HR: 10:45h
AN: OS52A-02    [Abstracts]
TI: Modification of ocean-estuary salt fluxes by density-driven advection of a headland eddy
AU: * Fram, J P
EM: jfram@berkeley.edu
AF: UC Berkeley, Environmental Engineering Group 760 Davis Hall , Berkeley, CA 94720 United States
AU: Stacey, M T
EM: mstacey@socrates.berkeley.edu
AF: UC Berkeley, Environmental Engineering Group 760 Davis Hall , Berkeley, CA 94720 United States
AB: Scalar exchange between San Francisco Bay and the coastal ocean is examined using shipboard observations made across the Golden Gate Channel. Ocean-estuary exchange is often described as a combination of two independent types of mechanisms: density-driven exchange such as gravitational circulation and tidal asymmetries such as tidal trapping. In this study we found that exchange is also governed by an interaction between these mechanisms. Tidally trapped eddies created in shallow shoals are mixed into the main channel earlier in the tidal cycle during the rainy season because the eddies are pushed seaward by gravitational circulation. This interaction increases the tidally averaged dispersive salt flux into the bay. The study consists of experiments during each of three 'seasons': winter/spring runoff (March 2002), summer upwelling (July 2003), and fall relaxation (October 2002). Within each experiment, transects across the channel were repeated approximately every 12 minutes for 25 hours during both spring tide and the following neap tide. Velocity was measured from a boat-mounted ADCP. Scalar concentrations were measured from a tow-yoed SeaSciences Acrobat. Salinity exchange over each spring-neap cycle is quantified with harmonic analysis. Harmonic results are decomposed into flux mechanisms using temporal and spatial correlations. The temporal correlation of cross-sectional averaged salinity and velocity (tidal pumping flux) is the largest part of the dispersive flux of salinity into the bay. From the tidal pumping portion of the dispersive flux, it is shown that there is less exchange than was found in earlier studies. Furthermore, tidal pumping flux scales strongly with flow due to density-driven movement of tidally trapped eddies and density-driven increases in ebb-flood frictional phasing. Complex bathymetry makes salinity exchange scale differently with flow than would be expected from simple tidal pumping and gravitational circulation models.
UR: http://www.ce.berkeley.edu/research/fluids
DE: 4235 Estuarine processes
DE: 4528 Fronts and jets
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly