PP53C-2354
206/207Pb and Radiocarbon: An Unlikely Pair for Identifying the Source and Delivery Time of Ocean Advection in the South China Sea
Friday, 18 December 2015
Poster Hall (Moscone South)
Nathalie Goodkin1, Annette Bolton1, Mengli Chen2, Ellen R M Druffel3, Edward A Boyle4 and Adam Switzer5, (1)Nanyang Technological University, Earth Observatory of Singapore, Singapore, Singapore, (2)Singapore-MIT Alliance for Research and Technology (SMART), Singapore, Singapore, (3)University of California Irvine, Irvine, CA, United States, (4)Massachusetts Institute of Technology, Cambridge, MA, United States, (5)Nanyang Technological University, Singapore, Singapore
Abstract:
Two independent studies were undertaken to use anthropogenic emissions to investigate natural systems using a massive Porites coral taken from off the coast of Vietnam (12ο12’49.90”N, 109 ο18’17.51”E). Annual uptake of bomb radiocarbon (14CO2) was measured to investigate the impact of coastal upwelling; while Pb/Ca levels and Pb isotopes were measured to investigate oceanic infiltration of anthropogenic Pb. Both records reveal a signal of sub-surface seawater advection from the tropical North Pacific to the South China Sea (SCS) providing independent evidence for the source and delivery time of the upwelled water off the coast of Vietnam. The radiocarbon record, extending from 1900-1986 at ~annual resolution, shows a post-bomb peak lower and broader than those found from other corals in the SCS and Japan, but higher than those found in the Makassar Strait in Indonesia. The Makassar coral experiences three water masses: the South Equatorial Current (SEC), upwelled and SCS water. The SEC has a relatively low radiocarbon content. However, water in the SCS does not mix with SEC water that enters the Indonesia Seas via the Halmahera as the main throughflow is from north to south. Hence, the upwelling signature must be from the North Equatorial Current that enters from the Luzon strait at depth. Leaded gasoline was phased-out between 1997 and 2000 in most Asian countries, however unlike other regional records, the Pb/Ca of the coral continued to increase until 2004 indicating a non-atmospheric source of Pb to the region. Both records indicate the source of upwelled water from the tropical North Pacific at roughly ~100-200 meters with a transport time of >2-5 years. This water is carried westward, via the Luzon Strait and into the South China Sea, where is it upwelled during the summer months. A higher resolution study of this coral combined with other coral records from the region could further narrow the location and timing of the advection and upwelling.
