LATE QUATERNARY OCEANOGRAPHY OF THE MOUTH OF THE GULF OF CALIFORNIA: THE POLYCYSTINE CONNECTION

The mouth of the Gulf of California is a region where three principal water masses converge: the Equatorial Water, the water associated with the California Current, and the water from the gulf itself. These water masses exhibit a complex interaction which has been recorded by the polycystine radiolarian distribution patterns defined in the underlying sediments. The occurrence in the gulf of water associated with the California Current is indicated by the distribution of Cycladophora (?) davisiana (Ehrenberg), while the occurrence of the Equatorial Water is characterized by high abundance of Tetrapyle octacantha Miller. Where the California Current meets the Equatorial Water, a water mass boundary is formed, and this is depicted by the distribution of Druppatractus cf. pyriformis (Bailey). Micropaleontological analysis of six sedimentary gravity cores located along the mouth of the Gulf of California, correlated through delta 18(0) stratigraphy, show that from approximately 33,000 to 15,500 years ago, the California Current frequently invaded the mouth of the gulf, displacing the water mass boundary system and the Equatorial Water southward. These oceanographic events preceded the global climatic changes indicated by the delta 18(0) stratigraphy, occurring first in the surface and subsurface water in the mouth of the gulf and then in the deep waters.