Climate variability effects on autotrophic picophytoplankton in the southern Gulf of California

Although autotrophic picophytoplankton (APP) is a sensitive component of phytoplankton responding to climate variability, little has been investigated in relatively undisturbed marine systems. This study aimed to assess the monthly dynamics of APP abundances from March 2009 to December 2010 and their association with regional climate variability at the Alfonso Basin station (Gulf of California). APP, the most abundant autotrophic component in the 0-100-m layer, and chlorophyll-a concentration (Chl-a) showed interannual variations associated with climate variability. APP abundance was positively correlated with temperature, salinity, and Chl-a, and significant negative correlations were established between nitrites + nitrates and phosphates. From July 2009 to April 2010, APP-integrated abundance explains at least 48% of the net primary productivity variation, suggesting a positive response to a prolonged influence of surface tropical water mass. According to the depth-integrated (0-100 m) abundance, APP variation was associated with the temporal evolution of Central Pacific El Ni & ntilde;o 2009-2010 and multiannual warming that explains the positive trends in satellite sea surface temperature and stratification, and lower nutrient concentrations and N:P ratios values in the upper pycnocline layer at Alfonso Basin. These results highlight the importance of maintaining regional marine observatories.