The Influence of Large-Scale Phenomena on La Paz Bay Hydrographic Variability

Abstract

We analyzed the hydrographic variability of La Paz Bay, the largest coastal water body in the Gulf of California, and its relationship with Pacific large-scale phenomena, including the El Ni?o-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Pacific-North America pattern (PNA), and North Pacific pattern (NP). We used several indices related to these phenomena and the hydrographic variability data of La Paz Bay, consisting of the annual sea surface temperature patterns from satellite imagery from 2000 to 2010 and the mixed layer depths measured with in situ data from 1994 to 2009. The results indicate the sea surface temperature fluctuated during the study period, with 2007 as the coldest year and 2009 as the warmest. Two periods were identified in the annual thermal cycle of the bay, one period of warmth from June to November, and one of cold from December to May. The sea surface temperature is primarily influenced by the ENSO. The mixed layer depth analysis showed its absence during August-September, while the deepest ones were in November-March. The unusual 100 m mixed layer depth noted during February 2002 and its absence in March 1996 and 2009 were related to uncommon atmospheric conditions in the annual patterns of the ENSO, PNA, and NP. The variability of the mixed layer depth is primarily related to the variability of the NP. We concluded that the hydrographic conditions of La Paz Bay are most influenced by the NP during the cold phase of its annual cycle, and by the ENSO during the warm phase.