Abstract
Seasonal anomalies of salinity, phytoplankton chlorophyll a, and zooplankton volume off Baja California were examined from data obtained during 2001–2007. The analyses helped to identify a strong effect of physical processes on the pelagic ecosystem, diminishing near surface salinity and water column integrated phytoplankton biomass, and enhancing zooplankton volume. These changes are associated with an increase of the Pacific Decadal Oscillation (PDO) index, characterizing a warm phase of the index from summer 2002 to at least summer 2006. Negative chlorophyll a anomalies appear to respond to zooplankton grazing activity, with a possible top down effect during this period. Empirical orthogonal functions (EOFs) of Ekman drift reveal the seasonal and interannual patterns that describe the influence of upwelling zones, and there was a strong response to changes in the equatorward wind forcing from 2002 to 2006. The relationship between negative salinity anomalies and the two temporal EOF modes of Ekman drift was evident as a result of relaxation of coastal upwelling during this period. After 2006, the PDO index showed more neutral or negative values, defining the beginning of a cool phase, with positive nearsurface salinity anomalies off Baja California.
Highlights
The pelagic ecosystem off Baja California has been influenced by large-scale processes like the 1997–1998 El Niño (Durazo and Baumgartner 2002), which was characterized by low chlorophyll, high sea surface height, high surface salinity, and high sea surface temperature, with opposite conditions during the 1998–1999 La Niña (Espinosa-Carreón et al 2004)
Seasonal and interannual patterns are found off Baja California, with a maximum of phytoplankton chlorophyll occurring in spring as a result of phytoplankton growth in response to the seasonal maximum in upwelling-favorable winds
We examine the association between temporal physical forcing and plankton variability off Baja California, in the southern region of the California Current System
Summary
The pelagic ecosystem off Baja California has been influenced by large-scale processes like the 1997–1998 El Niño (Durazo and Baumgartner 2002), which was characterized by low chlorophyll, high sea surface height, high surface salinity, and high sea surface temperature, with opposite conditions during the 1998–1999 La Niña (Espinosa-Carreón et al 2004). El ecosistema pelágico frente a Baja California ha sido influenciado por procesos de gran escala temporal y espacial como El Niño 1997–1998 (Durazo y Baumgartner 2002), el cual dio como resultado bajas concentraciones de clorofila, incremento en el nivel del mar, aumento en la salinidad y la temperatura superficial del océano, con condiciones contrarias. La biomasa del zooplancton es mayor en verano y otoño, compuesta principalmente por copépodos, eufáusidos y otros grupos con menores abundancias, así como por gran abundancia de salpas observadas principalmente durante eventos cálidos como El Niño 1997–1998 (Lavaniegos et al 2002)
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