What shipwrecks, tree rings tell us about hurricanes

What shipwrecks, tree rings tell us about hurricanes

A new study led by researchers at the University of Arizona uses tree ring records combined with records of Spanish shipwrecks to show that the period from 1645 to 1715 had the fewest Caribbean hurricanes since the year 1500.

From 1645 to 1715, there was little sunspot activity and cool temperatures in the northern hemisphere. The researchers concluded that there was a 75 percent reduction in the number of Caribbean hurricanes during that same time period.

According the the lead author of the study, Valerie Trouet, an associate professor in the UA Laboratory of Tree-Ring Research, "We're the first to use shipwrecks to study hurricanes in the past. By combining shipwreck data and tree-ring data, we are extending the Caribbean hurricane record back in time and that improves our understanding of hurricane variability."

Trouet and her coauthors came up with the idea while sitting on the patio of Hotel Congress during a science conference in 2013.

Grant Harley of the University of Southern Mississippi in Hattiesburg mentioned that he had tree-ring records from the Florida Keys that went back to 1707.  He pointed out that the growth of the trees was retarded during years with hurricanes and that the reduction in growth is reflected in the annual ring of the trees.

Marta Dominguez-Delmas, a dendroarchaeologist from the University of Santiago de Compostela in Lugo, Spain, figured out when Spanish ships were built by retrieving wood from shipwrecks and dating it.

The team used ship logs and data from several books that documented shipwrecks in the Caribbean to compile a list of ships that had wrecked during the hurricane seasons between the years of 1495 and 1825. The team found that the hurricane patterns from the shipwreck database closely matched the tree-ring information that Harley provided. They also compared the tree-ring data to the hurricane records kept by the U.S. government from 1850 through 2009 and found that the patterns matched nicely there as well.

When they compared the tree-ring and shipwreck data, the researchers discovered that there was a 75 percent reduction in hurricane activity between the years of 1645 and 1715.  This is a time period known as the Maunder Minimum, which is a time when there was low sunspot activity.  Since the Earth receives less solar radiation during periods of low sunspot activity, the Northern Hemisphere was cooler during that period.

Proving that there was a 75 percent reduction in hurricane activity during a time when there was less incoming solar radiation will help scientists to better understand the influence of large changes in solar intensity on hurricane activity.

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