The authors characterize impacts on heat in the ocean climate system from transient ocean mesoscale eddies. Their tool is a suite of centennial-scale 1990 radiatively forced numerical climate simulations from three GFDL coupled models comprising the Climate Model, version 2.0–Ocean (CM2-O), model suite. CM2-O models differ in their ocean resolution: CM2.6 uses a 0.1° ocean grid, CM2.5 uses an intermediate grid with 0.25° spacing, and CM2-1deg uses a nominal 1.0° grid. Analysis of the ocean heat budget reveals that mesoscale eddies act to transport heat upward in a manner that partially compensates (or offsets) for the downward heat transport from the time-mean currents. Stronger vertical eddy heat transport in CM2.6 relative to CM2.5 accounts for the significantly smaller temperature drift in CM2.6. The mesoscale eddy parameterization used in CM2-1deg also imparts an upward heat transport, yet it differs systematically from that found in CM2.6. This analysis points to the fundamental role that ocean mesoscale features play in transient ocean heat uptake. In general, the more accurate simulation found in CM2.6 provides an argument for either including a rich representation of the ocean mesoscale in model simulations of the mean and transient climate or for employing parameterizations that faithfully reflect the role of eddies in both lateral and vertical heat transport.

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Eddies in the Southern Ocean act to moderate the response of the Antarctic Circumpolar Current (ACC) to changes in forcing. An updated analysis of the Southern Ocean satellite altimetry record indicates an increase in eddy kinetic energy (EKE) in recent decades, contemporaneous with a probable decrease in ACC transport. The EKE trend is largest in the Pacific (14.9 6 4.1 cm 2 s 22 per decade) and Indian (18.3 6 5.1 cm 2 s 22 per decade) sectors of the Southern Ocean. We test the hypothesis that variations in wind stress can account for the observed EKE trends using perturbation experiments conducted with idealized high-resolution ocean models. The decadal increase in EKE is most likely due to continuing increases in the wind stress over the Southern Ocean, albeit with considerable interannual variability superposed. ACC transport correlates well with wind stress on these interannual time scales, but is weakly affected by wind forcing at longer periods. The increasing intensity of the Southern Ocean eddy field has implications for overturning circulation, carbon cycling, and climate.