THE STATE OF THE CALIFORNIA CURRENT, 1996-1997 - MIXED SIGNALS FROM THE TROPICS

A large number of data sets from within the California Current region, and the large-scale fields that affect this region, are available for timely assessment of recent environmental conditions in this system, In addition to the long-running quarterly CalCOFI cruises, which featu red the initial research cruise of RV Roger Revelle, several surveys o ff Baja California and central California have provided information on coastal areas adjacent to the present CalCOFI coverage, Conditions th roughout the north Pacific and in the California Current are summarize d and interpreted for the 1996-97 period. Moderate to weak La Nina con ditions have affected the north Pacific since late 1995, But this part icular La Nina event displayed an unusual pattern of atmospheric heati ng in the tropical Pacific, compared to other La Nina events, This may have helped produce a different response over the north Pacific that was, in several important respects, different from a typical La Nina, The most notable differences were in the wind anomalies, which may hav e contributed to relatively high sea level and warm SSTs offshore of C alifornia and Mexico throughout this period. El Nino conditions began to develop in the tropics in early 1997, If this event continues to de velop, significant effects on the California Current region can be exp ected, Variability in coastal conditions is complex, and seems due to the combined effect of local processes and anomalies in large-scale at mospheric and ocean forcing, Coastal indices and time series show no d ominant pattern of variability, and the anomalies from their long-term seasonal means were generally not remarkable, Upwelling indices and b uoy time series suggest generally high upwelling in the spring and sum mer of 1996, and unusually high rates in early 1997, In May 1997, upwe lling was dramatically reduced along the entire coast, At SIO Pier, SS Ts were anomalously warm during the first half of 1996, but closer to the norm in late 1996 and early 1997. In spring 1997, SST and coastal sea-level anomalies began increasing, but it is premature to say this was related to El Nino forcing. What is certain is that warm, El Nino- like conditions have been observed in the region long before the initi al development of this latest apparent El Nino. Winter sea-level heigh ts were relatively high due to onshore winds and high fresh-water disc harge, and were connected with positive height anomalies extending acr oss the entire north Pacific, a consequence of La Nina. Oceanic circul ation patterns observed in 1996-97 were similar to the long-term mean, and have featured relatively high mesoscale activity since early 1996 , Salinities in the core of the California Current were noticeably low er than historical climatologies indicate, A strong coastal countercur rent was noted off southern California in August and October 1996 and April 1997, and along the Big Sur coast in June 1996, Warm, saline wat er that was low in chlorophyll was associated with this now, Despite r easonably high primary production based on chlorophyll concentrations, macrozooplankton biomass remains very low compared to historical leve ls in the California Current. In recent years, there have also been re duced abundances of juvenile rockfish and seabird populations. High pr imary production is not clearly related to coastal time series or circ ulation patterns, and does not appear to be a good predictor of produc tion at higher trophic levels in the California Current.