Huge volume of water detected under Antarctic ice
THis was reported from May, but first I'd seen it.
Vast quantities of water have been detected in
sediments that underlie a part of the West Antarctic
ice sheet.
The volume is equivalent to a reservoir that is several
hundred metres deep.
The water was detected below the Whillans Ice Stream,
but its presence is likely replicated elsewhere across
the White Continent.
That being the case, it could be an important influence
on how Antarctica reacts to a warmer world, researchers
tell the journal Science this week.
Water at the base of glaciers and ice streams generally
works to lubricate their movement.
The transfer of water into or out of this deep
reservoir has the potential therefore to either slow
down or speed up ice flow.
Models that simulate future climate impacts will now
have to account for it.
The detection was made by a team led by Dr Chloe
Gustafson from the Scripps Institution of Oceanography
in San Diego, US.
She said the deep sediments were ancient ocean muds and
sands that became saturated with salty seawater
thousands of years ago when the West Antarctic Ice
Sheet was much less extensive than it is today.
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I forgot to include rest of the article,
the article continues here or you can go see at link
"These sediments I like to think of as a giant sponge,"
she explained.
"If you could squeeze out all that water and pool it on
the surface, the water would range anywhere from about
220m in depth all the way up to 820m.
"For comparison, the Empire State Building is about
440m tall. So at the shallowest, this water would go
halfway up the Empire State Building, and at the
deepest it would almost submerge two Empire State
Buildings," the postdoctoral researcher told BBC News.
Dr Gustafson made her measurements during a six-week
expedition on the Whillans Ice Stream, an 800m-thick,
100km-wide convoy of fast moving ice that feeds into
the Ross Ice Shelf.
The technique she deployed is called magnetotellurics.
This records variations in the the Earth’s natural
electric and magnetic fields to determine the
properties of deeply buried materials, be that rock,
sediments, ice or water.
"You get a resistivity pattern and you have to invert
that to work out how much water is present, and it's
huge," said Scripps glaciology professor, Helen
Fricker.
"People had long suspected this groundwater was there,
but this is the first time we've really been able to
measure it."
Prof Fricker used satellite observations in the 2000s
to describe the dynamic hydrological system under
Whillans. From the way the ice surface rose and fell
over weeks and months, she could tell there were melt
rivers filling and draining water from lakes that lay
directly under the ice at its interface with the
sediments.
This newly discovered groundwater is held further down,
in the pore spaces of the 500m-2,000m of ancient muds
and sands that are sandwiched between the ice stream
and basement rock.
The key question being asked is: to what extent can the
groundwater add to or subtract from the network of
freshwater rivers and lakes just under the ice, to aid
lubrication? And the inference in the measured changes
in the saltiness of the upper part of the ground
reservoir is that there is exchange.
Dr Tom Jordan conducts geophysical investigations of
the deep structures of Antarctica.
He said the groundwater was potentially relatively warm
because of the heat of basement rocks.
"If you then dump that warm water at the ice-bed
interface, it could accelerate the flow of ice," the
British Antarctic Survey scientist told BBC News.
The Scripps-led team wants to repeat its work at
Thwaites Glacier. At roughly the size of Great Britain
or Florida, Thwaites is much, much bigger than the
Whillans Ice Stream. It is currently the subject of
intense study by US and UK researchers because of its
melt rate.
Thwaites' outflow speed has doubled in the past 30
years and there is concern that future ice losses could
add significantly to global-sea level rise.
Dr Jordan said his data suggested there were large
sediment basins under Thwaites that could hold
impressive volumes of groundwater, but there were also
places where the glacier ice was directly in contact
with bedrock. This meant the Scripps would likely find
a mixed picture if it pursued its investigations, he
added.
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