The preserved carbonate record in Holocene sediments of the Alfonso and Pescadero basins, Gulf of California, Mexico

The biogenic record was used as the basis for defining three climatic periods during the Holocene. (a) The early period, c. 10 000-7200 calendar (cal) years BP, is represented almost exclusively in the record for eastern Pescadero Basin (Alfonso Basin cores sample only the last 5800 years). It is characterized by high productivity and variability resulting from strong northwesterly winds and upwelling. (b) The middle period, 7200-4200 cal years BP, characterized by a general and steady decrease in productivity. Variability also reduces and the period appears to be one of climatic stability. (c) The late period, 4200 cal years BP to the present, during which there is an increase in productivity in the east but it declines in the west and with an increase in the carbonate-opal east-west asymmetry between the two basins. The records are marked by strong climate-ocean variability cycles with two modes −200 years (throughout the record) and c. 830 years (after 3000 cal years BP) - that appear related to latitudinal shifts of the Inter-tropical Convergence Zone (ITCZ), produced by solar cycles.