A Transport Hiatus in the North Atlantic Current in Early 2014 Led to the Coincident Trans-Atlantic Heat and Salt Anomaly Dipoles of 2015

Speculation surrounds the possibility that increasing world temperatures could trigger a decrease in the heat supplied to the Subpolar North Atlantic (SPNA) by the Gulf Stream (GS) and its extension, the North Atlantic Current (NAC). Here we provide evidence for just such a drop in heat and salt delivery in 2014, leading to the development of a cold fresh anomaly (CFA) in the SPNA and reciprocal warm salty anomaly (WSA) near North America in 2015. These coincident dipoles of heat and salt anomalies first appeared in February–March 2014 when cooling and freshening in the NAC near 45oN, 42oW was reciprocated by warming and increased salinity near 42oN, 50oW. The negative anomalies subsequently migrated north-eastwards along the path of the NAC to constitute the CFA centered on 50oN, 30oW by July 2015 while the reciprocal positive anomalies spread south-westwards to constitute the WSA centered on 40oN, 70oW. Sea surface temperature and height anomaly data revealed a rectangular three-fold structure for the CFA representing the path of the cooled and freshened NAC across the Mid-Atlantic Ridge. Surface current velocity data for early 2014 showed that northwards transport in the NAC was temporarily reversed near its exit from the Mann Eddy, possibly due to an influx of Labrador Sea Water from the Deep Western Boundary Current. We conclude that the unprecedented cooling/freshening of the SPNA and warming/salinification of the North American coastal region in 2014–2015 were reciprocal consequences of an interruption of northwards mass transport in the NAC near its exit from the Mann Eddy.