Cold-based ice limits the potential of cosmogenic nuclide dating in Antarctica.

Glacial geological and geomorphological surveys of the coastal mountains of Terra Nova Bay, northern Victoria Land, Antarctica, showed evidence of at least three glacial events that occurred before the Last Glacial Maximum (LGM). About 100 km from the coast, on a nunatak at the boarder of the East Antractic Ice Sheet (EAIS), still two pre-LGM events could be distinguished. Surface exposure dating with in situ produced cosmogenic nuclides (10Be and 21Ne) of both areas reveals more glacial events than previously observed and different histories of landscape evolu¬tion. The glacial deposits on the nunatak are directly related to EAIS fluctuations and show continuous exposure and low erosion rates for the oldest surfaces (929 ± 29; 678 ± 30 kyr), and burial periods of 330 and 530 kyr for two younger ones (284 ± 17; 83 ± 14 kyr). In the coastal area the landscape was much more affected by burial beneath snowdrifts or cold-based ice from local or outlet glaciers. All samples from this area have a complex exposure history; they were probably repeatedly exposed and buried. The burial period becomes increasingly important with lower elevations, ranging from 760 kyr at 910 m asl to about 2 Myr at 470 m asl. Calculations of the minimum total sample history (21Ne exposure age + burial age) show that seven out of ten erratic boulders yield a total history of about 2.15 Myr. Although, these calculations are based on over simplified assumptions (no erosion, continuous exposure followed by only one burial period) they are in agreement with surface exposure ages from rounded mountain tops (2.23 ± 0.086 Myr to 2.56 ± 0.230 Myr), which are evidence of the oldest glaciation in the coastal area. This finding suggests that a major (wet based?) glacial advance occurred in the Terra Nova Bay area ~2.5 Myr ago, eroding enough material to wipe out any inherited cosmo¬genic nuclides. All subsequent (cold-based) glacial events had insignificant subglacial erosion, hence didn’t modify the pre-existing Pliocene landscape and make it hard to develop an abso¬lutely dated glacial chronology. To gain more information about the exact timing of pre-LGM glaciations it is therefore important to focus on the nunataks adjacent to the EAIS, where burial is less significant. A combined cosmogenic nuclide analysis is a prerequisite for any meaningful surface exposure dating in Antarctica.