~90 ppmv

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90 ppmv
-Cooler oceans decrease CO2 by 22 ppmv -Saltier
oceans increase CO2 by 11 ppmv
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Modern exchange rates of Carbon in gigatons per
year
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Interglacial-to-glacial changes in carbon
reservoirs in gigatons
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Carbon reservoirs (in gigatons) and their
carbon-isotope values
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More 12C is transferred to the oceans, thereby
increasing carbon-isotope values.
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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

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Pumping of carbon into the deep ocean

• Iron fertilization hypothesis
• Increased nutrients hypothesis
• Shift in phytoplankton hypothesis

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Decreased CO2 degassing

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

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Ice core records show large fluctuation in
atmospheric dust loads.
Epica Group, 2004
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Ice core records show a good correspondence
between CO2 concentrations and dust content.
Epica Group, 2004
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From Xiao et al., 1995)
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Modern marine carbon production
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Available cores (dots) with carbon export
data. HNLC High nutrient, low chlorophyll regions
Kohfeld et al., 2005.
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Jickells et al., 2005
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• 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.