A reconstruction of large‐scale circulation in the Pacific Ocean north of 10°N

Abstract

A dynamically consistent steady state circulation pattern of the North Pacific (NP) ocean is presented. The fields describing oceanic state and atmospheric forcing are obtained by fitting a steady state large‐scale circulation model to the 1.0 release of World Ocean Circulation Experiment hydrology, da Silva atmospheric climatologies, TOPEX‐Poseidon altimetry, and Marine Environmental Data Service drifter data. Heat, salt, and mass transports of the major circulation features of the NP are presented. All the estimates are supplied with error bars obtained via the approximate inversion of the Hessian matrix. The optimized pattern shows, in particular, that NP is heated at an average rate of 11±7 W m−2 and loses 26±18 cm of fresh water from its surface per year. Zonal mean transport north of 20°N is characterized by an upwelling of 7±2 Sv (1 Sv = 106 m3 s−1) in the intermediate layers (500–3000 m) within the latitudes 30°–50°N. A weaker overturning cell characterized by the downwelling of 3±1 Sv at 55°–60°N contributes to the meridional circulation pattern north of 51°N. The net meridional advective heat transport in the midlatitudes is statistically undistinguishable from zero and amounts to −0.1±0.4 PW (1 PW = 1015 W). At 35°N, fresh water is transported southward at the rate equivalent to the average rainfall to the north of 35°N of 18±14 cm yr−1. Analysis of the water mass transformation rates reveals the major NP intermediate water formation site to be east of Hokkaido and South Kuril Islands. A much weaker source is detected in the Alaskan Gyre. The net production rate of the NPIW source water east of Kuril Islands is estimated as 2.5 Sv.