Inorganic carbon in the central California upwelling system during the 1997-1999 El Nino-La Nina event

Sea surface pCO(2) was monitored during 49 cruises from February 1997 to December 1999 along a section perpendicular to the central California Coast. Continuous measurements of the ocean-atmosphere difference Of pCO(2) were made on a mooring in the same region from July 1997 to December 1999. The El Nino/La Nina cycle of 1997-1999 had a significant influence on local ocean-atmosphere CO2 transfer. During the warm anomaly associated with El Nino, upwelling was suppressed and average sea surface pCO(2) was below atmospheric level. High rainfall and river runoff in the late winter and early spring of 1998 produced areas where pCO(2) was depressed by as much as 100 muatm. A flux ranging from 0.3 to 0.7 Mol C m(-2) y(-1) from the atmosphere into the ocean was estimated for the El Nino period from wind and DeltapCO(2) data. Temperatures and upwelling returned to near normal in the summer of 1998, but a cold anomaly developed during autumn of that year. Temperature and pCO(2) data indicate that upwelling continued throughout much of the 1998-1999 winter and intensified significantly in the spring of 1999. During strong upwelling events, the estimate of ocean to atmosphere flux approached rates of 50 mol C m(-2) y(-1). The estimate for the average CO2 flux from July 1998 to July 1999 was 1.5-2.2 mol C m(-2) y(-1) from the ocean to the atmosphere. While the flux estimate for the El Nino time period may be applicable to a larger area, the high ocean to atmosphere fluxes during La Nina might be the result of sampling near a zone of intense upwelling. (C) 2002 Elsevier Science Ltd. All rights reserved.