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HOLE FOR WOODS, Mass., November 16, 2020 / PRNewswire / – Intense tropical cyclones are expected to become more frequent as climate change raises temperatures in the Pacific Ocean. But not all areas will experience storms of the same magnitude. New research from the Woods Hole Oceanographic Institution (WHOI) published in Nature Geoscience reveals that tropical cyclones were indeed more frequent in the south Marshall Islands during the Little Ice Age, when temperatures in the Northern Hemisphere were cooler than today.
This means that changes in atmospheric circulation, driven by differential warming of the oceans, heavily affect the location and intensity of tropical cyclones.
In the first study of its kind so close to the equator, lead author James Bramante has reconstructed 3000 years of storm history on Jaluit Atoll in the south Marshall Islands. This region is the birthplace of tropical cyclones in the western North Pacific, the most active tropical cyclone zone in the world. Using the differences in sediment sizes as evidence of extreme weather events, Bramante found that tropical cyclones occurred in the region roughly once a century, but increased to a maximum of four per century from AD 1350 to AD 1700, a period known as the Little Ice Age.
Bramante, a recent graduate of the joint MIT-WHOI program in Oceanography / Applied Ocean Science and Engineering, says this finding sheds light on how climate change affects where cyclones can form.
“Changes in atmospheric circulation due to modern human-induced climate warming are opposed to changes in circulation due to the Little Ice Age,” notes Bramante. “So we can expect to see the opposite effect in the deep tropics: a decrease in tropical cyclones near the equator. This could be good news for the south. Marshall Islands, but other areas would be threatened as the average position of the cyclone generation moves north, “he adds.
During major storms, coarse sediments are lifted and deposited by currents and waves in “blue holes,” ancient caves that have collapsed and turned into sinkholes filled with seawater over thousands of years. In a 2015 field study, Bramante and his colleagues took samples from a blue hole on Jaluit Atoll and found coarse sediment among the finest grains of sand. After sorting the grains by size and analyzing data from Typhoon Ophelia, which devastated the atoll in 1958, the researchers had a model with which to identify other storm events that appear in the sediment record. They then used radiocarbon dating – a method of determining age based on the ratio of carbon isotopes in a sample – to date the sediment in each layer.
Armed with previously collected data on the ancient climate from tree rings, coral cores and fossilized marine organisms, the researchers were able to piece together the conditions that existed at the time. By linking this information with the record of storms preserved in the sediments of Jaluit Atoll, the researchers demonstrated through computer modeling that the particular set of conditions responsible for the equatorial trade winds heavily influenced the number, intensity, and location of cyclones would be formed.
Jeff Donnelly, a WHO senior scientist and a co-author of the study, used similar methods to reconstruct the history of hurricanes in the North Atlantic and Caribbean. He plans to expand the Marshall Islands study west Philippines study where tropical cyclones have historically formed and how climatic conditions affect the trace and intensity of a storm. A better understanding of how storms behaved under previous conditions will help scientists understand what causes changes in tropical cyclone activity and help people living in coastal communities prepare for extreme weather in the future, he said.
“Through the geological record, we can get a baseline that tells us how much risk we really are in any given place,” Donnelly says. “It turns out that the past provides some useful analogies for the climate change we are currently undergoing. Earth has already performed this experiment. Now we are trying to go back and determine the drivers of tropical cyclones.”
Other co-authors of this study include the WHOI geologist Andrew Ashton; Physical Oceanographer WHOI Caroline Ummenhofer; Murray ford (University of Auckland, New Zealand); Paul Kench (Simon Fraser University, British Columbia, Canada); Michael Toomey (US Geological Survey, Reston, Virginia); Richard Sullivan of Texas A&M University; is Kristopher Karnauskas (University of Colorado, Boulder).
Key points
- The researchers reconstructed the story of tropical cyclones in the south Marshall Islands over the past 3000 years. The western North Pacific is the world most active area for tropical cyclones, but has been little studied compared to the North Atlantic.
- During Little Ice Age, tropical cyclones formed in the deep tropics of the western North Pacific most frequently than any other time in the record. Sediment sample data recorded four tropical cyclones per century, which is well above the 3,000-year average of one per century.
- Climate change it is expected to create conditions opposite to the Little Ice Age, indicating that tropical cyclones will form less often in the south Marshall Islands, although storms are expected more frequent and intense at higher latitudes.
This research was funded by the Strategic Environmental Research & Development Program, a partnership between the Department of Defense, the Department of Energy and the Environmental Protection Agency.
The Woods Hole Oceanographic Institution (WHOI) is a private non-profit organization Cape Cod, Massachusetts, dedicated to marine research, engineering and higher education. Founded in 1930, its primary mission is to understand the ocean and its interaction with the Earth as a whole and communicate an understanding of the ocean’s role in the changing global environment. WHOI’s pioneering discoveries stem from an ideal combination of science and engineering, which has made it one of the most trusted and technically advanced leaders in basic and applied ocean research and exploration anywhere. WHOI is known for its multidisciplinary approach, superior naval operations and unprecedented deep-sea robotics capabilities. We play a leading role in ocean observation and manage the largest suite of data collection platforms in the world. The best scientists, engineers and students collaborate on more than 800 simultaneous projects around the world, both above and below the waves, pushing the boundaries of knowledge and possibility. For more information please visit www.whoi.edu
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SOURCE Woods Hole Oceanographic Institution
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