Atmospheric CO2 20 Million Year Foraminiferal B/Ca Reconstruction Tripati, A.K.; Roberts, C.D.; Eagle, R.A.; Li, G. Tripati, A.K. Roberts, C.D. Eagle, R.A. Li, G. 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model) earth science/paleoclimate/climate forcing (carbon dioxide,null,null,parts per million,null,climate forcing,null,null,N,B- model) earth science/paleoclimate/climate reconstructions|paleoceanography (pH,boron/calcium|sea water,range lower bound,dimensionless,null,climate reconstructions|paleoceanography,null,null,N,null) earth science/paleoclimate/climate reconstructions|paleoceanography (pH,boron/calcium|sea water,null,dimensionless,null,climate reconstructions|paleoceanography,null,null,N,T-1 model) earth science/paleoclimate/climate reconstructions|paleoceanography (pH,boron/calcium|sea water,null,dimensionless,null,climate reconstructions|paleoceanography,null,null,N,S-1 model) earth science/paleoclimate/climate reconstructions|paleoceanography (pH,boron/calcium|sea water,null,dimensionless,null,climate reconstructions|paleoceanography,null,null,N,Ca Griffith 1 model) earth science/paleoclimate/climate reconstructions|paleoceanography (pH,boron/calcium|sea water,null,dimensionless,null,climate reconstructions|paleoceanography,null,null,N,Griffith T+S+B+ model) earth science/paleoclimate/paleoceanography (depth,null,null,centimeter,null,paleoceanography,null,null,N,null) earth science/paleoclimate/paleocean earth science/paleoclimate/paleocean earth science/paleoclimate/paleocean (DSDP 588>LATITUDE -26>LONGITUDE 161) (ODP 806B>LATITUDE .32>LONGITUDE 159.35) We use new and published data representing a 20 million long record to discuss the systematics of interpreting planktic foraminiferal B/Ca ratios. B/Ca-based reconstructions of seawater carbonate chemistry and atmospheric pCO2 assume that the incorporation of boron into foraminiferal tests can be empirically described by an apparent partition coefficient, KD=(B/CaCaCO3)/(BOH4-/HCO3- seawater) (Hemming and Hanson, 1992). It has also been proposed that there is a species-specific relationship between KD and temperature (Yu et al., 2007). As we discuss, although these relationships may be robust, there remain significant uncertainties over the controls on boron incorporation into foraminifera. It is difficult to be certain that the empirically defined correlation between temperature and KD is not simply a result of covariance of temperature and other hydrographic variables in the ocean, including carbonate system parameters. There is also some evidence that KD may be affected by solution [HCO3-]/[CO32-] ratios (i.e., pH), or by [CO32-]. In addition, the theoretical basis for the definition of KD and for a temperature control on KD is of debate. We also discuss the sensitivity of pCO2 reconstructions to different KD-temperature calibrations and seawater B/Ca. If a KD-temperature calibration is estimated using ice core pCO2 values between 0 and 200 ka, B/Ca ratios can be used to reasonably approximate atmospheric pCO2 between 200 and 800 ka; however, the absolute values of pCO2 calculated are sensitive to the choice of KD-temperature relationship. For older time periods, the absolute values of pCO2 are also dependent on the evolution of seawater B concentrations. However, we find that over the last 20 Ma, reconstructed changes in declining pCO2 across the Mid-Pleistocene Transition, Pliocene glacial intensification, and the Middle Miocene Climate Transition are supported by the B/Ca record even if a constant coretop KD is used, or different KD-temperature calibrations and models of seawater B evolution are applied to the data. The inferred influence of temperature on KD from coretop data therefore cannot itself explain the structure of a published pCO2 reconstruction (Tripati et al., 2009). We conclude the raw B/Ca data supports a coupling between pCO2 and climate over the past 20 Ma. Finally, we explore possible implications of B/Ca-based pCO2 estimates for the interpretation of other marine pCO2 proxies. STUDY NOTES: Paleoatmospheric CO2 concentrations estimated from the boron/calcium ratio of planktonic foraminifera. Samples from Deep Sea Drilling Project Site 588 and Ocean Drilling Program Site 806 were used to reconstruct pCO2 values from the Miocene through Holocene (~20 to 0 Ma). Average, maximum, and minimum pCO2 estimates are calculated for each time. NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Tripati, A.K. Investigator : Roberts, C.D. Investigator : Eagle, R.A. Investigator : Li, G. 2014-03-09 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/16154 https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011isotope.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011species.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011co2.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011ph.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011.xlsx https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011bca-mgca.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011replicate.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011isotope.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011species.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011co2.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011ph.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011.xlsx https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011bca-mgca.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011replicate.txt English https://www.ncdc.noaa.gov/paleo/study/16154 https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011isotope.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011species.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011co2.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011ph.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011.xlsx https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011bca-mgca.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/tripati2011/tripati2011replicate.txt Aradhna K. Tripati, Christopher D. Roberts, Robert A. Eagle, Gaojun Li2011A 20 million year record of planktic foraminiferal B/Ca ratios: Systematics and uncertainties in pCO2 reconstructionsGeochimica et Cosmochimica Acta75102582-261010.1016/j.gca.2011.01.018http://www.sciencedirect.com/science/article/pii/S0016703711000263 START YEAR: 20000000 cal yr BP * END YEAR: 0 cal yr BP 159.35 -26 161 .32