DO THE ICE MARGIN CHANGES OF THE LAURENTIDE GREAT LAKE LOBES MATCH THE GREENLAND ISOTOPE RECORD?

The Greenland Ice Cores have long been held as a reference for climate change during the late Pleistocene. The isotopes from multiple cores now provide a detailed record that many paleoclimate records have been compared to. Glaciers are taken as being most responsive to temperatures during the summer ablation season. Oerlemans (2005) has show that a global network of small glaciers can provide a temperature record over the last two hundred years that matches the global temperature derived from instrumented records. It would be informative to ask if the margins of ice sheets match the reference for climate change. The lobes of the Laurentide ice sheet that occupied the Great Lakes are examined here in that context.

For the last glacial maximum records show that the ice sheet was south of the Great Lakes by 27.2 ka cal and continued to reach its maximum at 24.0 ka cal and started to retreat as early as 21.7 ka cal with major retreat underway by 17.0 ka cal. Superposed on this general pattern were advances at 24.0, 24.0, 22.2 and 21.2 ka cal. With the exception of a warm interstadial at 27.5 and 23.5 ka cal, the ice core is nearly linear during this time. In other words examination of the ice core alone would not suggest the growth, decay pattern, nor major advances of the ice sheet margin.

Possible explanations for this disconnect are 1) the ice core record does not represent the climate of the Great Lakes region; 2) the concept of seasonality, whereby the ice core records mean annual, not summer temperatures; 3) the dynamics of ice sheets are not driven by climate changes. Given that the above record was derived from and is consistent with both the Lake Michigan and Lake Erie lobes option 3 seems unlikely. This comparison can not distinguish between options 1 and 2.