A new study published in Science analyzed the first 21-month record of the Overturning in the Subpolar North Atlantic Program (OSNAP) observing system, which was launched in the summer of 2014. The OSNAP observing system comprises an integrated coast-to-coast array of two sections: OSNAP West, extending from the southeastern Labrador shelf to the southwestern tip of Greenland, and OSNAP East, extending from the southeastern tip of Greenland to the Scottish shelf. The highlight of the 21-month record is that the overturning circulation across OSNAP East (15.6 ± 0.8 Sv) is much larger than that across OSNAP West (2.1 ± 0.3 Sv). This suggests that, in a departure from the prevailing view that changes in deep water formation in the Labrador Sea dominate AMOC variability, the conversion of warm, salty, shallow Atlantic waters into colder, fresher, deep waters that move southward into the Irminger and Iceland basins is largely responsible for the AMOC and its variability.
Figure 1 from Lozier et al. (2019):The OSNAP section (red line) superposed on a map of mean absolute dynamic height (meters), with bathymetry <500 m shaded gray. The OSNAP observing system was designed to take advantage of the German Labrador Sea exit array at 53°N (operational since 1997); the recently installed U.S. Global OOI (Ocean Observatories Initiative) node in the southwest Irminger Sea; repeat A1E/AR7E hydrographic sections across the Irminger and Iceland basins; and the Ellett Line in the eastern basin (operational since 1976). OSNAP complements several monitoring programs in the North Atlantic: the Canadian repeat AR7W program in the Labrador Sea, Cape Farewell-Scotland sections at 59.5°N, the French OVIDE line across the eastern North Atlantic, and the U.K.-U.S. RAPID-MOCHA array at 26.5°N.
Lozier, M. S., Li, F., Bacon, S., Bahr, F., Bower, A. S., Cunningham, S. A., … & Greenan, B. J. W. (2019). A sea change in our view of overturning in the subpolar North Atlantic. Science, 363(6426), 516-521. http://science.sciencemag.org/content/363/6426/516