ENSO influence on satellite-derived chlorophyll trends in the Gulf of California

Abstract

ENSO impacts on the Gulf of California ecology remains a matter of controversy, because of contrasting field observations. In the present study, interannual variability is examined from fields of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) surface chlorophyll (Chl-a) from September 1997, the start of data from the SeaWiFS, until December 2006. Empirical orthogonal function (EOF) analysis and the spatial signature of the multivariate El Niño index (MEI), as revealed by a linear regression analysis (LRA), were used to quantify the degree of climate forcing (ENSO impacts) over the Gulf of California Chl-a. The spatial patterns of EOF1 (that explained 44% of the total variance) and the slopes and correlation coefficients (R) values resulted similar, suggesting that the effects of ENSO events in the gulf are not homogeneous, showing that eastern coast and the northern area were the most variable, affected and closely correlated with the MEI (r ≈ –0.5, P < 0.01), while at the Midriff Islands region and the western coast less variability and weaker correlation with the MEI were observed, explaining the apparent contradictions regarding the ecological ef­fects of ENSO in the Gulf of California. The EOF1 amplitude time series was significantly correlated to MEI (r = –0.69, P < 0.01) showing approximately one year lag between the 1999-2004 overall warming period onset, represented by the increase of MEI values and the decrease of the Gulf of California Chl-a interannual variability (2000-2004). ENSO conditions consisting of decreasing/increasing Chl-a patterns were observed along both coasts of the gulf, while opposite conditions were revealed in the surface sea temperature (SST) pattern, reflecting the strong physical-biological coupling during the El Niño-La Niña events.