Could octopus DNA reveal the secrets of west Antarctica’s ice sheet collapse?

Extract from The Guardian

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Environment

Planet Oz

Graham Readfearn

Understanding what happened to the ice sheet will be key to knowing what the future holds for global sea levels

A frozen section of the Ross Sea at the Scott Base in Antarctica. Photograph: Mark Ralston/AFP/Getty Images

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Friday 24 November 2017 04.00 AEDT Last modified on Friday 24 November 2017 04.01 AEDT

There are a lot of scientific eyes on west Antarctica right now, for some pretty obvious reasons.
The West Antarctic Ice Sheet (WAIS) holds a lot of water – enough to push up sea levels around the world by 3m or so.
Even though this sort of melting would play out over century-long time scales, getting a handle on how much melting there would be, and how fast it could happen, are big questions with big consequences.
Hundreds of millions of people living around coasts and cities around the globe might be interested in the answer, as would cartographers who would need to be redrawing maps of the world.
Deep underneath the ice in west Antarctica is a break in the continental landmass – a seaway that links the Weddell Sea to the north with the Amundsen Sea to the south.
About 120,000 years ago, the Earth was in an interglacial period with temperatures comparable to the 2C of warming that countries who are part of the UN’s Paris agreement (everyone but the US) are all trying to avoid.
But scientists are unsure if enough ice melted during the last interglacial (LIG) to expose that trans-Antarctic seaway.
But, if they could find some clues, then this would give them vital information about the fate of the world’s sea levels.
This is where octopuses come in or, more specifically, what evolutionary biologist Jan Strugnell thinks she could find out using octopus DNA.
In a scientific paper just published in the journal Quaternary Science Reviews, Associate Prof Strugnell, of James Cook University in Townsville, Australia, describes an ingenious plan.

The future of the planet is tied up in that ice.

Dr Ceridwen Fraser

Strugnell writes that by examining the DNA of some bottom-dwelling animals currently living around the entire Antarctic continent, you can work out if the ancestors of those species were able to move through that trans-Antarctic seaway.
It sounds complicated – and it is.
But, in the paper, Strugnell describes recent advances in genome sequencing that can “provide powerful insight into the demographic history of species including processes such as migration, population divergence and changes in effective population size”.

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Strugnell tells me if you match the DNA sequencing to powerful modelling, you could work out if that species was able to move across the seaway about 120,000 years ago. If they moved across the seaway, then that would mean enough ice had melted to clear the way. Ingenious!
In the paper, she says the best animals to test would be those that live on the ocean floor and currently exist all around the continent.
Speaking to me, she reveals she already has a possible candidate – the Pareledone turqueti, or Turquet’s octopus.
She says: “The genome of the species contains signatures of what happened to populations in the past and different demographic changes – these are all held within that DNA.
“The DNA contains a record of those processes and so we can investigate different hypothesis of what happened in the past – just like your own human DNA contains a record of your ancestors.”
Strugnell says a cruder version of these techniques are used in the popular human DNA tests to track a person’s own ancestry.
Strugnell has visited Antarctica three times, most recently earlier this year where she was helping gather octopus and other animals that live on the sea floor (scientists get them by either diving or dong small targeted trawling).

Jan Strugnell with an octopus sample in Antarctica. The octpous here is a Megaleledone setebos. Photograph: Peter Enderlein/British Antarctic Survey

She has already used similar DNA techniques to understand the evolution of octopus around Antarctica and now wants to push the technology even further.
“The future of the planet is tied up in that ice,” says Dr Ceridwen Fraser, of the Australian National University. Fraser also uses DNA analysis to work out how populations of species have moved around the plant, particularly in Antarctica.
She says the techniques partly use what is known as the “molecular clock” – an understanding of the way genes change, or mutate, in different species.
In recent years, Fraser says there have been giant leaps in the capability of genetic technologies and also in the computer power needed to analyse massive sets of data.
She says Strugnell’s proposal is a “cool idea” and, with recent developments in the technology, was certainly feasible.

I think the timing for this is right. We now have the genetic tools more refined than ever before and we are moving into the era of interdisciplinary scientific research. There’s a lot of eyes on Antarctica right now and a lot of scientists want to know what’s going to happen.

Prof Richard Alley, of Penn State University, is a glaciologist and expert on ice sheets.
He tells me there were multiple challenges in understanding how the ice sheets had behaved in the past but says Strugnell’s method “looks like a great idea worthy of testing”.

It is worth noting that historical science, including paleoclimatic research and other research into Earth’s past and life’s evolution, does indeed generate hypotheses and do new experiments, just as in other branches of science – our ‘historical science’ really is science.

He says the paleoclimate science community (those are researchers studying ancient climates) is constantly coming up with new ways to understand what happened in the past.

We are limited to studying the materials left behind from past times but other branches of science do face limitations as well and, like them, we work hard to find the ways to use the possible to answer key questions. We’re not even close to exhausting the possibilities, and may never be, so there is still much to learn. I hope that this new idea is similarly tested.

Prof John Church, of the University of New South Wales Climate Change Research Centre, is a leading authority on sea level rise.
He ays the WAIS was likely to have made a “significant contribution” to the rising sea levels during the last interglacial “but whether it was a complete collapse is not yet known”.
“But the question is an important one,” he says, because high levels of greenhouse emissions would likely cause several metres of sea level rise over the coming centuries.

We could be committing the world to these higher sea levels this century, depending on our emissions. In addition to what emission and climate trajectories we will choose, the question is how quickly these multimetre sea-level rises could occur. One of the major issues in refining estimates of rates of future sea level rise is the future of the WAIS and other marine ice sheet areas in Antarctica.