HR: 1340h
AN: OS13A-0505    [Abstracts]
TI: Distribution of Manganese, Silicic Acid, and Salinity Over Large Spatial Scales as Tracers of the Columbia River Plume off Oregon and Washington
AU: * Aguilar-Islas, A M
EM: aaguilar@ucsc.edu
AF: University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
AU: Bruland, K W
EM: bruland@ucsc.edu
AF: Institute of Marine Sciences, University of California Santa Cruz, Santa Cruz, CA 95064 United States
AB: The Columbia River provides a large source of silicic acid and trace metals such as manganese to the coastal waters off Oregon and Washington. Here we report the use of manganese, silicic acid, and salinity as tracers for the Columbia River plume. Dissolved manganese and silicic acid were measured on several surface transects off Oregon and Washington during June/July 2004. The concentrations of silicic acid and dissolved manganese in the near-field plume are markedly greater than those of surface oceanic waters (even during upwelling conditions). As the plume travels and mixes the concentrations of these two constituents remain relatively high within the plume providing, together with salinity, excellent tracers over large spatial scales for the Columbia River plume. California current water has low concentrations of both dissolved manganese and silicic acid (roughly 5 nM and 5 $\mu$M, respectively), freshly upwelled water is highly variable (2-20 nM) in dissolved manganese and can be as high as $\sim$35 $\mu$M in silicic acid, while in the near-field plume concentrations of silicic acid can excede 100 $\mu$M and dissolved manganese can be as high as 200 nM. Because the near-field plume is relatively low in nitrate ($\sim$20 $\mu$M) the biological drawdown of silicic acid is minor, and even after mixing, the far-field plume can contain over 30 $\mu$M of silicic acid. Similarly, the biological drawdown of manganese combined with dilution through mixing and scavenging are not sufficient to remove its signal from the plume, and concentrations of $\sim$25 nM manganese can be found in the far reaches of the plume.
DE: 4805 Biogeochemical cycles (1615)
DE: 4808 Chemical tracers
DE: 4815 Ecosystems, structure and dynamics
DE: 4235 Estuarine processes
DE: 4271 Physical and chemical properties of seawater
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting