Coral Reef Fossils Suggest Rapid Sea Level Rise During Global Warming

Author:  Yangguang Ou
Institution:  Florida State University
Date:  May 2009

In a recent study, fossilized coral reefs gave new insight into the direct correlation between an increase in global temperature and the rise in sea level. The results from the study, done by a team of collaborators from Mexico and Germany, were published on April 16, 2009 in the journal Nature.

Corals, a group of Anthozoans in the phylum of Cnidaria, are relatives of the sea anemones. They secrete a hard exoskeleton comprised of calcium carbonate and can cluster into massive foundations. The study focused on fossilized remains of coral reefs found in the excavation of the canal walls of Xcaret, a recreational park and water resort located 35 miles south of Cancun in the Yucatan Peninsula.

The team, led by Paul Blanchon of the National Autonomous University of Mexico's Institute of Marine Sciences, extracted the fossils and deduced their age via Thorium-230 Dating. By comparing the amount of thorium-230 remaining in the Xcaret fossil samples with previously dated coral reefs found in the Bahamas, Blanchon and his colleagues were able to estimate the age of the coral reefs as approximately 121,000 years old, the end period of the last warming gap between the ice ages.

In order to measure the change in sea level during that time, Blanchon and his colleagues observed the position shift of the corals. On the canal walls, there was a clear height above sea level where the corals died. This, according to the authors, was caused by the rapid rises in sea level during that period when an increase in global temperatures resulted in the melting of glacial ice. Once the sea level stabilized again, the same species of corals were found further inland and approximately 10 feet higher in elevation than their initial position. Geologists term this movement of the corals as "backstepping".

The authors concluded that the sea level rose 6.5 to 10 feet in a period of merely 50 to 100 years, well within the human lifetime. Furthermore, this study provides possible evidence for what scientists fear to be the consequences of the current warming period, during which glacial ice are melting and the temperature of the Earth is increasing steadily. "The potential for sustained rapid ice loss and catastrophic sea-level rise in the near future is confirmed by our discovery of sea-level instability," wrote Blanchon and his colleagues.

However, other experts say the work does not prove that global warming is the cause of rapid sea level rise. Daniel R. Muhs, a scientist from the United States Geological Survey, and William Thompson, a coral specialist at the Woods Hole Oceanographic Institution, both agreed that the dating of the two reefs was not precise and, given the weight of the conclusion, Blanchon and his colleagues did not have enough evidence to support it.

In an interview with the New York Times, Blanchon said: "The work will hold up...the signs of abrupt change is etched in the rock for everyone to examine."

Written By: Yangguang Ou

Edited by: News and Features Editor Brittany Raffa and Professional Reviewer Renee Gilberti

Published by Falishia Sloan