Sea-level rise threatens a billion people living in coastal zones worldwide and has the potential to cost trillions of dollars in damages from impacts to infrastructure and the global economy. During the last century, carbon dioxide, temperatures, and sea level all exceeded measurements over the previous 12,000 years (a geologic period known as the Holocene). This contributed to a seven year study recently concluding that the Earth has entered a new ‘human’ Epoch, referred to as the Anthropocene.
Climate change models predict a two meter rise in sea-level by 2100 coupled with increased storm intensity. Determining how vulnerable sandy coasts will respond to global warming in the future, requires past records of sea-level and storm impacts to be deciphered. Extracting a record of coastal evolution prior to and since seas began to rise 200 years ago offers the opportunity to detect any difference indicating if/how shorelines have responded. Extending this record back over millennia to understand how shorelines evolved when seas were at least 4 m higher than today in the Pleistocene and possibly two meters higher in the mid-Holocene, can offer insight on the impact to coasts as sea-level returns to this 2 meter height by the end of the century.
For almost twenty years I’ve been developing a methodology that combines state-of-the-art geophysics, luminescence, and remote sensing techniques on prograded barriers to extract comprehensive chronostratigraphic records. Ground Penetrating Radar (GPR) data is used to document beach and dune stratigraphic structure at decimetre resolution. Optically Stimulated Luminescence (OSL) is utilized to directly date the formation of paleo-beachfaces and dunes. Light Detection and Ranging (LiDAR) images allow the lateral extent of relict shorelines to be studied. The resulting records of paleo-beach profiles spanning from the present-day beach through Holocene and Pleistocene barriers, enables an in-depth understanding of the factors controlling coastal evolution: storms, sea level, and sediment supply versus accommodation space.
Exploiting the fundamental link between the geometry of beach profiles and wave energy, I was one of the first people to demonstrate that strong geophysical signatures within coastal barrier stratigraphy were actually a record of storm eroded beach profiles. The potential of this research propelled me from the complicated barrier islands in the northeast of America to the pristine prograded barriers Down Under, which provided me a unique natural laboratory. Replicating this research in New Zealand yielded recurrence intervals of erosional surfaces with differing coastal impacts, which captured storm intensity increases as frequency decreased. I then mapped the elevation of paleo-beaches, intrinsically linked to sea level, to construct the first new sea-level curve for New Zealand in 20 years. Extending this research to Australia, I now have data from 13 sites that captures Pleistocene and mid-Holocene sea-level highstands as well as the nature of their subsequent fall. Additionally, I have quantified the volume of sand in these barriers to provide insight on sediment supply and accommodation space. The results indicate that the amount of sand has increased in the last few centuries forming large foredunes anomalous to previous millennia.