Mapping the 45,000-Year-Old Shoreline of the Gulf of Mexico

To build this map, I started by downloading high-resolution seafloor data from GEBCO, focusing on the Gulf of Mexico. I converted the file into a format that ArcGIS could easily work with. Then, using a simple but powerful raster calculation I raised every elevation value by 75 meters (digital approximation of the lower sea level during the MIS 3 period around 45,000 years ago). Instantly, the continental shelf emerged from the depths, revealing the exposed coastal plain.

From that new elevation surface, I extracted the precise paleo shoreline by tracing a zero meter contour (the literal present day boundary). I styled the map to clearly distinguish deep ocean, shallow shelf and dry land, and exported the key outputs