C-QUEST, in co-operation with ICE-QUEST and AO-QUEST projects under QUEST umbrella, is focused on the following questions: What is a consequent chain of biogeochemical and physical mechanisms, presumably in the ocean, which have led to glacial-interglacial atmospheric pCO2 dynamics? What are the key non-linearities, switches and choke points in the glacial biogeochemistry in accordance with the CLIMBER model? Is the role of carbon cycle in the Quaternary as an amplifier of external changes not valid for the greenhouse climate? In co-operation with the SMART project, C-QUEST will address questions of the efficiency of oceanic carbon sequestration and its impact via pH changes on marine ecosystems.