Monday, April 20, 2020

Hmmm...."Global Ocean Circulation Is Speeding Up"

This is a couple months old but if I don't post it now it may not re-emerge from the link-vault in my lifetime.
(filing systems: very important you remember how things were indexed and cross-indexed)*

From The Scientist, February 5:

The movements of water within the ocean basins has been increasing in speed over the last 20 years, a new study shows, conflicting with prior models of climate change.
Contrary to previous predictions, the circulation of water in the world’s oceans appears to be accelerating, according to a study published in Science Advances today (February 5). Although the implications for this trend are, as yet, unknown, the discovery will be critical for informing future models of climate change, researchers say.

“This is quite an exciting paper,” says Joellen Russell, a geoscientist at the University of Arizona who was not involved in the study. “I think the results are robust, I think they’re important, and I think they are a little shocking,” she says.

The water of the Earth’s oceans is continuously circulating around the planet via currents, gyres, and eddies. These movements regulate the Earth’s climate by dispersing heat—they transport warm water from the tropics to the polar regions and drive cooler water back via the oceans’ depths. They also transport dissolved atmospheric gases, such as oxygen and carbon dioxide, and churn up nutrients from below. Ocean circulation is thus a fundamental process for life on Earth.

According to certain models—based on water temperature measurements and other factors—global warming has been predicted to weaken these currents. “Most people are expecting the global ocean circulation to slow,” says Russell, and consequently, for the seas to be more stratified in temperature gradient from the surface to their depths and therefore to be more stable with less mixing.

But, in contrast to these predictions, the new study that examines circulation on a global scale shows “a clear increase over the last twenty years . . . [in] the strengths of the currents,” says the University of Reading’s David Ferreira, who studies the dynamics of the oceans but who was not involved in the research. And that’s “pretty interesting,” he says.

There have been “numerous studies on various important but regional or basin-scale ocean circulations,” writes coauthor Shijian Hu of the Chinese Academy of Sciences’s Institute of Oceanology in an email to The Scientist. “However, it has not been well understood what the trend of the Earth’s large-scale ocean circulation is under the background of climate warming, partly because of a lack of systematic and continuous direct observations of the Earth’s oceans.”

Hu’s team examined historical observations and assimilated datasets from a wide range of sources, including satellite measurements, acoustic Doppler current profilers, and assorted temperature and salinity measurements, including those obtained by the global Argo system—a fleet of thousands of free-drifting floats that have been deployed in the worlds oceans since the early 2000s and that provide continuous monitoring of the temperature, salinity, and velocity of the upper ocean layer.

From these data, the team discovered that while ocean circulation in some regions shows a decelerating trend—for example, in the North Atlantic—across the planet as a whole there was a “surprising significant acceleration of global mean circulation during the past two decades,” Hu writes. Particularly prominent acceleration was apparent in the tropical oceans, the team notes....

*You may think of your filing system as a thing of beauty:
 Strahov Library, Prague via Wikimedia

When it has actually morphed, without your noticing, into something like this:
Central Social Institution, also Prague, via DesignYouTrust