RECORD COASTAL UPWELLING IN THE CALIFORNIA CURRENT IN 1999

Abstract

An extremely unusual level of coastal upwelling in the spring and summer of 1999 over much of the California Current system (CCS) is described, based on direct and indrect observations. Wind and ocean anomalies in 1999, a period characterized by an equatorial La Niiia, are compared to climate trends for the previous several years, and specifically contrasted with the extremes associated with the 1997-98 El Niiio event. Conditions in the CCS during the spring and summer of 1999 were consistent with extremely high levels of sustained coastal upwelling. The Pacific Fisheries Environmental Laboratory (PFEL) upwelling indices reached record highs for a series ex- tending back to 1946. Strong, sustained upwelling- favorable winds were measured at coastal buoys through late 1998 and much of 1999. Coastal sea-surface teni- peratures (SSTs) were 3-4C below their seasonal mean in spring 1999, and about 10 cooler than the region ex- perienced in late 1997. Hydrographic surveys off central California suggest upwelling of water by 100 m or more relative to the long-term spring average. Coastal sea-level (CSL) anomalies in the northern CCS were the lowest in at least 65 years. Greater than usual southward trans- port by the California Current is implied. A number of population and ecological changes observed during this period may be linked to the unusual ocean conditions and the striking transition from El Niiio to La Niiia. Physical conditions in the CCS can change swiftly and dramatically, and its marine populations appear to re- spond nearly as rapidly. The large physical and biological changes that occurred in 1999 may signi@ the initiation of a new climate regime for the CCS. INTRODUCTION In less than two years sea-surface temperatures (SSTs) over much of the California Current system (CCS) dropped from the warmest on record during the height of El Niiio in late 1997 (as much as 6°C above the sea- sonal mean; Lynn et al. 1998) to low temperatures in 1999 not seen in decades (more than 3 below normal). This rapid cooling is unprecedented, particularly in the