More Evidence: East Antarctica a Sleeping Giant

September 21, 2018

Nature:

Understanding ice sheet behaviour in the geological past is
essential for evaluating the role of the cryosphere in the climate
system and for projecting rates and magnitudes of sea level rise in
future warming scenarios.

Although both geological data and ice sheet models indicate that
marine-based sectors of the East
Antarctic Ice Sheet were unstable during Pliocene warm intervals,
the ice sheet dynamics during late Pleistocene interglacial intervals
are highly uncertain.

Here we provide evidence from marine sedimentological and
geochemical records for ice margin retreat or thinning in the vicinity of the
Wilkes Subglacial Basin of East Antarctica during warm
late Pleistocene interglacial intervals.

The most extreme changes in sediment provenance, recording changes
in the locus of glacial erosion, occurred during marine isotope
stages 5, 9, and 11, when Antarctic air temperatures were at least
two degrees Celsius warmer than pre-industrial temperatures for
2,500 years or more.

Hence, our study indicates a close link between
extended Antarctic warmth and ice loss from the Wilkes Subglacial
Basin, providing ice-proximal data to support a contribution to
sea level from a reduced East Antarctic Ice Sheet during warm
interglacial intervals. While the behaviour of other regions of the
East Antarctic Ice Sheet remains to be assessed, it appears that
modest future warming may be sufficient to cause ice loss from the
Wilkes Subglacial Basin.

antarctic_bed

Washington Post:

At this rate, Earth risks sea level rise of 20 to 30 feet, historical analysis shows
New research finds that a vast area of Antarctica retreated when Earth’s temperatures weren’t much warmer than they are now.

A flotilla of tabular icebergs adrift in the Southern Ocean, near the outlet of the Wilkes Subglacial Basin, East Antarctica. (Christina Riesselman)

Temperatures not much warmer than the planet is experiencing now were sufficient to melt a major part of the East Antarctic ice sheet in Earth’s past, scientists reported Wednesday, including during one era about 125,000 years ago when sea levels were as much as 20 to 30 feet higher than they are now.

“It doesn’t need to be a very big warming, as long as it stays 2 degrees warmer for a sufficient time, this is the end game,” said David Wilson, a geologist at Imperial College London and one of the authors of the new research, which was published in Nature. Scientists at institutions in Australia, New Zealand, Japan and Spain also contributed to the work.

The research concerns a little-studied region called the Wilkes Subglacial Basin, which is roughly the size of California and Texas combined and contains more than 10 feet of potential sea-level rise. Fronted by three enormous glaciers named Cook, Mertz and Ninnis, the Wilkes is known to be vulnerable to fast retreat because the ice here is not standing on land and instead is rising up from a deep depression in the ocean floor.

Moreover, that depression grows deeper as you move from the current icy coastline of the Wilkes farther inland toward the South Pole, a downhill slope that could facilitate rapid ice loss.

What the new science adds is that during past warm periods in Earth’s history, some or all of the ice in the Wilkes Subglacial Basin seems to have gone away. That’s an inference researchers made by studying the record of sediments in the seafloor just off the coast of the current ice front.

Here, they found several layers of sediments that appeared to come from beneath where the ice currently lies, providing a hint that when these layers of the seafloor were laid down, Wilkes contained either less ice or no ice at all.

Those sediments corresponded in time to several well-known past warm periods, when seas rose considerably. But what’s worrying is that these eras were in many cases not much warmer than the planet already is right now.

The study cannot reveal, however, just how quickly ice emptied out of the Wilkes Basin. The past warm periods in question are thought to have been driven by slight variations in Earth’s orbit as it rotates around the sun, leading to stronger summer heat. That warmth was maintained for thousands of years.

“What we definitely can say is that during the [geological] stages where temperatures were warm for a couple of degrees for a couple of millennia, this is where we see a distinct signature in our records,” Wilson said. “We can’t necessarily say things didn’t happen quick, but we can’t resolve that in our data.”

Below, my interview with Jamin Greenbaum, who spoke to research around the same part of Antarctica.

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One Response to “More Evidence: East Antarctica a Sleeping Giant”

  1. Abel Adamski Says:

    New research out
    http://www.sciencemag.org/news/2017/08/record-shattering-27-million-year-old-ice-core-reveals-start-ice-ages
    Record-shattering 2.7-million-year-old ice core reveals start of the ice ages

    Scientists announced today that a core drilled in Antarctica has yielded 2.7-million-year-old ice, an astonishing find 1.7 million years older than the previous record-holder. Bubbles in the ice contain greenhouse gases from Earth’s atmosphere at a time when the planet’s cycles of glacial advance and retreat were just beginning, potentially offering clues to what triggered the ice ages. That information alone makes the value of the sample “incredible,” says David Shuster, a geochemist at the University of California, Berkeley, who is unaffiliated with the research. “This is the only sample of ancient Earth’s atmosphere that we have access to.”

    Described at the Goldschmidt Conference in Paris by Yuzhen Yan, a graduate student at Princeton University, the ice revealed atmospheric carbon dioxide (CO2) levels that did not exceed 300 parts per million, well below today’s levels. Some models of ancient climate predict that such relatively low levels would be needed to tip Earth into a series of ice ages. But some proxies gleaned from the fossils of animals that lived in shallow oceans had indicated higher CO2 levels. If the new result holds up, says Yige Zhang, a paleoclimatologist at Texas A&M University in College Station, the proxies will need to be recalibrated. “We have some work to do.”

    Now, the Princeton team wants to go back to the blue ice and drill some more, Brook says—not only to fill in the climate cycles of the last 2.7 million years with a multitude of snapshots, but also to go even deeper in time, before the ice ages, when CO2 levels were higher. There’s evidence that Antarctica has hosted at least some ice for 30 million years. It’s plausible, Brook says, that the next attempt could come back with ice 5 million years old—a time when temperatures are thought to resemble what Earth is heading toward with human-driven warming.


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