"Until recently, researchers studying climate history in Brazil’s dry Nordeste region expected it to have wet and dry periods similar to the rest of South America. But over the past 9,000 years, the region has shown just the opposite, drought when rain was expected, and vice versa. Geoscientists from the University of Massachusetts Amherst and the University of Sao Paolo, Brazil, with others, report this week that they’ve identified the cause as a surprising air circulation pattern.
As Stephen Burns, a UMass Amherst geoscientist explains, “In general, the Northern Hemisphere tropics have been getting drier and the Southern Hemisphere tropics have been getting wetter as maximum summer solar heating shifts southward. But Northeast Brazil has been acting like a Northern Hemisphere site and it’s been getting steadily drier from about 9,000 years ago to today.” Millions of people there must cope with severely disruptive, recurring droughts, Burns and colleagues point out. A more accurate model of past conditions could help predict what to expect in the future.
In their paper published this week in Nature Geosciences, Burns and co-investigators Francisco Cruz of the University of Sao Paolo and Mathias Vuille of the State University of New York, Albany, say they have discovered an unexpected east-west atmospheric circulation pattern that fits their new data and explains the Nordeste anomaly.
For this study, the researchers collected speleothems, in this case stalagmite segments a few inches long from five formations in three different caves in Brazil’s dry northern interior, where the country bulges out into the Atlantic. Speleothems are cave features formed over tens of thousands of years by water seeping through cracks in bedrock and dissolving limestones rich in calcite and aragonite. Depending on cave temperature, carbon dioxide level and other factors, the mineral deposits precipitate out as stalagmites, stalactites, ribbons, domes or even delicate straws, for example. (...)"
Full text: Intersciences
As Stephen Burns, a UMass Amherst geoscientist explains, “In general, the Northern Hemisphere tropics have been getting drier and the Southern Hemisphere tropics have been getting wetter as maximum summer solar heating shifts southward. But Northeast Brazil has been acting like a Northern Hemisphere site and it’s been getting steadily drier from about 9,000 years ago to today.” Millions of people there must cope with severely disruptive, recurring droughts, Burns and colleagues point out. A more accurate model of past conditions could help predict what to expect in the future.
In their paper published this week in Nature Geosciences, Burns and co-investigators Francisco Cruz of the University of Sao Paolo and Mathias Vuille of the State University of New York, Albany, say they have discovered an unexpected east-west atmospheric circulation pattern that fits their new data and explains the Nordeste anomaly.
For this study, the researchers collected speleothems, in this case stalagmite segments a few inches long from five formations in three different caves in Brazil’s dry northern interior, where the country bulges out into the Atlantic. Speleothems are cave features formed over tens of thousands of years by water seeping through cracks in bedrock and dissolving limestones rich in calcite and aragonite. Depending on cave temperature, carbon dioxide level and other factors, the mineral deposits precipitate out as stalagmites, stalactites, ribbons, domes or even delicate straws, for example. (...)"
Full text: Intersciences
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