ICHNOLOGY IN A TIME OF CLIMATE CHANGE: PREDICTED EFFECTS OF RISING SEA LEVEL AND TEMPERATURES ON ORGANISMAL TRACES OF THE GEORGIA COAST

Ichnology, the study of modern and fossil traces, has a long-time connection to Georgia coastal geology via neoichnological studies that began in the 1960s. Furthermore, the ichnofacies paradigm, first proposed in the 1950s, was strengthened through actualistic examples provided by Georgia-coast ichnocoenoses, such as modern firmground ichnoassemblages (Glossifungites ichnofacies) and softground ichnoassemblages (Skolithos, Cruziana, and Psilonichnus ichnofacies). Recent applications of paleoichnology to sequence stratigraphy have also clarified the tight relationship between organismal responses to sea-level fluctuations and diagnostic trace-fossil assemblages at sequence boundaries. In this study, neoichnology and paleoichnology are used to predict future changes in organismal traces of the Georgia coast, given the conjoined assumptions of increasing global temperatures and sea level. One prediction is that onshore coastal ichnofacies (Psilonichnus) will be succeeded vertically by offshore ichnofacies (Skolithos and Cruziana), and higher temperatures will encourage more biogenic mixing of offshore sediments. Terrestrial and freshwater ichnofacies of the barrier islands will be squeezed into relatively smaller areas, especially where bracketed by shoreface sediments and back-barrier salt marshes. Consequently, insect nests, diagnostic of the Celliforma or Coprinisphaera ichnofacies, will decrease dramatically in number and size. Likewise, burrows of crayfish, amphibians, and other freshwater-only organisms on the Georgia islands will no longer be made; endemic species of crayfish (e.g., Procambarus lunzi, P. talpoides) may even become extinct. Traces of invasive species, such as feral cattle (Bos taurus), hogs (Sus crofa) and horses (Equus equus), will have added significance in coastal sediments as these species spread further. Frequent tropical storms should result in more ichnocoenoses associated with post-storm colonization of washover fans. Some of the predicted effects of global climate change on the Georgia coast may be affected by real-time monitoring of tracemakers, especially invasive species, but most will be inevitable as organisms accordingly shift their habitats and form traces in newly formed ecosystems.