~90 ppmv -Cooler oceans decrease CO2 by 22 ppmv -Saltier oceans increase CO2 by 11 ppmv

Modern exchange rates of Carbon in gigatons per year

Interglacial-to-glacial changes in carbon reservoirs in gigatons

Carbon reservoirs (in gigatons) and their carbon-isotope values

More 12C is transferred to the oceans, thereby increasing carbon-isotope values.

Hypotheses for the glacial reduction of atmospheric CO2. Temperature and salinity changes Cannot account for the change in CO2. Carbon sequestration on land Evidence suggest that terrestrial ecosystems became a source of carbon to the oceans and not a sink. Carbon sequestration in the upper ocean Small reservoir to account for the change. Carbon sequestration in the deep ocean Carbon sequestration in sediments

Pumping of carbon into the deep ocean Iron fertilization hypothesis Increased nutrients hypothesis Shift in phytoplankton hypothesis

Decreased CO2 degassing Increased stratification of the glacial ocean Reduced ventilation of CO2 due to enhanced ice cover or changes in ocean circulation.

Ice core records show large fluctuation in atmospheric dust loads. Epica Group, 2004

Ice core records show a good correspondence between CO2 concentrations and dust content. Epica Group, 2004

From Xiao et al., 1995)

Modern marine carbon production

Available cores (dots) with carbon export data. HNLC: High nutrient, low chlorophyll regions Kohfeld et al., 2005.

Jickells et al., 2005

Increased iron-rich dust affects regions with under-utilization of nutrients (Southern Ocean, North Pacific, Equatorial Pacific). Increased overall nutrient levels affect nutrient-poor regions (e.g., gyres). Shifts in phytoplankton from carbonate-producing to non-carbonate producing (e.g., diatoms) increases carbonate ion content in the oceans, enhancing the preservation of carbonates.