Atmospheric Carbon Dioxide Concentration Across the Mid-Pleistocene Transition

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Science  19 Jun 2009:
Vol. 324, Issue 5934, pp. 1551-1554
DOI: 10.1126/science.1171477

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  1. Fig. 1

    2.1-million-year estimation of atmospheric pco2 from marine proxies recorded at ODP site 668B in the eastern equatorial Atlantic. (A) The LR04 benthic oxygen isotope stack (4) reflects the change from the dominant 40-ky periodicity of glacial cycles before 1200 ka to the 100-ky ice-age cycles of the past 700 ky. The MPT is indicated by the horizontal gray bar and describes the transition period. (B) Planktic δ11B data reflect extreme glacial and interglacial times and few transitional periods, selected from the δ18O record, and are complemented by (C) Mg/Ca SST estimates and (E) local salinity estimates computed from (D) modeled global sea level (21). (F) Surface seawater pH on the seawater scale (SWS) was calculated as a function of δ11B, SST, and salinity. (G) Alkalinity estimates are based on a modeled global ocean estimate (3), adjusted to modern local alkalinity at the core site and varying sea level. (H) Surface ocean aqueous Pco2 was then calculated as a function of pH, alkalinity, SST, and salinity. Comparison with the ice core record of atmospheric pco2 [dark red line in (H)] reveals a remarkable match for the period from 800 ka to the present. Average glacial and interglacial Pco2 is indicated by solid horizontal black lines for different intervals in (H). Dashed lines indicate G/I averages. Error bars indicate the propagated error of the individual pH, SST, salinity, and alkalinity uncertainties on the Pco2 estimate (see SOM for details).