J. Phys. Oceanogr. http://doi.org/cxkq (2018)

Dense water formation in the Nordic Seas is a key component of the Atlantic Meridional Overturning Circulation. Convection in the Greenland Sea, for example, is thought to represent a significant proportion of dense water production, but large variability has been observed in recent decades. Using various hydrographic measurements, Ailin Brakstad from the University of Bergen, Norway, and colleagues further quantify the temporal variability of wintertime open-ocean convection — and subsequent dense water formation — in the Greenland Sea from 1986 to 2016.

Shallow convection (<300 m) is found to have dominated from 1988 to 1993, linked to a near-surface freshening that enhanced the stability of the upper water column, thereby inhibiting convection. After 1993, however, a transition to deep convection (500–1,000 m) occurred due to an increase in near-surface salinity and weaker stratification. As a consequence, a new class of less-dense intermediate water was formed, becoming the primary product of convection in the region, with an estimated 0.6 Sv produced annually. These results highlight increased understanding of dense water production in the Nordic Seas, with implications for quantifying future AMOC variability under anthropogenic forcing.