Due to its thick, vast ice sheet, Antarctica appears to be a single, continuous landmass centered over the South Pole and spanning both hemispheres of the globe. The Western Hemisphere sector of the ice sheet is shaped like a hitchhiker’s thumb – an apt metaphor, as the West Antarctic ice sheet is on the go. Affected by Earth’s warming oceans and atmosphere, the ice sheet that sits atop West Antarctica is melting, flowing outward and diminishing in size all at an amazing pace.
Much of the discussion about the melting of massive ice sheets during a time of climate change addresses its effects on people.That makes sense: Millions will see their homes damaged or destroyed by rising sea levels and storm surges.
But what will happen to Antarctica itself as the ice sheets melt?
In layers of sediment accumulated on the sea floor over millions of years, researchers like us are finding evidence that when west Antarctica melted, there was a rapid uptick in onshore geological activity in the area. The evidence foretells what’s in store for the future.
A voyage of finding
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As far back as 30 million years ago,an ice sheet covered much of what we now call Antarctica. But during the Pliocene Epoch, which lasted from 5.3 million to 2.6 million years ago, the ice sheet on West Antarctica drastically retreated. Rather than a continuous ice sheet, all that remained were high ice caps and glaciers on or near mountaintops.
About 5 million years ago, conditions around Antarctica began to warm and West Antarctic ice diminished. About 3 million years ago, all of Earth entered a warm climate phase, similar to what is happening today.
Glaciers are not stationary. These large masses of ice form on land and flow toward the sea, moving over bedrock and scraping off material from the landscape they cover, and carrying that debris along as the ice moves, almost like a conveyor belt. This process speeds up when the climate warms, as does calving int## Antarctica once had a thriving forest – and its remnants are now being revealed by melting ice
Antarctica is currently a frozen continent, but that hasn’t always been the case. Our team of international researchers recently discovered evidence of a surprisingly lush, ancient forest preserved beneath the ice. This finding, made possible by drilling into the seabed off the coast of West Antarctica, reveals a window into a warmer past and offers clues about the continent’s future in a changing climate.
The discovery came about during a research expedition aboard the JOIDES Resolution drillship, a specialized vessel designed to collect sediment cores from the ocean floor. As part of the ANDRILL program, we were investigating the history of the West Antarctic Ice Sheet, focusing on the sediments deposited beneath the ocean over millions of years.
What we found was unexpected. The cores contained not just fine-grained silt and mud, but also remarkably well-preserved roots, pollen, and even the remains of trees. These fossils date back to the Paleocene-Eocene Thermal Maximum, a period roughly 56 to 48 million years ago when Earth experienced a critically important warming event.
During this time, atmospheric carbon dioxide levels were much higher than they are today, and global temperatures were considerably warmer. In West Antarctica, this translated into a temperate rainforest environment, similar to those found in New Zealand or Tasmania today. The forest was dominated by trees like beech and cypress, and the understory was likely filled with ferns and other lush vegetation.
An unexpected finding
While onboard, one of us, Christine Siddoway, was surprised to discover an uncommon sandstone pebble in a disturbed section of the core. Sandstone fragments were rare in the core, so the pebble’s origin was of high interest.Tests showed that the pebble had come from mountains deep in the Antarctic interior, roughly 800 miles (1,300 kilometers) from the drill site.
For this to have happened, icebergs must have calved from glaciers flowing off interior mountains and then floated toward the Pacific Ocean. The pebble provided evidence that a deep-water ocean passage – rather than today’s thick ice sheet – existed across the interior of what is now Antarctica.
After the expedition,once the researchers returned to their home laboratories,this finding was confirmed by analyzing silt,mud,rock fragments,and microfossils that also came up in the sediment cores.The chemical and magnetic properties of the core material revealed a detailed timeline of the ice sheet’s retreats and advances over manny years.
Antarctica’s Ice Sheet Has Repeatedly Melted and Regrown, New Research Shows
New research reveals that the Antarctic ice sheet has undergone multiple cycles of melting and regrowth over the past several million years, challenging previous assumptions of its long-term stability. A team of scientists from the Woods Hole Oceanographic Institution (WHOI) and several other institutions analyzed sediment cores collected during the International Ocean Discovery Program (IODP) Expedition 379, uncovering evidence of significant ice sheet fluctuations.
Evidence from the Seabed
The team examined sediment cores drilled from the Amundsen Sea, a region of West Antarctica known for its vulnerability to climate change. These cores contained microscopic fossils and chemical signatures indicating past ocean conditions and ice sheet extent. The analysis revealed that the region was largely ice-free at times as recently as a few million years ago. That suggests the ice sheet melted and open ocean formed, then the ice sheet regrew, filling the interior, repeatedly, over short spans of thousands to tens of thousands of years.
Creating a fuller picture
Teammate Ruthie Halberstadt combined this chemical evidence and timing in computer models showing how an archipelago of ice-capped, rugged islands emerged as ocean replaced the thick ice sheets that now fill Antarctica’s interior basins.
The biggest changes happened along the coast. The model simulations show a rapid increase in iceberg production and a dramatic retreat of the edge of the ice sheet toward the Ellsworth Mountains. The Amundsen Sea became choked with icebergs produced from all directions. Rocks and pebbles embedded in the glaciers floated out to sea within the icebergs and dropped to the seabed as the icebergs melted.
Long-standing geological evidence from Antarctica and elsewhere around the world shows that as ice melts and flows off the land, the land itself rises becuase the ice no longer presses it down.That shift can cause earthquakes, especially in West Antarctica, which sits above particularly hot areas of the Earth’s mantle that can rebound at high rates when the ice above them melts.
The release of pressure on the land also increases volcanic activity.