Arrival of New Great Salinity Anomaly Weakens Convection in the Irminger Sea

Abstract

The Subpolar North Atlantic is prone to recurrent extreme freshening events called Great Salinity Anomalies (GSAs). Here, we combine hydrographic ocean analyses and moored observations to document the arrival, spreading, and impacts of the most recent GSA in the Irminger Sea. This GSA is associated with a rapid freshening of the upper Irminger Sea between 2015 and 2020, culminating in annually averaged salinities as low as the freshest years of the 1990s and possibly since 1960. Upon the GSA propagation into the Irminger Sea over the Reykjanes Ridge, the boundary currents rapidly advected its signal around the basin within months while fresher waters slowly spread and accumulated into the interior. The anomalies in the interior freshened waters produced by deep convection during the 2017–2018 winter and actively contributed to the suppression of deep convection in the following two winters.

Slantwise Convection in the Irminger Sea

“…The boundary current freshens significantly toward the end of our 4 year record (Figure 9b) (Biló et al, 2022). This results in an overall freshening of the subtropical Atlantic salinity maximum.…”

Freshwater Flux Variability Lengthens the Period of the Low‐Frequency AMOC Variability

“…Clearly, the freshwater transport by the East Greenland Current into the LS is markedly reduced prior to the LS salinity maximum, with the maximum reduction of transport occurring at lag −3. This notion is further supported by the propagating signal of high salinity anomalies along the boundary of the LS (Figure S5 in Supporting Information S1 ), and the exchange between the boundary and the interior can be realized through interior recirculation (Biló et al., 2022 ; Holliday et al., 2009 ) and eddies (Bracco et al., 2008 ) that are parameterized in this model.…”

“…Therefore, some studies have proposed that FWF can modulate the AMOC in a significant way. For example, hosing freshwater into the North Atlantic can immediately reduce local SSS and weaken the sinking rates of DWF, causing AMOC slowdown or even shutdown (e.g., Biló et al., 2022 ; Brady & Otto‐Bliesner, 2011 ; Kostov et al., 2019 ; Liu, Fedorov, et al., 2020 ; Stocker & Wright, 1991 ; Thomas & Fedorov, 2019 ). Liu and Fedorov ( 2021 ) suggest that anomalous freshening related to Arctic sea ice loss can propagate downstream to the subpolar North Atlantic and drive an AMOC slowdown with a multidecadal delay.…”

Cross‐Shelf Exchanges Between the East Greenland Shelf and Interior Seas

“…The EGC‐DrIFT deployments (Figure 2), as well as GDP data, suggest there is no short and fast route from the west Greenland shelf to the central Irminger Sea. The freshwater anomaly that formed off the Labrador shelf in 2012 (Holliday et al., 2020) traveled around the subpolar gyre, was further strengthened at the surface by precipitation, and was seen to arrive in the eastern Irminger Sea in 2016 (Biló et al., 2022; F. M. de Jong et al., 2020). In general, the seasonal appearance of a fresh layer suggests more regular and nearby sources.…”