Understanding past changes in the East Antarctic Ice Sheet is essential for predicting future changes and sea level. With a response time on the order of thousands of years, the ice sheet continues to adjust to changes from glacial to Holocene conditions. Ice sheet models are the best tools for understanding time-dependent, continental-scale ice fluctuations. Unfortunately, terrestrial field evidence is geographically sparse, and provides a weak horizontal and poorer vertical constraint of past ice extent. Quantifying Antarctic coastal ice sheet behaviour has become a critical test for such models and discrepancies persist regarding predictions of pervasive ice advance to the continental shelf during LGM times against field evidence which suggests a far reduced coastal ice sheet extent. We present new 10Be and 26Al exposure ages from the Framnes Mountains, a string of nunataks extending up to 50 km inland from Mawson Station in Mac.Roberston Land, East Antarctica. These steep nunataks lie as linear ranges that are transverse to ice flow, and thus provide excellent “dipsticks” to constrain ice volume changes through the last deglaciation. Fresh, glacially rounded and striated erratics indicate that the last glacial advance inundated the majority of the nunataks in the region. However, the bedrock is significantly more weathered (iron stained, shattered and tafonied) than the cobbles and it is likely that the last glacial advance in this area was non-erosive and cold based. The full set (20 samples) of cosmogenic ages, from ice edge to summit peaks, range from 6-55 ka, (with distinct populations at 6-7 and 8-12 ka ) indicating the timing of ice volume events all fall within the last global glaciation. This suggests that the maximum ice sheet thickening was ~400 m and was not as large as the ~1000 m thickening predicted by some ice sheet models in this area. Moreover, based on 26Al/10Be ratios, the last deglaciation of the ice sheet at Framnes occurred during the early Holocene, at ~6-7 ka, and appears delayed by 3-5 ka from the adjacent Lambert drainage graben. These results indicate that the East Antarctic Ice Sheet responds differently on a regional basis despite the same climatological forcing, and hence coastal deglaciation ages may not be indicative of when major ice lowering occurred. Models must address these issues before they are used to assess the future stability of the ice sheet in a warmer world.
See more of Poster Session I
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)