Ocean Circulation Accelerating, From Surface to Abyss

(CN) – Some studies have suggested climate change could slow ocean circulation worldwide, especially in tropical zones, but researchers in China, Australia and the U.S. have found ocean circulation has actually accelerated over the last two decades.

Ocean science researchers have found circulation of global oceans is accelerating in some areas (orange) and decelerating in others (blue) due to increased wind speed in the last two decades. (Courtesy of Shijian Hu)

The circulation of ocean waters redistributes Earth’s energy and helps shape global climate in a system that is sensitive to increased greenhouse gas emissions.

A United Nations report found this past September that along with increasing sea levels, climate change would also disrupt marine populations and weaken currents of our oceans. The planet’s oceans – which cover more than 70% of Earth’s surface – absorb and store nearly 90% of the heat produced by carbon emission pollution, the report found.

But climate change has also led to spikes in ocean temperatures, fueling a key trigger for more powerful hurricanes and other storm systems.

Shijian Hu, lead study author and researcher at the Chinese Academy of Sciences, found that increased wind speeds have played a major role in accelerating ocean currents.

Hu and colleagues scanned areas as deep as nearly 10,000 feet below the ocean surface and found that circulation at the deepest depths has been influenced by a 4% uptick in wind speed in the last two decades, according to the study published Wednesday in Science.

Most observations were limited to the upper 6,600 feet of the ocean, researchers said, adding that observations made in deeper ocean sectors are needed to understand how circulation will be further affected by climate change.

A diagram by ocean science researchers demonstrates the effect of spikes in greenhouse gas emissions causing increased wind speed and churning ocean circulation levels. (Courtesy of Shijian Hu)

Researchers did not immediately respond to a request for comment.

Ocean current measurements were collected by using the Global Marine Argo Atlas, a system of floating monitors that track changes in the ocean and calculate total global kinetic energy, the study said.

Global kinetic energy provides a calculation of ocean circulation intensity by measuring the movement of seawater.

Using measurements from the European Centre for Medium-Range Weather Forecasts Ocean Analysis/Reanalysis System and the Global Ocean Data Assimilation System, researchers found kinetic energy levels spiked at the onset of the 1990s.

In areas scanned from the upper 6,600 feet of global oceans, researchers found that 76% had increased kinetic energy due to increased wind speeds beginning in the 1990s, the study said.

A small portion of the change in global kinetic energy is due to natural variability in circulation, researchers said. And some ocean areas, such as the Kuroshio and Agulhas region currents, have not shown increased circulation since the 1990s – though these dynamics may be due to already complex regional trends, the study found.

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