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Author Topic: What's new in Antarctica ?  (Read 62129 times)

Hyperion

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Re: What's new in Antarctica ?
« Reply #250 on: April 12, 2017, 10:29:41 AM »
Cycles 57 and 49 (at ∼22.7 and 19.5 My ago), which are characterized by distinctly sawtooth-shaped ∼110-ky cycles, suggesting a causal link between cycle amplitude and asymmetry during the Early Miocene, but not during the MOGI. The distinctly asymmetric cycles suggest that the Early Miocene Antarctic ice sheets periodically underwent intervals of growth that were prolonged relative to astronomical forcing and then underwent subsequent rapid retreat in a manner akin to the glacial terminations of the Late Pleistocene glaciations, in which the large ice sheets of the Northern Hemisphere were major participants (27, 28, 32). The highly asymmetric (sawtooth) nature of Late Pleistocene glacial−interglacial cycles is thought to originate from a positive ice mass balance that persists through several precession- and obliquity-paced summer insolation maxima. This results in decreasing ice sheet stability and more rapid terminations every ∼110 ky, once the ablation of the Northern Hemisphere ice sheets increases dramatically in response to the next insolation maximum. The increase in ablation is caused by lowered surface elevation of the ice sheets resulting from crustal sinking and delayed isostatic rebound (33). Similar mechanisms are implied for the large Antarctic ice sheets of the OMT (∼22.5 My ago) but it is less clear why the smaller ice sheets of the Early Miocene (∼19.5 My ago) would exhibit this distinctly sawtooth-shaped pattern of growth and decay (Fig. 3).

As they point out here "delayed isostatic rebound" can be a factor in rapid ice sheet collapses. Though this is stated as causing rapid retreats through ablation, bottom melt processes could be a larger factor. Especially with Below sea level interiors like WA and Greenland. There is possibility here that this study, and even our data of the holocene deglaciation has even more rapid advance/ retreat behaviour smoothed out in published studies by preconceptions that have their root in the scientific consensus held until recently that major changes in large ice sheets take thousands of years to occur. Obviously data collected loses resolution with antiquity, and its not uncommon unfortunately for "anomalous" samples that don't fit the paradigm to be discarded and not even be mentioned in publication. As we appear to be learning that Atmosphere and ocean heat transport changes can produce large and rapid consequence, perhaps we should be considering the possibility that there may have been big Antarctic and Greenland melt backs in the meltwater pulses coming out of the last Glaciation. A process where the Laurentide and European Ice sheet melts trigger increased heat transport to poles via big storm systems caused by the temperature differentials in SSTs, then the process see-saws, causing a rapid meltback at the poles along with partial rebuilding of the L and E sheets via increased snowfalls caused by polar cyclone factories seems feasible. This would dampen the sea level changes as the 6x current total terrestrial ice sheet mass of 20ka bp crashed in several pulses over 10000 years to near current levels. Not a situation we currently can look forward to. With too much heat in the system the Temperate latitude caps can't build as the polar ones crash. But the runaway escalation of cyclone heat transport as Hansen's paper proposed for the end of the last interglacial 120 ka bp sure can. With the extra issues of far higher greenhouse burden and orbital forcings being more favourable to rapid meltings now.
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sidd

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Re: What's new in Antarctica ?
« Reply #251 on: April 20, 2017, 12:12:32 AM »
New paper about surface meltwater in Antarctica doi:10.1038/nature22049
I attach Fig 1

sidd

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Re: What's new in Antarctica ?
« Reply #252 on: April 20, 2017, 12:14:13 AM »
And a paper showing evidence for meltwater stabilization of an ice shelf (?!) doi:10.1038/nature22048

AbruptSLR

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Re: What's new in Antarctica ?
« Reply #253 on: April 20, 2017, 12:33:23 AM »
New paper about surface meltwater in Antarctica doi:10.1038/nature22049

The associated article is entitled: "Scientists have discovered vast systems of flowing water in Antarctica. And that worries them."

https://www.washingtonpost.com/news/energy-environment/wp/2017/04/19/the-surface-of-antarctica-is-covered-with-flowing-water-that-has-scientists-worried/?utm_term=.a447caa06cea

Extract: "The surface of the remote Antarctic ice sheet may be a far more dynamic place than scientists imagined, new research suggests. Decades of satellite imagery and aerial photography have revealed an extensive network of lakes and rivers transporting liquid meltwater across the continent’s ice shelves — nearly 700 systems of connected pools and streams in total.

“A handful of previous studies have documented surface lakes and streams on individual ice shelves over a span of a few years,” glaciologist Alison Banwell of the University of Cambridge wrote in a comment on the new research, published Wednesday in the journal Nature. “But the authors’ work is the first to extensively map meltwater features and drainage systems on all of Antarctica’s ice shelves, over multiple decades.”

The findings, presented Wednesday in a pair of papers in Nature, could upend our understanding of the way meltwater interacts with the frozen ice sheet."

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AbruptSLR

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Re: What's new in Antarctica ?
« Reply #254 on: April 24, 2017, 01:47:16 AM »
And a paper showing evidence for meltwater stabilization of an ice shelf (?!) doi:10.1038/nature22048

Here is a more complete reference & a linked to an open access cop of the paper:

Jonathan Kingslake, Jeremy C. Ely, Indrani Das & Robin E. Bell (20 APRIL 2017), "Widespread movement of meltwater onto and across Antarctic ice shelves", NATURE, VOL 544, 349; doi:10.1038/nature22049

https://www.nature.com/articles/nature22049.epdf?referrer_access_token=F81z0TqwjGmb71By493OxNRgN0jAjWel9jnR3ZoTv0NWLAFAcjzSECmaCP-TuhnQnGZAtnvyAOn7AnGvU4eFIhvSEXoC1C_eSvhX66G7wIrelRihqRI2ZJiLFK7noXL2wRaVkuwepFW4IPEnI18R27P44CGAGzLWoi2s9p-L4iIXUTf9xLPsUKVG5QyR-syQVj_dX8IR8ikWvtV8j6UV4zYWWaEHHTVDErJ8Je1mG9hoI8AgdRFZYtm_R8vq6R96&tracking_referrer=www.cbsnews.com
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sidd

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Re: What's new in Antarctica ?
« Reply #255 on: April 25, 2017, 02:26:02 AM »
"And a paper showing evidence for meltwater stabilization of an ice shelf (?!) doi:10.1038/nature22048"

the link above in the quote is to the Bell paper, not the Kingslake paper.

That Bell paper is quite interesting. Hydrofracture instability is slowed greatly by efficient export of surface melt.

"The ­calculated water export ranges from 0.04 km^3 to 0.56 km^3 in each season. In just seven days, the waterfall can export the entire annual surface melt volume produced by a melt rate of 0.5 m/yr over the shear-margin catchment. Present ice-sheet models produce rapid disintegration when surface melt rates reach 1.5 m/yr. However, our results show that this amount of ­surface melt could be removed by the waterfall in 21 days (Extended Data Fig. 6). This efficient export of surface meltwater highlights the capacity of rivers to efficiently buffer ice shelves against the damaging storage of melt."

Well, that immediately raises the question, why did this not buffer Larsen before it fell apart ? I wonder if Larsen has rivers for years before it fell apart, by we were not watching it carefully enuf. Well, good news, for a change, if it is borne out.

sidd


sidd

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Re: What's new in Antarctica ?
« Reply #256 on: April 25, 2017, 02:30:18 AM »
Re: Kingslake paper, doi:10.1038/nature22049

In the figure 1 i included earlier, inset d) is the the Roy Bauduoin shelf. There is a new paper at cryosphere-discuss by Berger et al. doi:10.5194/tc-2017-41 about spatial variation in basal melting on this shelf.

http://www.the-cryosphere-discuss.net/tc-2017-41/

sidd

crandles

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Re: What's new in Antarctica ?
« Reply #257 on: April 30, 2017, 05:20:21 PM »
Antarctica's troublesome 'hairdryer winds' (ie 'Foen' winds)
http://www.bbc.co.uk/news/science-environment-39759329

A new study has found an atmospheric melting phenomenon in the region to be far more prevalent than anyone had realised.

Juan C. García

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Re: What's new in Antarctica ?
« Reply #258 on: May 06, 2017, 04:00:50 AM »
UAE plans to drag an ICEBERG from Antarctica to provide drinking water for millions

http://www.dailymail.co.uk/sciencetech/article-4476272/UAE-plans-drag-ICEBERG-Antarctic.html

 :o :P
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

FredBear

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Re: What's new in Antarctica ?
« Reply #259 on: May 06, 2017, 12:50:09 PM »
The iceberg would set an interesting set of environmental questions :-
!. Presumeably it would become surrounded with a pool of very cold fresh water to upset the local aquatic life.
2.The cold would strip moisture from the atmosphere, making it even drier, fog might even form?
3. Would the iceberg remain stable during the "mining", or would it topple or even explode?
4. Where do you park it?
5. ??

( I did once use a 2 litre, -20oC ice block as emergency cooling for a marine aquarium with good circulation - it cracked quite loudly and melted fast!)

Juan C. García

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Re: What's new in Antarctica ?
« Reply #260 on: May 06, 2017, 04:11:31 PM »
The iceberg would set an interesting set of environmental questions :-
!. Presumeably it would become surrounded with a pool of very cold fresh water to upset the local aquatic life.
2.The cold would strip moisture from the atmosphere, making it even drier, fog might even form?
3. Would the iceberg remain stable during the "mining", or would it topple or even explode?
4. Where do you park it?
5. ??

( I did once use a 2 litre, -20oC ice block as emergency cooling for a marine aquarium with good circulation - it cracked quite loudly and melted fast!)

Suppose that it could work. Do we need to take out ice from Antarctica to make greener the African deserts? To make them cooler on a world in which humanity is still emitting greenhouse gases?

They are talking about having infrastructure to make a routine with this icebergs movement!

Hope it will not work, if they try it!
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

ghoti

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Juan C. García

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Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

sidd

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Re: What's new in Antarctica ?
« Reply #263 on: May 11, 2017, 06:52:20 PM »
Hellmer et al: Filchner-Ronne in jeopardy, as Hellmer had previously pointed out, he now puts timeframe on the cold-cavity to warm cavity transition.

"Derivatives of Circumpolar Deep Water are directed southward underneath the Filchner–Ronne Ice Shelf, warming the cavity and dramatically increasing basal melting ... The process is irreversible with a recurrence to twentieth-century atmospheric forcing and can only be halted through prescribing a return to twentieth-century basal melt rates. This finding might have strong implications for the stability of the Antarctic ice sheet."

"Our experiments indicate that the link between the hydrography on the southern Weddell Sea continental shelf and melt rates beneath the Filchner–Ronne Ice Shelf is controlled by a positive feedback mechanism: Once the reversal of the near-bottom density gradient across the Filchner Trough, together with a rising coastal thermocline, facilitates the direct inflow of the slope current into the trough, warm deep water flushes the ice shelf cavity, causing its warming, enhanced basal mass loss, and a vigorous outflow of glacial meltwater. The latter further freshens the shelf water and thus maintains a density and flow structure at the sill that supports further access of warm water to the ice shelf cavity. The increase in basal melting accelerates the cavity circulation, drawing in even more warm water of open ocean origin—a self-intensifying mechanism. Although the initial trigger for this transition is freshening on the continental shelf as a result of atmosphere–ocean interactions, once the system is in the warm-shelf phase, the only way to stop the inflow of the warm water is to return to twentieth-century atmospheric conditions and to reduce the meltwater input. At first, the latter could be realized by a reduction in the floating portion of the ice sheet. However, the resulting loss of buttressing of the inland ice sheet would accelerate the draining ice streams. The discharge of ice from the relevant catchment basin and a significant contribution to global sea level will be inevitable."

doi: 10.1175/JCLI-D-16-0420.1

open access. Read all about it.

sidd


sidd

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Re: What's new in Antarctica ?
« Reply #264 on: May 11, 2017, 07:18:59 PM »
An addendum to my previous comment:

Amundsen Sea glaciers are already destabilized. Filchner Ronne to go around 2070. Wonder how soon until the Ross goes, unleasing threeway attack on WAIS, and eventual open water communication as there once was. That recalled bryozoan data,  cf Vaughn(2011) doi:10.1029/2011GC003688 , also open access, read all about it. That paper says, hopefully,

"Continued ice-loss at present rates would open seaways between Amundsen and Weddell seas (A-W), and Amundsen and Bellingshausen seas (A-B), in around one thousand years. "

I think the timescale might be an order of magnitude faster. Ominously:

" ...  we conclude that opening could have occurred in MIS 5e (100 ka BP) when Antarctica was warmer than present and likely contributed to global sea levels higher than today."

Thats the Eemian. We are in Eemian temperatures now.

sidd

TerryM

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Re: What's new in Antarctica ?
« Reply #265 on: May 14, 2017, 02:43:39 PM »
Towing icebergs for fresh water is a zombie idea that comes up regularly and never pans out. Here's an article from 2011 about it...

[url]https://www.theatlantic.com/technology/archive/2011/08/the-many-failures-and-few-successes-of-zany-iceberg-towing-schemes/243364/]https://www.theatlantic.com/technology/archive/2011/08/the-many-failures-and-few-successes-of-zany-iceberg-towing-schemes/243364/]
[url]https://www.theatlantic.com/technology/archive/2011/08/the-many-failures-and-few-successes-of-zany-iceberg-towing-schemes/243364/
[/url]



Had a prof in the early 60's that had worked on Habakkuk and was still an enthusiast. Insisted that with chiller equipment aboard all that would be necessary after a bombing would be a fire hose to fill any craters. He was teaching in Hamilton at that time but did have a British accent.


I'd read something a decade or so ago where iceberg cowboys off Newfoundland were grounding them in coves and selling the melt water to a brewery because of it's purity.
Wonder it Cate would know?


Slightly OT, but I believe they mined the Mendenhall Glacier in Alaska for cooling cocktails in San Francisco from the Klondike days.
Terry

wili

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Re: What's new in Antarctica ?
« Reply #266 on: May 17, 2017, 04:07:10 AM »
Not sure if this has already been posted somewhere--Al Jazeera has a story on Antarctica:

http://interactive.aljazeera.com/aje/2017/antarctica-voyage/index.html#11

"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

wili

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"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

wili

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Re: What's new in Antarctica ?
« Reply #268 on: May 18, 2017, 11:25:59 PM »
And now there's a story in the Guardian, for the trifecta!

https://www.theguardian.com/science/2017/may/18/climate-change-is-turning-antarctica-green-say-reseatchers

 Climate change is turning Antarctica green, say researchers

In the past 50 years the quantity and rate of plant growth has shot up, says study, suggesting further warming could lead to rapid ecosystem changes
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

gerontocrat

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Re: What's new in Antarctica ?
« Reply #269 on: May 20, 2017, 04:41:10 PM »
Couldn't resist this image of the jetstream over Antarctica. An almost perfect outer ring with enormous (Rossby?) waves inside.


charles_oil

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Re: What's new in Antarctica ?
« Reply #270 on: May 21, 2017, 10:05:07 AM »

And CNN has picked up on greening too (quiet day in Trumpton for once)


http://edition.cnn.com/2017/05/19/europe/climate-change-antarctica-moss/index.html


Hyperion

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Re: What's new in Antarctica ?
« Reply #271 on: May 26, 2017, 02:25:07 PM »
GADZOOKS!

 :o
The Titan Hyperion was the first to understand, by diligent attention and observation, the movement of both the sun and the moon and the other stars, and the seasons as well, in that they are caused by these bodies, and to make these facts known to others; — Diodorus Siculus (5.67.1)