Analysis of Basin-Scale Mass Exchange between the Atlantic/Indian Oceans and the Pacific

It has been known for some time that there is a seasonal exchange of water mass between the Pacific and Atlantic Oceans that is due solely to variations in ocean transports related to wind forcing. This appears as a leading mode in most global barotropic models. In this presentation, we examine this exchange by averaging ocean bottom pressure from numerical models, GRACE, and steric-corrected altimetry for the Atlantic, Pacific, and Indian basins from late-2002 until early 2008, after the near eustatic global mass variation has been removed. As expected, the variations in the Pacific and Atlantic are highly negatively correlated with a dominant seasonal variation. After removing the seasonal variations, we find that the Indian and Atlantic Oceans have interannual variations that are highly correlated. We also find a strong variation in all basins at a period of approximately 1.5-years that is phase locked with a similar variation in the Southern Annular mode. In addition, we find significantly larger interannual variations in the GRACE observations than are predicted by either numerical model. The largest is an exchange of mass from the Atlantic and Indian Oceans to the Pacific that began in late-2006 and appears to be continuing through early-2008.