Sub-stage· The columns of time

Last Glacial Maximum

26.5 ka → 19 ka

The coldest seven and a half millennia of the last hundred thousand years, when the ice sheets stood at their greatest extent and the ocean sat roughly 130 metres below its present level.

What the evidence shows

Clark and colleagues fixed the interval at 26,500 to 19,000 years ago by asking a precise question: over what period were the ice sheets simultaneously at or near their maximum, everywhere they existed? Lambeck and colleagues measured what that cost the ocean, inverting a thousand shoreline observations to find sea level falling to 134 metres below present between 29,000 and 21,000 years ago, and still far below it when the main deglaciation began around 16,500. Those two results are the reference state against which every warmer world is measured, ours included.

Bounds and conventions

A maximum is easier to name than to date. Different ice sheets peaked at somewhat different times, and the interval given here is the window in which nearly all of them were close to theirs, a stricter definition than most and correspondingly shorter.

The maximum extent of the ice sheets, 26,500 to 19,000 years ago (Clark et al. 2009).

Sources

1. Clark, P. U., Dyke, A. S., Shakun, J. D., et al. (2009). The Last Glacial Maximum. Science 325, 710–714.
2. Lambeck, K., Rouby, H., Purcell, A., Sun, Y., Sambridge, M. (2014). Sea level and global ice volumes from the Last Glacial Maximum to the Holocene. PNAS 111(43), 15296-15303.
3. Lisiecki, L. E., Raymo, M. E. (2005). A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records. Paleoceanography 20, PA1003.