Intra-annual upwelling patterns and its linkage with primary production in the euphotic zone (24.5°N) of Southern Baja California coast

The continental shelf of Southern Baja California has been scarcely researched south of 25°N despite it being oceanographically necessary to gain a better understanding of the north-eastern Pacific transitional zone between middle and tropical latitudes. Therefore, the intra-annual patterns of the upwelling cycle and primary production were studied in a monitoring station (24.5°N, 112.1°W; 85m depth) from August 2008 to December 2011. Monthly, thermohaline vertical profiles were recorded and seawater sampled at 100, 33, 10, 3 and 1% irradiance depth levels. Dissolved oxygen, nutrients and chlorophyll-a concentrations and net primary production (NPP, remote sensed and in situ) were determined. Two half-yearly recurrent periods (P<0.001) were observed: an intense (cold) period from February to July and a faint (warm) period from August to January. In the euphotic layer, nitrate concentrations were inversely related to temperature, showing their dependence on upwelling. NPP was directly related to the upwelling process, with an annual average of 1.21 ±0.81 gC m^-2d^-1 in the triennium 2009-2011. Although the influence of La-Niña event was observed during the warm period of 2010 and the cold period of 2011, this change did not significantly affect NPP (P<0.05).