[quote]Winds are picking up worldwide, and that is making the surface waters of the oceans swirl a bit faster, researchers report. A new analysis of the ocean’s kinetic energy, measured by thousands of floats around the world, suggests that surface ocean circulation has been accelerating since the early 1990s.

Some of that sped-up circulation may be due to naturally recurring ocean-atmosphere patterns, such as the Pacific Decadal Oscillation, researchers report February 5 in Science Advances. But the acceleration is greater than can be attributed to natural variability alone — suggesting that global warming may also be playing a role, says a team led by oceanographer Shijian Hu of the Chinese Academy of Sciences in Qingdao.

The connected system of massive currents that swirl between the world’s oceans, sometimes called the Great Ocean Conveyor Belt, redistributes heat and nutrients around the globe and has a powerful effect on climate. Winds dominate mixing in the surface ocean: Prevailing winds in the tropics, for example, can push water masses aside, allowing deeper, nutrient-rich waters to surge upward.

In the deeper ocean, differences in water density due to salt and heat content keep the currents flowing (SN: 1/4/17). For example, in the North Atlantic Ocean, surface currents carry heat north from the tropics, helping to keep northwestern Europe warm. As the waters arrive at the Labrador Sea, they cool, sink and then flow southward, keeping the conveyor belt humming along.

How climate change might affect this Atlantic Meridional Overturning Circulation, or AMOC, has garnered headlines, as some simulations have predicted that global warming would lead to a slowdown in which could eventually bring a deep chill to Europe. In 2018, paleoceanographer David Thornalley of University College London and colleagues reported evidence that the AMOC has weakened over the last 150 years, although the question remains uncertain (SN: 1/31/19).

But the new study focuses on “the amount of swirling around of upper ocean waters due to wind,” rather than the speed of that overturning circulation, says Thornalley, who was not involved in the work.

Global warming has long been predicted to slow global wind speeds, called “global stilling.” That’s because the poles are warming faster than the equatorial region, and a smaller temperature gradient between the two zones might be expected to result in weaker winds (SN: 3/16/18). But recent studies, such as a report published November 2019 in Nature Climate Change, suggest that wind speeds around the world have actually been speeding up, at least since about 2010. [quote]

https://www.sciencenews.org/article/climate-change-speeding-up-ocean-circulation