Multiple deep gyres of the western North Pacific:: A WOCE section along 149°E

The top to bottom large-scale ocean circulation in the northwest Pacific is described using a World Ocean Circulation Experiment (WOCE) onetime hydrographic section along 149 degrees E between Papua New Guinea and Japan. The circulation is quantified using a combination of geostrophic and lowered acoustic Doppler current profiler velocity estimates. At the northern end of the section the flow regime is distinct in that the deep flow largely reflects that at the surface: the Kuroshio jet and its northern and southern recirculations have deep expressions. South of 25 degrees N, the deep and bottom water flows do not mirror the surface flows, and the circulation assumes a highly baroclinic structure. Below the depth of local North Pacific ventilation the how in the upper deep waters (800-2500 m) alternates in sign roughly every 10 degrees of latitude revealing a set of deep clockwise gyres with significant transports of 40 Sv (1 Sv 10(6)m(3)s(-1)) for a tropical gyre (south of 6 degrees N) and 20 Sv in a subtropical gyre (6 degrees - 24 degrees N). These gyres provide a pathway for South Pacific influences to reach 22 degrees N (the location of a strong water mass front) through exchange along the western boundary. Maps of properties on density surfaces suggest that the zonal extent of the upper deep water gyres found along 149 degrees E is basin wide. Below 2500 m, flow across the section is isolated from the Philippine Sea by the Izu-Ogasawara-Mariana Ridge and the how regime and property distribution reflect this: Lower Circumpolar Water flows west in a deep western boundary current near 10 degrees N and coalesces at the Izu-Ogasawara-Mariana Ridge with a tongue of North Pacific Deep Water also flowing west near 15 degrees N. About 4 Sv of a mixture of these waters flows east again near 25 degrees N, associated with an abyssal water mass front. North of the front, the water properties are laterally homogeneous on density surfaces in the strongly recirculating gyres associated with the deep Kuroshio system.