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南極沿岸ポリニヤでの海氷生成と底層水形成
大島, 慶一郎
Permalink : http://hdl.handle.net/2115/70322
JaLCDOI : 10.14943/lowtemsci.76.13
KEYWORDS : 沿岸ポリニヤ;南極底層水;海氷生産;マイクロ波放射計;ケープダンレーポリニヤ;coastal polynya;Antarctic Bottom Water;sea-ice production;microwave radiometer;Cape Darnley Polynya
Abstract
世界の海洋の深層まで及ぶ最も大きな循環は，重い水が沈み込みそれが徐々に湧き上がってくる，という密度差による循環である．沿岸ポリニヤでの大量の海氷生成が重い水のソースになっている．衛星マイクロ波放射計データ等による海氷生産量マッピングからは，南極沿岸ポリニヤでは，非常に高い海氷生産があることが示され，世界の深層に広がる南極底層水がここを起源として形成されることと整合する．南大洋ではロス棚氷ポリニヤが最大の海氷生産を持つ．第2 位の海氷生産量を持つのがケープダンレーポリニヤであることがわかり，日本の観測からここが第4（未知）の南極底層水生成域であることが発見された．第3 の南極底層水生成域であるメルツ氷河沖では，2000 年初頭の氷河崩壊後に海氷生産量が40％も減少し，その結果として，ここでの底層水生成も激減した．
Global overturning circulation is driven by density differences. Saline water rejected by sea-ice production in coastal polynyas is the main source of dense water, and thus sea-ice production is a key factor in the overturning circulation. The mapping of sea-ice production derived from satellite microwave radiometer data demonstrates that ice production rate is high in Antarctic coastal polynyas, in contrast to Arctic coastal polynyas. This is consistent with the formation of Antarctic Bottom Water (AABW), the densest water mass which occupies the abyssal layer of the global ocean. The Ross Ice Shelf polynya has by far the highest ice production in the Southern Hemisphere. The Cape Darnley polynya is found to be the second highest production area, leading to the discovery of the missing (fourth) source of AABW in this region. In the region off the Mertz Glacier Tongue, the third source of AABW, sea-ice production in the Mertz polynya decreased by as much as 40 %, due to the glacier calving in early 2010, resulting in a significant decrease in AABW production.
Global overturning circulation is driven by density differences. Saline water rejected by sea-ice production in coastal polynyas is the main source of dense water, and thus sea-ice production is a key factor in the overturning circulation. The mapping of sea-ice production derived from satellite microwave radiometer data demonstrates that ice production rate is high in Antarctic coastal polynyas, in contrast to Arctic coastal polynyas. This is consistent with the formation of Antarctic Bottom Water (AABW), the densest water mass which occupies the abyssal layer of the global ocean. The Ross Ice Shelf polynya has by far the highest ice production in the Southern Hemisphere. The Cape Darnley polynya is found to be the second highest production area, leading to the discovery of the missing (fourth) source of AABW in this region. In the region off the Mertz Glacier Tongue, the third source of AABW, sea-ice production in the Mertz polynya decreased by as much as 40 %, due to the glacier calving in early 2010, resulting in a significant decrease in AABW production.
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