Variability in Global Deep Ocean Circulation from GRACE

Although difficult if not impossible to observe routinely on a global scale from an in situ perspective, total water mass transport and inter-basin exchange are central to understanding long-term changes in ocean circulation. The limitation of in-situ observations in space and time preventing a global view of deep current variability. The representation of long-term transports in ocean models is highly dependent on the atmospheric forcing fields, which may misrepresent real interannual variability. Recent, advanced analysis of the bottom pressure observations from the Gravity Recovery And Climate Experiment (GRACE) provide for the first time the ability to observe this global water mass transport. Here, we present these first near-global maps of variability in the depth-independent ocean circulation derived from GRACE over the period 2002-2014. We find that significant variability on annual to decadal time scales exists in the deep large-scale circulation, some of which appear to be related to the Southern Annular Mode forcing dominating Southern Ocean variability.