SOUTHERN LAURENTIDE ICE SHEET FLUCTUATIONS DURING TERMINATION 1

After the Last Glacial Maximum the Laurentide Ice Sheet retreated for several millennium, before its eventual demise. There are numerous examples of cases where the ice sheet did not continuously retreat but rather fluctuated. Yet mapping out the spatial and temporal distribution of these is challenging.

Here we examine prior efforts and our unpublished work related to retreats and readvances of the ice sheet. With restrictive criterial (sufficient number of numerical age assignments) we can create probability distributions. When the context of the distribution is considered (brackets vs. peaks) we can compare sites that originally employed different dating techniques. Interstadial beds are an important in this regard as they provide a minimum age bracket for the advance below them and a maximum age bracket for the advance above them. For this preliminary examination we consider the southern Laurentide Ice Sheet spatially as extending from Maine to the Dakotas and temporally from ~20 to 10 ka before present.

Using this approach we find, for example, the retreat prior to the Valders readvance (WI) occurred from 17.8 to 15.3 ka. The readvance from 15.7 to 14.5 ka, has a peak probability of 15.0 ka. The following retreat was underway by 14.4 ka. This cannot be differentiated from sites far afield including Pineo Ridge readvance (ME) at 15.3 ka nor from the Steep Rock readvance (ONT) between 15.2 and 14.3 ka.

We find a broad correlation between distant sites along the southern margin with little correspondence to the temperature records of the Greenland ice core suggesting that other forcings are responsible for the Laurentide ice sheet fluctiatons during Termination 1.