There exists a cold layer with the temperature at freezing points around −1.5 ºC above the sea floor of the shelf, preventing the heat transport from above to melt the permafrost and release the methane from sediments. However, we observed a worrying warming trend at the seafloor caused by enhanced vertical mixing in the shelf of the East Siberian Sea. In an ice-reduced Arctic continental shelf, even a moderate cyclone can result in the rapid growth of high wave to stir the marginal sea uniformly, which is not observed before. The intensified mixing can transport enormous heat downward, leading to a remarkable warming of more than 3 °C at the bottom. As the Arctic is experiencing accelerated warming and the sea ice is rapidly retreating, the East Siberian Sea will undoubtedly suffer more extreme heatwaves, which might cause unpredictable climate impacts on the Arctic biochemical processes and greenhouse gas emission.