Interannual variability in chlorophyll concentrations in the Humboldt and California Current Systems

SeaWiFS data provide the first systematic comparison of 10 years (1997–2007) of chlorophyll interannual variability over the California (CCS) and Humboldt (HCS) Current Systems. Dominant signals are adjacent to the coast in the wind-driven upwelling zone. Maximum anomalies in both systems are negative signals during the 1997–1998 El Niño that persist into 1999 at most latitudes. Thereafter, anomalies primarily appear to be associated with shifts in phenology, with those in the CCS stronger than those of the HSC. Prominent signals in the CCS are positive anomalies in 2001–2002 at latitudes >35°N and <30°N, and in 2005–2006 from ∼30 to 45°N that persist at latitudes >40°N into 2007. In the HCS, latitudinally extensive positive events occur in austral summers of 2002–2003, 2003–2004. Relationships of chlorophyll anomalies to forcing are explored through correlations to local upwelling anomalies and three indices of Pacific Ocean basin-scale variability, the Multivariate El Niño Index (MEI), the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO). These show that each system has strong latitudinal regionality in linkage to forcing. At higher latitudes, correlations follow expected relationships of increased (decreased) chlorophyll with positive upwelling and NPGO (MEI and PDO). At specific latitudes, notably the Southern California Bight and off Peru, where circulation and/or chlorophyll phenology differ from canonical EBUS patterns, correlations weaken or oppose those expected. Correlations excluding the El Niño period remain similar in the CCS but substantially changed in the HCS, indicating much stronger domination of El Niño conditions on HCS anomaly relationships over this 10-year period.