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| André Droxler |
| Associate Professor of Earth Science |
| Bio Statement: |
| Dr. Andre Droxler is Associate Professor of Earth Science at Rice University. His research programs involve detailed studies of carbonate sedimentary records and environments. He has conducted research in the Atlantic, Pacific and Indian oceans, the Caribbean Sea and the Gulf of Mexico. Dr. Droxler¿s team is currently conducting comparative studies of deep-ocean sediments deposited in the Holocene, Pleistocene, and Neogene periods. They hope to learn more carbonate sediment formation and variation through time, as well as the global and regional implications of those variations with respect to paleoceanography, paleoclimatology, and paleoecology. Dr. Droxler has been involved with the Ocean Drilling Program for 10 years, serving as sedimentologist on four ODP voyages.
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| Research Statement: |
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The middle to late Miocene has been regarded as a time of extensive ice-sheet growth (Serravallian, 14.8-11.2 Ma) followed by a period of ice-sheet stability (Tortonian, 11.2-7.1 Ma). Sea level curves created using sequence stratigraphy along with oxygen isotope records serving as ice volume proxies have been the main evidence for this. Paired Mg/Ca and delta-18O measurements of benthic foraminifera present an alternative method for determining ice volumes. This method derives paleotemperatures using Mg/Ca temperature calibrations for calcite. The calculated paleotemperatures can be used to correct oxygen isotope records for temperature effects. The result is a record that should be solely dependent upon ice volume. If deep-water temperatures and ice-sheet growth/decay vary with one another, then the temperature and ice volume curves produced using paired Mg/Ca and delta 18-O measurements should be parallel. This study proposes to produce ice volume and deep-sea temperature curves for a period covering ~13-9.5 Ma (late Serravallian to mid Tortonian) using paired Mg/Ca and delta-18O measurements of benthic foraminifera from the equatorial Indian Ocean. The benthic foraminifera will be taken from cores of the Ocean Drilling Program (ODP) site 714A (2042 meters water depth) near the Maldives. A previous study done by Billups and Schrag (2001) has produced ice volume and deep-sea temperature curves for the Miocene using paired Mg/Ca and ?O18O measurements of benthic foraminifera from the Kerguelen Plateau in the Southern Ocean. They found discrepancies between deep-sea temperatures and ice volume during the Serravallian-Tortonian transition (~11.2 Ma) and the late Tortonian (~8.5 Ma). Deep-sea temperatures on the Kerguelen Plateau actually rose during periods of Antarctic ice-sheet expansion. The result was that the ice volume curve showed more extensive glaciations at ~11.2 and ~8.5 Ma than is seen in oxygen isotope records. We hypothesize that our ice volume and deep-sea temperature curves will have discrepancies similar to those seen by Billups and Schrag (2001). If this is the case, then the results found by those authors will be shown to be global in nature, and not simply a consequence of a anomalous regional water mass. Some evidence for major sea level regressions during the middle to late Miocene already exists at the Maldives from seismic sequence stratigraphy and planktonic oxygen isotope records. We believe that the more robust ice volume determinant of paired Mg/Ca and delta 18O measurements will verify these regressions as major glacial events. In conclusion, the proposed study has these aims: 1) Produce ice volume and deep-sea temperature curves for parts of the mid/late Miocene (~13-9.5 Ma). 2) Verify the applicability of paired Mg/Ca and delta 18O measurements to determine ice volume in the Neogene. 3) Determine the stability of the mid/late Miocene ice-sheet. |
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