Calusa Indian site reveals State may face more hurricanes

By Cathy Keen, ckeen@ufl.edu, 28 September 1998

GAINESVILLE—A stormy past warns that Florida may be in store for more destructive hurricanes if scientists are right about the threat of global warming, new University of Florida research suggests.

Nearly 1,700 years ago, devastating tempests associated with sea-level rise destroyed villages of the Calusa Indians on the southwest Florida coast, near present-day Fort Myers, forcing the native fishermen to move inland to relative safety, said UF anthropologist Karen Walker.

Walker's clues to storms, sea-level rise and migration include village remains buried by storm-surge sediment, and other village deposits found at higher elevations than where they should be. In addition, the modest shells and fishbones left behind by the Indians, she said, show ecological correlations between rising sea levels and global warming periods documented in the historical record of ancient Europe.

As we enter into a modern warming period, which seems to be the case, Florida is likely to experience flooded shorelines and an increase of intense storms, Walker said. I think that it's not a coincidence that there were major storms recorded at some of the archaeological sites that I study and that those storms happened during the warm Roman Optimum period. I have the storms closely dated to the fourth century AD.

Global warming is not new, said Walker, explaining that a variety of evidence points to a global episode of warming, dubbed the Roman Optimum, which occurred roughly from 200 B.C. and about A.D. 400, and a later episode, the Medieval Optimum, which took place from about A.D. 800 to A.D. 1200. A cooling episode named the Vandal Minimum occurred roughly between the two warmings.

By studying many archaeological deposits from many locations, I see a picture showing that sea-level fluctuations in Florida correlate to these climate fluctuations known from European history, she said.

Current global warming predictions call for at least a 50-centimeter rise in today's sea level over the next century, which would flood large portions of Florida's low-lying coastal lands, she said.

Walker did her research over the past 10 years on Pine Island, Sanibel Island and other smaller islands. To document rising and falling waters, she studied radiocarbon dates, shells and fish bones, inundation deposits, elevations and other evidence.

Among the evidence, mollusk shells indicate changes in water salinity patterns, with more salty waters during sea-level rises and decreased saltiness during lowerings, she said.

A combination of storm and sea-level rise deposits overlie earlier village layers and underlie later village layers. Walker believes changes in patterns of the Indians villages also reflect climate and sea-level change. During the Roman warming and sea-level rise, people moved their homes inland to higher ground. When climate cooled and sea level dropped, villages were built along the new, lower shoreline.

But by A.D. 800, when the Medieval warming began and sea level rose, the Calusas built massive shell mounds, suggesting they tried to get above the flood threat. There may be other, cultural reasons why they started living on top of these huge shell mounds, but I think it's too much of a coincidence that it happens at this same time, she said.

Although modern pollution, deforestation, ozone depletion and other human-related activity are likely to result in more extreme changes for today's climate, Walker says a growing number of researchers argue that earlier warming trends also were in part human-induced. The Roman Optimum warming, for example, correlates with the Romans' clearing of vast forests as they expanded their empire into northern Europe, and with African deforestation during the Iron Age, situations not unlike the practice of modern populations destroying tropical forests, she said.