HR: 17:00h
AN: PP32D-05    [PDF]
TI: Pliocene Warming, Contribution of Atmosphere, Oceans and Cryosphere
AU: * Haywood, A M
EM: ahay@bas.ac.uk
AF: British Antarctic Survey, Geological Sciences Division, High Cross, Madingley Road, Cambridge, CB30ET United Kingdom
AU: Valdes, P J
EM: p.j.valdes@bristol.ac.uk
AF: The University of Bristol, School of Geographical Sciences, University Road, Bristol, BS8 1SS United Kingdom
AB: The relative role of the atmosphere, oceans and cryosphere in contributing towards middle Pliocene warmth (ca. 3 Ma BP) is investigated using the HadCM3 coupled ocean-atmosphere general circulation model (GCM). The model was initialised with boundary conditions from the USGS PRISM2 data set and a Pliocene atmospheric CO$_{2}$ level of 400 ppmv and run for 300 simulated years. The simulation resulted in a global surface temperature warming of $3\deg$C compared to present-day. In contrast to earlier modelling experiments for the Pliocene, surface temperatures warmed in most areas including the tropics (1 to $5\deg$C). Compared with present-day, the model predicts a general pattern of ocean warming (1 to $5\deg$C) in both hemispheres to a depth of 2000 m, after which no significant differences are noted. Sea ice coverage is massively reduced (up to 90%). The flow of the Gulf Stream/North Atlantic Drift is up to 100 mms$^{-1}$ greater in the Pliocene case. Analysis of the model-predicted meridional stream function suggests a global pattern of reduced outflow of Antarctic bottom water (AABW; up to 5 Sv), a shallower depth for North Atlantic Deep Water formation and weaker thermohaline circulation (3 Sv). The decrease in AABW occurs mainly in the Pacific rather than Atlantic Ocean. Model diagnostics for heat transports indicate that neither the oceans nor the atmosphere are transporting significantly more heat in the Pliocene scenario. Rather, these results indicate that the major contributing mechanism to global Pliocene warmth was the reduced extent of high latitude terrestrial ice sheets (50% reduction on Greenland, 33% reduction on Antarctica) and sea ice cover resulting in a strong ice-albedo feedback. These results highlight the need for further studies designed to improve our knowledge regarding Pliocene terrestrial ice configurations before further coupled ocean-atmosphere modelling experiments are conducted.
DE: 1620 Climate dynamics (3309)
DE: 3309 Climatology (1620)
DE: 3344 Paleoclimatology
DE: 4203 Analytical modeling
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting