An international team of scientists has found new evidence that the glaciers of the Northern and Southern hemispheres evolved in a synchronized manner during the last Ice Age. The discovery challenges theories that have dominated to date and provides fundamental data for understanding how current ice masses may respond to ongoing climate changes.
study, led by researchers at the University of Queensland, allowed for the reconstruction, for the first time, of a complete record of glacial fluctuations in the Southern Alps of New Zealand. To do so, the scientists analyzed a marine sediment core, subsequently compared with glacier records in Europe and North America.
According to the researchers, the comparison revealed that the glaciers of New Zealand retreated at the same time as those in the Northern Hemisphere. For Professor Helen Bostock, of the School of the Environment at the University of Queensland, this result indicates that a period of global warming, probably associated with an increase in the planet’s energy imbalance, preceded the retreat of glaciers in both hemispheres simultaneously.
This conclusion challenges the so-called “bipolar balance” theory, which argued for an opposite response between the hemispheres during the so-called Heinrich Stadials. Until now, it was believed that the massive input of freshwater into the North Atlantic would have weakened the meridional circulation of the Atlantic, allowing heat to accumulate in the oceans of the Southern Hemisphere and thereby accelerating the retreat of glaciers in New Zealand.
Traditionally, the reconstruction of glacial movements was based on dating rock blocks left behind by the glaciers. However, this method has limitations, since these traces can be disturbed by later advances of ice. In contrast, marine sediments function as a continuous and well-dated archive of the expansion and retreat of glaciers.
Furthermore, these records allow a direct comparison with past variations in ocean temperatures, identified through microfossils preserved in the sediments. The data reveal a close link between warming of the oceans and glacier retreat.
For Samuel Toucanne, a researcher at Ifremer and the study’s lead author, the results underscore the complexity and interconnectedness of the Earth’s climate system. A better understanding of the climatic mechanisms of the past is, according to the scientist, essential to refine current forecasting models and anticipate the impacts of climate changes associated with human activity.
The study was published in the scientific journal Nature Geoscience.
