Abstract
Abstract. Interannual correlation between satellite-derived sea surface temperature (SST) and surface chlorophyll a (Chl a) are examined in the coastal upwelling zone off Punta Eugenia on the west coast of the Baja California Peninsula, an area than has been identified as having intense biological productivity and oceanographic transition between midlatitude and tropical ocean conditions. We used empirical orthogonal functions (EOF) analysis separately and jointly on the two fields from 1997 through 2007, a time period dominated by different remote forcing: ENSO (El Niño–Southern Oscillation) conditions (weak, moderate and strong) and the largest intrusion of subarctic water reported in the last 50 years. Coastal upwelling index anomalies (CUI) and the multivariate ENSO index (MEI) were used to identify the influence of local (wind stress) and remote (ENSO) forcing over the interannual variability of both variables. The spatial pattern of the individual EOF1 analysis showed the greater variability of SST and Chl a offshore, their corresponding amplitude time series presented the highest peaks during the strong 1997–2000 El Niño–La Niña cycles and during the 2002–2004 period associated to the intrusion of subarctic water. The MEI is well correlated with the individual SST principal component (R &amp;approx; 0.67, P < 0.05) and poorly with the individual Chl a principal component (R = −0.13). The joint EOF1 and the SST–Chl a correlation patterns show the area where both variables covary tightly; a band near the coast where the largest correlations occurred (| R | > 0.4) mainly regulated by ENSO cycles. This was spatially revealed when we calculated the homogeneous correlations for the 1997–1999 El Niño–La Niña period and during the 2002–2004 period, the intrusion of subarctic water period. Both, SST and Chl a showed higher coupling and two distinct physical–biological responses: on average ENSO influence was observed clearly along the coast mostly in SST, while the subarctic water influence, observed offshore and in Bahía Vizcaíno, mostly in Chl a. We found coastal chlorophyll blooms off Punta Eugenia during the 2002–2003 period, an enrichment pattern similar to that observed off the coast of Oregon. These chlorophyll blooms are likely linked to high wind stress anomalies during 2002, mainly at high latitudes. This observation may provide an explanation of why Punta Eugenia is one of the most important biological action centers on the Pacific coast.
Highlights
Continuous oceanographic observations carried out on the west coast of Baja California by the CalCOFI (California Cooperative Oceanic Fisheries Investigations) and IMECOCAL (Mexican Research of the California Current) programs have helped define the region of Punta Eugenia (Fig. 1) as an oceanographic transitional zone (Durazo and Baumgartner, 2002), characterized by the interaction of subarctic and tropical waters (Almazán-Becerril et al, 2012) as a result of Published by Copernicus Publications on behalf of the European Geosciences Union.H
Unlike the data gathered during oceanographic cruises, the temporal and spatial resolution of satellite-derived sea surface temperature (SST) and chlorophyll a (Chl a) data allowed for observation of the physical–biological coupling of very near-shore environments during large-scale processes that affected the region off Punta Eugenia
This region of intense biological productivity and oceanographic transition is highly influenced by the intrusion of subarctic water and by subtropical signatures triggered by poleward flow (e.g., ENSO cycles)
Summary
Continuous oceanographic observations carried out on the west coast of Baja California by the CalCOFI (California Cooperative Oceanic Fisheries Investigations) and IMECOCAL (Mexican Research of the California Current) programs have helped define the region of Punta Eugenia (Fig. 1) as an oceanographic transitional zone (Durazo and Baumgartner, 2002), characterized by the interaction of subarctic and tropical waters (Almazán-Becerril et al, 2012) as a result of Published by Copernicus Publications on behalf of the European Geosciences Union. The area is influenced by warm and dense water originating in the Gulf of California (Parés-Sierra et al, 1997), creating a complex mixing zone between coastal and oceanic flows and intense mesoscale variability characterized by a complex pattern of filaments, meanders, and semipermanent eddy structures (Gallaudet and Simpson, 1994) These structures carry nutrient-rich coastal waters to deep areas, causing important seasonal variability and interannual and long-term changes in the mean field of variables as SST and Chl a (EspinosaCarreón et al, 2004). The coastal ecosystem of this region is a natural refuge and a feeding and breeding area for many ecological and commercially important species (gray whale, sea turtles, spiny lobster, abalone, and clams) Maintenance of this ecosystem is based on three factors: rich coastal waters associated with an intense upwelling regime, successful implementation of cooperatives to safeguard existing resources, and relative isolation. We examine time series of coastal anomalies of SST, Chl a and wind stress to observe the propagation of the ENSO signals and subarctic water intrusion during two different time periods: 1997–2007 and 2002–2004
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