Understanding Patterns of Ocean Heat Content Change on Decadal Timescales Using a Global Ocean State Estimate

Internal climate variability has received considerable attention recently as a possible cause for apparent changes in the rate of global mean surface temperature rise from the 1990’s to the 2000’s. We examine ocean climate signals over this period using a recent global state estimate produced by the consortium for Estimating the Circulation and Climate of the Ocean (ECCO). The estimate is constrained by most available in situ and satellite data and also satisfies conservation laws for momentum, heat and freshwater, which permits consistent full diagnostics of ocean heat uptake and related quantities. In terms of estimated global averages, compared to the 90’s, the 00’s reveal higher ocean heat uptake of ~0.1-0.2 W/m² and a related increased rate of steric sea level rise, mostly in line with inferences made from available data. Corresponding regional anomalies in ocean heat content, sea level, and air-sea heat flux can be orders of magnitude larger, however, highlighting the difficulty in calculating and interpreting global averages. Largest increases in surface heat input in the 00's are seen in the central and eastern tropical Pacific, but vertical and horizontal advection anomalies act to redistribute heat to subsurface layers and over most of the tropical Pacific and Indian oceans. Other large regional redistributions of heat, also mainly associated with advection processes, are present in the North Pacific and North Atlantic. Spatial patterns in the Pacific resemble to some extent those expected under a change of phase of the Interdecadal Pacific Oscillation, but other more local mechanisms of variability also seem to be involved in the Pacific and elsewhere.