Northern Greenland coastlines are inaccurate

Hello,

I am compiling data to document deglacial sea level changes in Greenland, and I noticed there is an error in the coastlines in GSHHG. I have illustrated this error by comparing the shorelines to the GEBCO 2021 topography dataset (the black lines are the GSHHG shorelines):


The red dots are locations where radiocarbon dated fossil shells and driftwood have been found in glacial isostatically uplifted marine and shoreline deposits. Many of these data were reported in a paper by Funder et al., 2011 (https://doi.org/10.1126/science.1202760). I asked Dr. Funder about this, and he said that the locations of data they collected were measured using GPS, so they are undoubtedly accurate. The map in the paper shows the correct shoreline positions.

At its worse, the coastline in GSHHG dataset is about 35 km from the (apparent) true location. This error also affects Google Earth. The georeferencing of the satellite imagery in Google Earth appears to have used GSHHG as a base. It appears that the coastline west of about 53W and south of about 78N is accurate

I have attached the script I used to create the above image (though you will have to download GEBCO separately).

[test_greenland.zip](https://github.com/GenericMappingTools/gshhg-gmt/files/10955024/test_greenland.zip)

Start with the attached test_greenland.zip script and reproduce the comparison against the separately downloaded GEBCO 2021 topography data. Review the GSHHG shoreline source and the affected region west of about 53W and south of about 78N, using the cited Funder et al. paper and reported GPS locations as references. Done means the coastline positions match the available evidence in the affected northern Greenland areas.

Written by the indexing model from the issue text.