Similar to reading a tree ring to tell the age of a tree and the climate conditions that existed in a given year, scientists can read the sediment cores to tell when intense hurricanes occurred.
The study’s authors found evidence of 32 prehistoric hurricanes, along with the remains of three documented storms that occurred in 1991, 1675 and 1635.
The prehistoric sediments showed that there were two periods of elevated intense hurricane activity on Cape Cod – from 150 to 1150 and 1400 to 1675. The earlier period of powerful hurricane activity matched previous studies that found evidence of high hurricane activity during the same period in more southerly areas of the western North Atlantic Ocean basin – from the Caribbean to the Gulf Coast. The new study suggests that many powerful storms spawned in the tropical Atlantic between 250 and 1150 also battered the US East Coast.
The deposits revealed that these early storms were more frequent, and in some cases were likely more intense, than the most severe hurricanes Cape Cod has seen in historical times, including Hurricane Bob in 1991 and a 1635 hurricane that generated a 20-foot storm surge, according to Donnelly.
High hurricane activity continued in the Caribbean and Gulf of Mexico until 1400, although there was a lull in hurricane activity during this time in New England, according to the new study. A shift in hurricane activity in the North Atlantic occurred around 1400 when activity picked up from the Bahamas to New England until about 1675.
The periods of intense hurricanes uncovered by the new research were driven in part by intervals of warm sea surface temperatures that previous research has shown occurred during these time periods, according to the study. Previous research has also shown that warmer ocean surface temperatures fuel more powerful storms.
The sediment coring and analysis by Donnelly and his colleagues “is really nice work because it gives us a much longer period perspective on hurricanes,” said Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology in Cambridge. “It gives you something that you otherwise wouldn’t have any knowledge of.”
“The ability to produce and synthesize thousands of years of data on hurricane paths and frequencies is revolutionizing our understanding of what controls where and how often these dangerous storms make landfall,” said Candace Major, program director in the National Science Foundation’s Division of Ocean Sciences, which funded the research.
The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, Mass.