77°28′S 162°31′E / 77.467°S 162.517°E / -77.467; 162.517

Map of the McMurdo Sound and the Dry Valleys
Location of valleys (indicated by red dot) within the Ross Dependency
Map showing the delineation of the McMurdo Valleys Antarctic Specially Managed Area (ASMA-2)

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. It is one of the driest places on Earth and is sometimes claimed to have not seen rain in nearly two million years,[2] though this is highly unlikely and several anecdotal accounts of rainfall within the Dry Valleys exist.[3][4]

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.

The valleys are located within the McMurdo Valleys Antarctic Specially Managed Area (ASMA-2).[5]

Climate

McMurdo Dry Valleys, Landsat 7 imagery acquired on December 18, 1999.

The Dry Valleys are so named because of their extremely low humidity and 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 4,800 square kilometres (1,900 sq mi), 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.[6]

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 320 km/h (200 mph), heating as they descend and evaporating all water, ice and snow.[7] The dry wind evaporates the snow rapidly and little melts into the soil. During the summer, this process can take only hours.

Another important factor is a lack of precipitation. Precipitation averages around 100 millimetres (4 in) per year over a century of records, almost[3][4] exclusively in the form of snow. This contributes to the low humidity of the area.[8]

For several weeks in the summer, the temperature increases enough to allow for glacial melt, which causes small freshwater streams to form.[9] These streams feed the lakes at the base of the valleys, which do not have outflow to the sea, causing them to become highly saline.

Geology

ASTER image of the Dry Valleys.

The McMurdo Oasis constitutes approximately 4,000 square kilometres (1,500 sq mi) of "deglaciated mountainous desert", according to McKelvey, bounded by the coastline of south Victoria Land and the Polar Plateau. The Taylor and Wright Valleys are major ice-free valleys within the Transantarctic Mountains. These "dry valleys" include hummocky moraines, with frozen lakes, saline ponds, sand dunes, and meltwater streams. Basement rocks include the Late Precambrian or Early Palaeozoic Skelton Group metamorphic rocks, primarily the Asgard Formation, which is a medium-high-grade marble and calc schist. The Palaeozoic Granite Harbour intrusives include granitoid plutons and dykes, which intruded into the metasedimentary Skelton Group in the Late Cambrian-Early Ordovician during the Ross orogeny. The basement complex is overlain by the Jurassic Beacon Supergroup, which is itself intruded by Ferrar Dolerite sheets and sills. The McMurdo Volcanic Group intrudes, or is interbedded with, the Taylor and Wright Valleys' moraines as basaltic cinder cones and lava flows. These basalts have ages between 2.1 and 4.4 Ma. The Dry Valley Drilling Project (1971–75) determined the Pleistocene layer within the Taylor Valley was between 137 and 275 m thick, and composed of interbedded sandstones, pebble conglomerates, and laminated silty mudstones. This Pleistocene layer disconformably overlies Pliocene and Miocene diamictites.[10][11]

Life

Mummified seal carcass

Endolithic 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.[12] 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.

Anaerobic bacteria whose metabolism is based on iron and sulfur live in sub-freezing temperatures under the Taylor Glacier.

It was previously thought that algae were staining the red ice emerging at Blood Falls but it is now known that the staining is caused by high levels of iron oxide.[13][14]

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.[15]

In 2014, drones were used in the McMurdo Dry Valleys by a team of scientists from Auckland University of Technology (AUT) to create baseline maps of the vegetation. In 2015, the New Zealand Antarctic Research Institute granted funding to AUT to develop methods for operating unmanned aerial vehicles. Over successive summer seasons in Antarctica, the AUT team created three dimensional maps with sub-centimeter resolution, which are now used as baselines.[16]

Part of the Valleys was designated an environmentally protected area in 2004.

Field camp of scientists during the Antarctic summer, c. 1965

Major geographic features

Valleys

From north to south, the three main valleys are

West of Victoria Valley are, from north to south,

Stretching south from Balham Valley are, from west to east:

West of Taylor Valley is

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

Wright Valley

Taylor Valley

Lakes

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

Former lakes

Rivers

Other

See also

Further reading

  • Fountain, Andrew G.; Lyons, W. Berry; Burkins, Melody B.; Dana, Gayle L.; Doran, Peter T.; Lewis, Karen J.; McKnight, Diane M.; Moorhead, Daryl L.; Parsons, Andrew N.; Priscu, John C.; Wall, Diana H.; Wharton, Robert A.; Virginia, Ross A. (1999). "Physical Controls on the Taylor Valley Ecosystem, Antarctica". BioScience. 49 (12): 961–971. doi:10.2307/1313730. JSTOR 1313730.
  • Highfield, Roger (4 August 2008). "Lost world frozen 14m years ago found in Antarctica". The Telegraph.
  • Hoffman, Matthew J.; Fountain, Andrew G.; Liston, Glen E. (2017). "Near-surface internal melting: a substantial mass loss on Antarctic Dry Valley glaciers" (PDF). Journal of Glaciology. 60 (220): 361–374. doi:10.3189/2014JoG13J095.
  • Meekins, Jeannie (2013). Robinson, Jennifer (ed.). The Bleeding Glacier of Antarctica: A Strange But True Tale. Learning Island.

References

  1. ↑ Rejcek, Peter (29 November 2007). "In the cold of the night". The Antarctic Sun. Retrieved 2008-01-13.
  2. ↑ Cain, Fraser (2008-06-12). "What is the Driest Place on Earth?". Universe Today. Retrieved 2021-04-12.
  3. 1 2 Keys, Harry (J.R.) (September 1980). "5.5 Precipitation—Other forms of precipitation". Air temperature, wind, precipitation and atmospheric humidity in the McMurdo Region, Antarctica (PDF). Antarctic Data Series. Vol. 9. Additional credits on p. 51. Victoria University of Wellington, Department of Geology. p. 41. Archived (PDF) from the original on 8 March 2022. Retrieved 31 December 2023.
  4. 1 2 Obryk, M. K.; Doran, P. T.; Fountain, A. G.; Myers, M.; McKay, C. P. (16 July 2020). "Climate From the McMurdo Dry Valleys, Antarctica, 1986–2017: Surface Air Temperature Trends and Redefined Summer Season". Journal of Geophysical Research: Atmospheres. 125 (13): 1. Bibcode:2020JGRD..12532180O. doi:10.1029/2019JD032180. ISSN 2169-897X. S2CID 219738421.
  5. ↑ "ASMA 2: Mcmurdo Dry Valleys, Southern Victoria Land". Secretariat of the Antarctic Treaty. Archived from the original on 2013-08-14.
  6. ↑ Bockheim, J. G. (2002). "Landform and Soil Development in the McMurdo Dry Valleys, Antarctica: A Regional Synthesis". Arctic, Antarctic, and Alpine Research. 34 (3): 308–317. doi:10.2307/1552489. JSTOR 1552489.
  7. ↑ Lloyd, John; Mitchinson, John (2006). The Book of General Ignorance. Faber & Faber.
  8. ↑ Hund, Andrew J. (2014). Antarctica and the Arctic Circle: A Geographic Encyclopedia of the Earth's Polar Regions. ABC-CLIO. p. 74. ISBN 9781610693936. Retrieved 24 April 2019.
  9. ↑ "NASA: McMurdo Dry Valleys". NASA Earth Observatory. NASA. 26 January 2002. Retrieved 29 March 2022.
  10. ↑ McKelvey, B.C. (1991). Tingey, Robert (ed.). The Cainozoic glacial record in south Victoria Land: a geological evaluation of the McMurdo Sound drilling projects, in The Geology of Antarctica. Oxford: Clarendon Press. pp. 434–454. ISBN 0198544677.
  11. ↑ Adams, C.J.; Whitla, P.F. (1991). Thomson, M.R.A.; Crame, J.A.; Thomson, J.W. (eds.). Precambrian ancestry of the Asgard Formation (Skelton Group): Rb-Sr age of basement metamorphic rocks in the Dry Valley region, Antarctica, in Geological Evolution of Antarctica. Cambridge: Cambridge University Press. pp. 129–135. ISBN 9780521372664.
  12. ↑ Barrett, J. E.; Virginia, R. A.; Lyons, W. B.; McKnight, D. M.; Priscu, J. C.; Doran, P. T.; Fountain, A. G.; Wall, D. H.; Moorhead, D. L. (2007-03-01). "Biogeochemical stoichiometry of Antarctic Dry Valley ecosystems". Journal of Geophysical Research: Biogeosciences. 112 (G1): G01010. Bibcode:2007JGRG..112.1010B. doi:10.1029/2005JG000141. ISSN 2156-2202.
  13. ↑ Timmer, John (16 April 2009). "Ancient, frozen ecosystem produces blood-red ice flows". Ars Technica. Retrieved 17 April 2009.
  14. ↑ Mikucki, Jill A.; Pearson, Ann; Johnston, David T.; Turchyn, Alexandra V.; Farquhar, James; Schrag, Daniel P.; Anbar, Ariel D.; Priscu, John C.; Lee, Peter A. (17 April 2009). "A Contemporary Microbially Maintained Subglacial Ferrous "Ocean"". Science. 324 (5925): 397–400. Bibcode:2009Sci...324..397M. doi:10.1126/science.1167350. PMID 19372431. S2CID 44802632.
  15. ↑ Goordial, Jacqueline; Davila, Alfonso; Lacelle, Denis; Pollard, Wayne; Marinova, Margarita M.; Greer, Charles W.; DiRuggiero, Jocelyn; McKay, Christopher P.; Whyte, Lyle G. (19 January 2016). "Nearing the cold-arid limits of microbial life in permafrost of an upper dry valley, Antarctica". The ISME Journal. 10 (7): 1613–1624. doi:10.1038/ismej.2015.239. PMC 4918446. PMID 27323892.
  16. ↑ "Mapping biodiversity in a changing Antarctica". Antarctic Magazine, NZ Antarctic Society. 37: 20–21. 2019. ISSN 0003-5327.
  17. ↑ "Map A: Map of the McMurdo Dry Valleys Area" (PDF) (Map). Antarctica New Zealand. Archived from the original (PDF) on 2009-03-27.
Wikimedia Commons has media related to McMurdo Dry Valleys.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.