Peter B. Rhines (University of Washington, USA); Denise Worthen (Wyle STE Group/NASA GSFC, USA)

We have investigated the multidecadal warming and interannual and decadal heat content changes in the upper ocean from observational data sets and from a modeled state estimate. Multidecadal warming is dominated by a contribution from deepening of the mid-thermocline isopycnals, resulting in an expansion of the subtropical mode water volume, rather than shifts of the temperature/salinity relationship. In fact temperatures of the same mode waters have cooled slightly. The contribution from this volume increase outweighs the surface warming contribution in the upper ocean heat content. The multidecadal isopycnal sinking has been the strongest over the southern basins. On interannual to decadal scales, sinking and shoaling of density surfaces dominates ocean heat content changes, while the contribution from temperature changes along density surfaces decreases as time scales shorten. Decomposition of ocean heat content changes into heaving and isopycnal temperature changes is shown to provide insight to the satellite sea surface height measurements of the last two decades.