MSGID: 1:317/3 640177e3   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Wisconsin cave holds tantalizing clues to ancient climate changes,   
   future shifts    
      
     Date:   
         March 2, 2023   
     Source:   
         University of Wisconsin-Madison   
     Summary:   
         A newly published study of a stalagmite found in Cave of the Mounds   
         reveals previously undetected history of the local climate going   
         back thousands of years. Researchers describe evidence for an ice   
         age punctuated by massive and abrupt warming events across much   
         of the Northern Hemisphere.   
      
      
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   FULL STORY   
   ==========================================================================   
   Even in their dark isolation from the atmosphere above, caves can hold   
   a rich archive of local climate conditions and how they've shifted over   
   the eons.   
      
   Formed over tens of thousands of years, speleothems -- rock formations   
   unique to caves better known as stalagmites and stalactites -- hold   
   secrets to the ancient environments from which they formed.   
      
      
   ==========================================================================   
   A newly published study of a stalagmite found in a cave in southern   
   Wisconsin reveals previously undetected history of the local climate going   
   back thousands of years. The new findings provide strong evidence that   
   a series of massive and abrupt warming events that punctuated the most   
   recent ice age likely enveloped vast swaths of the Northern Hemisphere.   
      
   The research, conducted by a team of scientists at the University of   
   Wisconsin- Madison, appears March 2 in the journal Nature Geoscience. It's   
   the first study to identify a possible link between ice age warm-ups   
   recorded in the Greenland ice sheet -- known as Dansgaard-Oeschger   
   events -- and climate records from deep within the interior of central   
   North America.   
      
   "This is the only study in this area of the world that is recording   
   these abrupt climate events during the last glacial period," says   
   Cameron Batchelor, who led the analysis while completing her PhD at   
   UW-Madison. Batchelor is now a postdoctoral fellow with the National   
   Science Foundation working at the Massachusetts Institute of Technology.   
      
   The study is based on an exceptionally detailed chemical and physical   
   analysis of a stalagmite that formed in the Cave of the Mounds, a tourist   
   attraction and educational destination.   
      
   "At Cave of the Mounds our mission is to interpret this geologic wonder   
   for our many annual visitors," says Joe Klimczak, general manager of the   
   cave, which is a designated national natural landmark. "We are thrilled   
   to deepen our understanding of the cave thanks to this world-class   
   research and very exciting results."  The stalagmite Batchelor and her   
   team analyzed grew extremely slowly -- taking roughly 20,000 years to   
   reach the length of a human pinky finger.   
      
   The finger-length subterranean rock formed from a complex process that   
   began in the sky. Water that originally fell as precipitation from the   
   atmosphere soaked into the ground and percolated through soil and cracks   
   in bedrock, dissolving tiny bits of limestone along the way. Some of   
   that dissolved limestone was then left behind as countless drips of water   
   fell from the ceiling of Cave of the Mounds, gradually accumulating into   
   thousands of exceedingly thin layers of a mineral called calcite.   
      
   "And because those calcite layers are formed from that original   
   precipitation, they're locking in the oxygen in the H2O originating from   
   that precipitation," says Batchelor.   
      
   Therein lies the key to reconstructing an ancient climate record from   
   a small, otherwise unremarkable rock. The oxygen trapped in the calcite   
   exists in a couple varieties -- known as isotopes -- that scientists can   
   use to glean information about the environmental conditions present during   
   the precipitation events that formed it. That includes the temperature   
   and possible sources of rain and snow that fell atop the Cave of the   
   Mounds over thousands of years.   
      
   Batchelor's team used a specialized imaging technique that allowed them   
   to identify layers within the stalagmite representing annual growth bands   
   -- much like how tree rings record a season's worth of growth. Using   
   another technique, they identified the isotopes in the tiny layers,   
   revealing that present-day southern Wisconsin experienced a number of   
   very large average temperature swings of up to 10 C (or about 18 F)   
   between 48,000 and 68,000 years ago.   
      
   Several of the temperature swings occurred over the course of around   
   a decade.   
      
   While the dating information is not precise enough to definitively tie the   
   temperature swings to the Dansgaard-Oeschger events recorded in Greenland   
   ice cores, the researchers can say with confidence they occurred within   
   similar timeframes. The team also performed climate simulations that   
   bolstered the hypothesis that warming events occurred tens of thousands   
   of years ago in the region of North America that includes present-day   
   Wisconsin, and that the climate records from Cave of the Mounds and the   
   Greenland ice sheet are indeed linked.   
      
   This potential link is exciting for Batchelor because it offers a climate   
   story about central North America that has so far gone untold. Previous   
   research from the mid-continent has not resolved signals of these large   
   temperature swings, also called excursions.   
      
   "One theory was that the mid-continent is relatively immune to abrupt   
   climate changes, and that maybe that's because it's surrounded   
   by landmass, and there's some type of buffering happening," says   
   Batchelor. "However, when we went and measured, we saw these really   
   large excursions, and we were like, 'Oh, no, something is definitely   
   happening.'"  That something -- a rapidly changing climate -- is unfolding   
   yet again today, thanks to humans and our use of fossil fuels. Batchelor   
   says she hopes her work in Wisconsin, and now a cave in the Canadian   
   subarctic that she is studying for her postdoc, helps fill a big data   
   gap about the history and potential future of abrupt climate changes in   
   the mid-continent of North America.   
      
   This study was supported by grants from the National Science foundation   
   (P2C2- 1805629, EAR-1355590, EAR-1658823). Further resources were provided   
   by the U.S.   
      
   Department of Energy (DE-AC05-00OR22725), the Wisconsin Alumni Research   
   Foundation and the Isotope Laboratory at the University of Minnesota. At   
   UW- Madison, Shaun Marcott, Ian Orland and Feng He contributed to this   
   study, as did R. Lawrence Edwards at the University of Minnesota.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Climate # Caving # Global_Warming # Ice_Ages   
             o Fossils_&_Ruins   
                   # Early_Climate # Fossils # Ancient_Civilizations #   
                   Archaeology   
       * RELATED_TERMS   
             o Ice_age o Larsen_Ice_Shelf o Paleoclimatology o   
             Mammoth o Effects_of_global_warming o Stalagmite o   
             Temperature_record_of_the_past_1000_years o Lascaux   
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_Wisconsin-Madison. Original written by Will Cushman. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. C. J. Batchelor, S. A. Marcott, I. J. Orland, F. He, R. L. Edwards.   
      
         Decadal warming events extended into central North America   
         during the last glacial period. Nature Geoscience, 2023; DOI:   
         10.1038/s41561-023- 01132-3   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/03/230302113844.htm   
      
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