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To calculate the retreat rate, I averaged the northern and southern Latitudes for each method of dating, as well as the average Calibrated Age for the northern and southern samples for each method. Using an online coordinate calculator, I determined that 3.1 degrees latitude is equal to 186 miles. Retreat rate was then calculated (distance over time) and converted to meters per year.
The three dating methods varied quite a bit, with cosmogenic nuclide data showing only 32 meters of recession on average per year and the macrofossil data showing 402 meters per year of recession.
I believe the cosmogenic dating method here is the most accurate. Macrofossil and Bulk Sediment work with Radiocarbon dating, whereas cosmogenic works based on exposure to cosmogenic rays. The reason cosmogenic dating is more reliable is that it will line up with the rock's exposure after deposition along a moraine. Radiocarbon dating requires the presence of organic material. Glacial recession exposes areas, however the amount of time between then and development/formation of organic matter may vary based on the environmental conditions, leading to more variability.
The cosmogenic dating lines up with a major increase in sea level, shown below. This graph is from Lambeck et. al. 2014.
The Cosmogenic dating shows maximum southern extent around 23k years ago, which lines up with the beginning of sea level rise. This was caused by the melting/recession of the glacial northward. The other methods show maximum southern extent ages to be just under 15k years ago, which does not line up with sea level rise according to the graph.
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