Interannual variations in the Atlantic meridional overturning circulation and its relationship with the net northward heat transport in the South Atlantic

Abstract

Variability of the Atlantic Meridional Overturning Circulation (AMOC) and its effect on the net northward heat transport (NHT) in the South Atlantic are examined using a trans-basin expendable bathythermograph (XBT) high-density line at 35°S (AX18). The time-mean AMOC is 17.9 ± 2.2 Sv during 2002-2007. Although the geostrophic transport dominates the time-mean AMOC, both geostrophic and Ekman transports are important in explaining the AMOC variability. The contributions of geostrophic and Ekman transports to the AMOC show annual cycles, but they are out of phase, resulting in weak seasonal variability of the AMOC. The NHT variability is significantly correlated with the AMOC, where a 1 Sv increase in the AMOC would yield a 0.05 ± 0.01 PW increase in the NHT. Partition of transport into the western and eastern boundaries and interior suggests that, to quantify changes in the AMOC and NHT, it is critical to monitor all three regions. Copyright 2009 by the American Geophysical Union.