~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 carbonisotope 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 nutrientpoor 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.