Refining search areas for submerged archaeological resources using subbottom data and applied geomorphology

During the last glacial maximum, eustatic sea level was ~120 m below present, exposing most of the world’s continental shelves, and providing a vast landscape for human migration and occupation that is now submerged due to post glacial sea level rise. Locating archaeological sites on the now submerged shelf could have implications for our understanding of human migration pathways and human adaptation to a changing climate. Given this vast expanse and the difficulty of underwater survey, however, it is critical to refine search areas to make the best use of time and resources. We present two case studies where the use of subbottom reflection data have revealed new ways in which the geomorphology of the continental shelf can be used to inform the search for submerged archaeological resources. First, along the Northern Channel Islands, California, subbottom data were used to map paleoshorelines based on their characteristic morphology. Results showed a mismatch between these paleoshorelines and those modeled using modern bathymetry, primarily due to the presence of Holocene sediment that buries paleoshoreline features. Second, on the continental shelf offshore central Oregon, subbottom mapping of paleovalleys showed that variable channel morphology could be predicted by the characteristics of the continental shelf. In both cases, the observed subbottom morphology refines the area for archaeological searches through identification of paleolandscape features and provides information on preservation and burial of these features. Furthermore, these observations could be applied to predictive modeling over much larger regions where modern bathymetry alone may misrepresent the paleolandscape.