Washington, May 2 A new study has found that for the last 7,000 years, glaciers south of the equator in South America and New Zealand have often moved out of step with glaciers in the Northern Hemisphere, pointing to strong regional variations in climate.
"This research should provide much more accurate reconstructions of glacial advances worldwide, allowing us in turn to make climate models more accurate," said Paul Filmer, program director in the National Science Foundation's (NSF) Division of Earth Sciences, which funded the research.
Conventional wisdom holds that during the era of human civilization, climate has been relatively stable.
The new study is the latest to challenge this view, by showing that New Zealand's glaciers have gone through rapid periods of growth and decline during the current interglacial period known as the Holocene.
"New Zealand's mountain glaciers have fluctuated frequently over the last 7,000 years, and glacial advances have become slightly smaller through time," said Joerg Schaefer, lead author of the paper and a geochemist at Columbia University's Lamont-Doherty Earth Observatory.
"This pattern differs in important ways from the northern hemisphere glaciers. The door is open now towards a global map of Holocene (a geological time period that began about 11,700 years ago and continues to the present) glacier fluctuations and how climate variations during this period impacted human civilizations," he added.
By refining the analysis of a method called cosmogenic dating, Schaefer and colleagues were able for the first time to assign precise ages to young Holocene moraines.
They accomplished this by measuring minute levels of the chemical isotope beryllium 10 in the rocks, which is produced when cosmic rays strike rock surfaces, and builds up over time.
The researchers were thus able to pinpoint exactly when glaciers in New Zealand's Southern Alps began to recede, exposing the rocks to the cosmic rays.
From the results, they constructed a glacial timeline for the past 7,000 years and compared it against historic records from the Swiss Alps and other places north of the equator.
They found that within that timeframe, the glaciers around Mount Cook, New Zealand's highest peak, reached their largest extent about 6,500 years ago, when the Swiss Alps and Scandinavia were relatively warm.
That's about 6,000 years before northern glaciers hit their Holocene peak during the Little Ice Age, between 1300 and 1860 AD.
That finding was a surprise to some scientists who assumed that the northern cold phase happened globally.
The record in New Zealand shows other disparities that point to regional climate variations in both hemispheres. (ANI)
