Variations in sea level are increasing along the eastern Gulf of Mexico coast, potentially increasing the risk of flooding from hurricanes, researchers say. While sea levels typically rise a little in summer and fall again in winter around the globe, a study shows that from the Florida Keys to southern Alabama those fluctuations have been intensifying over the past 20 years, scientists report in the journal Geophysical Research Letters. The summer during the past two decades means storm surges can rise higher than previously thought, increasing how much sea level rise contributes to the flooding risk from hurricanes, said study lead author Thomas Wahl, a postdoctoral researcher from the University of Siegen in Germany working at the University of South Florida in St. Petersburg. While global sea levels rose by about 2 inches from 1993 to 2011, the newly discovered trend of summer sea level rise has added about 1.9 inches on top of that in the eastern Gulf, Wahl and his colleagues said. Additionally, the growing difference in the region between summer and winter sea levels might be disrupting coastal ecosystems adapted to what was once a relatively stable difference from season to season, Wahl said. "Very sensitive ecosystems along the Gulf coast depend on the seasonal cycle," he said. "If there are significant changes in the seasonal cycle then this very likely has an effect" on these ecosystems. For example, he said, changes in sea levels in the winter could throw off the salt balance in sensitive coastal wetlands.