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First Ever 5,000-Year Record of Hurricanes Compiled
Hurricane researchers have put together the longest-ever record of
hurricane strikes--going back 5,000 years--in the Atlantic, and it shows
that the El Niño weather pattern plays a critical role in ramping up and
tamping down intense hurricanes.
Hurricane records extend only as far back as historical texts and modern
meteorological techniques have been collecting information about them,
which is to say, not very far.
To extend the record past these limited sources, two geologists from the
Woods Hole Oceanographic Institute in Massachusetts, in 2003, began
digging up sediment cores from the bottom of Laguna Playa Grande on the
Puerto Rican Island of Vieques, which is very vulnerable to hurricane
strikes.
Laguna Playa Grande is usually protected and separated from the ocean
during storms, but when an intense hurricane strikes, storm surges carry
sand from the ocean beach over the dunes and into the lake.
Clues
in the dirt
When scientists examined the sediment cores from the lake, the
coarse-grained beach sand, as well as bits of shell, stood out from the
lake’s normal finer-grained silt--a tell-tale signal that a hurricane
struck the island at that point in history.
The 5,000-year record the researchers lifted from the dirt showed large
and dramatic fluctuations in hurricane activity, with long stretches of
both intense storm activity and quiet periods. The research was
detailed in the May 24 issue of the journal
Nature 2007.
To make sure the lulls weren’t just a result of hurricanes veering away
from the island, they checked their records with previous studies of
hurricane history in New York and the Gulf Coast and found that the
variability in hurricane activity matched in all three places.
The team also compared their data to existing records of El Niño and
other global and regional climate influences and found that the number
of intense hurricanes (those with wind speeds above 111 mph) increased
during years when El Niño was weak.
El Niño, characterized by warmer-than-normal waters off the Pacific
coast of South America, can fuel winds that shear off the tops of
hurricanes, preventing them from intensifying.
“The processes that govern the formation, intensity and track of
Atlantic hurricanes are still poorly understood,” said Jeff Donnelly,
one of the two scientists on the team. “Based on this work, we now think
that there may be some sort of basin-wide ‘on-off switch’ for intense
hurricanes."
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