The cooling of the Atlantic inflow toward the Arctic in a global warming perspective – from hourly current and temperature records 1995-2019

Kjell Arild Orvik, Geophysical Institute, University of Bergen, Bergen, Norway
An extraordinary cooling of the Atlantic inflow to the Nordic Seas toward the Arctic is observed over the last 4 years. In light of that, we investigate the seasonal and interannual variation of the heat flux in the core of the eastern Norwegian Atlantic Current in the Svinøy section (62oN), using hourly temperature and current records during 1995-2019. The Svinøy section capture the entire Atlantic inflow toward the Arctic and has strengthen its importance because of recent studies, showing that the major heat loss (70%) is associated with the MOC-branch that continues into the Nordic Seas. There the North Atlantic deep overflow water is produced and returns to the North Atlantic as a deep western boundary current. The dominating seasonal and inter-annual heat flux signals coincide almost completely with the volume transport, while the temperature has a minor modulating effect. Overall, removing the seasonality, there is no trend in the volume transport. There is an extraordinary 1oC temperature increase during the first 8 years of the measurements, followed by a fairly stable temperature over the next 10 years, before the extreme cooling started from an absolute fall maximum in 2014 to an absolute winter minimum in 2018. This cooling event coincides, presumably, with a propagating anomaly from the eastern Subpolar North Atlantic. On a longer timescale, there appears to be a half wavelength over the nearly 25-year period, likely in accordance with the striking AMO. The temperature minimum in 2018 also coincide with an absolute minimum of the volume transport, where the seasonal winter maximum is nearly absent. The loss of the prominent seasonal signal in the volume flux during 2018 appears to be caused by the striking wintertime blocking situation with a high pressure over Europe and eastern North Atlantic. Could it be that these concurrent minima in temperature and volume flux have led to the extraordinary warm summer over Western Europe and Scandinavia in 2018?