MAGNITUDES AND RATES OF CENOZOIC CRYOSPHERE VARIABILITY: IMPLICATIONS FOR FUTURE CLIMATE AND SEA LEVEL

Fundamental steps in the long-term evolution of the cryosphere include the rapid, initial growth of the Antarctic ice sheet ~34 million years ago, the first glaciation of Greenland, and the eventual onset of Northern Hemispheric glacial cycles ~3 million years ago. Numerical modeling combined with new proxy records of ice volume, ocean temperatures, pCO₂, and sea level is painting a revised picture of this evolution, especially with regards to the size of the first Antarctic ice sheet and the possibility of some Northern Hemispheric land ice before 3 million years ago. Yet fundamental questions remain. For example, what was the source of apparent high-magnitude ice volume variability prior to the appearance of Northern Hemispheric ice sheets, in light of presumably strong Antarctic ice sheet hysteresis?

In the more recent geologic past, new proxy and sea-level records are pointing to a much more dynamic and sensitive cryosphere than previously appreciated. This includes compelling evidence that 1) the East Antarctic Ice Sheet retreated substantially as recently as the Pliocene, 2) the West Antarctic Ice Sheet (WAIS) has collapsed and re-advanced many times over the last few million years, and 3) WAIS retreated as recently as the Last Interglacial. These new records of past cryosphere behavior will be discussed in the context of new climate-ice model simulations of Antarctic and Northern Hemispheric ice sheets that include more complete representations of ice sheet physical processes (particularly those associated with ice shelf calving, buttressing, and grounding line dynamics) that for the first time, are capable of capturing the observed range and rates of past cryosphere variability. When applied to long-term future scenarios, these new mechanisms have dire consequences for possible magnitudes and rates of future sea-level rise.