An international research team, including Australian scientists, has published findings suggesting that glaciers in both the Southern and Northern Hemispheres retreated simultaneously during the last ice age. The study, published in Nature Geoscience, challenges existing theories regarding glacial activity and offers data that may inform models predicting how contemporary ice sheets could respond to climate change.
Key Research Findings
The research established the first comprehensive record of glacial fluctuations in New Zealand's Southern Alps. This was achieved through the analysis of a marine sediment core, which provided a continuous historical account of glacial expansion and retreat. When comparing this record with existing data on glaciers in Europe and North America, the researchers observed that glacial retreats occurred simultaneously across both hemispheres.
University of Queensland Professor Helen Bostock, who collaborated with partners in New Zealand, France, and Germany, indicated that the study suggests a period of global warming preceded these synchronous retreats. This warming is attributed by the research to a likely increase in global energy imbalance.
Challenging Previous Theories
The findings directly challenge the previously held "bipolar seesaw" theory. This theory proposed that the Northern and Southern Hemispheres experienced opposing climatic changes during events known as Heinrich Stadials. During these periods, it was believed that a substantial influx of meltwater into the North Atlantic Ocean slowed the Atlantic Meridional Overturning Circulation (AMOC). This process was thought to lead to a buildup of heat in the Southern Hemisphere's oceans, subsequently accelerating glacial retreat in regions like New Zealand while the Northern Hemisphere cooled. The new research suggests a different, more synchronous global response.
Methodological Approach
The research team emphasized the advantages of using marine sediment cores for their study. Unlike traditional methods such as boulder dating, which can yield incomplete records, marine sediment cores offer a continuous and well-dated history of glacial activity. This methodology also enabled a direct comparison between glacial sediment records and past ocean temperature changes, as indicated by microfossils preserved within the sediment. The study demonstrated a strong connection between warming ocean temperatures and subsequent glacial retreat.
Implications for Climate Modeling
The insights gained from this research are noted to offer valuable information for improving models that predict the response of current ice sheets to ongoing climate change. Understanding past mechanisms of global glacial retreat is considered relevant for forecasting future impacts.