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Stuart N. Thomson / UA Department of Geosciences
This 3-D reconstruction of the topography hidden under Antarctica's two-mile-thick coating of ice was made using data from radar surveys. The continent was relatively flat before glaciers started carving deep valleys 34 million years ago, a new study finds.
By Becky Oskin
LiveScience
Like Alaska's mighty Yukon, a broad river once flowed across Antarctica, following a gentle valley shaped by tectonic forces at a time before the continent became encased in ice. Understanding what happened when rivers of ice later filled the valley could solve certain climate and geologic puzzles about the southernmost continent.
The valley is Lambert Graben in East Antarctica, now home to the world's largest glacier. Trapped beneath the ice, the graben (which is German for ditch or trench) is a stunning, deep gorge. But before Antarctica's deep freeze 34 million years ago, the valley was relatively flat and filled by a lazy river, leaving a riddle for geologists to decode: How did Lambert Graben get so steep, and when was it carved?
The key to Lambert Graben's history was found in layers of sediments just offshore, in Prydz Bay. In a new study, Stuart Thomson, a geologist at the University of Arizona (UA) in Tucson, looked into the past by decoding sands deposited by the river, and the messy piles left behind by the glacier. The river sands are topped with a thick layer of coarser sediment that signals the onset of glacial erosion in the valley, the researchers found. The erosion rate more than doubled when the glaciers moved in, Thomson said.
"The only way that could happen is from glaciers," he said. "They started grinding and forming deep valleys."
WHOI
Antarctica and the Gondwana supercontinent, 150 million years ago.
Understanding when glaciers first wove their way across Antarctica will help scientists better model the ice sheet's response to Earth's climate shifts, the researchers said.
"There's a big effort to model how glaciers flow in Antarctica, and these models need a landscape over which glaciers can flow," Thomson told OurAmazingPlanet. "Once these models can predict past changes, they can more accurately predict what will happen with future climate changes."
The sediments also hold clues to the tectonic evolution of East Antarctica, and a mountain range buried beneath the vast, thick ice sheet. [Album: Stunning Photos of Antarctic Ice]
The findings are detailed in the March 2013 issue of the journal Nature Geoscience.
History of the ice
Lambert Graben formed during the breakup of Gondwana, an ancient supercontinent, a process that happened in stages. Antarctica, India and Africa tore apart in the Late Cretaceous (about 80 million years ago). The split created long, linear valleys oriented perpendicular to the continental coastlines. At the time, Earth's climate was warmer than it is today, and as Antarctica moved southward, settling into its home over the South Pole, the continent teemed with plants and animals.
Scientists can partially reconstruct this past environment with fossils and through radar that peers beneath the ice to map the shapes of the rock below. A 3-D map of Antarctica today shows chasms carved by glaciers, rugged mountains and other remnants of its warmer existence.
But the surveys tell nothing about how the landscape looked before the ice carved out all those features. "People have speculated when the big fjords formed under the ice," Thomson said. "But no one knows for sure until you sample the rocks or the sediments."
Thomson and his colleagues analyzed sediments drilled from the ocean floor just offshore of Lambert Glacier, as well as from onshore moraines, the rock piles pushed up by glaciers. Tests on minerals in the sands and muds helped them figure out when and how fast the surface eroded.
Here's what the sediments say: From about 250 million to 34 million years ago, the region around Lambert Glacier was relatively flat, and drained by slow-moving rivers, Thomson said. About 34 million years ago, which coincides with a cooling of Earth's climate, big glaciers appeared, shaping the spectacular valley now hidden under thick ice.
"It seemed like it occurred very early on, 34 (million) to 24 million years ago," Thomson said. Erosion slowed dramatically as the ice sheet stabilized about 15 million years ago, he said.
Some 5,250 to 8,200 feet (1.6 to 2.5 kilometers) of rock have since disappeared, ground down by glaciers and carried away by the ice, according to the study.
"Glaciers can carve deep valleys quickly — and did so on Antarctica before it got so cold that the most of it got covered by 1 or 2 miles (1.6 to 3.2 km) of thick, stationary ice," Peter Reiners, a UA geologist and study co-author, said in a statement.
Clues to buried mountain range
Lambert Graben extends about 375 miles (600 km) inland, ending at one of Antarctica's most enigmatic features — an entombed mountain range called the Gamburtsev Mountains. Buried under the ice, the mountains rose during Gondwana's rifting. Geologic evidence suggests two pulses of uplift from rifting events about 250 million years ago and 100 million years ago pushed up the jagged peaks.
But Thomson and his colleagues did not find evidence in the sediments for a second uplift phase 100 million years ago. The river sands contain minerals from the Gamburtsev Mountains, and the tiny grains suggest the mountains got their height with one tectonic push.
"This underscores both the mountain range's remarkable age and the extraordinary degree of subglacial landscape preservation," writes Darrel Swift in an accompanying article in Nature Geoscience. Swift, a geologist at the University of Sheffield in the United Kingdom, was not involved in the study.
Email Becky Oskin or follow her @beckyoskin. Follow us @OAPlanet, Facebook or Google+. Original article on LiveScience's OurAmazingPlanet.
- Images: The Majestic Transantarctic Mountains
- Video - Antarctica: Solving Geologic Mysteries
- Images: Scientists at the End of the Earth
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Leave a Comment:
When the ice melts someday in the near future the continent will rise up thousands of feet after the weight of the ice is gone and will look very different than today. And this might not be so far off in the future either thanks to CO2 (mostly from man) and CH4 releases (from permafrost and methane hydrates). But the good news is will have a lot of new ski slopes!
It would take thousands of years to melt that much ice. Hopefully we won't be changing things THAT much.
When Ice Ages come and go it only has takens decades to go from all ice to all melted, so don't bet on thousands of years, Jock. The Arctic Ice is expected to be gone soon. The Greenland Ice and glaciers are melting and calving furiously. Great chuncks of Antarctic ice are breaking off and drifting into the Southern Ocean. Melting Arctic tundra will release lots of Methane, a stronger greenhouse gas than carbon dioxide.
I believe that the timeline for melting all the polar ice will be more like a few hundred years. My big concern is what life forms on Earth can survive all that, including us.
34 million years...still blows my mind that length of time with not much going on. Wonder if there were crickets to hear during the countdown to humans?
So Antarctica cooled down because it moved south - not that south was warm enough at one point of time?
Actually, there's a bit of both, but mainly the continental drift. It was in subtropical zones once.
What do you mean rise? Do you think Antarctica is floating on the ocean?
@Tony Thanks.
On the second one - I think he means that the continental plate that has all the weight of that ice will lift up once all that ice is gone. I doubt it ... but that's the logic.
That's probably what he meant, but with two miles of ice melted,and the oceans rising from the extra water, it would seem like it would appear to sink rather than rise.
"What do you mean rise? Do you think Antarctica is floating on the ocean?" -Tony
I believe that he is referencing the upward rebound effect by the continental crust once the weight of 1-2 miles of ice is removed.
See: http://en.wikipedia.org/wiki/Post-glacial_rebound
Even today in N. America, northern Europe it is still measurable. -joe
one of the biggest mystery's on Earth; the Preis Reis map, showing antiartic , inlets , coastline and harbors, found in the 15th century in a museum in Turkey 9had been there for many hundreds of years.
@Tony - the weight of the ice is localized but the melt and resulting water will be distributed globally. So the water level rise will not be dramatic. But neither will be the plate rise because the plate size is thosaunds of miles in length and width and about 40 miles in height. 2 miles of ice is like a grain of rice on on that entire plate.
Yes, PJ, that's where I was going. But shaving 2 miles of ice off the top is noteworthy, because the average height of the continent would shrink by almost 2 miles.
Saxon, The Piri Reis map is only half a map, and what little outline there is of Antartica is so bad that many are not convinced it IS the Antarctic. It DOES have a great rendering of eastern Brazil, which was well known by the 16th century, when the map was made, not found.
If you examine any globe, you may be struck as I was by the obvious former connection of Antarctica with Australia, and the yin-yang connection between the southern tip of South America with that of Antarctica, forming a design that suggests the Old South Pole. The fracturing of the two continents by some interloping addition to the Earth's bulk, seems to me to have relocated the pole twenty three-degrees off from its present location, where the two tips meet; and separating all of the continents at their weakest connections, suggesting that Antarctica was further North beforehand, and naturally a warmer place. Check it out! Twenty three degrees is the amount of slant the Earth now features in its tilt, a coincidence that is fascinating and hardly coincidental. It also suggest that not only did some large mass expand our planet, but that it may have 'stood' upright originally, and not have had seasons as such. This would have put the North Pole somewhere in Northern Russia, twenty-three degrees off it's present location, and explain the 'creep' of the magnetic pole now being perceived. If I'm right, the 'creep' will end when the magnetic pole returns to its original position, at the yin-yang continental connection between South America and Antarctica, and Northern Russia. We'll see!
So much for the 6,000 years belief.
When the earth was much warmer, Al Gore's forefathers screamed "we're going to freeze. Burn more coal"
LOL ..."if we don't stop global cooling, the poles are going to freeze over and we'll be able to build a rail line from NYC to London!!" ... dumb ass 'experts", no matter what, they will come up with some sort of a crisis scenario in order to promote some ridiculous agenda that most can't even figure out, yet go right along with it, totally clueless to certain basic physics laws.
DA STexan in my state. The climate change is devastating the state and you continue to deny reality.
Yeah that about sums you up. The debate over GW was resolved 40 years ago and we still have people like you who continue to show their ignorance and denial. Beyond stupidity.
Don't beat up STexan, Greg. When it's hot here, it's just hot, so it's hard to notice the warming.
Personally, I'd like to see some climate change to the cooler around here.
A "number" of Texans think PHYSICS are to be taken when constipated, eh .... Tony/Greg? :)
Bottom line: People having faith in their "Common Sense" when those "inconvenient facts" get in the way, are probably the biggest detriments to progress.
The word -FAITH may be replaced by GULLIBILITY! -joe
It's not just hot. In Dallas apparently you missed out on the extreme drought like West Texas. 9 months without a drop of rain. Not to mention the number of days over 100 which we normally don't see much of. That's not good at all.
We had too many days over 100, and a purty long drought, though not quite 9 months.
Where're you located, Greg?
Amarillo
It will be interesting if future scientists discover traces of a civilization on Antarctica once the ice is gone.
If found, the Holy Koran will be shown to have predicted that!
I would, too, or even if humans had migrated there like they did to Easter Island and all other remote places on Earth. It seems like a settlement could have been there at one time. I would be curious how long it might have survived.
"If found, the (Holy Koran/Wholey Babble/Karma Sutra/Analects/Tao te Ching/Torah/Book of Bony Mo-rony/-the NAME of your favorite book of BS, right here) will be shown to have predicted that!
What else is new? -joe
"It will be interesting if future scientists discover traces of a civilization on Antarctica once the ice is gone."
The problem with that statement is that 34 million years ago humans did not exist. It was only 10 million years ago that our ancestors began walking upright on two legs. The chance of their being any signs of civilization prior to the time when we were walking on two legs is zero.
Now I am a firm believer that there were civlizations prior to the last Ice Age, signs of which are evident off the coast of India.
Not if people settled on Antarctica while in its current position. Could be that it was less icy at one time, especially along the coasts. People could have lived there like they live in the arctic circle, fishing and hunting penguins.
The Savage Land? (X-Men reference)
deprogramer,, I believe both Neaderthal and Cro-Magnon were both in Europe between the last two ice ages..
So Antarctica is on the way to reliving its past and Al Gorable calls it global warming ... Good up-date. ©2013
Today the frozen Antarctic ice sheet borders the Southern Ocean. But tropical palm trees once flourished there.
An intense warming phase occurred 52 million years ago, leading tropical vegetation, including palms and relatives of today's tropical Baobab trees, to grow on the continent’s now frozen coasts.
The surprising discovery came from a study of drill cores obtained from the seafloor near Antarctica. The results, published in the journal Nature, show that warm ocean currents and high carbon dioxide (CO2) levels in the air boosted temperatures, allowing tropical vegetation to grow where visitors today meet only icebergs and freezing cold. Important factor was the transfer of heat via warm ocean currents that reached Antarctica. When the warm ocean current collapsed and the Antarctic coast came under the influence of cooler ocean currents, the tropical rainforests, palm trees and Baobab relatives also disappeared. evidence of extremely mild temperatures was provided by analysis of organic compounds that were produced by soil bacteria populating the soils along the Antarctic.
Forget the fact that Antarctica is STILL gaining ice and forget the fact that in 2012 Antarctica set a new record of the MOST sea ice extent.
http://wattsupwiththat.com/2012/09/10/icesat-data-shows-mass-gains-of-the-antarctic-ice-sheet-exceed-losses/
http://wattsupwiththat.com/2012/05/17/new-paper-using-radarsat-data-antarctic-ice-shelves-slowed-down-have-not-been-changed-in-a-significant-way-in-the-past-12-years/
http://wattsupwiththat.com/2012/09/29/according-to-noaa-data-all-time-antarctic-sea-ice-rxtent-record-was-set-on-sept-22nd-2012/
http://nsidc.org/data/seaice_index/images/daily_images/S_timeseries.png
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seaice.anomaly.antarctic.png
You do know that Antarctica is the driest desert in the world and gets the least precipitation of any continent?
http://www.environmentalgraffiti.com/desert/news-antarctic-desert-fascinating-facts-about-highest-driest-largest-coldest-and-windiest-con
did you know that the inside of Joe Biden's head is the emptiest, most vacuous place of any continent? Sorry, I don't have any web support for that allegation.... :)
Between Iceland and Greenland, ther used to exist a group of Islands known to the Norse as the Skellig Islands. They are no longer above the surface, dropped down 200 feet by the weight of the ice in Greenland on the earths crust there. Today the are listed as the Skellig Sea Mounts.
I think that was different process, not ice weight.
The entire area between England, France and Denmark used to be above sea level as well and humans lived there, but rising sea levels flooded the area. Same thing that happened to the islands.
Since this conversation took the tone that it did, I will point all interested in climate - and related, but different issues - again to another great, new film: A Fierce Green Fire.
read your Bibles people. It says that the earth was surrounded by a cloud/ vapor called the firmament. It created the green house effect over the whole earth. The whole earth was tropical. Have you heard of Noah? In the days of Noah the thoughts of men were continually evil. God sent a flood. It rained 40 days and 40 nights. The water came from the firmament, the vapor surrounding the earth and some came out of the ground. Once that occurred the green house was gone. The sun shined directly on the earth creating warmer and colder spots. This really is the best explaination. Most scientists just say it happened over millions of years, because anything can happen over millions and millions of years. the biblical explanation makes the most sense, but then you would have to believe.
No need to read the book of myths. Your god is imaginary like the rest. There is no physical evidence of a flood such as you stated ever happening, nor could it physical ever happen. There is nothing that makes sense in that book. You are delusional.
I thought there had been some geological evidence of a massive flood at some point in the earth's development. And we also have the epic of Gilgamish from India, I think. Perhaps Moses simply incorporated that myth as he did so many others into the bible.
Not that I believe any of this stuff, mind you, but I thought I had read about geological evidence some years back. Just asking.
Just Read the whatever wholey babble texts of whatever religious fantasy -you care to have
FAITH(GULLIBILITY) in and some reeeally foolish Caca can be pulled up. -joe"Here's what the sediments say: From about 250 million to 34 million years ago, the region around Lambert Glacier was relatively flat, and drained by slow-moving rivers, Thomson said. About 34 million years ago, which coincides with a cooling of Earth's climate, big glaciers appeared, shaping the spectacular valley now hidden under thick ice."
Here's a question for all you blind leftist dogmatics out there. WHY did the Earth's climate cool 34 million years ago? Solar output? Orbital mechanics? ....naaah, Al Gore doesn't accept that. How inconvenient.
Moderation.. The earth cooled because of continental drift..The continents re-joined to form Pangea.. this blocked the ocean flow / heat transference phenomenon and the polar caps expanded.. This is a run-away event similar to global warming and ice ages..