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Explanation offered for Antarctica’s ’blood falls’

05.11.2003


Researchers here have discovered that a reddish deposit seeping out from the face of a glacier in Antarcticas remote Taylor Valley is probably the last remnant of an ancient salt-water lake. The lake probably formed as much as 5 million years ago when the sea levels were higher and the ocean reached far inland.



A view up one of the gulleys where water runs downslope from the margin of the Taylor Glacier. Iron salt deposits which give blood Falls its name are clearly visible.



Ohio State University scientists reported their conclusions today at the annual meeting of the Geological Society of America in Seattle.

Berry Lyons, a professor of geological sciences and director of OSUs Byrd Polar Research Center, offered the best explanation to date for a strange, nearly-century-old discoloration halfway up the face of the Taylor Glacier in Antarcticas Dry Valleys. The Dry Valleys are well known to polar scientists who have studied these remarkably snow-free troughs leading from the Ross Sea onto the East Antarctic Ice Sheet.


Geologist Griffith Taylor first found the red discoloration in 1911 as he explored the valley that would one day bear his name. Nearly a half-century later during the mid-1960s, University of Wisconsin scientist Robert Black discovered that the reddish stain on the polar ice was really iron salts, or ferric hydroxide, that was being squeezed out of the ice sheet.

The phenomenon came to be called Blood Falls and its origin has puzzled researchers ever since.

Lyons, who heads one of the National Science Foundations Long-Term Ecological Research (LTER) sites in Taylor Valley, led a team of researchers from Ohio State, the University of Colorado and Montana State University that analyzed samples of the reddish discharge over a 10-year period. That analysis suggests that the reddish salts were deposits formed at the site of an ancient lakebed when the ocean receded from the valley.

Perhaps at a time when this valley resembled more a Scandanavian fjord, some sea water was trapped in the lower portion of the valley, Lyons explained. When the Taylor Glacier eventually advanced over the top of that lake, the seawater was essentially freeze-dried and trapped.

We think we are looking at the remains of some very old seawater trapped during the Miocene period, some 5 million years ago, he said.

Lyons and his colleagues believe that as the glacier moved forward down through the valley, it captured some of the deposit and forced it up into the body of ice. Eventually, the deposit reached the margin, or edge, of the glacier and is being slowly pushed out or the ice.

As the reddish, icy sludge melts at the margin of the glacier, it runs off into Lake Bonney, one of only four ice-covered lakes in the Dry Valleys. Three of the lakes Bonney, Fryxell and Hoare are in Taylor Valley while Lake Vanda is in the nearby Wright Valley. But each of these lakes is very different chemically and the explanation for those differences has puzzled researchers for years.

The water at the bottom of Lake Bonney, the most landward of the Taylor Valley three, is saturated with salts, Lyons said. But Lake Hoare a short distance down the valley from Bonney is filled with fresh water. Lake Fryxell is also a saltwater lake.

Scientists have wondered for years how three lakes so close together, with the same climate regime and the same geology, can be so different chemically, Lyons said. We think it has to do with the ages of these lakes.

"The research team believes that orginally water drained down the valley to Lake Fryxell. But at some point in the past as temperatures warmed, the Canada Glacier flowed further into Taylor Valley and blocked this flow. Lake Hoare was then formed on the lower side of the Canada Glacier and filled with fresh water from glacial runoff.

Lake Hoare basically forms only during the warm times when the Canada Glacier advances down into the valley.

Aside from the oddity of Blood Falls itself, a better understanding of how these lakes formed and exactly when should enhance our knowledge of climate history in the region.

We know that life exists in all of these lakes and we are trying to understand how it functions and how it relates to the climate, he said. Were interested in the impact of climate change and the effect it will have on these ecosystems. So we need to understand how it was affected in the past.

Maybe Blood Falls is just another lobe of Lake Bonney that has been frozen over, or maybe it was a different lake, like Bonney, that existed when the glacier had receded further up the valley.

Lyons said the answers to such questions would only come after drilling through the glacier to sample the bedrock below. He said that it is possible that these salt deposits might underlie this entire arm of the Taylor Glacier. If that were true, it would explain one of the glaciers strange behaviors.

Most Antarctic glaciers are frozen to the rock below but Taylor apparently isnt, Lyons said. That could be because there are salt deposits underneath it which would lower the freezing point of the ice and better lubricate the flow of the glacier. That probably allows this glacier to move in very different ways compared to others.

Along with Lyons, Kathleen Welch research scientist at the Byrd Center, Diane McKnight from the University of Colorado and John Priscu from Montana State University all contributed to this study. This work was supported in part by the Division of Polar Programs within the National Science Foundation and by the Byrd Polar Research Center.

Berry Lyons | Ohio State University
Further information:
http://www.osu.edu

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