Sedimentation in the Southern Okinawa Trough: Enhanced particle scavenging and teleconnection between the Equatorial Pacific and western Pacific margins
Abstract
Owing to its location, geomorphology and hydrodynamic conditions, the southernmost part of the Southern Okinawa Trough (SOT) acts like an efficient receptacle for sediments from Taiwan and the East China Sea shelf. The high sediment flux coupled with the passage, bifurcation, upwelling, swirling and detour of Kuroshio in the SOT area result in intense particle scavenging, with sedimentary inventories of 210Pb and 239, 240Pu for greater than expected from local atmospheric input and in-situ water column production. The unusually high inventories as well as the deposition history of Pu isotopes must be explained by advective transport of Pu westward from the Marshall Islands, the largest source of Pu n the Pacific, by the North Equatorial Current (NEC) followed by northward transport of Kuroshio to the SOT area. The high sedimentation rate in the SOT area enabled us to differentiate the subsurface peak of 239, 240Pu resulting from the global fallout maximum in 1963 A.D. and the subsurface maximum of 240Pu/239Pu caused by close-in fallout from neutron-rich thermonuclear tests conducted by the U.S. during 1952-54 at the Enewetak and Bikini Atolls. The vertical offset between the subsurface peaks of 239, 240Pu and 240Pu/239Pu in sediments suggests that deposition of the 240Pu/239Pu maximum preceded that of the 239, 240Pu maximum by 3-5 years and that the transit time of the 240Pu-enriched Pu from its source (at ~12oN, 162oE) to the SOT area is ~6 years. The mean velocity of NEC thus calculated is ~0.022 m s-1.
The present is the key to the past. This study reveals teleconnection between the Equatorial Pacific and the western Pacific margins and suggests that ODP and IMAGES cores recently collected from the SOT area holds great promise for the reconstruction of high resolution paleoceanographical records along the trajectories of NEC and Kuroshio.