Decadal variations in Labrador Sea ice cover and North Atlantic sea surface temperatures

The spatial and temporal evolution of winter sea ice anomalies in the Labrador Sea and associated sea surface temperature (SST) variations in the North Atlantic are documented for three periods of above‐normal ice cover: 1972–1974, 1983–1985, and 1990–1992. These events are notable for their winter‐to‐winter persistence, despite the fact that the ice margin retreats to northern Baffin Bay each summer, and for their spatial evolution, progressing from the northern Labrador Sea to the southern tip of Newfoundland over a 3 year period. Above‐normal sea ice is consistently accompanied by below‐normal SSTs in the subpolar Atlantic: the latter persist 1–3 years after the decay of the ice anomalies and in some cases exhibit a tendency for eastward movement across the gyre. Spring–summer freshwater anomalies at 100 m depth in the West Greenland Current are found to precede by ∼8 months the initial occurrence of above‐normal ice cover in the northern Labrador Sea. The role of atmospheric forcing in the joint evolution of anomalous sea ice and SST is assessed by means of an ice‐ocean mixed layer model forced with observed air temperature and wind fields. The model results indicate that thermodynamic atmospheric forcing accounts for much of the winter‐to‐winter persistence and spatial evolution of the ice and concurrent SST anomaly patterns. However, the subsequent persistence of SST anomalies in the subpolar region is not well simulated, suggesting that oceanic processes omitted from the simple slab mixed layer formulation play a contributing role.