Ross Sea ANDRILL-2A Middle Miocene Biomarker Data Feakins, S.J.; Warny, S.; Lee, J.-E. Feakins, S.J. Warny, S. Lee, J.-E. earth science/paleoclimate/paleocean (AND-2A>LATITUDE -77.7581>LONGITUDE 165.2769) From 20 to 15 million years (Myr) ago, a period of global warmth reversed the previous ice growth on Antarctica, leading to the retreat of the West Antarctic Ice Sheet and the contraction of the East Antarctic Ice Sheet. Pollen recovered from the Antarctic shelf indicates the presence of substantial vegetation on the margins of Antarctica 15.7 Myr ago. However, the hydrologic regime that supported this vegetation is unclear. Here we combine leaf-wax hydrogen isotopes and pollen assemblages from Ross Sea sediments with model simulations to reconstruct vegetation, precipitation and temperature in Antarctica during the middle Miocene. Average leaf-wax stable hydrogen isotope (dD) values from 20 to 15.5 Myr ago translate to average dD values of -50 per mil for precipitation at the margins of Antarctica, higher than modern values. We find that vegetation persisted from 20 to 15.5 Myr ago, with peak expansions 16.4 and 15.7 Myr ago coinciding with peak global warmth and vegetation growth. Our model experiments are consistent with a local moisture source in the Southern Ocean. Combining proxy measurements with climate simulations, we conclude that summer temperatures were about 11°C warmer than today, and that there was a substantial increase in moisture delivery to the Antarctic coast. STUDY NOTES: Paleoprecipitation dD and estimated from leaf wax dD and converted to temperature with modern spatial slope and iGRAM model temporal slope. Vegetation evidence from pollen assemblages and abundances as well as leaf wax abundance. Samples from Antarctic Drilling Project (ANDRILL) Site AND2A were used to reconstruct vegetation, precipitation and temperature during the Middle Miocene (~20 to 12 Ma). ANDRILL site AND-2A: 77°45.488’ S, 165°16.613’ E, ~384 m water depth, core to 1139 mbsf, 20-12 Ma The model is an idealized gray-radiation aquaplanet moist General Circulation Model (GRAM) with the addition of isotopic tracers (iGRAM). Results are for experiments where optical depth of the atmosphere to longwave radiation was varied to mimic the effect of changing greenhouse gases and thus to change temperatures in the model. The model was run in T42 resolution (2.8° x 2.8°) and has 30 vertical layers. The simulation was performed for 1400 days with perpetual modern equinox and the results of the last 900 model days are analyzed. NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Feakins, S.J. Investigator : Warny, S. Investigator : Lee, J.-E. 2012-06-17 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/13014 https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/feakins2012/feakins2012.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/feakins2012/feakins2012.xls https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/feakins2012/feakins2012.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/feakins2012/feakins2012.xls English https://www.ncdc.noaa.gov/paleo/study/13014 https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/feakins2012/feakins2012.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/feakins2012/feakins2012.xls Feakins, S.J., S. Warny, and J.-E. Lee. 2012. Hydrologic cycling over Antarctica during the Middle Miocene warming. Nature Geoscience, Published online 17 June 2012. doi:10.1038/ngeo149 START YEAR: 20070000 cal yr BP * END YEAR: 15590000 cal yr BP 165.2769 -77.7581 165.2769 -77.7581