Cross-shelf subtidal variability in San Pedro Bay during summer, 2001

Abstract A total of 16 moorings were deployed across the San Pedro shelf, one of the two wider embayments in the Southern California Bight, from near the surfzone to the upper-slope. On the middle and outer shelf in the summer of 2001, the currents flowed strongly equatorward at the surface and had large vertical shears through the well-stratified water column. This equatorward flow differs from predominantly poleward flow found in previous studies of the coastal margin further west. In deeper water, near the shelf break, the shears were such that near-bottom flows were poleward and incorporated into the upper parts of the Southern California Undercurrent over the slope. Mid-shelf current fluctuations, with periods of 10–25 days, along with upwelling over the shelf, were not related to local winds, but were significantly correlated with the large-scale alongshore pressure gradient. Shorter period (∼7–10 days) inner shelf alongshore currents, however, were significantly correlated with the alongshore wind at the shelf break. A CEOF analysis gives two significant modes, with the first mode dominant over the outer and middle shelf. The wind-forced second mode connects the inner shelf to the poleward undercurrent over the slope such that increases in the poleward flow over the slope are correlated with increases in the equatorward current inshore of the 15 m isobath.