Scientists seeking an oceanic counterpart to the tree rings that document past weather patterns on land have found one in the subtropical waters of Dry Tortugas National Park near the Florida Keys, where long-lived boulder corals contain the chemical signals of past water temperatures. By analyzing coral samples, USGS researchers and their colleagues have found evidence that an important 60- to 85-year-long cycle of ocean warming and cooling has been taking place in the region as far back as the 1730s.
The cycle called the Atlantic Multidecadal Oscillation, or AMO, is linked to rainfall over most of the US, Midwestern droughts, hurricane intensification and landfalls, and the transfer of ocean heat from the tropical Caribbean Sea to the North Atlantic Ocean by way of the Gulf Stream. It interacts with ongoing climate change in poorly understood ways, and it is very hard to spot in pre-20th century records.
“The AMO has a huge impact on human populations and the economy, mainly through its influence on rainfall patterns,” said geochemist Jennifer Flannery of the USGS Coastal and Marine Science Center in St. Petersburg, Florida, who led the study. “Climatologists suspect the AMO is a natural climate cycle that has existed for more than 1,000 years. But until recently most of the evidence came from ships at sea, and only went back 150 years or so.
“The record we obtained from the Dry Tortugas coral cores captures several complete AMO cycles stretching back 278 years. That gives climate modelers a lot of new evidence to work with as they try to understand past AMOs and predict future ones.”
Continue reading at US Geological Survey
Photo: Scientists used a core from this Massive Starlet (Siderastrea siderea) coral colony in Dry Tortugas National Park to reconstruct ocean temperatures going back to 1837.
Credit: US Geological Survey
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