Climate-induced variations in productivity and planktonic ecosystem structure from the Younger Dryas to Holocene in the Cariaco Basin, Venezuela

A high-resolution molecular organic geochemical study of sediments in the a noxic Cariaco Basin indicates significant changes in primary productivity a nd planktonic community structure associated with the transition from the Y ounger Dryas to the Holocene. Variations in climate conditions over the pas t 12 C-14 kyr have induced large-scale changes in upwelling intensity, whic h directly affected levels of primary productivity as reflected in accumula tion rates of bulk productivity proxies. Concentrations and accumulation ra tes of sterol and alkenone biomarkers have been used to identify how produc tivity changes affected the structure of the planktonic ecosystem. A shift in the dominant primary producer from diatoms (Younger Dryas) to coccolitho phores (Holocene) is identified. If productivity and ecosystem variations l ike those identified in the tropical upwelling zone of the Cariaco Basin re gion, occur throughout the tropical oceans, they have the potential to affe ct global climate through perturbations in the biogeochemical cycle of carb on.