GRACE Satellites Confirm Huge Decline In N. Atlantic Overturning Current In 2009-2010

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Now, in a new paper in Geophysical Research Letters, researchers from NASA’s Jet Propulsion Laboratory and the University of Texas at Austin use a new and sophisticated tool — the “Gravity Recovery and Climate Experiment” satellites, or GRACE — to confirm some pretty odd behavior in the circulation in 2009 and 2010 that has also been linked to a sudden and extreme 4-inch sea-level rise on the East Coast.

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The new research now shows that the same can be done with changes in the oceans. Specifically, the researchers used GRACE to detect what they call ocean “bottom pressure anomalies” between 3,000 and 5,000 meters deep in the Western part of the North Atlantic in 2009 and 2010. The anomalies were so big that the researchers estimate that they translate into a decline of 5.5 sverdrups of ocean flow — and a sverdrup is a gigantic number. It refers to a water flow of one million cubic meters of water per second. “The Mississippi is a fraction of a sverdrup,” says study co-author Michael Watkins at UT-Austin. “You’re talking about huge flows in the ocean, compared to what we think of as typical river flux.”

Sme figures provided by Landerer give another way of looking at how big a change this is. A sverdrup, he explains, translates into the transport of 84.6 billion tons of water per day, or 84.6 gigatons. 5.5 sverdrups is therefore more than 450 gigatons per day, and this seems to have happened over an extended period of time. “The time-mean AMOC flow (16-18 Sv) moves about 350 times as much (salt)water every day as CA is short in the 4-year drought,” adds Landerer by email.

What GRACE picks up on, specifically, is regions where the ocean contains more or less mass because more water is collected in that area, due to the actions of waves, winds or currents. “If you imagine putting a bathroom scale under that water it would weigh more,” says Watkins. “So that’s really what GRACE measures. As ocean circulation piles up water somewhere, we see it, and the AMOC has a particular geographic distribution of that piling up of water, and that’s the thing that we’re grabbing.”

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https://www.washingtonpost.com/news/energy-environment/wp/2015/11/04/nasa-can-now-detect-worrying-ocean-circulation-changes-from-space/