Plio-Pleistocene Ice Volume, Antarctic Climate, and the Global δ18O Record

We recently proposed (Science, v. 313, p. 492) that throughout the late Pliocene and early Pleistocene (LP/EP) a terrestrial ice margin may have characterized much of the East Antarctic ice sheet (EAIS). This margin would have been maintained by above freezing summer temperatures and its position would thus have been sensitive to orbitally-induced changes in local summer insolation at both obliquity and precession frequencies. Because Earth's orbital precession is out of phase between hemispheres, 23 ky changes in ice volume in each hemisphere would cancel in globally integrated proxies such as ocean δ18O or sea level leaving the in-phase obliquity (41 ky) component of insolation to dominate the δ18O record. Geochemical and sedimentological evidence for a reduced EAIS will be presented as well as ice sheet model results. Possible tests of our hypothesis will also be discussed including: looking for evidence for LP/EP moraines or above freezing temperatures on Antarctica; looking at the meltwater discharge record of major northern and southern hemisphere ice sheets for evidence for precession pacing in "41 ky world"; recovering ice cores from the EP to assess local Antarctic climate response; building more realistic ice sheet models forced by varying insolation parameters; finding independently dated climate records in which the timescale errors are small relative to the scale of insolation forcing. It would also be extremely useful to determine how much of the global δ18O signal over the last 4 million years is due to ice volume versus temperature variations. Numerous approaches are being developed to address this question including the alkenone and Mg/Ca temperature proxies.