南米チリ・北パタゴニア氷原の溢流氷河の1944/45-2004/05の変動とその要因

Abstract

北氷原に分布する21の溢流氷河の1944/45-2004/05年の60年間の変動を, 各種のリモート・センシング・データを使って明らかにした. それによると過去60年間は全般的に後退傾向にあり, 面積約101km[2]が減少した. 氷原の西側(偏西風帯の風上側)に分布する氷河の平均後退量は約8.1km[2]で東側に分布する氷河の4倍強である. 氷原最大の氷河サン・キンテイン氷河の後退量は約29km[2]で突出して大きく, 全体の1/3弱に当たる. 距離ではレイチェル氷河の約6kmが最大である. 21の溢流氷河のうち17がカーピング氷河で, いくつかの氷河では氷河前縁湖での末端崩壊による短期間の大規模な後退が起きている. 一方, 60年間でほとんど変動していない氷河が氷原の東側(偏西風帯の風下側)に見られる. このような大規模な後退は一般に地球温暖化による気温の上昇の結果と考えられるが, サン・ラファエル氷河で見られた停滞/前進/後退・前進という変動はフィヨルドの地形の影響(主に幅, 深さも一部関係?)と解釈される.

Variations of 21 outlet glaciers of Hielo Patag6nico Norte (HPN: northern Patagonia Icefield), Chile, were elucidated for a period 1944/45-2004/05, using various sources of remote sensing data. Over the last 60 years, the icefield lost an area of ca. 101km[2] . Those glaciers that are located on the west side of the icefield (windward side of the Westerlies) have retreated with an average of 8.1km[2] per glacier, which is more than four times larger than that of those located on the east side (leeward). The largest glacier of the HPN, Glaciar San Quintin lost an area of ca. 29 km[2], which is by far the largest and close to a third of the total. In terms of the distance, Glacier Reicher retreated most with ca. 6 km. Of the 21 monitored glaciers, 17 are currently calving glaciers, some of which retreated extensively in a short period of time due to snout disintegration in the pro glacial lake. On the other hand, on the east side of the icefield, there are some glaciers that have varied very little. The general trend of the retreat over the past 60 years is considered to be the result of response to temperature rising due to global warming. However, there is another factor such as fjord topography (primary width; secondary, depth), with which to account for a unique variation (stagnation/advance/retreat) of Glaciar San Rafael since the 1990s.