2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 7
Presentation Time: 9:40 AM

Seven Million Year History of the Antarctic Peninsula Ice Sheet Revealed by Coupled Glaciovolcanic and Climate Modelling Studies

SMELLIE, John L., Geological Sciences Division, British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, United Kingdom, jlsm@bas.ac.uk

Glaciovolcanic studies have advanced substantially over the past 10 years through increasingly detailed process-orientated outcrop investigations linked to observations of modern eruptions. They are slowly becoming established as an important ice sheet proxy tool capable of yielding the widest and most precise range of critical ice sheet parameters of any terrestrial proxy, and are particularly important for pre-LGM periods, when most other terrestrial proxies typically get erased or cannot be dated. For the first time, a coupled glaciovolcanic—climate modelling study has been used to infer the configuration of the Antarctic Peninsula Ice Sheet (APIS), for the period between c. 7 Ma and present, using information contained in volcanic outcrops scattered along the length of the Antarctic Peninsula. The volcanism is exclusively basaltic and varies from multiple monogenetic volcanic fields to large stratovolcanoes. Precision of K-Ar and 40Ar/39Ar dating of young basaltic lavas throughout the region is relatively poor compared with the duration of glacial—interglacial periods and precludes any Milankovitch-scale cyclicity being identified. However, the results indicate that the APIS was relatively thin throughout the period, typically less than 400 m although rarely thicker (up to c. 900 m), and increased in thickness toward the present mirroring the trend to colder temperatures globally. The APIS was predominantly wet-based and erosive. Thus it had a temperate or, perhaps more likely, sub-polar thermal regime and must also have had a low profile. Estimated net snow accumulation was derived from numerical palaeoclimate model experiments using warm Pliocene boundary conditions. The results are consistent with the geological information and indicate that an ice sheet was present during the period. Overall the simulations indicate the potential existence of an APIS over a global mean temperature change spanning from +1.9 to +4.5°C. Thus, the APIS may be more robust than is generally assumed.