­­DEVELOPMENT OF A TERRESTRIAL PROXY FOR PALEO SEA-LEVEL USING LITHIFIED COASTAL-DUNE MORPHOLOGY

The landscape of The Bahamas and Turks and Caicos Islands is dominated by weakly-cemented Pleistocene aeolian dunes that were active during the Last Interglacial (LIG) (128 – 116 ka), which produced a sea-level peak of 6-9 m above present. Digital elevation models from the islands expose detailed aeolian geomorphology including individual-to-amalgamated dune ridges, sandsheets, and parabolic dune fields. Coastal dunes source sand from the shoreline, pinning the original dune front position near sea-level. Downwind dune morphology is a function of sediment supply, wind climate, and land surface properties (e.g. vegetation or moisture). The response of morphology and stratigraphy to environmental factors makes dunes reliable paleoclimate recorders and suggests coastal dunes can also be used as paleo sea-level markers.

Individual-to-shingled parabolic dune ridges have widths only slightly greater than one dune wavelength and form compound topography that can exceed 40 m. We focus on two distinct types within individual-to-shingled ridges distinguished by stoss morphology: ridges with rugose, low angle stoss faces preserving original depositional morphology and ridges with straight, steep, stoss faces that are laterally continuous over 1-10 kilometers on their seaward edge. The straight edges up to 10-15 m above modern sea level demarcating the stoss faces are interpreted as erosional surfaces formed by wave attack. For both dune forms, the toes of lee slopes are interpreted to have built into lagoons, recording mean sea-level through preserved toe elevations. The two distinct types are observed on multiple islands across the archipelago, suggesting the conditions producing the morphologies were regional and pervasive. However, differing morphologies and interpreted formational processes suggest the two dune morphologies were not forming simultaneously, potentially signaling a transition in rates of sea level rise at the time of formation or in wave energy within the LIG.

Our compilation of dune morphometrics allows us to ask new questions about the link between erosional and constructional processes via wave and wind energy and the evolution of the coastal dune landscape during the LIG, an interval that is widely used as analog for the near-future climate and environment.