Dating Deglaciation

The three graphs above depict age vs. latitude for bulk sediment radiocarbon, plant macrofossil radiocarbon and cosmogenic nuclides. Latitude in decimal degrees is plotted on the y-axis and age in years before present is plotted on the x-axis.

In order to calculate the ice sheet's rate of retreat for each of the three dating methods, I used Google Earth Pro to measure the distance between the northernmost and southernmost sampling sites. These distances were divided by the difference in age between the northernmost and southernmost samples to determine the rate for each method. The bulk sediment (140 m/yr) and macrofossil (814 m/yr) methods show much faster rates of retreat than the cosmogenic nuclide rate (41 m/yr). The macrofossil rate in particular seems extremely fast. The calculated cosmogenic nuclide rate is much more consistent with the cosmogenic nuclide dating in the Lambeck paper. Cosmogenic nuclides appear to provide the best estimate of glacial retreat based on the literature reviewed this week because this type of dating determines the age of the rock itself rather than fossils or sediments. Corbett et al. discusses how ice covered higher elevation for a very long time after glaciers had begun to retreat. This could make a major difference in the calculation of retreat rates. I used Sterling Pond to calculate the retreat rate for the bulk sediment method, which sits at an elevation of 3000 ft, while Glover's Pond, NJ is only about 560 ft above sea level. Sites at similar elevations may control for this better than the sites I used. Dates may also be skewed by materials like erratics that were moved by glaciers rather than exposed from beneath the glacier.