Evidence of past Southern hemisphere rainfall cycles related to Antarctic temperatures

Jan 17, 2012
These stalagmites in Pacupuhuain Cave in the Andes of Peru are similar to ones sampled by Stephen Burns, Lisa Kanner and colleagues for their study of tropical rainfall cycles in the Southern hemisphere. Analysis of oxygen isotopes in such features provide a 34,000-year record of rainfall variation in the Amazon Basin. Credit: UMass Amherst

Geoscientists at the University of Massachusetts Amherst and the University of Minnesota this week published the first evidence that warm-cold climate oscillations well known in the Northern Hemisphere over the most recent glacial period also appear as tropical rainfall variations in the Amazon Basin of South America. It is the first clear expression of these cycles in the Southern Hemisphere.

The work by Stephen Burns and his doctoral student Lisa Kanner at UMass Amherst is reported in the current issue of Science Express. Burns says, "The study also demonstrates that rainfall in the of South America is, though to a lesser extent, also influenced by temperature changes in the Antarctic, which has not been previously observed."

The last glacial period, from about 10,000 to about 120,000 years ago, saw North America and Western Europe covered in a thick continental ice sheet, the geoscientist points out. Yet climate was also highly unstable during the period, cycling every few thousand years between warm and cold, dry periods in the high northern latitudes. Temperatures could change by as much as 10 to 15 degrees Celsius.

Known as Dansgaard/Oeschger (D/O) cycles, these millennial-scale rapid were first recognized in the Greenland ice cores, but have since been found throughout the , Burns points out.

The UMass Amherst climate researcher is an expert in reading past from the ratio of oxygen isotopes found in calcite in speleothems, another name for stalagmites, stalactites and other water-deposited cave features. Analyzing radioactive isotopes and stable oxygen isotopes in the calcite sampled from ancient cave formations can provide information on past rainfall over many thousands of years, Burns says.

He and Kanner used oxygen isotopic analyses from a 16-centimeter (about 6.3 inches) stalagmite recovered from a cave 2.4 miles (3,800 meters) above sea level in the for this study. The sample grew from 49,500 to 16,000 years ago, providing a 34,000-year-long record of rainfall changes in the Amazon Basin. Kanner and colleagues found that cold periods in the high Northern latitudes are associated with an increase in precipitation, the South American Summer Monsoon, in the Amazon Basin.

They found that cold periods in the Northern Hemisphere are associated with an increase in precipitation, the South American Summer Monsoon, in the .

"This relationship is the exact opposite of changes in rainfall in the Northern Hemisphere tropics, where cold intervals result in a decrease in rainfall," Burns says.

Revised chronology for several major climate events that took place in the last glacial period proposed in this study could lead to a better understanding of Antarctic warming during the same period and its relationship to warming the subtropical North Atlantic, the authors state.

Explore further: Study shows air temperature influenced African glacial movements

Provided by University of Massachusetts at Amherst

5 /5 (3 votes)

Related Stories

Peruvian stalagmites a new basis for 'Inconvenient truth'?

Apr 29, 2009

Will the Netherlands that is dominated by water succumb to the 'Inconvenient Truth' predicted by Al Gore? Dutch researcher Martin van Breukelen analysed stalagmites from the South American Amazon tributaries in Peru. He used ...

Cave study links climate change to California droughts

Nov 10, 2009

California experienced centuries-long droughts in the past 20,000 years that coincided with the thawing of ice caps in the Arctic, according to a new study by UC Davis doctoral student Jessica Oster and geology professor ...

Recommended for you

Melting during cooling period

13 hours ago

(Phys.org) —A University of Maine research team says stratification of the North Atlantic Ocean contributed to summer warming and glacial melting in Scotland during the period recognized for abrupt cooling ...

Warm US West, cold East: A 4,000-year pattern

16 hours ago

Last winter's curvy jet stream pattern brought mild temperatures to western North America and harsh cold to the East. A University of Utah-led study shows that pattern became more pronounced 4,000 years ago, ...

User comments : 0

More news stories

Melting during cooling period

(Phys.org) —A University of Maine research team says stratification of the North Atlantic Ocean contributed to summer warming and glacial melting in Scotland during the period recognized for abrupt cooling ...

Down's chromosome cause genome-wide disruption

The extra copy of Chromosome 21 that causes Down's syndrome throws a spanner into the workings of all the other chromosomes as well, said a study published Wednesday that surprised its authors.