About 125,000 years ago, the Earth was in the last warm period between ice ages. The global average temperature during this interglacial period was about 05–1.5°c。
There are strong parallels to our time. Driven by climate change, a third of the time in 2023, the Earth's temperature is 15°c 。
For nearly 50 years, physicists have been searching for answers to the question of whether the massive West Antarctic ice sheet collapsed the last time global temperatures were so high. Rather than relying solely on geological sampling, we looked to the DNA of a small Antarctic octopus for clues to the distant past.
DNA gives the answer. Our new research suggests that yes, it may well have crashed.
The West Antarctic ice sheet is very susceptible to warming. If it melts, it will have enough water to raise global sea levels by 33 to 5 meters.
Sediment records and other ice cores show us that the ice sheet receded at some point during the last million years of the Late Pleistocene, but the exact timing and extent of any collapse remains unclear.
To get a more accurate answer, we looked at cephalopod genetics.
The DNA of every organism is a history book, and we now have the technology to read it. We can use DNA to look back and pinpoint when different animal populations interbred.
The Tequit octopus (pareledone turqueti) is quite small in size, weighing up to 600 grams. They live on the ocean floor around Antarctica, but individuals do not travel far from their homeland. Antarctica is a vast continent and the populations of different regions are often not able to interbreed.
There are crevices in the rocks deep in West Antarctica. Currently, these areas have been filled with ice sheets, separating the Weddell Sea, the Amundsen Sea and the Ross Sea from each other.
If the ice melts, the seaways open up and connect these isolated basins. Octopuses can migrate directly to these areas, and evidence of their reproduction will be recorded in the DNA.
But if the ice sheet hadn't melted, we would only see evidence of breeding between octopus populations along the perimeter of the continent.
We compared the DNA patterns of the Tequit octopus genome across Antarctica to see if there is a direct and unique link between octopus populations in the Weddell Sea, Amundsen Sea, and Ross Sea. We used statistical models to figure out whether these connections could be explained by the connections around the current Antarctic coastline.
The story in DNA is clear: yes, there is a direct link between these three octopus populations. The link between them cannot be statistically explained by hybridization around the present-day Antarctic coastline. These populations can only be accessed through shipping lanes that are now blocked by the West Antarctic ice sheet.
More interestingly, we first found a direct link between these three populations in the middle of the Pliocene, between 3 million and 3.6 million years ago, when temperatures were 2 3°C warmer than today and sea levels were 25m higher. This supports the available geological evidence that the West Antarctic ice sheet collapsed in that era.
The most recent DNA signature of the direct link between the octopuses of these three oceans was during the last interglacial period about 125,000 years ago. This suggests that when the average global temperature is about 1 above pre-industrial levelsAt 5°C, the ice sheet collapses.
Our work provides the first empirical evidence that if we exceed the Paris Agreement to limit warming to 1With a target of 5°C or even 2°C, the West Antarctic ice sheet could begin to collapse.
In order to harness animal DNA as a catalyst for ice sheet change, we must work across disciplines and countries. Bringing together physical scientists and biologists has resulted in new ways to answer long-standing questions that are critical to all of us.
We also sought samples from museum collections. Some of these date back three decades – long before the genetic sequencing and analysis technologies we use became available. This demonstrates the critical importance of carefully preserving the sample, relating to the metadata, and protecting the sample for future access.
Interdisciplinary science is hard. Understanding new terms, scales, and methods takes time, effort, and an open mind. Journal editors and scientists may be reluctant to review such because some aspects of the research are necessarily outside their area of expertise. But we hope that our results will prove the value of this approach.
We hope to continue using DNA as a ** to explore other parts of Antarctica where little is known about the history of the climate.
I'm a tech creator A great deal of information about Antarctica's recent and distant past is also hidden in moss beds and peat profiles, vertebrate groups, and other types of living organisms of terrestrial and marine invertebrates. To date, very few of these biological archives have been brought into our knowledge of Antarctica's past climate. As the world heats up at an unprecedented rate, we need to use these types of methods to understand what else might be happening on the ice.