PNAS - West Antarctic Ice Sheet Retreated Repeatedly & Rapidly During Pliocene Epoch @ Temps 3-4C Higher Than Now

A team led by Keiji Horikawa at the University of Toyama decided to look for answers in the deep past. By analyzing sediment cores drilled from the Amundsen Sea floor, the researchers found that the West Antarctic Ice Sheet retreated far inland at least five times during the Pliocene Epoch, a warm period between 5.3 and 2.58 million years ago when global temperatures ran about 3 to 4 degrees Celsius higher than today. Sea levels then stood more than 15 meters above where they are now.

The findings, published in Proceedings of the National Academy of Sciences, suggest the ice sheet isn’t the permanent fixture it might appear to be. Under the right conditions, it can hold steady for long stretches, then slip back quickly.

The evidence comes from sediments collected during International Ocean Discovery Program Expedition 379 at a site on the Amundsen Sea continental rise. In the core, thick gray clays mark cold glacial periods when ice blanketed the continental shelf. These layers feel smooth, finely laminated. Thinner greenish bands tell a different story. They’re packed with microscopic algae that only bloom in open, ice-free water. Those warmer layers also contain iceberg-rafted debris: small rock fragments frozen into glaciers on the continent, carried out to sea by calving icebergs, then dropped onto the seafloor as the ice melted. The team identified 14 prominent melt-event intervals between 4.65 and 3.33 million years ago.

To figure out where the rocks originated, the researchers measured isotope ratios of strontium, neodymium, and lead in the fine-grained sediment. These ratios act as chemical barcodes pointing back to the parent rocks. At certain intervals, around 3.88, 3.6, and 3.33 million years ago, a distinctive signature appeared that could only come from the Ellsworth-Whitmore Mountains deep in the Antarctic interior. That’s the key finding. Those mountains sit far from where the ice margin rests today. For their debris to reach the ocean, the ice had to have pulled back dramatically toward the heart of the continent.

EDIT

https://scienceblog.com/ancient-seafloor-mud-shows-west-antarctic-ice-has-a-history-of-sudden-collapse/