“McMurdo Dry Valleys”的意思、由来-开放百科全书

The McMurdo Dry Valleys are a row of largely snow-free valleys in Antarctica, located within Victoria Land west of McMurdo Sound.^[1] The Dry Valleys experience extremely low humidity and surrounding mountains prevent the flow of ice from nearby glaciers. The rocks here are granites and gneisses, and glacial tills dot this bedrock landscape, with loose gravel covering the ground.

The region is one of the world's most extreme deserts, and includes many features including Lake Vida, a saline lake, and the Onyx River, a meltwater stream and Antarctica's longest river. Although no living organisms have been found in the permafrost here, endolithic photosynthetic bacteria have been found living in the relatively moist interior of rocks and anaerobic bacteria, with a metabolism based on iron and sulfur, live under the Taylor Glacier.

Climate

The Dry Valleys are so named because of their extremely low humidity and their lack of snow or ice cover. They are also dry because, in this location, the mountains are sufficiently high that they block seaward flowing ice from the East Antarctic ice sheet from reaching the Ross Sea. At {{convert|4800|km2|mi2}}, the valleys constitute around 0.03% of the continent, and form the largest ice-free region in Antarctica. The valley floors are covered with loose gravel, in which ice wedge polygonal patterned ground may be observed.^[2]

The unique conditions in the Dry Valleys are caused, in part, by katabatic winds; these occur when cold, dense air is pulled downhill by the force of gravity. The winds can reach speeds of {{convert|320|km/h|mi/h}}, heating as they descend, and evaporating all water, ice and snow.^[3]

Geology

The valleys cut through the Beacon Supergroup, as well as older granites and gneisses of the Ross Orogeny. Deposited directly from ice, tills dot this bedrock landscape. These are relatively thin and patchy, and differ markedly from the extensive, mud-rich tills of the Laurentide ice sheet in the Northern Hemisphere. One reason for the difference is that most of the tills in the Dry Valleys were deposited from cold-based ice (ice with basal temperatures below {{convert|0|C|F}}), whereas the Laurentide ice sheet was largely wet-based, with significant melting at the base and at the glacier surface.

Life

Endolithic photosynthetic bacteria have been found living in the Dry Valleys, sheltered from the dry air in the relatively moist interior of rocks. Summer meltwater from the glaciers provides the primary source of soil nutrients.^[4] Scientists consider the Dry Valleys perhaps the closest of any terrestrial environment to the planet Mars, and thus an important source of insights into possible extraterrestrial life.

Canadian and American researchers conducted a field expedition in 2013 to University Valley in order to examine the microbial population and to test a drill designed for sampling on Mars in the permafrost of the driest parts of the valleys, the areas most analogous to the Martian surface. They found no living organisms in the permafrost, the first location on the planet visited by humans with no active microbial life.^[7]

Major geographic features

Valleys

Further south, between Royal Society Range in the west and the west coast of McMurdo Sound at the lobe of Koettlitz Glacier are, from north to south:

Glaciers

Lakes

Some of the lakes of the Dry Valleys rank among the world's most saline lakes, with a higher salinity than Lake Assal (Djibouti) or the Dead Sea. The most saline of all is small Don Juan Pond.

Rivers

Further reading

References

1. ^{{cite news |last=Rejcek |first=Peter |title=In the cold of the night |work=The Antarctic Sun |date=29 November 2007 |url=http://antarcticsun.usap.gov/science/contenthandler.cfm?id=1283 |accessdate=2008-01-13}}
2. ^{{cite journal |last=Bockheim |first=J. G. |title=Landform and Soil Development in the McMurdo Dry Valleys, Antarctica: A Regional Synthesis |journal=Arctic, Antarctic, and Alpine Research |volume=34 |issue= 3 |pages=308–317 |date=2002 |url=http://instaar.colorado.edu/AAAR/browse_abstracts/abstract.php?id=2113 |doi=10.2307/1552489 |jstor=1552489 |subscription=yes}}
3. ^{{cite book |first=John |last=Lloyd |authorlink1=John Lloyd (writer) |first2=John |last2=Mitchinson |authorlink2=John Mitchinson (researcher) |title=The Book of General Ignorance |publisher=Faber & Faber |date=2006|title-link=The Book of General Ignorance }}
4. ^{{Cite journal|last=Barrett|first=J. E.|last2=Virginia|first2=R. A.|last3=Lyons|first3=W. B.|last4=McKnight|first4=D. M.|last5=Priscu|first5=J. C.|last6=Doran|first6=P. T.|last7=Fountain|first7=A. G.|last8=Wall|first8=D. H.|last9=Moorhead|first9=D. L.|date=2007-03-01|title=Biogeochemical stoichiometry of Antarctic Dry Valley ecosystems|journal=Journal of Geophysical Research: Biogeosciences|language=en|volume=112|issue=G1|pages=G01010|doi=10.1029/2005JG000141|issn=2156-2202}}
5. ^{{cite web |first=John |last=Timmer |url=https://arstechnica.com/science/news/2009/04/ancient-frozen-ecosystem-produces-blood-red-ice-flows.ars |title=Ancient, frozen ecosystem produces blood-red ice flows |website=Ars Technica |date=16 April 2009 |accessdate=17 April 2009}}
6. ^{{cite journal |last=Mikucki |first=Jill A. |first2=Ann |last2=Pearson |first3=David T. |last3=Johnston |first4=Alexandra V. |last4=Turchyn |first5=James |last5=Farquhar |first6=Daniel P. |last6=Schrag |first7=Ariel D. |last7=Anbar |first8=John C. |last8=Priscu |first9=Peter A. |last9=Lee |title=A Contemporary Microbially Maintained Subglacial Ferrous "Ocean{{"-}} |journal=Science |volume=324 |issue=5925 |pages=397–400 |date=17 April 2009 |url=http://www.sciencemag.org/cgi/content/abstract/324/5925/397 |doi=10.1126/science.1167350 |accessdate=2009-04-21 |pmid=19372431 |subscription=yes}}
7. ^{{cite journal |first=Jacqueline |last=Goordial |first2=Alfonso |last2=Davila |first3=Denis |last3=Lacelle |first4=Wayne |last4=Pollard |first5=Margarita M. |last5=Marinova |first6=Charles W. |last6=Greer |first7=Jocelyn |last7=DiRuggiero |first8=Christopher P. |last8=McKay |first9=Lyle G. |last9=Whyte |title=Nearing the cold-arid limits of microbial life in permafrost of an upper dry valley, Antarctica |journal=The ISME Journal |volume=10 |issue=7 |pages=1613–1624 |date=19 January 2016 |doi=10.1038/ismej.2015.239 |pmid=27323892 |pmc=4918446 }}
8. ^{{cite web |website=Antarctica New Zealand |url=http://www.antarcticanz.govt.nz/downloads/environment/Map%20A%20McMurdo%20Dry%20Valleys%20Area.pdf |title=Map of the McMurdo Dry Valleys Area |archiveurl=https://web.archive.org/web/20090327024059/http://www.antarcticanz.govt.nz/downloads/environment/Map%20A%20McMurdo%20Dry%20Valleys%20Area.pdf |archivedate=2009-03-27}}