Synchronous glacier retreats across hemispheres challenge ice age theories: study

SYDNEY, Jan. 13 (Xinhua) -- An international research team involving Australian scientists has uncovered evidence that glaciers in the Southern and Northern hemispheres were synchronous during the last ice age.

Published in Nature Geoscience, the finding challenges prevailing theories and provides critical information to help model how today's ice sheets will respond to a changing climate, said a news release from Australia's University of Queensland (UQ) on Tuesday.

Researchers constructed the first complete record of glacial fluctuations in the Southern Alps of New Zealand by analyzing a marine sediment core, the release said.

When the evolution of the New Zealand glaciers was compared to their European and North American counterparts, they were found to retreat simultaneously, said UQ Professor Helen Bostock, who conducted the research with partners in New Zealand, France, and Germany.

"Our work shows a period of global warming, likely caused by an increase in the global energy imbalance, preceded by glacial retreats in both hemispheres at the same time," Bostock said, adding the finding challenges previous theories of an inter-hemispheric "bipolar seesaw."

Until now, it was thought that the Northern and Southern Hemispheres changed in opposite ways during the Heinrich Stadials, a period when a large influx of meltwater to the North Atlantic slowed the Atlantic Meridional Overturning Circulation, which caused heat to accumulate in the Southern Hemisphere's oceans, enhancing glacial retreat in New Zealand, the release said.

Marine sediment cores provide a continuous, well-dated history of the glacial expansion and retreat, unlike boulder dating, which offers incomplete records disturbed by subsequent glacier advances, Bostock said.

"The record of glacial sediments can also be directly compared with past changes in ocean temperatures recorded by microfossils preserved in the sediment," she said, adding the record shows a tight connection between warming oceans and glacial retreat. ■