Geological discovery reveals when and where today’s Antarctic ice sheet formed

In recent years, global warming has significantly impacted the Antarctic ice sheets, with the "eternal" ice melting faster than previously thought. West Antarctica is experiencing more rapid ice loss compared to East Antarctica. The reason for this difference may be rooted in their formations. An international research team, led by the Alfred Wegener Institute, discovered that permanent glaciation of Antarctica began around 34 million years ago.

Contrary to earlier beliefs, this glaciation initially occurred only in East Antarctica, spreading to West Antarctica at least 7 million years later. These findings, published in the journal Science, highlight how East and West Antarctica respond differently to external forces.

Around 34 million years ago, Earth underwent a significant climate shift from a greenhouse world, with little to no continental ice, to an icehouse world with large, permanent ice sheets. During this transition, the Antarctic ice sheet formed. However, the specifics of how, when, and where this occurred were not well understood due to a lack of reliable data, particularly from West Antarctica. Researchers from the Alfred Wegener Institute, in collaboration with colleagues from various institutions, have now filled this knowledge gap.

Using a drill core retrieved with the MARUM-MeBo70 seafloor drill rig from a site offshore the Pine Island and Thwaites glaciers on the Amundsen Sea coast of West Antarctica, the researchers pieced together the history of Antarctica's glaciation. Surprisingly, no evidence of ice was found in this region during the first major phase of Antarctic glaciation.

Dr. Johann Klages, a geologist at the Alfred Wegener Institute who led the research team, stated, "This means that a large-scale, permanent first glaciation must have begun somewhere in East Antarctica." West Antarctica remained ice-free during this initial glaciation phase, covered instead by dense broadleaf forests and experiencing a cool-temperate climate that prevented ice formation.

To better understand where the first permanent ice formed, paleoclimate modelers at the Alfred Wegener Institute combined the new data with existing data on air and water temperatures and the occurrence of ice. "The simulation has supported the results of the geologists' unique core," said Prof. Dr. Gerrit Lohmann, a paleoclimate modeler at the Institute. This new understanding significantly changes our knowledge of the first Antarctic glaciation.

The study indicates that the climatic conditions necessary for the formation of permanent ice were present only in the coastal regions of East Antarctica’s Northern Victoria Land. Here, moist air masses reached the rising Transantarctic Mountains, creating ideal conditions for permanent snow and ice cap formation. From there, the ice sheet rapidly spread into East Antarctica’s interior.

However, it took several million years for the ice to reach West Antarctica. "It wasn't until about seven million years later that conditions allowed for the advance of an ice sheet to the West Antarctic coast," explained Hanna Knahl, a paleoclimate modeler at the Alfred Wegener Institute. "Our results clearly show how cold it had to get before the ice could advance to cover West Antarctica, which was already below sea level in many parts."

The study also demonstrates how differently East and West Antarctica react to external influences and climatic changes. "Even a slight warming is enough to cause the ice in West Antarctica to melt again—and that's exactly where we are right now," added Johann Klages.

The findings are critical for understanding the extreme climate transition from the greenhouse climate to our current icehouse climate. The study provides new insights that enable climate models to more accurately simulate how permanently glaciated areas affect global climate dynamics, including the interactions between ice, ocean, and atmosphere. This is crucial, as Klages emphasized, "Especially in light of the fact that we could be facing such a fundamental climate change again in the near future."

The researchers closed this knowledge gap by using a unique drill core retrieved during the PS104 expedition on the research vessel Polarstern in West Antarctica in 2017. The MARUM-MeBo70 drill rig, developed at MARUM in Bremen, was used in Antarctica for the first time.

The seabed off the West Antarctic Pine Island and Thwaites glaciers is so hard that it was previously impossible to reach deep sediments using conventional drilling methods. The MARUM-MeBo70, equipped with a rotating cutterhead, made it possible to drill about 10 meters into the seabed and retrieve the samples.

These new insights into the early glaciation of Antarctica and the different responses of its eastern and western regions to climatic changes are pivotal for understanding past and future climate dynamics. This research underscores the importance of continued scientific exploration and technological innovation in uncovering the history and mechanisms of Earth's climate system.

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