HR: 1340h
AN: T33A-0522    [Abstracts]
TI: Ridge Flank Flux as a Potential Source for the North Pacific Silica Plume
AU: * Johnson, H P
EM: johnson@ocean.washington.edu
AF: School of Oceanography, Box 357940 University of Washington, Seattle, WA 98195-7940 United States
AU: Hautala, S L
EM: susanh@ocean.washington.edu
AF: School of Oceanography, Box 357940 University of Washington, Seattle, WA 98195-7940 United States
AU: Bjorklund, T A
EM: tor@ocean.washington.edu
AF: School of Oceanography, Box 357940 University of Washington, Seattle, WA 98195-7940 United States
AB: The North Pacific silica plume is a global scale anomaly, extending from the North American continental margin to west of the Hawaii-Emperor seamount chain. Inventory of the plume at depths between 2000 and 3000 meters indicates that it contains 164 Teramols of dissolved silica, and is maintained by a horizontal flux of approximately 1.5 Tmols/year from the Eastern Pacific. The source region of this silica plume has been previously reported to be Cascadia Basin in the NE Pacific. However, simple box models based both on new hydrostations and compilations of archive data indicate that only a third of the dissolved silica that enters the larger North Pacific plume originates locally within the Cascadia/Gorda Basin. As it encounters the North American continental margin, the eastward-flowing deep Pacific bottom water is forced into `a U-turn' by seafloor topography. A portion of the bottom water is elevated from 4000 to 2300 meter depths by the high geothermal heat flow during rapid passage through Cascadia/Gorda Basin, and subsequently flows westward as the North Pacific mid-water plume. The plume water also absorbs an estimated 0.47 Tmol/year of locally derived silica during its passage adjacent to the continental margin. However, the Pacific bottom water is already relatively enriched in dissolved silica when it passes the Gorda Ridge/Mendocino junction, and the remaining 1 Tmol/year of silica must be acquired during near-bottom transit from the Western Pacific, over the portion of the easternmost Pacific plate where basement is younger than 65 Ma. Global compilations based on heat flow data argue that the upper crustal section of the young, eastern Pacific plate is an enormous aquifer, with active hydrothermal circulation and presumably diffuse venting into the bottom water. The suggestion that the large-scale flux of silica-rich hydrothermal fluid from the young eastern portion of the Pacific plate contributes to the North Pacific silica plume is a consequence of that interpretation, but is only a plausible and still untested hypothesis. If correct, however, it implies that the ridge flanks of the eastern Pacific Ocean are a global-scale source of a critically important nutrient.
DE: 0330 Geochemical cycles (1030)
DE: 3615 Intra-plate processes (1033, 8415)
DE: 4835 Marine inorganic chemistry (1050)
DE: 8415 Intra-plate processes (1033, 3615)
SC: Tectonophysics [T]
MN: Fall Meeting 2005