Above are two separate cut outs of the same region around Disko Bugt coastline in southwestern Greenland, with the one on the right showing higher resolution and detail. The axis shows surface elevation of the topography. This kind of high resolution topography data is critical for calculating the location of the ice margin of the Greenland Ice Sheet ~9000-5000 years BP.  At that time temperatures were estimated at 1° to 2° C warmer than today leading to melt and a smaller ice sheet footprint. Most of the geologic evidence has been overprinted as the ice sheet expanded to its present size.

To address this challenge, the Snow on Ice project is matching continuous sediment sequences collected from the bottom of pro-glacial lakes along the perimeter of the ice and created by meltwater from the ice sheet, with newly developed sub-elevation maps like the ones above created from radar data. The map above shows Greenland’s central western coastline without the ice cover. Removing the ice allows the viewer to see the drainage pathways that trace back under the ice. These pathways can be matched to lakes along the ice margin to see which ones reach under the ice and how far back. Lakes sitting along the edge of the ice sheet  collect erosional silts when ice covered, and organic materials when they become exposed in a warmer climate.

Read about lake sediments, another method used to determine Greenland’s Mid-Holocene Ice Extent

Read about exposure dating, another method used to determine Greenland’s Mid-Holocene Ice Extent