• Eerie fingers of ice — 'brinicles' — form in sea

    Escribano et al

    A 'brinicle" is a length of sea ice that forms beneath the ocean's surface.

    By Douglas Main
    LiveScience

    What's cooler than being cool? Brine-cold.

    When salt-rich water leaks out of sea ice, it sinks into the sea and can occasionally create an eerie finger of ice called a brinicle. New research explains how these strange fingers of ice form and how the salty water within sea ice could have been a prime environment in which life may have evolved.

    The study, published in the American Chemical Society's journal Langmuir, suggests that brinicles form in the same way as hydrothermal vents, except in reverse. Hydrothermal vents are spiny-looking towers on the ocean bottom where boiling, chemical-rich water flows out of the seafloor.

    The brinicle-forming process goes like this: When sea ice freezes in the Arctic and Antarctic, the salt and other ions in the water is excluded from the water crystals, said study author Bruno Escribano, a researcher at the Basque Center for Applied Mathematics in the Basque Country in northern Spain. This salt-heavy brine accumulates in fractures and compartments within the sea ice.

    Inevitably, however, sea ice cracks, and the brine leaks out. The brine itself is colder than the freezing point of seawater, since salt-rich water freezes at lower temperatures (hence the reason people put salt on icy sidewalks in the winter, enabling the ice to remain a liquid when it's below freezing), Escribano told OurAmazingPlanet.

    Since the concentration of water in the brine is lower than that in the ocean — and water moves from high to low concentrations, via osmosis — water is attracted to the brine. But the brine is so cold that the water freezes, forming a descending tube of ice, Escribano said.

    Hydrothermal vents form by an analogous method:  Ion-rich hot water is expelled from the seafloor and then begins to dissolve, forming a porous shell of metal extending upward. Water then rushes in, moving from high to low concentration, rupturing the membrane and causing more metal-rich water to spurt out, extending the tube and repeating the process.

    Both are examples of "chemical gardens," a type of chemical process and the name of an experiment common in chemistry sets that operates along the same principles and forms tubes of crystals that make plant-like shapes, Escribano said.

    Brine-rich compartments within sea ice have some properties that could have helped life originate, Escribano said. "Inside these compartments inside the ice, you have a high concentration of chemical compounds, and you also have lipids, fats that coat the inside of the compartment," he said. "These can act as a primitive membrane — one of the conditions necessary for life." They also contain a mixture of acidic and basic components that could provide energy necessary to form more complex molecules, perhaps even DNA, he said.

    Email Douglas Main or follow him @Douglas_Main. Follow us @OAPlanet, Facebook or  Google+. Original article on LiveScience's OurAmazingPlanet.

    Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

  • What Antarctica looked like before the ice

    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.

    Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

  • Rapid retreat of Antarctica glacier is called 'unprecedented'

     

    NSIDC

    Pine Island Glacier (right) and Thwaites Glacier (middle) in December 2012, as seen by the MODIS instrument on NASA's Terra satellite.

    By Becky Oskin
    Our Amazing Planet

    Like a plug in a leaky dam, little Pine Island Glacier holds back part of the massive West Antarctic Ice Sheet, whose thinning ice is contributing to sea level rise.

    In recent decades, Pine Island Glacier's rapid retreat raised fears that the glacier could "collapse," freeing the ice sheet it buffers to flow even more rapidly into the southern seas. The West Antarctic Ice contributes 0.15 to 0.30 millimeters per year to sea level rise.

    The big question is whether the hasty retreat is a recent change, caused by climate change, or a more long-term phenomenon.

    "We need to know if what we observe today is something that started perhaps at the end of the last Ice Age or something that started in more recent times," said Claus-Dieter Hillenbrand, a marine geologist with the British Antarctic Survey.

    Pine Island Glacier's small ice shelf, a platform of ice floating on the ocean's surface, acts as a plug, holding the rest of the ice stream in place on land. As warm ocean currents melt the ice shelf from below, inland glaciers flow down to the coast and feed the thinning ice shelf. Changes to Antarctic wind currents, driven by global warming, have pushed relatively warmer ocean waters beneath the ice shelves.

    In the past 20 years, Pine Island Glacier's grounding line, the location where the glacier leaves bedrock and meets the ocean, has retreated at a rate of more than 1 kilometer a year. The glacier itself has thinned at a rate of 5 feet (1.5 meters) a year since the 1990s, and its flow rate has accelerated by 30 percent in the past 10 years.

    NASA Earth Observatory

    A massive crack in Pine Island Glacier is steadily growing, as seen in a Sept. 14, 2012, satellite image.

    Pine Island Glacier stretches only 45 miles (40 km) across where it meets the ocean, but it drains an area of 62,665 square miles (162,300 square km).

    To determine why Pine Island Glacier and its nearby cousin, Thwaites Glacier, are changing so rapidly, the British Antarctic Survey looked to the past. They studied sediments from Pine Island Bay, where the ice shelves stick tongues into the ocean.

    Microfossils in mud retrieved by ocean drilling aboard a research ship pinpoint when and were ice covered the bay. This is because the microscopic marine life is only present if the ice shelf is absent. Radiocarbon dating of the fossils gave researchers a 10,000-year history of the past location of the ice.

    "For the first time, we can put these modern observations of fast grounding-line retreat in a long-term context," Hillenbrand told OurAmazingPlanet.

    "We can show that the present grounding-line retreat is really exceptional over a longer time scale, over the last 10,000 years," he said. "In the previous 10,000 years, the grounding line retreated by just about 90 kilometers (56 miles), but in the last 20 years, it retreated by 25 kilometers (15 miles)."

    The results appear in the January 2013 issue of the journal Geology.

    Hillenbrand and his colleagues also discovered there could have been three or four episodes of rapid retreat in the past 10,000 years, but these were short-lived, lasting just 25 to 30 years. Researchers found no evidence the glaciers had advanced in the past 10,000 years.

    "Some say the fast grounding-line retreat will stop in a few years, others in a few decades. Others say that this retreat will actually continue and may lead to the complete collapse of the Pine Island Glacier drainage system," Hillenbrand said. "What we know is that, on the basis of this data, the current retreat is unprecedented."

    As Pine Island Glacier retreats, it drops huge icebergs. In 2011, NASA's Operation IceBridge discovered a giant crack crossing the ice shelf. (The IceBridge expedition tracks yearly changes in the Antarctic ice.) The fissure, about 20 to 25 km inland from the edge of the ice shelf, could birth an iceberg the size of New York City.

    IceBridge scientists say the calving is part of the natural process by which glaciers flow to the sea. The last calving event (the sudden release of ice) let loose in an iceberg that measured 26 by 11 miles (42 km by 17 km) in 2001. The Pine Island Glacier seems to generate big bergs on a decade-long cycle, scientist say. [ Photo Album: Antarctica, Iceberg Maker ]

    The British team now plans to investigate what's driving the thinning of the glaciers in Pine Island Bay. "We're pretty sure the most important driver is warm ocean water, but this is still an open question," Hillenbrand said.

    "Now that we have this retreat history, we can study the past dynamic behavior of these glaciers, so we can predict better the future behavior of these ice streams and their contribution to future sea level rise."

    Reach Becky Oskin at boskin@techmedianetwork.com. Follow her on Twitter @beckyoskin. Follow OurAmazingPlanet on Twitter @OAPlanet. We're also on Facebook and Google+.

  • Saturn moon Titan may have ice floating in lakes

    NASA/JPL-Caltech/USGS

    This artist's concept envisions what hydrocarbon ice forming on a liquid hydrocarbon sea of Saturn's moon Titan might look like. Image released Jan. 8, 2012.

    By SPACE.com

    Chunks of hydrocarbon ice may float atop the lakes and seas of Saturn's huge moon Titan, a new study reveals.

    The presence of such ice floes in the ethane and methane seas on Titan would make the moon an even more exciting target for astrobiologists, researchers said.

    "One of the most intriguing questions about these lakes and seas is whether they might host an exotic form of life," study co-author Jonathan Lunine of Cornell University said in a statement. "And the formation of floating hydrocarbon ice will provide an opportunity for interesting chemistry along the boundary between liquid and solid, a boundary that may have been important in the origin of terrestrial life."

    Titan — Saturn's largest moon, with a diameter of 3,200 miles — is the only body in our solar system apart from Earth known to host stable bodies of liquid on its surface. While Earth's weather cycle is based on water, Titan's involves hydrocarbons, with liquid ethane and methane falling as rain and pooling in large lakes and seas. [Amazing Photos of Titan]

    NASA's Cassini spacecraft has spotted a huge network of these seas in Titan's northern hemisphere, along with a handful in the moon's southern reaches.

    Cassini scientists had previously assumed that these seas would not have floating ice, since solid methane is denser than its liquid counterpart and should thus sink. But the new study suggests that things are not so simple.

    The researchers created a model investigating how Titan's seas interact with the moon's nitrogen-rich atmosphere, creating pockets of varying composition and temperature.

    The team determined that hydrocarbon ice should indeed float in the moon's seas, as long as the temperature is just below methane's freezing point — minus 297 degrees Fahrenheit, or minus 183 degrees Celsius — and the ice is at least 5 percent "air," which is the average composition for young sea ice here on Earth.

    This ice may be colorless, perhaps with a reddish-brown tint provided by Titan's atmosphere, researchers said.

    "We now know it's possible to get methane-and-ethane-rich ice freezing over on Titan in thin blocks that congeal together as it gets colder — similar to what we see with Arctic sea ice at the onset of winter," lead author Jason Hofgartner, also of Cornell, said in a statement. "We'll want to take these conditions into consideration if we ever decide to explore the Titan surface some day."

    Floating sea ice could be a fleeting phenomenon on Titan, if it exists at all. If the temperature drops a few degrees, the ice will begin to sink, researchers said.

    Cassini should be able to test the new model out, and soon. Titan's northern spring is underway, meaning lakes and seas in the moon's northern reaches are warming up.

    As this happens, ice may rise to the top, creating a surface that appears brighter and more reflective to Cassini's radar instrument. As the area continues to warm, the ice should melt, producing an entirely liquid surface that will look darker to Cassini, researchers said.

    "Cassini's extended stay in the Saturn system gives us an unprecedented opportunity to watch the effects of seasonal change at Titan," Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement. "We'll have an opportunity to see if the theories are right."

    The $3.2 billion Cassini mission, a joint effort of NASA, the European Space Agency and the Italian Space Agency, launched in 1997 and arrived at Saturn in 2004. It will continue to observe the ringed planet and its many moons through at least 2017.

    Follow SPACE.com on Twitter @Spacedotcom. We're also on Facebook & Google+.

     

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