Research Document 2021/072

Meteorological, Sea Ice and Physical Oceanographic Conditions in the Labrador Sea during 2019

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

Abstract

In the Labrador Sea, the coldest and freshest North Atlantic basin south of the Greenland-Iceland-Scotland Ridge, 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 2018–2019, the central Labrador Sea gave out less heat through its surface than in any of the five preceding winters. The recent reduction in the seasonal cooling of the Labrador Sea contrasts a 25-year record high winter heat lost in 2015. The winter (December–March) North Atlantic Ocillation (NAO) index was moderately positive in 2019. However, atmospheric circulation associated with a low-atmospheric-pressure anomaly in the Labrador Sea in winter resulted in above-normal air temperatures in the northern and central Labrador Sea. Sea-surface temperatures were near-normal in winter and above-normal in spring. Sea-ice-extent anomalies in winter and spring were generally negative, except for a near-normal winter anomaly on the central Labrador Shelf. With respect to annually-averaged, temperature-anomaly values, in 2018, the upper 100 m layer of the central Labrador Sea was the coldest since 2000. However, between 2018 and 2019, this layer warmed by 0.5 °C. The intermediate (200–2,000 m) layer cooled between 2011 (the layer’s warmest year since 1972) and 2018. This cooling trend can be associated with persistent deepening of winter convection over the same time period. The key factor that has contributed to the recurrent deepening of convective mixing in the three winters following the winter of 2015 was not as much air-sea heat exchange as it was the water-column preconditioning caused by convective mixing in the previous years. Such multiyear persistence of deepening winter convection, which lasted until the winter of 2018–2019 and exceeded 2,000 m in depth, has resulted in the most voluminous, densest, and deepest formation of Labrador Sea Water since 1994. In the winter of 2018–2019, the situation has, however, changed with winter convection not generally exceeding 1,200 m and the intermediate layer warming slightly but enough to reverse the seawater-density trend. Between 2018 and 2019, the annual mean-intermediate-layer density reduced by 0.007 kg/m³. Overall, the changes in the depth of winter convection and intermediate-layer properties between these years imply that the effect of the water-column preconditioning on winter convection has weakened since 2018. 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. The Atlantic Meridional Overturning Circulation index based on this model demonstrates a general weakening trend since mid-1990s, and continued weakening in recent years is present in this model hindcast.

Research Document 2021/072 (PDF, 6,788 KB)

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