HR: 1340h
AN: PP43A-0617    [Abstracts]
TI: Summer Temperatures of Late Eocene to Early Oligocene Freshwaters: a Multi-proxy Approach
AU: * David, M P
EM: mattey@gl.rhul.ac.uk
AF: Department of Geology, Royal Holloway University of London Geology Department, Royal Holloway University of London, Egham Hill, Egham, Surrey, TE20 0EX United Kingdom
AU: Grimes, S T
EM: stephen.grimes@plymouth.ac.uk
AF: School of Earth, Ocean and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, Devon, PL4 8AA United Kingdom
AU: Hooker, J J
EM: jjhooker@bmnh.ac.uk
AF: Department of Palaeontology, Natural History Museum, Cromwell Road,, London, SW7 5BD United Kingdom
AU: Collinson, M
EM: collinson@gl.rhul.ac.uk
AF: Department of Geology, Royal Holloway University of London Geology Department, Royal Holloway University of London, Egham Hill, Egham, Surrey, TE20 0EX United Kingdom
AB: We report northern hemisphere summer palaeotemperatures derived from multiple palaeoproxies from the Hamphire Basin Eocene-Oligocene succession. Continental freshwater \delta$^{18}$O values have been determined at six horizons spanning a 3 ma interval across the Eocene-Oligocene boundary from large sets of analyses of rodent tooth enamel phosphate. Surface water \delta$^{18}$O values permit use of associated carbonate and phosphate thermometers (gastropods, charophyte gyrogonites and fish otoliths) to bracket either the mean summer growing season temperature (gastropods), the mean temperature of the warmest months of the growing season (fish otoliths) and the mean temperature of a single month in the latter part of the growing season (charophtyte gyrogonites). We argue that calculated temperatures, which range from 26\deg C to 37\deg C are independent of freshwater evaporation effects and of variations in initial seawater \delta$^{18}$O that may be modified by distal changes in ice volume. The time averaged mean palaeotemperatures for each fossil horizon are generally indicative of warm mesothermal conditions. However, the large standard deviations on each of the summer season palaeotemperatures suggest climate perturbations during these times and/or that the period of mineralization of the rodent teeth encompasses some seasonal variation. This succession is a key interval where the positive \delta$^{18}$O shift in the early Oligocene marine foraminiferal isotope record identifies the onset of the Antarctic Oi-1 glaciation. The data suggest there was no significant summer temperature fall across the Oi-1 glaciation itself. This result is concordant with several other recent studies in suggesting that the majority of the isotopic shift in the marine realm across the Oi-1 glaciation is linked to ice volume, not temperature change. Our new approach has allowed us to put numerical values on summer season temperatures as well as to reconstruct relative temperature change across this key interval of the Eocene-Oligocene transition.
DE: 3344 Paleoclimatology
DE: 1600 GLOBAL CHANGE (New category)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting