Eddy Transport of Heat and Thermocline Waters in the North Pacific: A Key to Interannual/Decadal Climate Variability?

Abstract

High-resolution XBT transects in the North Pacific Ocean, at an average latitude of 22°N, are analyzed together with TOPEX/Poseidon altimetric data to determine the structure and transport characteristics of the mesoscale eddy field. Based on anomalies in dynamic height, 410 eddies are identified in 30 transects from 1991 to 1999, including eddies seen in multiple transects over a year or longer. Their wavelength is typically 500 km, with peak-to-trough temperature difference of 2.2°C in the center of the thermocline. The features slant westward with decreasing depth, by 0.8° of longitude on average from 400 m up to the sea surface. This tilt produces a depth-varying velocity/temperature correlation and hence a vertical meridional overturning circulation. In the mean, 3.9 Sv (Sv ≡ 106 m3 s?1) of thermocline waters are carried southward by the eddy field over the width of the basin, balanced mainly by northward flow in the surface layer. Corresponding northward heat transport is 0.086 ± 0.012 pW. The eddy field has considerable variability on seasonal to interannual timescales. For the 8-yr period studied here, eddy variability was the dominant mechanism for interannual change in the equatorward transport of thermocline waters, suggesting a potentially important forcing mechanism in the coupled air?sea climate system.