Variation of atmospheric CO 2 by ventilation of the ocean ' s deepest water

A new box model for glacial-interglacial changes in atmospheric CO2 produces lower levels of atmospheric CO 2 without changes in biological production or nutrient chemistry. The model treats the boundary between middepth water and deep water as a chemical divide that separates low-CO 2 water above from high-CO 2 water below. Atmospheric CO 2 is reduced 21 ppm by reduced ventilation of the deep water below the divide. A further reduction of 36 ppm is due to CaCO 3 compensation in response to lower CO3 = below the divide. Colder surface temperatures account for an additional 23 ppm of CO 2 reduction. The new mechanism leaves the glacial atmosphere lighter in õ13C than in preindustrial time, as seen in ice cores and fossil plant material. Bottom water below the divide becomes strongly depleted in õ13C without a change in nutrient concentrations.