Observations of increased wind-driven coastal upwelling off central California

Alongshore wind speed and sea surface temperature (SST) from coastal National Data Buoy Center buoys are used to study the variability of wind-driven coastal upwelling from 1982 to 2008. A long-term increase in upwelling is observed in central California (35 degrees N-39 degrees N) with stronger upwelling-favorable winds, colder water, and more frequent occurrences of upwelling days during the upwelling season (March-July). Further, a longer upwelling season is observed in the same region, starting earlier in the spring and persisting later in the fall. These interannual changes in upwelling strength and seasonal duration are investigated in this study. Changes in alongshore wind (forcing of upwelling) are poorly correlated with the El Nino-Southern Oscillation or the Pacific Decadal Oscillation, but the Northern Oscillation and the North Pacific Gyre Oscillation correlate with the geostrophic upwelling-favorable winds in the region. However, changes in SST (an upwelling response) are correlated with both changes in wind (upwelling forcing) and the climate indices. Although this short record cannot differentiate between multidecadal cycles and persistent trends, this data-based result does corroborate model-based projections of increased upwelling in this region due to global climate change. This increase in upwelling is understood to be a response to the strengthening of large-scale pressure gradient fields partially due to global-scale climate change. Farther north and farther south in California, other processes also have a significant influence on coastal conditions, such that the tendency for increased upwelling is not evident in the same way.