冰下湖

冰下湖（英語：Subglacial lake）是在冰川下的湖泊，位於冰帽或冰蓋下方，冰和底層基岩之間的邊界中。在此處由於壓力的增加而降低了冰的壓力熔點^[1]^[2]。當上面的冰逐漸以每年幾毫米的速度融化時。融水會從高水壓區域流向低水壓區域，而形成液態水體，這些液態水體可與外部環境隔離數百萬年^[3]。

冰下湖首次在南極冰蓋下發現的，目前已在南極冰蓋、格陵蘭冰原下方和冰島瓦特納冰原下發現了400多個冰下湖泊。冰下湖所含的液態淡水，約佔地球上所有液態淡水的 15%。僅南極冰蓋的冰下湖的面積估計約為10,000平方公里^[4] ^[5]^[6] ^[7]。

冰下湖的生態系統是與地球大氣隔絕的，受到冰、水、沉積物和生物之間相互作用的影響。嗜極生物的微生物群落在此處很活躍，這些微生物適應寒冷及低營養條件。其生物化學循環亦不依靠太陽能量，對天體生物學和尋找外星生命領域的研究，具特別價值^[8]^[9]。

物理特性

由於地熱平衡了冰表面的熱量損失，所以冰下湖中的水能保持液態。上覆冰川的壓力導致水的熔點低於0°C。冰下湖的上限將位於水的壓力熔點與溫度梯度相交的水平處。因此在南極最大的冰下湖沃斯托克湖中，其湖上的冰比周圍的冰蓋厚得多。含高鹽的冰下湖，也因其含鹽量高，而保持液態^[4]。

並非所有常年被冰覆蓋的湖泊都可以稱為冰下湖，因為有些湖泊是被普通湖冰覆蓋，例如麥克默多干谷的邦尼湖和霍爾湖。

靜壓密封

冰下湖中的水位可能遠高於地面。理論上，冰下湖甚至可以存在於山頂，只要其上的冰足夠薄以形成所需的靜水密封。浮動水位可以被認為是穿過冰進入湖中的鑽孔中的水位。它相當於在正常冰架上一塊冰漂浮的高度。當湖周圍的冰層太厚以至於等位面下降到不透水的地面時，就會形成靜水密封。然後，冰緣下方的水被靜壓密封壓回湖中。據估計，沃斯托克湖的冰緣只有7米，而浮面則高出湖面約3公里^[10]。

冰島的冰下湖泊是一個已知危害，因為火山活動可以產生足夠的融水來淹沒冰壩和湖封，並導致冰川潰決洪水^[10]。

參考文獻

[1]
Palmer, Steven J.; Dowdeswell, Julian A.; Christoffersen, Poul; Young, Duncan A.; Blankenship, Donald D.; Greenbaum, Jamin S.; Benham, Toby; Bamber, Jonathan; Siegert, Martin J. (2013-12-16). "Greenland subglacial lakes detected by radar: GREENLAND SUBGLACIAL LAKES DISCOVERED". Geophysical Research Letters. 40 (23): 6154–6159. Bibcode:2013GeoRL..40.6154P. doi:10.1002/2013GL058383. hdl:10871/30231. S2CID 55286616.
[2]
Siegert, Martin John; Kennicutt, Mahlon C. (2018-09-12). "Governance of the Exploration of Subglacial Antarctica". Frontiers in Environmental Science. 6: 103. doi:10.3389/fenvs.2018.00103. hdl:10044/1/63886. ISSN 2296-665X
[3]
Drewry, D (1983). "Antarctica: Glaciological and Geophysical Folio". University of Cambridge, Scott Polar Research Institute. 2.
[4]
Davies, Bethan. "Antarctic Glaciers". AntarcticGlaciers.org. Retrieved 2019-12-16.
[5]
Bowling, J. S.; Livingstone, S. J.; Sole, A. J.; Chu, W. (2019-06-26). "Distribution and dynamics of Greenland subglacial lakes". Nature Communications. 10 (1): 2810. Bibcode:2019NatCo..10.2810B. doi:10.1038/s41467-019-10821-w. ISSN 2041-1723. PMC 6594964. PMID 31243282.
[6]
Björnsson, Helgi (2003-02-01). "Subglacial lakes and jökulhlaups in Iceland". Global and Planetary Change. Subglacial Lakes: A Planetary Perspective. 35 (3): 255–271. Bibcode:2003GPC....35..255B. doi:10.1016/S0921-8181(02)00130-3. ISSN 0921-8181.
[7]
Dowdeswell, Julian A; Siegert, Martin J (February 2003). "The physiography of modern Antarctic subglacial lakes". Global and Planetary Change. 35 (3–4): 221–236. Bibcode:2003GPC....35..221D. doi:10.1016/S0921-8181(02)00128-5.
[8]
Petit, Jean Robert; Alekhina, Irina; Bulat, Sergey (2005), Gargaud, Muriel; Barbier, Bernard; Martin, Hervé; Reisse, Jacques (eds.), "Lake Vostok, Antarctica: Exploring a Subglacial Lake and Searching for Life in an Extreme Environment", Lectures in Astrobiology: Volume I, Advances in Astrobiology and Biogeophysics, Springer Berlin Heidelberg, pp. 227–288, Bibcode:2005leas.book..227P, doi:10.1007/10913406_8, ISBN 978-3-540-26229-9
[9]
Rampelotto, Pabulo Henrique (2010). "Resistance of Microorganisms to Extreme Environmental Conditions and Its Contribution to Astrobiology". Sustainability. 2 (6): 1602–1623. Bibcode:2010Sust....2.1602R. doi:10.3390/su2061602.
[10]
Priscu, John C.; Tulaczyk, Slawek; Studinger, Michael; Ii, Mahlon C. Kennicutt; Christner, Brent C.; Foreman, Christine M. (2008-09-11). Antarctic subglacial water: origin, evolution, and ecology. Oxford University Press. doi:10.1093/acprof:oso/9780199213887.001.0001. ISBN 978-0-19-170750-6.

[”Palmer”-1] [1]
Palmer, Steven J.; Dowdeswell, Julian A.; Christoffersen, Poul; Young, Duncan A.; Blankenship, Donald D.; Greenbaum, Jamin S.; Benham, Toby; Bamber, Jonathan; Siegert, Martin J. (2013-12-16). "Greenland subglacial lakes detected by radar: GREENLAND SUBGLACIAL LAKES DISCOVERED". Geophysical Research Letters. 40 (23): 6154–6159. Bibcode:2013GeoRL..40.6154P. doi:10.1002/2013GL058383. hdl:10871/30231. S2CID 55286616.

[”Sieger”-2] [2]
Siegert, Martin John; Kennicutt, Mahlon C. (2018-09-12). "Governance of the Exploration of Subglacial Antarctica". Frontiers in Environmental Science. 6: 103. doi:10.3389/fenvs.2018.00103. hdl:10044/1/63886. ISSN 2296-665X

[”Drewry”-3] [3]
Drewry, D (1983). "Antarctica: Glaciological and Geophysical Folio". University of Cambridge, Scott Polar Research Institute. 2.

[”Davies”-4] [4]
Davies, Bethan. "Antarctic Glaciers". AntarcticGlaciers.org. Retrieved 2019-12-16.

[Bowling”-5] [5]
Bowling, J. S.; Livingstone, S. J.; Sole, A. J.; Chu, W. (2019-06-26). "Distribution and dynamics of Greenland subglacial lakes". Nature Communications. 10 (1): 2810. Bibcode:2019NatCo..10.2810B. doi:10.1038/s41467-019-10821-w. ISSN 2041-1723. PMC 6594964. PMID 31243282.

[”Björnsson”-6] [6]
Björnsson, Helgi (2003-02-01). "Subglacial lakes and jökulhlaups in Iceland". Global and Planetary Change. Subglacial Lakes: A Planetary Perspective. 35 (3): 255–271. Bibcode:2003GPC....35..255B. doi:10.1016/S0921-8181(02)00130-3. ISSN 0921-8181.

[”Dowdeswell”-7] [7]
Dowdeswell, Julian A; Siegert, Martin J (February 2003). "The physiography of modern Antarctic subglacial lakes". Global and Planetary Change. 35 (3–4): 221–236. Bibcode:2003GPC....35..221D. doi:10.1016/S0921-8181(02)00128-5.

[”Petit”-8] [8]
Petit, Jean Robert; Alekhina, Irina; Bulat, Sergey (2005), Gargaud, Muriel; Barbier, Bernard; Martin, Hervé; Reisse, Jacques (eds.), "Lake Vostok, Antarctica: Exploring a Subglacial Lake and Searching for Life in an Extreme Environment", Lectures in Astrobiology: Volume I, Advances in Astrobiology and Biogeophysics, Springer Berlin Heidelberg, pp. 227–288, Bibcode:2005leas.book..227P, doi:10.1007/10913406_8, ISBN 978-3-540-26229-9

[”Ramp”-9] [9]
Rampelotto, Pabulo Henrique (2010). "Resistance of Microorganisms to Extreme Environmental Conditions and Its Contribution to Astrobiology". Sustainability. 2 (6): 1602–1623. Bibcode:2010Sust....2.1602R. doi:10.3390/su2061602.

[”Priscu”-10] [10]
Priscu, John C.; Tulaczyk, Slawek; Studinger, Michael; Ii, Mahlon C. Kennicutt; Christner, Brent C.; Foreman, Christine M. (2008-09-11). Antarctic subglacial water: origin, evolution, and ecology. Oxford University Press. doi:10.1093/acprof:oso/9780199213887.001.0001. ISBN 978-0-19-170750-6.

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