Southern Ocean Eocene-Oligocene Foraminiferal d18O and Mg/Ca Data Bohaty, S.M.; Zachos, J.C.; Delaney, M.L. Bohaty, S.M. Zachos, J.C. Delaney, M.L. earth science/paleoclimate/paleoceanography (delta 18O,foraminifer,null,per mil,null,paleoceanography,null,null,N,S. angiporoides and Cibicidoides sp.) earth science/paleoclimate/paleoceanography (depth at sample start,null,null,centimeter,null,paleoceanography,null,null,N,null) earth science/paleoclimate/paleoceanography (age,null,null,million years ago,null,paleoceanography,null,null,N,null) earth science/paleoclimate/paleoceanography (manganese/calcium,foraminifer,null,dimensionless,null,paleoceanography,null,null,N,S. angiporoides and Cibicidoides sp.) earth science/paleoclimate/paleoceanography (depth at sample end,null,null,centimeter,null,paleoceanography,null,null,N,null) earth science/paleoclimate/paleoceanography (depth,null,null,meter,null,paleoceanography,null,null,N,mbsf) earth science/paleoclimate/paleoceanography (magnesium/calcium,foraminifer,null,dimensionless,null,paleoceanography,null,null,N,S. angiporoides and Cibicidoides sp.) earth science/paleoclimate/paleocean earth science/paleoclimate/paleocean (ODP744>LATITUDE -61.6>LONGITUDE 80.6) (ODP 738B>LATITUDE -62.709>LONGITUDE 82.7878) (ODP 689B>LATITUDE -64.517>LONGITUDE 3.0999) (ODP748>LATITUDE -58.441>LONGITUDE 78.9981) Constraining the magnitude of high-latitude temperature change across the Eocene-Oligocene transition (EOT) is essential for quantifying the magnitude of Antarctic ice-sheet expansion and understanding regional climate response to this event. To this end, we constructed high-resolution stable oxygen isotope (d18O) and magnesium/calcium (Mg/Ca) records from planktic and benthic foraminifera at four Ocean Drilling Program (ODP) sites in the Southern Ocean. Planktic foraminiferal Mg/Ca records from the Kerguelen Plateau (ODP Sites 738, 744, and 748) show a consistent pattern of temperature change, indicating 2-3°C cooling in direct conjunction with the first step of a two-step increase in benthic and planktic foraminiferal d18O values across the EOT. In contrast, benthic Mg/Ca records from Maud Rise (ODP Site 689) and the Kerguelen Plateau (ODP Site 748) do not exhibit significant temperature change. The contrasting temperature histories derived from the planktic and benthic Mg/Ca records are not reconcilable, since vertical d18O gradients remained nearly constant at all sites between 35.0 and 32.5 Ma. Based on the coherency of the planktic Mg/Ca records from the Kerguelen Plateau sites and complications with benthic Mg/Ca paleothermometry at low temperatures, the planktic Mg/Ca records are deemed the most reliable measure of Southern Ocean temperature change. We therefore interpret a uniform cooling of 2-3 °C in both deep surface (thermocline) waters and intermediate deep waters of the Southern Ocean across the EOT. Cooling of Southern Ocean surface waters across the EOT was likely propagated to the deep ocean, since deep waters were primarily sourced on the Antarctic margin throughout this time interval. Removal of the temperature component from the observed foraminiferal d18O shift indicates that seawater d18O values increased by 0.6±0.15‰ across the EOT interval, corresponding to an increase in global ice volume to a level equivalent with 60–130% modern East Antarctic ice sheet volume. STUDY NOTES: High-resolution stable oxygen isotope (d18O) and magnesium/calcium (Mg/Ca) records from planktic and benthic foraminifera at four Ocean Drilling Program (ODP) sites in the Southern Ocean covering the Eocene-Oligocene transition (EOT), ~35 - 32 Ma. NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Bohaty, S.M. Investigator : Zachos, J.C. Investigator : Delaney, M.L. 2012-02-15 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/12524 https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bohaty2012/bohaty2012.xls https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bohaty2012/bohaty2012.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bohaty2012/bohaty2012.xls https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bohaty2012/bohaty2012.txt English https://www.ncdc.noaa.gov/paleo/study/12524 https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bohaty2012/bohaty2012.xls https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bohaty2012/bohaty2012.txt Bohaty, S.M., J.C. Zachos, and M.L. Delaney. 2012. Foraminiferal Mg/Ca evidence for Southern Ocean cooling across the Eocene-Oligocene transition. Earth and Planetary Science Letters, Vols. 317-318, pp. 251-261, 1 February 2012. doi:10.1016/j.epsl.2011.11.037. START YEAR: 34998000 cal yr BP * END YEAR: 32501000 cal yr BP 3.0999 -64.517 82.7878 -58.441