Overview

"An outstanding problem in the oceanic sciences is the rate of heat and freshwater transport from the equator to the poles, for it is this transport which powers the Earth's weather and climate system."  Keffer and Holloway, Nature  (1988).

MOCHA is a collaborative project, partnered with the UK RAPID Program, to measure the meridional overturning circulation (MOC) and ocean heat transport in the North Atlantic Ocean (Figure 1). These transports are primarily associated with the Thermohaline Circulation. Simply put, warm waters move poleward at the surface of the ocean, where they cool and sink, to return equatorward in the deep ocean.

Figure 1. A schematic for the North Atlantic Overturning (click on the image for details, courtesy of RAPID/NERC)

Climate models suggest that the MOC in the Atlantic, and the accompanying oceanic heat flux, vary considerably on interannual time scales. In addition to abrupt climate change scenarios in which the MOC can virtually shut off (Manabe and Stouffer, 1993; Vellinga and Wood, 2002), the “normal” interdecadal variation may range from 20% to 30% of its long-term mean value, according to some models (e.g., Hakkinen, 1999). However, until recently no direct measurement system had been put in place that could provide regular estimates of the meridional overturning circulation to determine its natural variability or to assess these model predictions. Such a system is now deployed along 26.5°N in the Atlantic as part of the joint U.K./U.S. RAPID-MOCHA program, which has been continuously observing the MOC since March 2004.

To visit the U.K. RAPID MOC website, click here.