Paleo-pCO2 Database Atlantic ODP925 40 Million Year Alkenone and CO2 Data Zhang, Y.G.; Pagani, M.; Liu, Z.; Bohaty, S.M.; DeConto, R.M. Zhang, Y.G. Pagani, M. Liu, Z. Bohaty, S.M. DeConto, R.M. earth science/paleoclimate/paleoceanography (delta 13C,dissolved inorganic carbon,null,per mil,null,paleoceanography,null,null,N,null) earth science/paleoclimate/climate reconstructions|paleoceanography (sea surface temperature,glycerol dialkyl glycerol tetraether index,null,degree Celsius,null,climate reconstructions|paleoceanography,null,null,N,based on TEX86) earth science/paleoclimate/climate reconstructions|paleoceanography (depth,null,null,meter,null,climate reconstructions|paleoceanography,null,null,N,meter below sea floor) earth science/paleoclimate/climate forcing|paleoceanography (carbon dioxide,bulk atmosphere,null,parts per million,null,climate forcing|paleoceanography,null,null,N,null) earth science/paleoclimate/paleoceanography (alkenone unsaturation index Uk37 prime,null,null,dimensionless,null,paleoceanography,null,null,N,null) earth science/paleoclimate/climate reconstructions|paleoceanography (sea surface temperature,alkenone unsaturation index,null,degree Celsius,null,climate reconstructions|paleoceanography,null,null,N,null) earth science/paleoclimate/climate reconstructions|paleoceanography (age,null,null,million years ago,null,climate reconstructions|paleoceanography,null,null,N,null) earth science/paleoclimate/paleoceanography (delta 13C,alkenone,null,per mil,null,paleoceanography,null,null,N,null) earth science/paleoclimate/climate forcing (ODP 925B>LATITUDE 4.204133>LONGITUDE -43.48915) The alkenone-pCO2 methodology has been used to reconstruct the partial pressure of ancient atmospheric carbon dioxide (pCO2) for the past 45 million years of Earth's history (Middle Eocene to Pleistocene epochs). The present long-term CO2 record is a composite of data from multiple ocean localities that express a wide range of oceanographic and algal growth conditions that potentially bias CO2 results. In this study, we present a pCO2 record spanning the past 40 million years from a single marine locality, Ocean Drilling Program Site 925 located in the western equatorial Atlantic Ocean. The trends and absolute values of our new CO2 record site are broadly consistent with previously published multi-site alkenone-CO2 results. However, new pCO2 estimates for the Middle Miocene are notably higher than published records, with average pCO2 concentrations in the range of 400-500 ppm. Our results are generally consistent with recent pCO2 estimates based on boron isotope-pH data and stomatal index records, and suggest that CO2 levels were highest during a period of global warmth associated with the Middle Miocene Climatic Optimum (17-14 million years ago, Ma), followed by a decline in CO2 during the Middle Miocene Climate Transition (approx. 14 Ma). Several relationships remain contrary to expectations. For example, benthic foraminiferal d18O records suggest a period of deglaciation and/or high-latitude warming during the latest Oligocene (27-23 Ma) that, based on our results, occurred concurrently with a long-term decrease in CO2 levels. Additionally, a large positive d18O excursion near the Oligocene-Miocene boundary (the Mi-1 event, approx. 23 Ma), assumed to represent a period of glacial advance and retreat on Antarctica, is difficult to explain by our CO2 record alone given what is known of Antarctic ice sheet history and the strong hysteresis of the East Antarctic Ice Sheet once it has grown to continental dimensions. We also demonstrate that in the Neogene with low CO2 levels, algal carbon concentrating mechanisms and spontaneous biocarbonate-CO2 conversions are likely to play a more important role in algal carbon fixation, which provides a potential bias to the alkenone-pCO2 method. STUDY NOTES: Alkenone data and estimated atmospheric pCO2 data from core ODP925, Western Equatorial Atlantic, for the past 40 milion years NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Zhang, Y.G. Investigator : Pagani, M. Investigator : Liu, Z. Investigator : Bohaty, S.M. Investigator : DeConto, R.M. 2018-08-11 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/24850 https://www1.ncdc.noaa.gov/pub/data/paleo/climate_forcing/trace_gases/Paleo-pCO2/zhang2013alkenone.txt https://www1.ncdc.noaa.gov/pub/data/paleo/climate_forcing/trace_gases/Paleo-pCO2/zhang2013alkenone.xlsx https://www1.ncdc.noaa.gov/pub/data/paleo/climate_forcing/trace_gases/Paleo-pCO2/zhang2013alkenone.txt https://www1.ncdc.noaa.gov/pub/data/paleo/climate_forcing/trace_gases/Paleo-pCO2/zhang2013alkenone.xlsx English https://www.ncdc.noaa.gov/paleo/study/24850 https://www1.ncdc.noaa.gov/pub/data/paleo/climate_forcing/trace_gases/Paleo-pCO2/zhang2013alkenone.txt https://www1.ncdc.noaa.gov/pub/data/paleo/climate_forcing/trace_gases/Paleo-pCO2/zhang2013alkenone.xlsx Yi Ge Zhang, Mark Pagani, Zhonghui Liu, Steven M. Bohaty, Robert DeConto2013A 40-million-year history of atmospheric CO2Philosophical Transactions of The Royal Society A371200110.1098/rsta.2013.0096 http://rsta.royalsocietypublishing.org/content/371/2001/20130096 START YEAR: 38490000 cal yr BP * END YEAR: 20000 cal yr BP -43.48915 4.204133 -43.48915 4.204133