Mapping Estimated Paleoshorelines in QGIS

Archaeology GIS

Shorelines around the world have changed dramatically through time, often due to sea level rise. When working on archaeological sites from thousands of years ago, mapping these changes is important.

Patrick Morrison https://padmorrison.com
05-18-2021

In the past 22,000 years, global sea levels have risen up to 130m (Grant et al. 2012). Using QGIS, we can make a first-order estimate of past shorelines and landscapes using sea level curves and modern bathymetry data1.

If you want to skip everything below, and just want to explore, here’s one I prepared earlier:2

The bathymetry data

The Geoscience Australia Australian Bathymetry and Topography Grid (Whiteway, T. 2009) has elevation data for the entire Australian continent at a 250m horizontal resolution. It is available as a 1.3Gb *.ers grid file. Globally, a database like GEBCO is very useful.

Once you have the data downloaded, you can drag it (e.g. ausbath_09_v4_ex_ex.ers) into the QGIS main window. It should look like this:

Styling

In the layers pane in the bottom left, right click on the layer, and select Properties. Using the Symbology tab, we will colour the layer by relevant contours. Change the render type to Singleband pseudocolour, the interpolation to Discrete, and then define custom colours3 based on your research question, like so:

Colour palette, using some from ochRe
Value <= Colour (HTML Notation) Label
-130 #FFFFFF Deeper than -130m
-30 #6E8DAF 30m to 130m depth (LGM contour)
0 #8DACCF Sea level to 30m depth (dive depth)
inf #8B3400 Land

It should now look like this:

Final map

To finalise your map, create a new print layout (⌘P). Add a scale bar and a legend using the left hand pane. Don’t forget to reference the data, and note the limitations of your estimate!

Estimate of submerged landscape extent using modern bathymetry (Whiteway, T. 2009)

Video version

For more detail, here is an extended version of the tutorial:

Grant, K. M., E. J. Rohling, M. Bar-Matthews, A. Ayalon, M. Medina-Elizalde, C. Bronk Ramsey, C. Satow, and A. P. Roberts. 2012. “Rapid coupling between ice volume and polar temperature over the past 150,000 years.” Nature 491 (7426): 744–47. https://doi.org/10.1038/nature11593.
Whiteway, T. 2009. Australian Bathymetry; Topography Grid, June 2009. Record 2009/021. Geoscience Australia, Canberra. 2009. http://dx.doi.org/10.4225/25/53D99B6581B9A.

  1. Be careful assuming modern bathymetry is a good proxy for past land surfaces. If you have access to estimates of past land surfaces derived from sub-bottom profiling, you should use this instead.↩︎

  2. This is the whole GEBCO dataset processed as described in this post, then exported using GDAL2Tiles and hosted on Github pages. Full code is here: https://github.com/patrick-morrison/submerged_landscapes_world_map/↩︎

  3. Alternatively, you can click Style (at the bottom), and load this: submerged_map.qml↩︎

References

Citation

For attribution, please cite this work as

Morrison (2021, May 18). Patrick Morrison: Mapping Estimated Paleoshorelines in QGIS. Retrieved from https://padmorrison.com/posts/2021-04-03-mapping-paleoshorelines-in-qgis/

BibTeX citation

@misc{morrison2021mapping,
  author = {Morrison, Patrick},
  title = {Patrick Morrison: Mapping Estimated Paleoshorelines in QGIS},
  url = {https://padmorrison.com/posts/2021-04-03-mapping-paleoshorelines-in-qgis/},
  year = {2021}
}