Global impact of oceanic variability in the subpolar North Atlantic

Strong decadal climate variability is a signature of the subpolar North Atlantic Ocean, which is also home to the global overturning circulation. Changes in the region, thus, have the potential to significantly impact global climate—via changes in the overturning itself or via the inter-basin impact on decadal Pacific variability, which acts as a pacemaker of global mean temperatures.

In a new research paper by Chafik et al., hydrographic observations are employed to show that decadal shifts of subsurface Atlantic Water temperatures, along the North Atlantic Current, are associated with a progression of heat anomalies from the Gulf Stream region that coincide with sea surface temperatures extending to cover most of the subpolar and tropical North Atlantic—a signal similar to that of the Atlantic Multidecadal Oscillation.

This basin-wide change in the Atlantic climate (both warming and cooling) induces a basin-scale sea surface temperature seesaw with the Pacific Ocean, which in turn modifies the position of the Walker circulation (the language by which the tropical basins communicate) and the strength of the Pacific trade winds. The Pacific decadal variability is thus amplified, which triggers pronounced atmospheric circulation anomalies extending from the tropical Pacific along a circle route into the Atlantic. An important point is that Atlantic climate variability appears to lead that of the Pacific.

Decadal oceanic variability in the subpolar North Atlantic is an essential aspect of the tropical interactions between the Atlantic and Pacific Oceans. And a better understanding of North Atlantic Ocean dynamics is central to understanding Pacific Ocean variability and vital in predicting how global mean temperatures may evolve on decadal timescales.