The coupling between the thermohaline, chemical and biological variables on the northeast continental shelf of the Gulf of Cádiz was determined during the Emigas I survey in summer 2006. Samples were collected to chemically characterize the different water types and to analyze the chlorophyll a distribution. Four different water masses were identified: North Atlantic Central Water (NACW), Surface Atlantic Water (SAW), considered a modification of NACW, and South and North Surface Waters. The highest nutrient levels were found in subsurface NACW, while surface waters were almost nutrient-depleted except in the Guadalquivir region. The isopycnal level of 26.3 kg m-3 marked the limit between nutrient-rich NACW and nutrient-poor surface waters. At the offshore stations, the subsurface cholorophyll a maximum was located at the depth of nitracline and associated with the 26.3 kg m-3 isopycnal level rather than with the pycnocline depth. At the inshore stations, chlorophyll a maxima were observed at the bottom, except for the surface maximum in the River Guadalquivir region.