Ocean heat transport across 24°N in the Pacific

Abstract

Ocean heat transport across 24°N in the North Pacific is estimated to be 0.76 × 10 15 W northward from the 1985 transpacific hydrographic section. This northward heat transport is due half to a zonally averaged, vertical meridional circulation cell and half to a horizontal circulation cell. The vertical meridional cell is a shallow one, in which the northward Ekman transport of warm surface waters returns southward only slightly deeper and colder, all within the upper 700 m of the water column. In terms of its meridional heat transport, the horizontal circulation cell is also shallow with effectively all of its northward heat transport in the upper 700 m of the water column. Previous estimates of North Pacific heat transport at subtropical latitudes had ranged between 1.14 × 10 15 W northward and 1.17 × 10 15 southward. The error in this new direct estimate of Pacific heat transport is approximately 0.3 × 10 15 W. In addition, it is suggested that the annual variation in poleward heat transport across 24°N in the Pacific is of order 0.2 × 10 15 W, as long as the deep circulation below 1000 m exhibits little variation in water mass transport. Together, the Pacific and Atlantic transoceanic sections essentially close off the global ocean north of 24°N so that the total ocean heat transport across 24°N is estimated to be 2.0 × 10 15 W northward. This ocean heat transport is larger than the northward atmospheric energy transport across 24°N of 1.7 × 10 15 W. The ocean and atmospheric together transport 3.7 × 10 15 W of heat across 24°N, which is in reasonable agreement with classic values of 4.0 × 10 15 W derived from consideration of the Earth's radiation budget but which is markedly less than the 5.3 × 10 15 W required by recent satellite radiation budget determinations.