A new analysis shows that the northeast corner of what is now the United States was slammed by at least 23 severe hurricanes from the years 250 to 1150, many of them reaching category 3 and 4 status. Researchers say these hurricanes, which formed in relatively warm seas, could be a harbinger of things to come.

Top image: Hurricane Bob (19 August 1991). At a category 2 storm, it was the most powerful hurricane to hit Cape Cod in recent history. Storms of this intensity have only struck the region three times since the 1600s. But in the centuries prior to that, storms even more powerful that Bob were surprisingly common. (NOAA)

As noted by the American Geophysical Union in a release, "The findings could have implications for the intensity and frequency of hurricanes that the U.S. East and Gulf coasts could experience as ocean temperatures increase as a result of climate change."

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In the first millennium, warmer sea surface temperatures fueled these monstrous hurricanes. The seas have cooled slightly since then, but we could see a return to these earlier conditions.

By analyzing a new record of sediment deposits from Cape Cod in Massachusetts, a research team led by Jeff Donnelly of the Woods Hole Oceanographic Institution were able to compile a timeline showing that 23 severe hurricanes struck the New England region between 250 and 1150 AD. That's one every 40 years or so. These hurricanes were more intense than any that have struck the area since record keeping began.

The researchers documented a total of 32 hurricanes, plus the remnants of three storms known to have happened in 1635, 1675, and 1991.

A section of sediment core from Salt Pond. The light colored sand layer at 693 cm (22.7 feet) down the core provides evidence of an intense storm that occurred approximately in 540 CE ,about 1,080 years before the first Europeans settle New England. Caption and image credit: Jeffrey Donnelly, WHOI

The AGU explains more:

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 Ocean between 250 and 1150 also battered the U.S. 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.

The researchers say the shift in hurricane activity in the North Atlantic occurred in 1400 when storm activity picked up from the Bahamas to New England, lasting until about 1675.

Read the entire scientific paper here.

[ AGU ]