HR: 1340h
AN: PP43C-1530    [Abstracts]
TI: Late Pliocene enhancement of Greenland glaciation: CO2 vs. direct tectonic forcing
AU: Foster, G
EM: g.l.foster@bris.ac.uk
AF: University of Bristol, School of Geographical Sciences, University of Bristol, University Road, Bristol, BS8 1SS, United Kingdom
AU: * Lunt, D J
EM: d.j.lunt@bristol.ac.uk
AF: University of Bristol, School of Geographical Sciences, University of Bristol, University Road, Bristol, BS8 1SS, United Kingdom
AU: Haywood, A
EM: a.haywood@see.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment Environment Building The University of Leeds, Leeds, LS2 9JT, United Kingdom
AB: Loss of mass from the Greenland ice sheet (GrIS), and in particular the associated sea level rise, is one possible impact of anthropogenic global warming which is of fundamental concern. Therefore, significant effort has recently been applied to modelling the future response of the GrIS to increasing or elevated greenhouse gas concentrations. However, it is currently not known what fundamental forcing mechanisms or critical thresholds have determined the evolution of the GrIS in the past, in particular on geological timescales. In this paper, we address this issue by testing three alternative hypotheses used to explain the enhancement of Greenland glaciation in the Late Pliocene. (1) the "Panama Hypothesis", whereby ocean circulation changes following the formation of the Panama Isthmus enhanced poleward transport of moisture and brought more snowfall to the incipient GrIS; (2) the "Rockies Hypothesis" whereby changes in atmospheric circulation via storm track and Rossby wave deflection, following the uplift of the Rockies, led to cooling over Greenland ; and (3) the "CO₂ Hypothesis" whereby decreasing CO₂ in the Mid and Late Pliocene led to a global cooling. We use the UK Met Office GCM, HadCM3, and the UK ice sheet model, GLIMMER, and carry out Pliocene and pre- industrial simulations with various combinations of prescribed boundary conditions, in order to elucidate the relative importance of CO₂ vs. direct tectonic forcings in controlling the evolution of the GrIS. The study indicates that the decrease in atmospheric CO₂, from the elevated values of the mid-Pliocene to lower values of the Quaternary, drove a significant enhancement of Greenland glaciation, which was further increased by climate-ice sheet-vegetation feedbacks, resulting in a GrIS similar to that observed today. Conversely, it shows that climatic shifts associated with the tectonically-driven closure of the Panama Seaway and uplift of the Rockies were not large enough to contribute significantly to enhanced Greenland glaciation.
DE: 0726 Ice sheets
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4930 Greenhouse gases
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting