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Research Document 2021/042

Meteorological, Sea Ice, and Physical Oceanographic Conditions in the Labrador Sea during 2018

By Yashayaev, I., Peterson, I., and Wang, Z.

Abstract

In the Labrador Sea, wintertime surface heat losses result in the formation of dense waters that play an important role in ventilating the deep ocean and driving the global ocean overturning circulation. In the winter of 2017–18, as in the previous two winters, the subpolar North Atlantic experienced below-average (2017–18) to average (2015–16 and 2016–17) surface heat losses, which were significantly lower than the 2014–15 winter heat loss, that was the highest since 1993–94. The winter (December–March) North Atlantic Oscillation (NAO) index in 2017–18, and winter ocean-atmosphere heat fluxes, in the central Labrador Sea, were near their long-term average values. However, atmospheric circulation, associated with a high atmospheric pressure anomaly extending throughout the Labrador Sea in winter, resulted in above-normal air and sea surface temperatures in the western Labrador Sea, and below-normal temperatures in the northeastern Labrador Sea. For sea surface temperature, these conditions persisted into the spring season, appearing to propagate cyclonically. Sea ice concentration anomalies in February and March, 2018, were generally negative in the western Labrador Sea, and positive in the northeastern Labrador Sea, consistent with the atmospheric circulation and air temperature anomalies. The upper 100 m layer of the central Labrador Sea has been cooling since 2010. However, the intermediate (200–2000 m) layer only started to cool after 2011, which was the layer’s warmest year during 1972–2018. This cooling was mainly caused by ongoing deepening of winter convection. Indeed, despite a reduction in the cumulative heat losses from the sea surface after 2014–15, the depth of winter convection continued to increase in the three winters that followed. This is mainly due to the water column preconditioning caused by convective mixing in the previous years. The multiyear persistence of deepening winter convection (eventually exceeding 2000 m in depth) has resulted in the most voluminous, densest and deepest formation of Labrador Sea Water since 1994. Bedford Institute of Oceanography North Atlantic model simulations suggest that the transport of the Labrador Current decreased between 1995 and 2014, but has since increased slightly.

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