Effects of seasonal and interannual events on satellite-derived phytoplankton biomass and production in the southernmost part of the California Current System during 2003–2016

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José Carlos Ortiz-Ahumada
Saúl Álvarez-Borrego
Jose Gómez-Valdés

Abstract

We characterized the spatial and temporal variations of sea surface temperature (SST), satellite-derived chlorophyll a (Chlsat) con-centration, and phytoplankton production (PP) along two 300-km long transects in the southernmost part of the California Current System, one off Cabo San Lázaro (TCSLa) and the other off Cabo San Lucas (TCSLu). Moderate Resolution Imaging Spectroradiometer (Aqua-MODIS) SST and Chlsat monthly composites and PP monthly composites were used for the 2003–2016 period. An “average year” was generated for each transect and each variable, as an approximation to the climatology. The Chlsat and PP values were higher in the inshore area than in the offshore area: 4.0 mg·m–3 and 4.5 g C·m–2·d–1, respectively, for the inshore area of TCSLa and 1.4 mg·m–3 and 1.8 g C·m–2·d–1, respectively, for the inshore area of TCSLu; ~0.1 mg·m–3 and 0.4 g C·m–2·d–1, respectively, for the offshore area of both transects. In general, SST showed minimum values (~17.0 ºC) in the inshore area and maximum values (~29.4 ºC) in the offshore area. Chlsat values in the coastal zone were higher on TCSLa than on TCSLu, but offshore Chlsat values were often higher on TCSLu than on TCSLa. Seasonal and interannual variations were observed on both transects, but the seasonal variations were dominant. The effects of “the Blob” in 2014 and of the 2015–2016 eastern Pacific type of El Niño were similarly strong off both capes but caused no collapse in phytoplankton biomass, which decreased to only approximately half the values for the non-El Niño years. The 2003 and 2010 central Pacific type of El Niño events also had strong impacts. The 2005 central Pacific type of El Niño had a strong impact on the biology of TCSLu, like the impact of the 2014 and 2015–2016 events, but not on the biology of TCSLa. The coastal dynamics in the California Current System show spatial variations; thus, seasonal and interannual events have different effects at different geographic locations.

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