Warming-to-Cooling Reversal of Overflow-Derived Water Masses in the Irminger Sea During 2002-2021

Abstract : Shipboard hydrography along the A25-Ovide section (2002-2018) is combined with a high-resolution mooring array (2014-2020) and a regional fleet of Deep-Argo floats (2016-2021) to describe temperature changes of overflow-derived water masses in the Irminger Sea. Removing dynamical influences enables to identify a new statistically significant trend reversal in Iceland Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW) core temperatures in the mid-2010s. A basin-wide cooling trend of −16 ± 6 m°C yr⁻¹ during 2016-2021—but reaching as strong as −44 ± 13 m°C yr⁻¹ for DSOW in recent years—is found to interrupt a warming phase that was prevailing since the late 1990s. The absence of an apparent reversal in the Nordic Seas and the faster changes detected in DSOW compared to ISOW point out the entrainment of subpolar signals within the overflows near the Greenland-Iceland-Scotland sills as a most likely driver.