Observed interannual variability of the Atlantic meridional overturning circulation at 26.5°N
Article first published online: 12 OCT 2012
©2012. American Geophysical Union. All Rights Reserved.
Geophysical Research Letters
Volume 39, Issue 19, 16 October 2012
How to Cite
2012), Observed interannual variability of the Atlantic meridional overturning circulation at 26.5°N, Geophys. Res. Lett., 39, L19609, doi:10.1029/2012GL052933., , , , , , , , , and (
- Issue published online: 12 OCT 2012
- Article first published online: 12 OCT 2012
- Manuscript Revised: 21 AUG 2012
- Manuscript Accepted: 21 AUG 2012
- Manuscript Received: 28 JUN 2012
- Atlantic meridional overturning circulation;
- heat transport;
- thermohaline circulation
 The Atlantic meridional overturning circulation (MOC) plays a critical role in the climate system and is responsible for much of the heat transported by the ocean. A mooring array, nominally at 26°N between the Bahamas and the Canary Islands, deployed in Apr 2004 provides continuous measurements of the strength and variability of this circulation. With seven full years of measurements, we now examine the interannual variability of the MOC. While earlier results highlighted substantial seasonal and shorter timescale variability, there had not been significant interannual variability. The mean MOC from 1 Apr 2004 to the 31 March 2009 was 18.5 Sv with the annual means having a standard deviation of only 1.0 Sv. From 1 April 2009 to 31 March 2010, the annually averaged MOC strength was just 12.8 Sv, representing a 30% decline. This downturn persisted from early 2009 to mid-2010. We show that the cause of the decline was not only an anomalous wind-driven event from Dec 2009–Mar 2010 but also a strengthening of the geostrophic flow. In particular, the southward flow in the top 1100 m intensified, while the deep southward return transport—particularly in the deepest layer from 3000–5000 m—weakened. This rebalancing of the transport from the deep overturning to the upper gyre has implications for the heat transported by the Atlantic.