New perspectives on paleoglaciology

• Quaternary ice sheets are modeled for the Northern Hemisphere.
• Nucleation of a glaciation cycle is emphasized.
• A bottom-up model emphasizes ice-bed coupling and glacial geology.
• A top-down model emphasizes ice-surface conditions and climate.
• Both “snapshots” and “motion pictures” in time are modeled.
• New perspectives on Paleoglaciology are provided by our work.

Paleoglaciology deals with glaciation cycles of the Quaternary Ice Age. It combines the dynamics of present-day ice sheets deduced from glaciology with the history of former ice sheets deduced from glacial geology. Cosmogenic dating now makes a detailed chronology of a cycle possible. Radiocarbon dating has provided a detailed chronology for Termination of the last cycle, but cannot date how the cycle began. Here we identify the central challenge in applying paleoglaciology to Quaternary glaciation cycles in general, and initiation of these cycles in particular. The challenge is the role of thickening sea ice in the Arctic Ocean, possibly becoming thick ice shelves floating over deep Arctic basins and high marine ice sheets grounded on shallow Arctic continental shelves. In that case, an Arctic Ice Sheet existed that was larger and less stable than the Antarctic Ice Sheet is now or in the past. Two approaches to this problem are presented as Part 1 and Part 2. In Part 1, the height of these former ice sheets is linked primarily to the strength of ice-bed coupling, which is deduced from glacial geology. It provides “snapshots” of ice sheets that give ice elevations independent of the past history and largely independent of ice-surface conditions, temperatures and the mass balance in particular. In Part 2, heights of former ice sheets depend on both their past history, particularly initial conditions, and changing surface conditions during the glaciation cycle. This provides a “motion picture” of ice sheets during the full cycle. The challenge is to establish a “mind meld” of these two approaches. They allow new perspectives on paleoglaciology.