鑑古知今：以雨水及鐘乳石氧同位素數值重建東南亞季風變化
From the past to the future: Reconciling rain-water and speleothem δ18O to reconstruct the southeast Asian monsoon
計畫主持人：臺大地質系-施路易、中研院地球所-梁茂昌
The results from the project period 2021-2022 can be divided into two parts. Our first result concerns the collection and analysis of rainwater isotopes in precipitation collected at Krabi Airport in southern Thailand. In collaboration with researchers and airport personnel we have now collected a unique record of daily resolved isotopic data. In short, our data demonstrate that oxygen and hydrogen isotope variations on a daily basis are controlled by variations in local convection. More interestingly, however, is that we can show that isotopic variations are closely tied to a third monsoon phase, the fall monsoon. This suggests that paleorecords from speleothems or compound specific isotopes in leaf waxes should be interpreted primarily as a shift in the relative strength of the fall monsoon, rather than in precipitation amount, as previously thought.
The second part of our project has focused on how variations in rain amount and isotopic composition are reflected in speleothems in caves from the Phang Nga and Krabi provinces in southwestern Thailand. We now have automatic samplers installed both outside and inside the caves (Figure 1) and the first water samples have been analyzed at Academia Sinica. Unfortunately, this part of the project has suffered serious delays because of covid-19 restrictions and because of machine failure. However, we now have established an efficient collaboration with local collaborators and expect routine analysis and interpretations to start during spring and summer 2023.
本計畫於2021年至2022年間之研究成果可分為兩部分。
第一部分的研究成果為在泰國南部喀比機場所收集的降水樣本中雨水同位素的分析。透過研究學者與機場工作人員的合作，我們獲得了每日降雨的雨水同位素資料。簡而言之，分析後的數據表示：每日的氫氧同位素變化是由局部對流變化所控制的。而更有趣的是，同位素變化更與第三季風階段，即秋季季風有密切相關。這樣研究顯示來自喀斯特地形之鐘乳石以及葉臘中的古紀錄，所指示的應該是秋季季風相對強度的變化，而非先前所認為的降水量變化。
第二部分著重於降雨量及同位素組成於石灰岩洞穴中的變化，研究地點為泰國西南部攀牙及喀比地區之石灰岩洞穴。目前已將自動水樣採樣器安裝於研究地點的洞穴內外用以對比（如圖一所示），所採集之第一批水樣已送至中央研究院進行分析。不幸的是，受到新冠肺炎疫情及採樣器故障之影響，此部分的研究進度有嚴重延誤。然而，我們目前已經與當地合作者建立了高效率的合作關係，預計將於2023年春季及夏季開始有穩定的分析及結果產出。
Figure 1. Automatic water samplers installed in Tham Murd in northern Krabi Province.
圖一：設置於泰國喀比區域北部Tham Murd洞穴中的自動水樣採集器。