Transport variability of the Irminger Current: Results from four years of mooring deployment between 2014 – 2018

As an extension of the North Atlantic Current, the Irminger Current is an important component of the overturning in the subpolar North Atlantic. It contains warm, saline Subpolar Mode Water and cold, dense North East Atlantic Deep Water flowing northward along the western flank of the Reykjanes Ridge. As part of OSNAP (Overturning in the Subpolar North Atlantic Project) the Irminger Current has been monitored with a mooring array consisting of four long moorings and one short mooring, all equipped with current meters, ADCPs and CTDs.

Results from July 2014 to July 2018 resolve the current system containing two northward branches (western and eastern core) and a southward recirculation. While both surface branches equally contribute to the northward volume transport of ~10± 8.8 Sv, the intra-seasonal variability of the western branch (4.6 ±6.8 Sv) was higher than for the eastern branch (5.5 ±5.2 Sv).

The first two years have a higher transport (10.6 Sv) than the transport from 2016-2018 (9.6 Sv). The difference was mainly due to a reduced transport in the western core which reduced by 25% from 5.3±7.0 Sv to 3.9±6.63 Sv. The transport variability of both branches in 2016 – 2018 was lower compared to the first two years. During 2014 – 2016, the warmer and saltier eastern branch contributed more to the overall heat and freshwater transport.

On 3-month time scales and longer the velocity results from the mooring array are in good agreement with available altimetry data. On shorter time scales, however, the variability is more dependent on mesoscale activity which was investigated by using available drifter and satellite data. The time series will be extended with new mooring data in the summer of 2020.