SESTON DISTRIBUTION IN RELATION TO WINTER HYDROGRAPHIC CONDITIONS IN CENTRAL GULF-OF-CALIFORNIA

The influence of water exchange, between the upper and central Gulf of California, on the spatial distribution of photosynthetic and non-pho tosynthetic carbon (chlorophyll-a, proteins and carbohydrates) of nano , micro and mesoparticles was studied. The results revealed typical wi nter circulation patterns of primarily mixed, stratified and frontal s tructures. The photosynthetic fraction (nano and microphytoplankton) d ominated the southern stratified structure of the sampling area, while the northern mixed structure was mainly influenced by non-photosynthe tic particles. The observed spatial distribution pattern of organic pa rticles suggests a northern influence from surface and subsurface wate rs flowing from the shallow upper Gulf, dominated mostly by detritus a nd hence, a microheterotrophic food chain. The encounter of this upper Gulf water with clear and fertile waters moving northward, create a f rontal zone dominated by phytoplankton and the classical food chain. T his process could be the origin of the high phytoplankton biomass in t he central Gulf of California during the winter. A general scheme desc ribing these interactions is proposed.