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Variability of Chlorophyll a Concentration and Halocline Depth in La Paz Bay (Gulf of California, Mexico) and the Relationship to Pacific Large-Scale Climatic Phenomena

ABSTRACT Guevara-Guillén, C.; Shirasago-Germán, B.; Pérez-Lezama, E.L., and Obeso-Nieblas, M., 2018. Variability of chlorophyll a concentration and Halocline depth in La Paz Bay (Gulf of California, Mexico) and the relationship to Pacific large-scale climatic phenomena. Variability of the chlorophyll a (Chl a) concentration and halocline depth in La Paz Bay were analyzed and compared against the variability of North Pacific (NP) large-scale phenomena and local winds during 1999–2009. Chl a data were obtained from satellite images, and halocline depth was obtained from in situ data. Eight large-scale phenomenon climate indices and satellite wind data were also used in this work. Chl a was processed on three timescales—interannual, mean annual cycle, and monthly time series. The halocline depth was processed as a time series. The Chl a interannual analysis revealed a high variability in the study period, with the highest concentration in 2001 and the lowest in 2005. The Pacific Decadal Oscillation (PDO) was the dominant phenomenon in this timescale. The Chl a mean annual cycle showed two concentration periods, a higher one during December to March and lower one during April to November. The El Niño Southern Oscillation (ENSO) and PDO were the most determinant phenomena in the mean annual cycle. The monthly time series also showed high variability with the highest anomalies during 2000–01 and the lowest anomalies in 2003 and 2005. The ENSO and PDO were the most influential phenomena on the monthly timescale. The halocline depth analysis revealed high and noncyclic variability, contrasting depths of 90 m during February 2002 and November 2005 with other sampling dates such as July 2001 and July 2002, when the halocline reached the surface. The NP and local winds were the main factors that influenced the halocline depth.