Sergey Gladyshev, Vsevolod Gladyshev, Sergey Gulev, Andrey Demidov and Larisa Pautova, P. P. Shirshov Institute of Oceanology, RAS, Moscow, Russia
Using CTDO/ADCP data from the annual summer transatlantic section along 59.5° N along with AR07E data and ERA Interim reanalysis data we analyze anomalously deep winter convection in the Irminger Sea in 2014/15 in context of the history of properties of the North Atlantic intermediate water for the last two decades. Labrador Sea Water (LSW) was defined through the minimum potential vorticity. Oxygen saturation rate was used to separate the newly ventilated LSW from the old one as well as from the LSW advected from the Labrador Sea. Comparative analysis of the LSW properties from 1991 onwards shows that such a deep winter convection (down to 1800 m) with the potential density of the convected water amounting to 27.75 σΘ did not happen in the Irminger Sea during the last twenty years. During a single winter the mean LSW temperature dropped by 0.18°C and became just 0.05° C higher compared to the temperature observed in 2007. It is noteworthy that the LSW core held relatively high salinity (34.893 PSU) after 2008. Average LSW oxygen saturation rate of 94.5% unambiguously testifies its local origin and implies the LSW total renewal during the last winter. LSW filled the entire southern part of the deep Irminger Basin and was not observed in the region of the Western Boundary Current and the Irminger Current in June 2015. Analysis of the circulation reveals that most of LSW was generated outside of the Irminger Gyre. Anomalously deep winter convection can be explained by the anomalously large number of days with north-westerly - westerly winds exceeding 15 m/c which (along with the negative air temperatures over the large area spanning far beyond the vicinity of southern Greenland tip to the Reykjanes Ridge) was responsible for the anomalous cooling of surface ocean layer by extreme air-sea turbulent fluxes.