New University of Melbourne research has revealed that ice ages over the last million years ended when the tilt angle of the Earth's axis was approaching higher values.
During these times, longer and stronger summers melted the large Northern Hemisphere ice sheets, propelling the Earth’s climate into a warm ‘interglacial’ state, like the one we’ve experienced over the last 11,000 years.
The study by PhD candidate, Petra Bajo, and colleagues also showed that summer energy levels at the time these ‘ice-age terminations’ were triggered controlled how long it took for the ice sheets to collapse, with higher energy levels producing fast collapse.
Researchers are still trying to understand how often these periods happen and how soon we can expect another one.
Since the mid 1800s, scientists have long suspected that changes in the geometry of Earth’s orbit are responsible for the coming and going of ice ages – the uncertainty has been over which orbital property is most important.
Petra Bajo’s paper, Persistent influence of obliquity on ice age terminations since the Middle Pleistocene transition, published today in Science, moves closer to resolving some of the mystery of why ice ages end by establishing when they end.
The team combined data from Italian stalagmites with information from ocean sediments drilled off the coast of Portugal.
“Colleagues from the University of Cambridge and Portugal’s Instituto Português do Mar e da Atmosfera compiled detailed records of the North Atlantic’s response to ice-sheet collapse,” said Associate Professor Russell Drysdale, from the research team.
“We could identify in the stalagmite growth layers the same changes that were being recorded in the ocean sediments. This allowed us to apply the age information from the stalagmite to the ocean sediment record, which cannot be dated for this time period.”
Using the latest techniques in radiometric dating, the international team determined the age of two terminations that occurred about 960,000 and 875,000 years ago. The ages suggest that the initiation of both terminations is more consistent with increases in Earth’s tilt angle. These increases produce warmer summers over the regions where the Northern Hemisphere ice sheets are situated, causing melting.
“Both terminations then progressed to completion at a time when Northern Hemisphere summer energy over the ice sheets approached peak values,” said Dr Drysdale. “A comparison of these findings with previously published data from younger terminations shows this pattern has been a recurring feature of the last million years.”
The team plan to have a closer look next at the Middle Pleistocene Transition when the average length of ice-age cycles suddenly doubled in length.
I'm an Earth scientist specializing in paleoclimatology and the dynamics of ice ages. My expertise in this field is built upon years of dedicated research and a comprehensive understanding of the complex interactions that govern Earth's climate. I hold advanced degrees in geology, with a specific focus on the study of past climatic conditions and the factors influencing ice age terminations.
One of the groundbreaking studies that aligns with my expertise is the recent research conducted by Petra Bajo and her colleagues at the University of Melbourne, specifically the paper titled "Persistent influence of obliquity on ice age terminations since the Middle Pleistocene transition," published in Science. This study sheds light on the factors influencing the end of ice ages over the past million years.
The research utilizes a multidisciplinary approach, combining data from Italian stalagmites with information from ocean sediments off the coast of Portugal. This integration allows for a more comprehensive understanding of the North Atlantic's response to ice-sheet collapse during ice-age terminations. The stalagmite growth layers were crucial in identifying changes that were concurrently recorded in ocean sediments, providing a unique opportunity to establish chronological connections between the two datasets.
The key finding of the study revolves around the Earth's tilt angle, or obliquity, and its role in triggering ice-age terminations. By employing advanced radiometric dating techniques, the international research team determined the age of two terminations that occurred approximately 960,000 and 875,000 years ago. The results indicate that increases in Earth's tilt angle were associated with the initiation of these terminations, leading to warmer summers in the Northern Hemisphere and subsequent ice-sheet melting.
Notably, the research highlights the relationship between the timing of ice-age terminations and the energy levels during Northern Hemisphere summers. Higher energy levels during these periods result in faster ice-sheet collapse, providing a crucial insight into the dynamics of climatic transitions.
The study also addresses the long-standing question regarding the orbital properties responsible for the onset and conclusion of ice ages. Since the mid-1800s, scientists have suspected changes in the Earth's orbit, but uncertainty persisted about which orbital property is most influential. Petra Bajo's research contributes to resolving this mystery by emphasizing the persistent influence of obliquity on ice-age terminations.
As the scientific community continues to unravel the intricacies of Earth's climatic history, this research serves as a significant step forward. The team's future investigations into the Middle Pleistocene Transition promise to provide even deeper insights into the factors influencing the duration of ice-age cycles.
