Schwing, F.B., T.L. Hayward, T. Murphree, K.M. Sakuma, A.S. Mascarenas Jr., A.W. Mantyla, S.I. Larios Castillo, S.L. Cummings, K. Baltz, D.G. Ainley and F. Chavez.

ABSTRACT

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 featured the initial research cruise of the R/V Roger Revelle, several surveys off Baja California and central California have provided information in coastal areas adjacent to the present CalCOFI coverage. Conditions throughout the north Pacific and in the California Current are summarized and interpreted for the 1996-1997 period.

Moderate to weak La Niña conditions have affected the north Pacific since late 1995. However this particular event displayed an unusual pattern of atmospheric heating in the tropical Pacific, compared to other La Niñas. This may have helped produce a different response over the north Pacific that was, in several important respects, different from a typical La Niña. The most notable differences were in the wind anomalies, which may have contributed to relatively high sea level and warm SSTs offshore of California and Mexico throughout this period. El Niño conditions began to develop in the tropics in early 1997. If this event continues to develop, significant impacts on the California Current region can be expected.

Variability in coastal conditions is complex, and appears to be due to the combined effect of local processes and anomalies in large-scale atmospheric and ocean forcing. Coastal indices and time series show no dominant pattern of variability, and generally no unusual anomalies from their long-term seasonal means. Upwelling indices and buoy time series suggest generally high upwelling in the spring and summer of 1996, and unusually high rates in early 1997. In May 1997, upwelling was dramatically reduced along the entire coast. SSTs at SIO Pier were anomalously warm during the first half of 1996, but closer to the norm in late 1996 and early 1997. SST and coastal sea level anomalies began increasing in spring 1997, but it is premature to say this is related to El Niño forcing. What is certain is that warm El Niño-like conditions have been observed in the region long before the initial development of this latest apparent El Niño event. Winter sea level heights were relatively high due to onshore winds and high freshwater discharge, and were connected with positive height anomalies extending across the entire north Pacific, an consequence of La Niña.

The circulation patterns observed in 1996-1997 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 lower than historical climatologies indicate. A strong coastal countercurrent was noted off southern California in August and October 1996 and April 1997, and along the Big Sur coast in June 1996. Warm, saline water that was low in chlorophyll was associated with this flow.

Despite reasonably high primary production based on chlorophyll concentrations, macrozooplankton biomass remains very low compared to historical levels in the California Current. Juvenile rockfish and seabird populations also have displayed reduced abundances in recent years. High primary production is not clearly related to coastal time series or circulation patterns, and does not appear to be a good predictor of production at higher trophic levels in the California Current.