The past and future of coastal and open ocean upwelling in the NE Pacific

0.5° latitude-longitude monthly QuikScat surface stress estimates for 2000-08 from the French satellite oceanography center (IFREMER) were employed to document seasonal and interannual variability of wind stress-forced January through July upwelling within 5-degrees of the Pacific eastern boundary (Queen Charlotte Islands to Baja). The covariability of the upwelling and global NCEP - NCAR reanalysis sea level pressure was analyzed to develop a pressure index that could be used to infer historical and simulated future upwelling variability.

The leading upwelling - pressure pattern explains 77% of the covariance, and is dominated by the seasonal enhancement or onset of upwelling along the entire coast, weakening of the Aleutian Low pressure, northwestward shift of the semipermanent subtropical high, and the development of a heat low (low pressure) over the central U.S. The interannual variablity of this pattern is characterized by anomalous upwelling of like-sign along the entire coast, pressure anomalies of like-sign over the ocean and land centered at 45N, and both geostrophic and down-gradient winds along the coast. Projection of this pressure pattern onto 20 of the IPCC AR4 simulations for the twentyfirst century (A1B greenhouse gas scenarios) showed springtime enhancement of the seasonal pattern. Pressure observations for the twentieth century did not show this shift, and instead are dominated by variations on interannual and multi-decadal time scales.