12.12.2016: FB1-Seminar

11:00 h, Hörsaal, Düsternbrooker Weg 20

Abstract:
The Labrador Sea is the primary region in the Northern Hemisphere for the atmospheric ventilation of the Atlantic Ocean's intermediate-depth waters, through winter cooling of surface water and subsequent sinking to depths of 500-2500 m. The resulting denser water, known as Labrador Sea Water (LSW) spreads and feeds the global ocean's "overturning" circulation or ocean conveyor belt.
There has been a progressive deepening of winter convection in the Labrador Sea since 2012 associated with above-average regional winter cooling over the past five years. The depth to which cooled waters sank during this time has progressively increased from 1000 m in 2011 to 2100 m in 2016. The resulting 2016 volume of newly-ventilated LSW is the largest since the record volume observed in the early 1990s, and the recent intensified-ventilation period may be the largest since 1938 except for the 1987-1994 record strong period. In fact, this recent increase in convection resembles that during the formation of the record-depth (2500 m) LSW class in 1987-1994, with both being attributed to repeated positive phases of the winter North Atlantic Oscillation provided critical forcing and preconditioning.
As a result of this intermittent recurrence of intensified Labrador Sea Water formation, the annual average temperature and density in the region's upper 2000 m have predominantly varied on a bi-decadal time scale, rather than having a long-term trend as might be expected from anthropogenic climate change. These results have potential implications for broader-scale changes in heat content and other oceanographic variables in the North Atlantic, and for changes in the Atlantic component of the overturning circulation and its regulation of global climate.

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