Freshening over the whole water column as a result of the 2012 subpolar
freshwater anomaly increased the transport of lighter waters of the
Irminger Current between 2014 - 2022
Abstract
The North Atlantic subpolar gyre experienced strong freshening in recent
years starting around 2012. Here, we investigate the imprint of this
freshwater anomaly on the water column hydrography and transport
variability of the Irminger Current (IC). The IC transports warm and
saline waters northward along the western flank of the Reykjanes Ridge
as part of the upper limb of the Atlantic Meridional Overturning
Circulation (AMOC). To investigate if the salinity anomaly spread and
propagated downward, we used high-resolution mooring data from the IC
covering the period 2014 – 2022 combined with hydrographic sections
from the Irminger Sea and Iceland Basin. We found that the IC
experienced a strong freshening starting in summer 2016. By 2018, this
salinity anomaly covers the whole water column down to 1500 m depth and
freshened the IC until 2022. In 2022, the IC was at its freshest state
observed since the early 1990’s. Hydrographic sections across the
adjacent basins showed that the recent freshening spread across the
Irminger Sea and was also comparable to its fresh state in the early
1990’s. The salinity anomaly increased the freshwater transport of the
IC by a factor of three from 2014-2015 to 2021-2022 and caused a
decrease in density over much of the water column. This resulted in an
increase in the transport of waters lighter than 27.55 kg m-3,
potentially strengthening the upper limb of the AMOC.