臺灣北部中全新世古環境研究：麟山鼻珊瑚骨骼岩芯的穩定碳氧同位素組成及Sr/Ca比值紀錄
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2023
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本研究分析採自新北市麟山鼻附近的珊瑚岩芯（約6100-4100年前但非連續紀錄；U-Th 及AMS 14C定年）的穩定碳、氧同位素成分及珊瑚Sr、Ca的元素含量，重建臺灣北部地區的古環境。珊瑚岩芯自頂部往下可分為A、B（均為Porites）、C及D（均為Cyphastrea）四段，本研究沿著標本X光相片辨識出的最大生長軸方向鑽取碳酸鈣粉末標本，共完成245個穩定氧碳同位素成分及245個Sr/Ca比值分析。穩定氧同位素成分數值介於-5.4‰和1.8‰之間，穩定碳同位素成分數值介於-2.8‰ 和 3.5‰之間。A、B、C、D段的氧同位素平均值分別為-4.2 ± 0.5‰（1σ；N = 74）、-4.4 ± 0.5‰（N = 56）、-2.6 ± 0.3‰（N = 31）及-4.2 ± 0.6‰（N = 84）。整體而言，C段（約5.2ka年前）的氧同位素數值比A、B及D段的氧同位素數值大， C段的碳同位素數值（0.5‰ - 3.5‰）比A、B及D段的碳同位素數值（-2.8‰ - 1.3‰）大，而C段的Sr/Ca比值（10.2 至 10.9 mmol/mol）也比A、B及D段的Sr/Ca比值（8.8 至 10.5 mmol/mol）大。C段Sr/Ca比值海表溫度（0.9oC- 9.2oC）比A、B及D段Sr/Ca比值海表溫度（5.3oC - 27.4oC）為低，與中央氣象局2007-2022麟山鼻海表溫資料比較，臺灣北部於6.1-4.1ka 年前的海表溫整體而言較現今為低。根據穩定氧同位素數值及Sr/Ca比值海表溫度數據估算，臺灣北部6.1-4.1ka 年前的海水氧同位素數值介於-1.2‰ 和 1.5‰（SMOW；0±0.5‰, N=245）之間，以現代開放大洋的0‰為參考基準且6.1-4.1ka 年前至今的全球冰川體積的變化可略，低於0‰的區間代表較強降水的環境（約6.0ka及4.2ka年前），反之，高於0‰的區間代表較弱降水及強蒸發的環境（約6.1ka及5.2ka年前）。約5.2ka年前C段珊瑚岩芯所紀錄的低溫及蒸發作用較強的古環境紀錄亦見於東亞地區的洞穴石灰岩紀錄，伴隨高碳同位素數值，或許當時於臺灣北部有較強的湧昇流，導致較低溫及高基礎生產力的環境。
To reconstruct the middle Holocene paleoenvironment in northern Taiwan, stable oxygen and carbon isotope compositions, as well as Sr/Ca ratios of four discontinuous segments derived from the LSC coral core collected from Linshan Cape (New Taipei City), were studied. The order from youngest to oldest segment is as follows: A, B, C, and D. The U-Th and AMS 14C dating results indicate that the age range is from 6.1ka to 4.1ka BP. A total of 245 carbonate powder subsamples were drilled along the maximum growth axis for analyzing the stable isotope compositions and trace element components.d18Oc and d13Cc values of four segments varied from -5.4‰ to 1.8‰ and from -2.8‰ to 3.5‰, respectively. Generally, d18Oc values of segment C (-3.0‰ to -1.8‰, average±1σ, N=31) are greater than those of three segments A, B, and D (-5.4‰ to -2.1‰, N=214). d13Cc values of segment C (0.5‰ to 3.5‰) fluctuated at a higher range than those of the other segments (-2.8‰ to 1.3‰) as well. The scope of Sr/Ca ratios of segment C (10.2 to 10.9 mmol/mol) is also higher than those of segments A, B, and D (8.8 to 10.5 mmol/mol).The Sr/Ca-SST values of segment C (0.9oC to 9.2oC, N=31) are lower than those of the other segments (5.3oC to 27.4oC, N=214). Compared to the 2007-2022 modern SST statistic at Linshan Cape Station, the Sr/Ca-SST records of the 6.1-4.1ka BP period are generally cooler than that of the present. The estimated seawater d18O values varied from -1.2‰ and 1.5‰ (0±0.5‰, N=245) in the 6.1-4.1ka BP period. Two periods of strong summer monsoon and two periods of weak summer monsoon with drier conditions have been identified by the seawater d18O records in northern Taiwan. The transition of seawater d18O values from segment C to segment B was possibly influenced by the sea level changes at 5.2ka BP. The d13Cc values of LSC coral skeletons were typically influenced by the d13C dissolved inorganic carbonate (d13CDIC) variations and primary productivity in northern Taiwan.The low temperature and dry conditions at 5.2ka BP have been globally observed, especially in many regions of China. A simultaneous increment of d18Oc values and Sr/Ca ratios of segment C possibly recorded an intense cooling in Linshan Cape during this time period. Additionally, the seawater d18O values of segment C indicated aridity. Thus, segment C was able to document the 5.2ka BP climate event. The significant differences in d13Cc values and Sr/Ca ratios of segment C compared to those of the others also suggested an occurrence of upwelling in Linshan Cape.
To reconstruct the middle Holocene paleoenvironment in northern Taiwan, stable oxygen and carbon isotope compositions, as well as Sr/Ca ratios of four discontinuous segments derived from the LSC coral core collected from Linshan Cape (New Taipei City), were studied. The order from youngest to oldest segment is as follows: A, B, C, and D. The U-Th and AMS 14C dating results indicate that the age range is from 6.1ka to 4.1ka BP. A total of 245 carbonate powder subsamples were drilled along the maximum growth axis for analyzing the stable isotope compositions and trace element components.d18Oc and d13Cc values of four segments varied from -5.4‰ to 1.8‰ and from -2.8‰ to 3.5‰, respectively. Generally, d18Oc values of segment C (-3.0‰ to -1.8‰, average±1σ, N=31) are greater than those of three segments A, B, and D (-5.4‰ to -2.1‰, N=214). d13Cc values of segment C (0.5‰ to 3.5‰) fluctuated at a higher range than those of the other segments (-2.8‰ to 1.3‰) as well. The scope of Sr/Ca ratios of segment C (10.2 to 10.9 mmol/mol) is also higher than those of segments A, B, and D (8.8 to 10.5 mmol/mol).The Sr/Ca-SST values of segment C (0.9oC to 9.2oC, N=31) are lower than those of the other segments (5.3oC to 27.4oC, N=214). Compared to the 2007-2022 modern SST statistic at Linshan Cape Station, the Sr/Ca-SST records of the 6.1-4.1ka BP period are generally cooler than that of the present. The estimated seawater d18O values varied from -1.2‰ and 1.5‰ (0±0.5‰, N=245) in the 6.1-4.1ka BP period. Two periods of strong summer monsoon and two periods of weak summer monsoon with drier conditions have been identified by the seawater d18O records in northern Taiwan. The transition of seawater d18O values from segment C to segment B was possibly influenced by the sea level changes at 5.2ka BP. The d13Cc values of LSC coral skeletons were typically influenced by the d13C dissolved inorganic carbonate (d13CDIC) variations and primary productivity in northern Taiwan.The low temperature and dry conditions at 5.2ka BP have been globally observed, especially in many regions of China. A simultaneous increment of d18Oc values and Sr/Ca ratios of segment C possibly recorded an intense cooling in Linshan Cape during this time period. Additionally, the seawater d18O values of segment C indicated aridity. Thus, segment C was able to document the 5.2ka BP climate event. The significant differences in d13Cc values and Sr/Ca ratios of segment C compared to those of the others also suggested an occurrence of upwelling in Linshan Cape.
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古環境, 珊瑚骨骼, 穩定碳氧同位素, Sr/Ca比值, 臺灣北部, Paleoenvironment, Coral skeletons, Stable oxygen and carbon isotope, Sr/Ca ratios, Northern Taiwan