HR: 11:05h
AN: PP22A-04    [Abstracts]
TI: Quantifying Ice Volume and Temperature Change for the Greenhouse to Icehouse Transition: A Coupled Palaeoceanographic and Palaeoclimate Modelling Approach
AU: * Peck, V L
EM: vlp@bas.ac.uk
AF: British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, United Kingdom
AU: Riesselman, C
EM: criessel@pangea.Stanford.EDU
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115, United States
AU: Haywood, A M
EM: A.M.Haywood@leeds.ac.uk
AF: School of Earth & Environment, University of Leeds, Leeds, LS2 9JT, United Kingdom
AU: Valdes, P J
EM: P.J.Valdes@bristol.ac.uk
AF: School of Geographical Sciences, University of Bristol, University Road, Bristol, BS8 1SS, United Kingdom
AB: The abrupt and widespread glaciation of Antarctica in the earliest Oligocene marked a fundamental change in global climate leading to the Earth's current glaciated state. An increase in benthic δ¹⁸O of up to 1.5 ‰ occurred over a 300-400 kyr interval and is widely assumed to document both cooling and ice sheet growth marking the inception of the icehouse world. Resolving the relative contribution of ice volume and temperature changes to this shift is essential to understanding, and accurately modelling, this climate transition. In an attempt to quantify relative ice volume and temperature changes at the Eocene-Oligocene boundary we present the initial results from a coupled paleoceanographic and paleoclimate modelling approach. Coupled δ¹⁸O and Mg/Ca records of surface dwelling Turborotalia ampliapertura and thermocline dwelling Subbotina angiporoides have the potential to document upper ocean temperature and δ¹⁸O seawater at ODP site 1263, Walvis Ridge in the South Atlantic. %CaCO3 measurements from the suite of sites drilled on ODP Leg 208 place the lyscoline at ~3.8 km in the latest Eocene, prior to deepening in the earliest Oligocene. Collected at a present day water depth of 2717 m, ODP Site 1263 was positioned above the lysocline throughout the Eocene-Oligocene transition. Carbonate concentrations vary between 84 and 96 % (within the studied interval) and planktonic foraminifera appear well preserved. Spanning 33.8 to 32.8 Ma, initial records have a temporal resolution averaging <20 kyrs and compliment an existing benthic δ¹⁸O record from the same site with data points every ~6 kyrs. Preliminary records suggest a temperature shift of less than 0.5° C in the Mg/Ca records of both the surface and subsurface-dwelling species. This finding matches that of the simulated response of sea surface temperatures (SST) at the paleolatitude associated with ODP Site 1263 to the growth of an Antarctic ice sheet during the earliest Oligocene using the HadCM3L General Circulation Model. Two Early Oligocene experiments are being performed which are identical in all respects expect in their prescribed Antarctic ice volumes (either zero ice volume or an ice volume close to modern given the Early Oligocene land-sea mask employed). The response of SST to the growth of an Antarctic ice sheet is predicted to be spatially heterogeneous with some areas subject to changes >3° C, yet a temperature change <0.5° C at ODP Site 1263 is suggested in both the modelling and proxy data presented here. Furthermore, modelling results suggest that intermediate and deep waters cooled by not more than 0.5° C in open ocean areas, indicating that the benthic δ¹⁸O shift at the Eocene-Oligocene boundary cannot be accounted for by glaciation of Antarctica alone. Further work will include the incorporation of a Northern Hemisphere ice sheet in an additional model run to assess the response of SST and BWT to bipolar glaciation and the production of geographically diverse SST and BWT records to compare with model simulations.
DE: 1065 Major and trace element geochemistry
DE: 1621 Cryospheric change (0776)
DE: 4928 Global climate models (1626, 3337)
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting