DID THE SOUTHERN MARGIN OF THE LAURENTIDE ICE SHEET RESPOND TO HEINRICH STADIAL COOLING?

To explore the link between ice sheet behavior and climate, we asked what happened to the margin of an ice sheet during established cold intervals. We chose the Heinrich Stadials, as recorded as cooler surface water temperatures across the North Atlantic in marine records. Of specific interest were Heinrich Stadials 2 and 1, which occurred from 27.1 to 23.3; and 17.7 to 14.6 ka, respectively. In the simplest view, the ice sheet margin should be advancing during these times.

We compiled all available chronologic data defining the advance and retreat patterns of the Laurentide Ice Sheet from samples collected within 50 kilometers of the southernmost extent. This analysis only considered ages that fall between 12.0 and 30.0 ka. We summarize the behavior of various sectors of the ice sheet during HS2 and HS1 in the table below.

Ice Sheet Sector	HS2	Interstadial	HS1
New England	Reached maximum >HS2; Retreat	Retreat	Retreat
Lake Huron/Erie Lobe	Advance	Reached maximum extent	Retreat
Lake Michigan Lobe	Advance	Reached maximum early interstadial; Retreat	Retreat
Green Bay/Chippewa Lobes	Reached maximum >HS2; Retreat	Retreat	Retreat
Des Moines Lobe	Unknown	Unknown	Advance
James Lobe	Unknown	Unknown	Unknown

Based on our analysis, it appears that the lobes of the southern margin of the LIS did not advance and retreat synchronously. More important, the southern LIS margin did not respond to cooling in the North Atlantic during Heinrich Stadials 2 and 1. We put forth the suggestion that local climate conditions, or more specifically ablation rates, may have played a large role in the behavior of the individual lobes.