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Author Topic: What's new in Antarctica ?  (Read 56331 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson