Record deep convection in the Irminger Sea: Observations from the LOCO mooring during winter 2014-2015

Anomalously strong cooling over the Irminger Sea during the winter of 2014-2015 caused record depths convective mixing. Active mixed layer depths at the LOCO mooring site, near the center of the Irminger Gyre, reached down to 1200 m. A further reduction of stratification suggests mixed layers down to 1500 m. The deep mixing eroded the intermediate salinity minimum associated with Labrador Sea Water and replaced it with a cold, fresh homogeneous layer rich in oxygen. This layer was seen to extend across the basin in the hydrographic section of summer 2015, suggesting that a significant part of the basin participated in the mixing. The winter 2014-2015 convective event exceeded the previous maximum of 1000 m in the winter of 2007-2008. The main cause is the surface buoyancy forcing. Strong surface buoyancy loss (monthly mean > 125 W/m²) lasted for an additional month. The 2015 hydrography is reminiscent of the situation in the 1990s when a large volume of homogeneous water filled the Irminger basin.