VARIABILIDAD ESPACIO TEMPORAL DE LA CLOROFILA a Y LA PRODUCTIVIDAD PRIMARIA EN EL SISTEMA FRONTAL DE BAJA CALIFORNIA SUR

Abstract

Phytoplankton forms the initial stage in the process of organic matter production in the ocean, constituting the first link in the trophic plot. The dynamic mechanisms that control the variations in the availability of nutrients and light modify its patterns of the variability space-temporary. The concentration of chlorophyll a (Cla a) has been used as an indicator of the phytoplankton biomass, the phytoplankton is responsible for the CO2 assimilation of in the ocean, this process is known as Primary Production (PP). The Southern Baja California Frontal System (SFBCS) is located to south of the California Current System in front of Southern Baja California coasts (20º y 24º N, 107º y 117º W). Even though it’s part of one of the most productive ecosystems in the world, this system has been barely studied, which is why the variability of the Cla a and PP is still unknown. The objective of this work is to describe the space-temporary variability of the Cla a and PP, starting with monthly and weekly compounds of color images of the ocean coming from the SeaWiFS sensor, as well as the sea superficial temperature (TSM) from the AVHRR sensor, during the 1997 – 2010 period for the SFBCS region. The seasonal cycles of the Cla-a and TSM were calculated by Fourier analysis, obtained the average value of each series and the explained variance (VE) for the seasonal cycles. The average distribution of Cla a presented high values near the coast (>2mg m-3), with a gradient that diminishes out to sea, the highest concentrations of Cla a were registered from April to June (Spring) and the seasonal cycle showed 54% of VE for all the time series. The general average of the TSM shows perpendicular isotherms to the coast and presented a latitudinal gradient. The lowest temperatures in the study area were presented in Spring, these results suggest that the upwelling could be the main contributing factor for the seasonal variations of the Cla a concentration during spring. The VE of the TSM was of 82% for the whole time series, when subtracting the seasonal cycle from both Cla a and TSM time series, the interanual events were magnified, finding a relationship with the El Niño and La Niña events, in addition a strong relationship with the Oscillation of the North Pacific index (NPGO) in their positive phase. The first mode of the Orthogonal Empirical Functions (FEOs) for PP represents the 14.2% of VE, this variation is given mainly by interanual events, finding two areas of influence, one coastal an the other oceanic.