The coccolithophore record for the last 11 000 years in the Gulf of California

We analysed changes in the coccolithophore assemblage over the last 11 000 years in laminated sediments recovered near the mouth of the Gulf of California (NW Mexico). Coccolith preservation in the samples was good: the assemblage was represented by seven taxa. Statistical studies revealed that the group of “small” Gephyrocapsa was the dominant taxa and Florisphaera profunda and Emiliania huxleyi the following species in abundance. We calculated the ratio between inhabitants of the surface and deep photic zones, which allowed us to analyse variations in water column stratification. Oceanographic conditions during the Holocene were relatively constant, and the coccolithophore record was dominated by small placoliths, revealing upwelling conditions and high productivity, which progressively weakened towards the present. Two different events were found around 11 000 B.P. (Younger Dryas) and 6000 B.P. (mid-Holocene). Both intervals were characterised by the dominant presence of F. profunda in the assemblage, revealing stratification conditions in the water column and low productivity, the same oceanographic conditions defined during an ENSO (El Niño-Southern Oscillation) event.