ESTIMATING LAST GLACIAL MAXIMUM ICE THICKNESS USING POROSITY AND DEPTH RELATIONSHIPS: EXAMPLES FROM AND-1B, MCMURDO SOUND, ANTARCTICA

We have estimated ice thicknesses at the AND-1B drillsite during the Last Glacial Maximum by adapting an existing technique used to calculate eroded overburden. We analyze the porosity as a function of depth and lithology from measurements taken on the AND-1B core, and compare these results to reference data obtained on Ocean Drilling Program Legs 178, Leg 188, and Integrated Ocean Drilling Project Leg 318. These reference datasets are deep marine sediments of similar lithology and have not been overcompacted by overriding ice sheets. Using these reference datasets we estimate the amount of overburden required to compact the sediments to the porosity observed in AND-1B. This analysis is a function of lithology, depth and porosity, and generates sediment-equivalent overburden estimates between 500 and 900 meters. These are translated into ice thickness estimates by accounting for differences in sediment and ice densities. The lithologies analyzed are most likely to compact consistently and predictably, and result in a range of ice thickness between 1,059 – 1,984 meters, with a best-fit estimate of 1,630 meters of ice at Last Glacial Maximum. These values compare well with mass-balance corrected, independently calculated, ice-thicknesses estimates of 1,730 meters based on exposures of Last Glacial Maximum till deposits. While this analysis can only specifically estimate ice thicknesses during Last Glacial Maximum, due to the overprinting effect of Last Glacial Maximum ice on previous ice advances, it also has implications for previous maximum ice thickness during earlier Pleistocene glacial maximums. Lastly, as ice thickness at Last Glacial Maximum is unknown in existing ice sheet reconstructions, this analysis provides constraint on model predictions.