Because of its thick and extensive ice sheet, Antarctica appears to be one continuous landmass centered over the South Pole and spanning both hemispheres of the globe. The Western Hemisphere's ice sheet sector is shaped like a hitchhiker's thumb—an apt metaphor since the West Antarctic ice sheet is on the move. Under the influence of warming oceans and the Earth's atmosphere, the ice sheet located at the top of West Antarctica is gradually collapsing. melts, flows out and decreases in sizeand all this with amazing speed.
Much of the discussion about the melting of massive ice sheets during climate change focuses on its impact on people. It makes sense: millions of people will see their homes damaged or destroyed sea ​​level rise and storm surges.
In layers of sediment that have accumulated on the seabed over millions of years, researchers like us finds evidence that as West Antarctica melted, there was a rapid surge in coastal geological activity in the area. evidence predicts what's to come for the future.
Journey of Discovery
Until 30 million years ago, ice covered most of what we now call Antarctica. But during the Pliocene epoch, which lasted from 5.3 to 2.6 million years ago, the West Antarctic ice sheet retreated sharply. Instead of a continuous sheet of ice, only high ice caps and glaciers remained on or near the tops of mountains.
About 5 million years ago conditions around Antarctica have begun to warm upand West Antarctic ice has decreased. About 3 million years ago, the entire 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 towards the sea, moving over bedrock and scraping material from the landscape they cover and carrying this debris along with the movement of the ice, almost like a conveyor belt. This process is accelerating with a warming climate, as well as with calving at sea, which results in the formation of icebergs. Debris-laden icebergs can then carry this continental rock material out to sea, dumping it on the seafloor as the icebergs melt.
At the beginning of 2019, we went on a major scientific trip – International Ocean Discovery Program Expedition 379 – in the Amundsen Sea, south of the Pacific Ocean. The goal of our expedition was to collect material from the seabed to find out what happened in West Antarctica during its melting period all that time ago.
Aboard the drilling vessel JOIDES Resolution, workers lowered the drill nearly 13,000 feet (3,962 meters) to the seafloor and then drilled 2,605 feet (794 meters) deep into the ocean floor, just offshore from the most vulnerable part of the West Antarctic ice sheet.
The drill raised long tubes called “cores” containing layers sediments deposited between 6 million years ago and the present. Our research focused on deposits from the Pliocene era, when Antarctica was not yet completely covered by ice.
An unexpected find
While on board, one of us, Christine Siddoway, was surprised to find unusual sandstone pebbles in the damaged part of the core. Sandstone fragments were rare in the core, so the origin of the pebbles was of great interest. Tests showed the pebbles came from mountains deep in Antarctica, about 800 miles (1,300 kilometers) from the drilling site.
For this to happen, the icebergs would have to break off from glaciers flowing down from the inland mountains and then float towards the Pacific Ocean. The pebbles provided evidence that there was a deep-sea ocean passage within what is now Antarctica rather than the current thick ice sheet.
After the expedition, when the researchers returned to their home laboratories, the discovery was confirmed by analysis of silt, mud, rock fragments and microfossils also found in sediment cores. The chemical and magnetic properties of the underlying material revealed a detailed chronology of the ice sheet's retreat and advance over many years.
One of the key signs was the analysis carried out by Keiji Horikawa. He tried to match the thin layers of mud at the core with bedrock from the continent to test the idea that icebergs carried such materials over very long distances. Each layer of mud was deposited immediately after an episode of deglaciation as the ice sheet retreated, resulting in a layer of pebbly clay carried by icebergs. By measuring the amounts of various elements, including strontium, neodymium and lead, he was able bind certain thin layers of drilling fluid in drill cores chemical signatures in outcrops of the Ellsworth Mountains, 870 miles (1,400 km) away.
Horikawa discovered not just one instance of this material, but as many as five layers of mud, deposited between 4.7 and 3.3 million years ago. This suggests that the ice sheet melted and an open ocean formed, and then the ice sheet grew again, repeatedly filling the planet's interior over short periods of thousands to tens of thousands of years.
Creating a more complete picture
Teammate Ruthie Halberstadt combined this chemical data and time into computer models showing how an archipelago of harsh islands covered with ice appeared. when the ocean replaced the thick ice sheets that now fill Antarctica's interior basins.
The biggest changes have occurred along the coast. Modeling shows a rapid increase in iceberg formation and a sharp retreat of the ice sheet edge toward the Ellsworth Mountains. The Amundsen Sea was filled with icebergs flying in from all directions. Rocks and pebbles trapped in glaciers floated out to sea with the icebergs and fell to the seabed as the icebergs melted.
Long-term geological data from Antarctica and around the world show that as ice melts and flows off land, the earth itself is rising because the ice no longer presses him. This shift may cause earthquakesespecially in West Antarctica, which lies above particularly hot regions of the Earth's mantle that can high stakes rebound when the ice above them melts.
Reducing pressure on the earth also increases volcanic activity – as happens in Iceland today. Evidence of this in Antarctica is the layer of volcanic ash that Siddoway and Horikawa identified in the cores as having formed 3 million years ago.
Long-standing ice loss and upward movement in West Antarctica has also triggered massive rock avalanches and landslides in cracked, damaged rocks, forming glacial valley walls and coastal cliffs. Landslides under the sea have displaced huge amounts of sediment from the sea shelf. Huge masses of rock, no longer supported by the weight of glacial ice and ocean water, broke off and poured into the water, causing a tsunami that caused more destruction in coastal areas.
The rapid onset of all these changes made the disappearance of the West Antarctic glaciers an example of what has been called “catastrophic geology“
The rapid surge in activity is reminiscent of what has happened in other parts of the planet in the past. For example, at the end of the last ice age in the Northern Hemisphere, 15,000 to 18,000 years ago, the region between Utah and British Columbia was affected by an ice age. floods due to erupting glacial meltwater lakesland rebound, rock avalanches and increased volcanic activity. In the coastal Canada And Alaskasimilar events continue to occur today.
Dynamic ice sheet retreat
Our team's analysis of rock chemistry clearly shows that West Antarctica is not necessarily undergoing one gradual and massive transition from ice-covered to ice-free, but rather fluctuates back and forth between very different states. Every time an ice sheet has disappeared in the past, it has resulted in geological chaos.
The future implications for West Antarctica are that the next time its ice sheet collapses, catastrophic events will return. This will happen repeatedly as the ice sheet retreats and advances, opening and closing connections between different areas of the world's oceans.
This dynamic future could lead to equally rapid reactions in the biosphere, such as Algal blooms around icebergs in the oceanresulting in an influx of marine species into newly opened seaways. Vast tracts of land on the West Antarctic islands will then open up to the growth of mossy ground cover and coastal vegetation, which make Antarctica greener than its current icy whiteness.
Our data on the past of the Amundsen Sea and the resulting forecast indicate that changes on land in West Antarctica will not be slow, gradual or unnoticeable from a human perspective. Most likely, what happened in the past is likely to repeat itself: geologically rapid shifts that are locally experienced as apocalyptic events such as earthquakes, eruptions, landslides and tsunamis – with global consequences.
This edited article is republished from Talk under Creative Commons license. Read original article.
