Causes of interannual-decadal variability in the meridional overturning circulation of the mid-latitude North Atlantic Ocean

• Published in: Journal of Climate
• Main Authors: Biastoch, Arne, Böning, Claus W., Getzlaff, Julia, Molines, Jean-Marc, Madec, Gurvan
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2008
• Subjects: North Atlantic; Orca; Subarctic
• Online Access: https://eprints.soton.ac.uk/64312/; http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F2008JCLI2404.1

The causes and characteristics of interannual to decadal variability of the meridional overturning circulation (MOC) in the North Atlantic are investigated with a suite of basin-scale ocean models (FLAME) and global ocean-ice models (ORCA) varying in resolution from medium- to eddy-resolving (1/2° – 1/12°), using various forcing configurations built on bulk formulations invoking atmospheric reanalysis products. Comparison of the model hindcasts indicates similar MOC variability characteristics on time scales up to a decade; both model architectures also simulate an upward trend in MOC strength between the early 1970s and mid-1990s. The causes of the MOC changes are examined by perturbation experiments aimed selectively at the response to individual forcing components. The solutions emphasize an inherently linear character of the mid-latitude MOC variability by demonstrating that the anomalies of a (non eddy-resolving) hind-cast simulation can be understood as a superposition of decadal and longer-term signals originating from thermohaline forcing variability, and a higher-frequency wind-driven variability. The thermohaline MOC signal is linked to the variability in subarctic deep water formation, and rapidly progressing to the tropical Atlantic. However, throughout the subtropical and mid-latitude North Atlantic this signal is effectively masked by stronger MOC variability related to wind forcing and, especially north of 30–35° N, by internally-induced (eddy) fluctuations.