Climate and upper ocean variability off Baja California, Mexico: 1997–2008

Temperature and salinity anomalies derived from observations obtained in the period 1997–2008 are used to study the changes in physical properties off the Baja California west coast (24–31 N). Near surface anomalies were used to characterize four periods of distinctive variability: (1) a warm and saline phase of El Niño 1997–1998, (2) a saline period from 1999 to 2002, (3) fresh subarctic water in 2002–2006, and (4) a saline-fresh (El Niño-La Niña) phase in late 2006 to early 2008. Subsurface (200 m) salinity anomalies depicted a trend towards saltier conditions (ΔS ∼ 0.1) from 2001 onwards, and did not show the four periods discernible near surface. EOF analysis of sea surface wind stress and wind stress curl suggested that after the intense westerly winds in late 2001, freshening during late 2002–2006 was due to the weakening (strengthening) of the North Pacific Current (Aleutian Low), and to a decrease of wind stress curl produced upwelling. Data also showed differences in the timing and magnitude of anomalies observed between the north (poleward of 28 N) and the south (equatorward of 28 N). Subsurface geostrophic currents demonstrated the existence of two large scale cyclonic gyres, one associated with a subarctic domain in the northern region, and another having tropical characteristics. The likely role of subsurface cyclonic pairs in the definition of a provincial boundary, and the importance in influencing the CCS ecosystem, are discussed.