Hidden river once flowed under Antarctica
By
Deborah Byrd in Earth
|
August
25, 2017
“Ice, by itself, is only capable of flowing at velocities of no more than tens of meters per year. That means the ice is being helped along. It’s sliding on water or mud or both.” The West Antarctic ice sheet. Its ice drains to the sea via glaciers, and via ice streams that accelerate over distances of hundreds of kilometers. A new study focuses on the question of what causes the ice streams’ fast rate of flow. Image via NASA. Rice University said on August 21, 2017 that its Antarctic researchers have discovered what they called “one of nature’s supreme ironies.” That is:
What Antarctic scientists call ice streams are not liquid, flowing water. Instead, an ice stream is a wide corridor of noticeably fast flow within an ice sheet, that is, a wider mass of glacial ice. Antarctic ice streams flow at different rates, but surface observations show that a typical rate of flow might be hundreds of meters per year. The new study – led by Rice postdoctoral researcher Lauren Simkins – focuses on what might be happening under the ice streams. Simkins explained:
Now there’s evidence for this idea, in these researchers’ discovery of a fossilized river system beneath the Ross Sea. The finding appeared online on August 21 in the peer-reviewed journal Nature Geoscience. Antarctica is covered by ice that’s more than 2 miles (3 km) thick in some places, and this ice is replenished each year by falling snow. So much of Antarctica’s ice is flowing seaward, and some of that seaward flow occurs in ice streams. If you’re standing on an ice stream, you can’t feel or see it move, but indeed it is moving. Gravity compresses the ice, and it moves under its own weight. Ice streams carry ice and sediment from the Antarctic interior to the surrounding ocean. Even with the best modern instruments, the undersides of Antarctic ice streams can’t be observed directly. So it’s hard to know for sure what’s making them move so much faster than ice alone would be expected to move. The researchers at Rice University did a two-year analysis of sediment cores and precise seafloor maps covering 2,700 square miles (about 7,000 square km) of the western Ross Sea. The maps reveal that – only 15,000 years ago – the Ross Sea was covered by thick ice year-round; the ice later retreated hundreds of miles inland to its current location. The statement from the researchers said:
EarthSky asked Lauren Simkins how the new evidence of ancient water courses fits with the idea of possible flowing water under the ice streams today. She told us:
She also said that – because there’s so little accessible information about how water presently flows beneath Antarctic ice – the fossilized river system offers a unique picture of how Antarctic water drains from subglacial lakes via rivers to the point where ice meets sea:
According to the statement from Rice, Simkins said meltwater builds up in subglacial lakes. First, intense pressures from the weight of ice causes some melting. In addition, Antarctica is home to dozens of volcanoes, which can heat ice from below. Simkins found at least 20 lakes in the fossil river system, along with evidence that water built up and drained from the lakes in episodic bursts rather than a steady stream. She worked with Rice co-author and volcanologist Helge Gonnermann to confirm that nearby volcanoes could have provided the necessary heat to feed the lakes. Study co-author John Anderson, a Rice oceanographer and veteran of nearly 30 Antarctic research expeditions, said the size and scope of the fossilized river system could be an eye-opener for ice-sheet modelers who seek to simulate Antarctic water flow. For example, the maps show exactly how ice retreated across the channel-lake system. The retreating ice stream in the western Ross Sea made a U-turn to follow the course of an under-ice river. Simkins said that’s notable because:
Simkins and Anderson said the study might ultimately help other researchers better predict how today’s ice streams will behave and how much they’ll contribute to rising sea levels. Read more about this study via Rice University Bottom line: Using seafloor maps of Antarctica’s Ross Sea, researchers have discovered a long-dead river system that once flowed beneath Antarctica’s ice and influenced how ice streams melted after Earth’s last ice age. © 2017 EarthSky Communications Inc.http://earthsky.org/earth/hidden-river-ross-sea-antarctica-ice-streams |