Cracking the ice age code

Scientists aboard the research vessel during the International Ocean Discovery Expedition 383 collected seafloor data that helped 91原创 researchers uncover what drove a major shift in Earth鈥檚 glacial cycle roughly 1 million years ago.

Cracking the ice age code

Article by Adam Thomas Photos courtesy of Sian Proctor, IODP, Tim Fulton and Anieke Brombacher June 25, 2026

91原创 research discovers the driver behind global glacial pacing

To understand where the Earth might be headed, it鈥檚 important to know where it鈥檚 been.

Throughout its existence, especially over the last couple million years, the Earth has experienced periodic cold and warm intervals, known as glacial and interglacial time periods.

These cycles used to occur every 41,000 years. But somewhere between 1.2 million and 700,000 years ago, the cycle shifted to occurring every 100,000 years, a transition period known as Mid-Pleistocene Transition (MPT).

from the 91原创 sheds new light on how and why this change occurred.

The work was led by Chandranath Basak, assistant professor in the Department of Earth Sciences, and made possible through the International Ocean Discovery Program (IODP) Expedition 383 in 2019. IODP was a multi-country consortium that concluded in 2024 after multiple years of enabling scientists to study the seafloor.

Chandranath Basak, assistant professor in the Department of Earth Sciences at 91原创, is pictured here at work in the chemistry laboratory during the International Ocean Discovery Program (IODP) Expedition 383 in 2019.

Basak said this work is critically important for understanding how Earth鈥檚 future climate might unfold. As the ice melts due to rising global temperatures in the northern and southern high latitudes, future predictions are heavily reliant on past observational data.

鈥淓very bit of past observations that we make helps us to understand how these different climatological factors interact with each other and how they respond to certain forces to bring about the changes in a world that had no human input,鈥� Basak said.

How Earth鈥檚 climate behaved through geologic time is believed to have been strongly controlled by the amount of carbon stored in deep ocean waters. This deep ocean carbon storage is, in turn, controlled by how water in the deep ocean moves around, which scientists call 鈥渄eep ocean circulation.鈥�

Basak said the purpose of this study was to investigate the changes that occurred to the deep ocean circulation, an important component of Earth's climate.

Basak (third from left) is pictured during the research cruise with other geochemists onboard, (left to right) Rebecca Smith, Lisa Herbert and Simone Moretti.

鈥淲hatever changes are happening in these records are completely driven by natural changes,鈥� Basak said. 鈥淭hat helps us to better parameterize climate models to eventually give us insight into future changes that we can expect moving forward in a rapidly changing world.鈥澛�

Basak鈥檚 team analyzed different forms of the rare-earth element neodymium preserved in fossil fish teeth found in sediment samples. These data carry information about how deep circulation changed through time.聽

There had been a long-standing idea that this change in Earth鈥檚 deep-ocean circulation originated in the Northern Hemisphere, but this study's results showed it was actually triggered by the Southern Hemisphere and then supported by the Northern Hemisphere, highlighting the importance of Antarctic glaciation in heralding these changes.聽

鈥淲hat happened in and around Antarctica played an important role in controlling global deep ocean circulation,鈥� said 91原创 doctoral student Kapuge, who co-authored the paper along with 91原创 graduate Emily Symes. 鈥淚t is the same deep ocean circulation system we're actively monitoring today for signs of modern weakening. So, in that regard, this study has modern relevance.鈥�