洞穴沈積物指示58萬至44萬年以來北地中海氣候紀錄

Speleothem-inferred paleoclimate records in northern Mediterranean from 580-440 thousand years ago

簡瑋頤(Wei-Yi Chien)

指導教授 ： 沈川洲

國立臺灣大學/理學院/地質科學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202100188

摘要

在海洋同位素階(MIS) 14-13，也就是距今約五十六至四十八萬年前，地球氣候處於相當弱的冰期與間冰期循環，過去研究指出北半球此時期異常的溫暖，為了更深入地了解地中海地區在此時期的水文變化以及機制，需要完善的代用指標紀錄以及好的定年控制。本研究利用北義大利Basura cave的洞穴沈積物岩心為材料，於過去五十八至四十四萬年以來，進行高解析度的鈾釷定年以及碳氧同位素分析。鎂鈣比與鍶鈣比的測量也同時用於支持同位素的數據。結果顯示氧同位素介於-8.4至-2.8‰之間，同時受到來源效應與雨量效應的影響，並不能直接反應水文氣候狀況。碳同位素與微量元素有一定的相關性，反映了生物活動力與植被的覆蓋率，也間接表示西風的變化。對於降雨敏感的碳同位素在第六個冰期終止期 (T-VI)，也就是MIS 14-13的轉換僅只有1.5‰的變化，但在下一個冰期終止期，T-V，卻有約6‰幅度的變化；顯示應屬於冰期的MIS 14是個較濕暖的時期。這表示了MIS 14到MIS 13氣候相對穩定，且地中海在MIS 14處於相對濕潤時期。這個現象可能是受到強烈的大西洋經向反轉環流所影響，以及大西洋上高低緯度接收到的熱量差變化不大的因素，使得整個時期西風偏南吹拂，為地中海地區帶來降水。本研究提出海洋循環在相當溫暖的時期，對於西風的變化以及地中海地區水文氣候有著重要的影響。

關鍵字

海洋同位素階14-13 ； 洞穴沈積物 ； 地中海 ； 西風

並列摘要

Marine isotope stages 14 to 13 (MIS 14-13) from 562 to 478 thousand years ago (ka, before 1950 AD) were characterized by a weak glacial-interglacial cycle. To in-depth understand the hydroclimate dynamics and forcings in the Mediterranean realm, detailed proxy records with good chronology are required. We present carbon and oxygen isotope records of 230Th-dated flowstone cores from 580 to 440 ka in Basura cave, northern Italy. Mg/Ca and Sr/Ca time series were also determined as supportive data. The flowstone δ18O records, ranging from -8.4 to -2.8‰, were controlled by both source and amount effects, which couldn’t directly reflect the hydroclimate conditions. Flowstone δ13C data match with trace element records, reflecting the extent of precipitation-triggered bio-activity and vegetation coverage, governed by westerly variabilities. The precipitation-sensitive δ13C record shows a small change of only 1.5‰ from MIS 14 to 13, glacial termination VI (T-VI). It instead reveals a large shift of 6‰ in the following glacial termination, T-V. The phenomenon suggests a stable climate through MIS 14 to 13 and a humid condition in Mediterranean region in MIS 14. The observation could be attributed to strong Atlantic meridional ocean circulation and the associated small contrast of latitudinal heat differences. The results emphasize the important oceanic forcing on glacial Mediterranean hydroclimate.

並列關鍵字

MIS 14-13 ； speleothem ； Mediterranean ； the westerlies

參考文獻

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