Changes in Ocean Heat Transport and Heat Content in SODA-POP for the Period 1958- 2001

A recently completed ocean reanalysis is used to investigate climate change in the global oceans for the period from 1958-2001. The forecast model utilizes Parallel Ocean Program physics with an average 0.25° × 0.4° × 40-level resolution and is forced with the European Center for Medium Range Weather Forecast ERA-40 wind stress. The model uses the SODA assimilation package, with observations from the historical archive of hydrographic profiles supplemented by ship intake measurements, moored hydrographic observations and remotely sensed SST. The reanalysis variables are mapped onto a uniform 0.5° × 0.5° × 40-level grid in monthly-mean form which is used to explore global ocean climate change. The results show trends of heat transport in the world oceans and in individual ocean sectors. The variation of ocean heat transport is largely due to changes in ocean currents instead of changes in the temperature field, implying a dominant role of ocean dynamics in variability of oceanic heat transport. Significant change in the global ocean heat transport is found in the upper 1000 meters with modest latitudinal dependence. Shallow overturning (0-500m) cells in the Atlantic and Indo-Pacific sectors play an essential role in changes of tropical ocean heat transport. In the Atlantic, the role of oceanic processes at depths of 500-1000m (the upper branch of deep overturning cells) increases and acts as a secondary contributor to the variation of heat transport. The lower branch of deep cells (1000-5000m) associated with deep water formation appears to play a negligible role in altering heat transport. Heat storage rate, heat transport, and diffusive heat flux are calculated to form a heat budget, and surface heat flux is derived as a residual. We find a global mean heating of 0.16 Wm^-2 is needed to account for ocean heat content changes for the period from 1958-2001 and is similar to Levitus's findings (0.20 Wm^-2 per unit area of the earth's surface). However, the mean divergence of heat transport in the North Atlantic Ocean (10°N - 60°N) is much larger than the mean time rate of change of heat content (1.06 Wm^-2), and contributes a 14.60 Wm^-2 to mean surface heat flux in the North Atlantic Ocean.