ESTIMATING THE MAGNITUDE AND RATE OF ICE VOLUME FLUCTUATIONS DURING THE LAST GLACIATION

The relationship between temperature and ice volume during the late Pleistocene glacial cycles provides an important measure of the sensitivity of the Earth system to climate change. Analyses of marine oxygen isotopic records indicate that ice volumes fluctuated markedly throughout the last glaciation phase. Notable examples are the triplet of oscillations in δ¹⁸O (and presumably ice volume) during Marine Isotope Stage (MIS) 5 that are strongly correlated with fluctuations in northern hemisphere summer solar insolation. However, uncertainties related to the effects of temperature, salinity, and isotopic composition of ice sheets complicate the mapping between δ¹⁸O and ice volume, and thus estimates of the magnitude and rate of the ice volume fluctuations remain highly uncertain. We revisit this issue by including constraints on ice history associated with a set of widely distributed geological indicators of sea-level highstands dated to ~80 ka and ~100 ka (MIS 5a and 5c, respectively). Specifically, we run a large suite of ice age sea-level simulations in which the time history of ice volume fluctuations is consistent with the δ¹⁸O record. These calculations indicate that continental ice sheets were characterized by significant dynamic variability during MIS5, indicating a high sensitivity to changes in summer solar insolation. This sensitivity presents a target – and a challenge – for models of ice sheet evolution across the last glacial cycle.