Record Coastal Upwelling in the California Current in 1999

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 extending back to 1946. Strong, sustained upwellingfavorable winds were measured at coastal buoys through late 1998 and much of 1999. Coastal sea-surface teniperatures (SSTs) were 3"-4"C below their seasonal mean in spring 1999, and about 10" cooler than the region experienced 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 transport 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 respond 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 seasonal 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 [Manuscript received 6 March 2000.1 148 STEPHEN RALSTON, KEITH M. SAKUMA Tiburon Laboratory National Marine Fishenes Service, NOAA 31.50 I'nradise Drive Tiburon, California 94020 context of the very warm regional ocean temperatures of the past decade, and is especially impressive given that the annual range of SST is about 3°C off central California, and its interannual variance is only 1°C. Coastal upwelling is arguably the dominant process affecting the physical and ecological structure of the CCS and other eastern boundary current ecosystems. Upwelling in spring and summer significantly affects regional and local ocean circulation, thermohaline structure and stabhty, and water-mass exchange between the coastal and deep ocean. It drives the biological productivity and energetics of the system through the vertical transport of nutrients into the photic zone and the lateral advection of nutrients, primary and secondary producers, and larvae of higher predators. This process also contributes to the generation of ocean fronts, where organisms and material often aggregate. Interannual variability in coastal upwelling is reflected in the physical, biochemical, and ecological nature of the CCS (Chelton et al. 1982). Much of the variability on this time scale is attributed to El Niiio and La Niiia; another major contribution is from longer-term climate change (Mantua et al. 1997; Schwing and Mendelssohn 1997; Schwing et al. 1997). Yet it is not always clear whether unseasonable levels of upwelling are locally or remotely forced. It is also noted that interannual fluctuations in CCS transport or biological character (e.g., population distribution or recruitment) do not always have a corresponding shift in coastal upwelling. The goal of this paper is to describe the extremely unusual level of coastal upwelling that occurred in the spring and summer of 1999 over much of the CCS, based on direct and indirect observations. Anomalies of coastal winds, ocean temperature, structure, circulation, and coastal sea level are compared to coastal California climate trends for the previous several years, and specifically contrasted with the extremes associated with the 1997-98 El Niiio event. We speculate on the impact of the resulting anonialous conditions on coastal marine populations. We also look at the possible role of 1999 in predicting future conditions. This paper complements the article on the status of the California Current in this volume (Bograd et al. 2000). SCHWING ET AL.: COASTAL UPWELLING IN CALIFORNIA CURRENT, 1999 CalCOFl Rep., Vol. 41, 2000 Nay 1999 SST and A ~ r ~ l ~ a ~ 1999 Vector Wind Anomalies