Continued warming of deep waters in Fram Strait

Fram Strait is the only deep gateway between the Arctic and the rest of the World Ocean, and is thus a key region to understand how the deep Arctic will evolve. However, studies and data regarding the deep ocean are scarce, making it difficult to understand its role in the climate system. Here we analyse oceanographic data from the deep ocean from two long-term mooring locations (F11 and HG-FEVI) in Fram Strait between 2010–2023, to investigate long-term changes in the hydrographic properties. We compile hydrographic profile data since the 1980’s for additional context in the upstream basins: the Greenland Sea, and the Eurasian Basin. At mooring F11 in western Fram Strait, we find a clear seasonality, with increased Greenland Sea Deep Water (GSDW) presence during summer, and increased Eurasian Basin Deep Water (EBDW) presence during winter. Evaluating long-term changes, we find a modest temperature increase of ∼ 0.1 °C for EBDW since the 1980’s. For GSDW, south of Fram Strait, we find a strong temperature increase of ∼ 0.4–0.5 °C for the same period. The different warming rates have led to GSDW becoming warmer than EBDW since ∼ 2017/2018. This means that the Greenland Sea is no longer a heat sink for the Arctic Ocean at depth, but a heat source. It is therefore possible that EBDW temperatures will increase faster in the future.