#AceNewsReport – June.14: This latest acceleration in flow speed and the mechanisms which caused it, mean the melting of the glacier could be “much more rapid” than previously expected, the researchers said:
Scientists said the glacier increased its rate of flow toward the Amundsen Sea in West Antarctica by 12 per cent between 2017 and 2020, in a paper published today in Science Advances……..Antarctica’s Pine Island Glacier has started moving faster again, according to new research.
The Pine Island Glacier has contributed the most to sea-level rise from Antarctica over the past few decades, and holds enough water to raise global sea-levels by half a metre.
“What is worrying is that we weren’t expecting this much shelf loss from this part of the ice sheet,” said lead author Ian Joughin from the Polar Science Centre at the University of Washington.
“It’s entirely possible that the rest of the shelf could break up in the next decade or two now that the process has started,” Professor Joughin said.
Between 1973 and 2009 there was a general trend of acceleration of the glacier, from 2.3 kilometres per year to 4 kilometres per year over that period.
The acceleration was attributed to thinning of the ice shelf due to ocean warming, and a retreat of what is called the “grounding line” — the boundary where the glacier lifts from the land and begins to float over the water.
But between 2009 and 2017, that process of thinning remained fairly stable and there was a pause in the acceleration of the glacier.
The speedup which began in 2017 is not thought to have been caused by further thinning, but instead by the ice shelf — the leading edge of the glacier that sits out over the sea — “ripping apart”, the researchers said.
Several large ice-shelf calving events, where large slabs of ice break away from the shelf, have been captured in satellite monitoring images since 2017.
These resulted in a 19 kilometre retreat, or a loss of one-fifth of the ice shelf during the 2017-20 period. That’s compared to a 7.5 kilometre loss between 2015-17.
The rate of the glacier’s movement, which was measured at a point above and below the grounding line, is now estimated to be 4.6 kilometres per year.Loading
Trend of more acceleration likely
The floating section of the glacier helps to slow the advance of the “grounded ice” — the part of the glacier still over the land.
That’s because the floating section is pushing through an embayment. The friction of the ice against the walls of the embayment holds the entire glacier back.
Sea-ice scientist Petra Heil from the Australian Antarctic Division, who wasn’t involved in the study, said it was like removing an obstacle from cars in traffic.
“We have seen this in some other locations as well — if you lose the buttresses you make the traffic faster flowing,” Dr Heil said.
“It also happened for example, with the Mertz Glazier, but there, there were a whole heap of other processes as well.
“But here they’ve shown [the process] really clearly. They have the satellite imagery — they were lucky it happened during those years where we had Sentinel.”
The European Space Agency’s Sentinel-1A satellite was launched in 2014 to scan the Earth’s surface as a way of monitoring the environment.
Sentinel’s images of the Pine Island Glacier — taken every 6 to 12 seconds since 2015 — provided the imagery that allowed the researchers to measure the scale of the loss.
Will this trend continue?
There are myriad influences on the rate that glaciers flow and melt, and so it’s difficult to ascertain whether this glacier will slow down again or continue at this new pace.
The researchers’ models predicted there was a chance the Pine Island Glacier would slow back down to around 4 kilometres per year over the next decade, but that the longer term trend was likely to be continued acceleration, according to co-author Pierre Dutrieux from Columbia University.
“It may be that this is just a momentary speedup, and that in this new configuration the ice will resume its lower-paced acceleration driven by ocean melt,” Dr Dutrieux said.
“[But] if the breakup continues, a reevaluation will indeed become inevitable.”
Professor Joughin said even without further acceleration, the Pine Island Glacier is “way out of balance”.
“At the present rate it is losing about 85 per cent more ice than it is gaining through snowfall.”
“We clearly need to watch this shelf because its breakup could happen way sooner than expected.”
He said that unless global temperatures actually drop, which is a highly unlikely scenario, it’s “more than likely” we’ll lose the majority of the West Antarctic ice sheet.
The crucial factor now, according to Professor Joughin, is the rate at which that happens.
“If we get say 3.5 metres of sea level rise over a century or two, that’s a big deal.
“On the other hand, if it’s over a millennium or two, that’s much more manageable.
“So even if the loss is committed, we have the power to slow that rate by slowing the rate of warming.”
#AceNewsDesk report ………Published: Jun.14: 2021:
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