Modeling the Dispersal of the San Francisco Bay Plume over the Northern
and Central California Shelf
Abstract
High-resolution simulations by the Regional Ocean Modeling System (ROMS)
were used to investigate the dispersal of the San Francisco Bay (SFB)
plume over the northern-central California continental shelf during the
period of 2011 to 2012. The modeled bulk dynamics of surface currents
and state variables showed many similarities to corresponding
observations. After entering the Pacific Ocean through the Golden Gate,
the SFB plume is dispersed across the shelf via three pathways: (i)
along the southern coast towards Monterey Bay, (ii) along the northern
coast towards Point Arena, and (iii) an offshore pathway restricted
within the shelf break. On the two-year mean timescale, the along-shore
zone of impact of the northward-dispersed plume is about 1.5 times
longer than that of the southern branch. Due to the opposite surface
Ekman transports induced by the northerly or southerly winds, the
southern plume branch occupies a broader cross-shore extent, roughly
twice as wide as the northern branch which extends roughly two times
deeper due to coastal downwelling. Besides these mean characteristics,
the SFB plume dispersal also shows considerable temporal variability in
response to various forcings, with wind and surface-current forcing most
strongly related to the dispersing direction. Applying
constituent-oriented age theory, we determine that it can be as long as
50 days since the SFB plume was last in contact with SFB before being
flushed away from the Gulf of the Farallones. This study sheds light on
the transport and fate of SFB plume and its impact zone with
implications for California’s marine ecosystems.