Post-glacial Sea Level rise on the Isthmus of Panama

The Caribbean and Pacific coasts of Panama have changed dramatically as sea levels rose over the last twenty-six thousand years

Present day Panama coastline (left frame) & Panama coastline 26 thousand years before present. Sea level curve sourced from Miller et al. 2005.

Why is it important to model past sea-level on the Isthmus of Panama?

The Isthmus of Panama is a narrow strip of land that connects the continents of North and South America and separates the Atlantic (Caribbean) and Pacific oceans. It is rich in native biodiversity, with tropical rain and cloud forests, island archipelagos, coral reefs, mangrove and estuarine ecosystems.

When it formed, three million years ago, the Isthmus split the oceans and connected the continents. The land-bridge allowed massive inter-continental migrations in what is termed the Great American Biotic Interchange; an event that includes the migration of humans from North to South America within the last 20,000 years. Although small in size, the Isthmus of Panama has played a pivotal role in the evolution and ecology of life on the land and in the seas across the Americas.

After the Last Glacial Maximum (LGM) global sea levels rose rapidly in response to melting ice sheets and glaciers, as well as through thermal expansion of the oceans. Over the last 20,000 years the sea rose by more than 100 meters before it reached close to modern-day levels around 8,000 years ago. This water rise dramatically altered the geography of all coastal areas with important biological implications both below and above sea level. Flooded coastal plains created greater area for shallow marine ecosystems, mountains became islands that isolated native faunas, floras, and pre-historical human populations, and rivers that had shared outflows became disconnected resulting in splits of fresh-water populations.

In this study our aim is to model how post-glacial sea-level rise changed the land- and sea-scapes of the Isthmus of Panama. This helps provide more precise historical context to better understand modern biogeographical patterns of both terrestrial and marine ecosystems on the Isthmus.

Approach

In collaboration with the  GIS unit at the Smithsonian Tropical Research Institute  we combined bathymetric and topographic data with historical sea level data of the Western Atlantic and Tropical Eastern Pacific to produce maps and videos showing the changing land and sea-scapes of the Isthmus.

The Process

The data used to create the bathymetric maps were digitized from two sources: charts from the UK Hydrographic Office and the Instituto Geográfico Nacional Tommy Guardia based out of Panama City, Panama. The UK Hydrographic office maps contained bathymetric points collected from 1982 to 1990 by the US and Colombian Governments. The Tomas Guardia maps contained bathymetric points that were collected in U.S. Navy surveys up until 1979. For the entire Panama sea level model the maps used were at a scale of 1:300,000. For each of the smaller localities such as Coiba and Bocas del Toro, the maps used were of a 1:50,000 to 1:80,049 scale as indicated below each animation. The historical maps utilize mostly the horizontal datum of NAD27, some using the more recent WGS 1984 UTM Zone 17N. The final digitized products contain DEM's projected to the horizontal datum WGS 1984 Web Mercator Auxiliary Sphere. The original bathymetric points had plotted soundings in both fathoms and meters, using mean low water springs as reference. These points were all converted to meters when digitized.

All maps were first georeferenced in ArcGIS Pro and then the bathymetry points were digitized using the parameters as described above. In order to create a fluid digital elevation model (DEM), the spaces between digitized depth points were interpolated using the spatial analyst technique of inverse distance weighting (IDW). Topography data was sourced from NASA Shuttle Radar Topography Mission (SRTM) 1 Arc-Second Global DEM with a 30 meter cell size. This data was merged with the interpolated bathymetry DEMs and then used to create the models shown below. The sea level data used for the animations is sourced from the paper  The Phanerozoic Record of Global Sea-Level Change  by Kenneth G. Miller (Miller et al. 2005).

A segment of Bocas del Toro

Caveats

It is important to note that these models do not take into account the progradation of coastlines or sedimentary deposition, both of which can have significant impacts on the estimated shape of ancient seascapes, particularly where sedimentation is high in basins and bays (e.g. the Parita and Pacora regions in the Gulf of Panama). Submarine erosion of sediments could also alter predicted ancient seascapes but the impact is unlikely to be as important as depositional processes.

Marine sedimentary deposition causes our digital elevation models to be depicted higher in the animations than they were in the past. The amount of error depends on the shape of the sea floor and the amount of rainfall that will bring eroded sediments into a marine area. Seismic profiling of sediments can help determine the thickness of submarine sedimentary depositions, and radiometric dating can determine the extent of progradation of coastlines, both of which would help improve our seafloor models. Without them, we recommend using these data with care. For example, ages of island formation during post-glacial flooding should be considered a minimum age.

The models also do not take into account tectonic subsidence or uplift of lands. Some regions of the Isthmus, such as the Burica Peninsula have experienced rapid uplift, while others (e.g. Bocas del Toro) may be experiencing subsidence. On average, the isthmus has been uplifting at a rate of less than 100 m per million years over the last 5 Myr (O'Dea et al. 2016). This translates to approximately 2 m of error in the models presented here.

Localities of Interest

The goal of the project was to produce sea level animations at a lower resolution for the whole of Panama (including neighboring regions in Costa Rica and Columbia) and at a higher resolution for the Coiba and Bocas del Toro archipelagos.

Sea Level Model Animations

WGS 1984 Web Mercator Auxiliary Sphere - Scale 1:300,000

WGS 1984 Web Mercator Auxiliary Sphere - Scale 1:300,000

WGS 1984 Web Mercator Auxiliary Sphere - Scale 1:50,000

WGS 1984 Web Mercator Auxiliary Sphere - Scale 1:300,000

WGS 1984 Web Mercator Auxiliary Sphere - Scale 1:80,049

Post-glacial Marine Shelf Area Changes on the Isthmus of Panama (Miller et al. 2005)

Acknowledgements

This project would not have been possible without the support and skills of GIS Specialist Milton Solano. We also thank Steve Paton and Stewart Redwood. Data were kindly provided by the Instituto Geográfico Nacional Tommy Guardia, the UK Hydrographic Office, and NOAA National Centers for Environmental Information. Financial support was given by the Smithsonian Tropical Research Institute and the Sistema Nacional de Investigadores (SENACYT, Panamá).

References

O’Dea A, Aguilera O, Aubry M-P, Berggren WA, Budd AF, Cione AL, Coates AG, Collins LS, Coppard SE, Cozzuol MA, de Queiroz A, Duque-Caro H, Eytan RI, Farris DW, Finnegan S, Gasparini GM, Grossman EL, Johnson KG, Keigwin LD, Knowlton N, Leigh EG, Leonard-Pingel JS, Lessios HA, Marko PB, Norris RD, Rachello-Dolmen PG, Restrepo-Moreno SA, Soibelzon E, Soibelzon L, Stallard RF, Todd JA, Vermeij GJ, Woodburne MO, Jackson JBC. 2016. Formation of the Isthmus of Panama. Science Advances.  e1600883 .

Kenneth G. Miller, Michelle A. Kominz, James V. Browning, James D. Wright, Gregory S. Mountain, Miriam E. Katz, Peter J. Sugarman, Benjamin S. Cramer, Nicholas Christie-Blick, Stephen F. Pekar. 2005. The Phanerozoic Record of Global Sea-Level Change. SCIENCE.  10.1126/science.1116412 

Project Resources

An important goal of this project was to provide ready to use and freely accessible bathymetry data for Panama. Thus we have included the Digital Elevation Model data used above in a ArcGIS Pro Layer Package Format (LPKX) and as TIF files. For more GIS resources hosted by the Smithsonian Tropical Research Institute, please visit  https://stridata-si.opendata.arcgis.com/ .

Coiba:

Regional Coiba

Bocas Del Toro:

Regional Bocas del Toro:

Panama Wide Data:

Citing the Study

The Digital Elevation Models used above and the high resolution animations can be downloaded from the Smithsonian Figshare data repository  here . Please use the following citation for acknowledgement when sharing or using the data and animations:

Titcomb M, O’Dea A. 2020. Post-glacial Sea Level rise on the Isthmus of Panama. DOI:  https://doi.org/10.25573/data.11919276 .

A segment of Bocas del Toro