一萬六千五百年來東帝汶降雨變遷

Abstract

本研究利用取自東帝汶猴洞(南緯八度四十七分十點八秒，東經一百二十六度二十三分三十一點一秒，海拔六百二十六公尺)之三株石筍，重建並分析16.5千年前(ka, before 1950AD)以來之區域古水文變遷(於11.5至5.7千年具年代間斷)。具重現性之東帝汶石筍之穩定氧同位素(δ18O)時間序列顯示，相對於中晚全新世，該區域之氣候於末次冰期處於相對乾燥之狀況。本紀錄於新仙女木期(Younger Dryas, YD)時間段之石筍18O相對匱乏，顯示該時期為相對潮濕、高降雨之氣候狀況，與鄰近區域前人研究結果一致(Liang Luar cave, Flores)，並與典型亞洲季風(Asian Monsoon, AM)區域古氣候紀錄於該時期所呈現之相對乾燥、低降雨狀況，呈反向對應。本紀錄中，16千年至12千年間之千年尺度氣候事件波動並不似典型亞洲季風區所顯示之明顯與強烈，Bolling-Allerod (B-A)暖期亦未有明顯暖化跡象，猜測可能原因為:(一)，印澳夏季季風(Australian-Indonesian summer monsoon, AISM)之增強;(二)，間熱帶輻合區(Intertropical Convergence Zone, ITCZ)之位移;以及/或(三)，巽他陸棚(Sunda Shelf)出露所導致之區域水氣循環變遷。

Here we present replicated stalagmite analysis δ18O records over the past 16.5 thousand years (ka, before 1950 AD) with a gap of 11.5-5.7 ka of three stalagmites from Lekiraka cave in East Timor (8o47’10.8”S, 126o23’31.1”E; 626 m above sea level). Lekiraka δ18O record suggests a relatively dry condition during the glacial period, comparing with the late Holocene. Depletion in 18O during Younger Dryas (YD) stadial suggests a wet condition with high precipitation, which is consistent with that of Liang Luar cave record in Flores, but in contrary to a dry condition in the Asian monsoon (AM) territory. Insignificant δ18O change during 16-12 ka indicates that a wet Bolling-Allerod (BA) interstadial in AM territory is not clear at this low-latitude zone. We propose that the intensified precipitation in YD and “muted” BA could be attributed to: (1) enhanced Australian-Indonesian summer monsoon (AISM), (2) displacement of Intertropical Convergence Zone (ITCZ), and/or (3) exposed Sunda shelf landmass lead to change of the regional atmospheric circulation.