Global Warming Alters Arctic Food Chain, Scientists Say, With Unforeseeable Results

Nov 23, 2016

By Carl Zimmer

The Arctic Ocean may seem remote and forbidding, but to birds, whales and other animals, it’s a top-notch dining destination.

“It’s a great place to get food in the summertime, so animals are flying or swimming thousands of miles to get there,” said Kevin R. Arrigo, a biological oceanographer at Stanford University.

But the menu is changing. Confirming earlier research, scientists reported Wednesday that global warming is altering the ecology of the Arctic Ocean on a huge scale.

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2 comments on “Global Warming Alters Arctic Food Chain, Scientists Say, With Unforeseeable Results

  • Meanwhile in Antarctica there are two new related news items:-

    The melting Antarctic glacier that now contributes more to sea-level rise than any other ice stream on the planet began its big decline in the 1940s.

    This is when warm ocean water likely first got under Pine Island Glacier (PIG) to loosen the secure footing it had enjoyed up until that point.

    Researchers figured out the timing by dating the sediments beneath the PIG.

    It puts the glacier’s current changes in their proper historical context, the scientists tell Nature magazine.

    These changes can now be regarded as unprecedented in thousands of years.

    Not only is the glacier going backwards, it is also thinning fast – losing more than 2m in elevation every year.

    Other field studies and computer models suggest a runaway collapse might even be possible. The PIG on its own could add up to 10mm to sea levels over the next couple of decades.

    “This glacier used to be pinned to a ridge and once it moved away from that ridge, it started to retreat rapidly; and without other pinning points it could continue to retreat rapidly inland, contributing significantly to global sea level,” Dr James Smith from the British Antarctic Survey told BBC News.

    The PIG is a colossal feature that drains a region of the West Antarctic Ice Sheet some two-thirds the size of the UK.

    It is a marine-terminating glacier, which means its front flows off the land and pushes out into the ocean along the seafloor until its mass begins to lift up and float. Eventually, the buoyant section breaks up to form icebergs.

    Currently, the PIG is dumping about 130 billion tonnes of ice in the ocean every year.

    Submersible surveys under its floating front – its “ice shelf” – had revealed the contact point with the seabed once draped over a large ridge.

    Having a “grounding line” in such a position would have helped anchor and constrain the whole glacier.

    Some of the earliest satellite imagery indicated the PIG must have broken free completely of this pinning bump in the 1970s, but when exactly it started to disengage was far less certain.

    It could have been many decades previously; several centuries or even millennia ago.

    Now, Dr Smith and colleagues look to have solved this problem.

    They drilled through the ice shelf to sample, analyse and date the muddy sediments that cover the ridge. And their investigation reveals that warm water is likely to have started to melt a cavity in the grounded glacier behind the pinch point in about the mid-1940s.

    One of the reasons they can be sure of the timing is because of where plutonium traces start to appear in the sediment layers.

    This radioisotope is a tell-tale signature for the atomic bomb tests that began in earnest after WWII and which peaked in the 1960s.

    It leaves open the question of why the unpinning of the PIG occurred when it did, but the team point to the strong warming the region would have experienced following a big El Nino event between 1939 and 1942.

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  • The second news item is on the extent of the floating summer sea-ice around Antarctica.

    Log books from the early Antarctic expeditions indicate that the area of summer sea-ice around the continent has barely changed in size in a century.

    Researchers have studied the records of pioneering explorers, including Captain Robert Scott and Sir Ernest Shackleton.

    The study suggests that Antarctic sea-ice is much less sensitive to climate change than the Arctic, which has declined dramatically.

    The research has been published in The Cryosphere journal.

    A century ago Captain Scott and Sir Ernest Shackleton were among those who ventured into completely uncharted territory.

    They were the bravest explorers of their age. At the time, their voyages brought a totally new understanding of the Antarctic landscape. And now their records are giving scientists new data on the impacts of climate change.

    Some data collected by whaling vessels suggests the extent of Antarctic summer (December, January, February, March) sea-ice was significantly higher during the 1950s, before a steep decline returned it to around six million square kilometres (average across the four months) in recent decades.

    But the log books of the “heroic explorers” show that over the long term, the amount of ice has changed very little. It has merely ebbed and flowed.

    Dr Jonathan Day of the University of Reading who led the study says his analysis indicates that the extent of Antarctic summer sea-ice is at most 14% smaller now than during the early 1900s.

    “The Antarctic sea-ice a hundred years ago was fairly similar to what it is today. That is not much if you contrast this with the Arctic which has lost 26% of its extent,” he told BBC News.

    Any guesses as to which bits of which report, the deniers will pick out and circulate to their followers?

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