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-photosynthetic carbon (chlorophyll-a, proteins and carbohydrates) of nano, micro and mesoparticles was studied. The results revealed typical winter circulation patterns of primarily mixed, stratified and frontal structures. The photosynthetic fraction (nano and microphytoplankton) dominated the southern stratified structure of the sampling area, while the northern mixed structure was mainly influenced by non-photosynthetic particles. The observed spatial distribution pattern of organic particles suggests a northern influence from surface and subsurface waters flowing from the shallow upper Gulf, dominated mostly by detritus and hence, a microheterotrophic food chain. The encounter of this upper Gulf water with clear and fertile waters moving northward, create a frontal zone dominated by phytoplankton and the classical food chain. This process could be the origin of the high phytoplankton biomass in the central Gulf of California during the winter. A general scheme describing these interactions is proposed.