Terrestrial biomarker isotope records of late Quaternary climate and source-to-sink sediment transport processes in southwestern Taiwan

IF 1.9 3区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY American Journal of Science Pub Date : 2021-04-01 DOI:10.2475/04.2021.01
Q. Chang, M. Hren, A. Lin, C. Tabor, Shun Yu, Y. Eley, G. Harris
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引用次数: 2

Abstract

Fluvial sediments are important archives of paleoenvironments. However, variations in sediment production and transport processes greatly influence sediment geochemistry and resultant interpretations of ancient conditions. Tectonically-active tropical regions are particularly sensitive to climate feedbacks because these areas are often characterized by high precipitation rates, rapid erosion and short sediment residence times. We analyzed the hydrogen and carbon isotope composition of plant-derived n-alkanes (δ2Hn-alkane and δ13Cn-alkane) in sediment cores along the Gaoping River-submarine canyon system in southwestern Taiwan to examine climatic and geomorphic controls on isotope geochemical signatures of fluvial sedimentary archives. These records span the last ∼26 kyr and provide critical insight into the temporal and spatial variations in sedimentary biomarker isotopes within a source-to-sink system. Isotope data are coupled with new results from an iCESM 1.2 Earth System Model of precipitation isotopes during the last glacial-interglacial cycle. Biomarker isotope and modeling results support two important conclusions. First, biomarker isotope values change by ∼10 to 15‰ in δ2Hn-alkane and ∼1 to 2‰ δ13Cn-alkane in offshore SW Taiwan through the late Quaternary deglaciation. These shifts are consistent with iCESM predictions and other records from the South China Sea and are best explained by a shift in isotope hydrology due to regional warming and biologic responses to increased atmospheric pCO2. Second, the δ2Hn-alkane of biomarkers preserved in onshore sediments proximal to the mountain range is ∼15 to 20‰ more negative than biomarkers deposited in offshore sites, and the temporal change in carbon isotopes exceeds that observed in the offshore deposits. The onshore core locality is proximal to the orogen and characterized by a mean elevation > 1 km compared to the offshore site, which has a mean catchment elevation of ∼500 m. These data show that depositional setting and catchment hypsometry strongly bias the geochemical signature of sediments transported through the river system. The magnitude of isotopic variability generated by catchment geometry and sediment integration greatly exceeds the change associated with warming during deglaciation. This result suggests that catchment integration processes may play a similar or larger role in shaping fluvial geochemical records in tropical mountain systems than climatic factors.
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台湾西南部晚第四纪气候与源汇输沙过程的陆相生物标记同位素记录
河流沉积物是古环境的重要档案。然而,沉积物产生和运输过程的变化极大地影响了沉积物地球化学以及由此产生的对古代条件的解释。构造活跃的热带地区对气候反馈特别敏感,因为这些地区通常具有高降水率、快速侵蚀和沉积物停留时间短的特点。我们分析了台湾西南部高坪河-海底峡谷系统沉积物岩心中植物源正构烷烃(δ2正构烷烃和δ13正构烷烃)的氢和碳同位素组成,以检验气候和地貌对河流沉积档案同位素地球化学特征的控制。这些记录跨越了最近~26千年,为源-汇系统内沉积生物标志物同位素的时间和空间变化提供了重要的见解。同位素数据与iCESM 1.2地球系统模型中最后一次冰川-间冰循环期间降水同位素的新结果相结合。生物标志物同位素和建模结果支持了两个重要结论。首先,在台湾西南近海的δ2正构烷烃和δ13正构烷烃中,生物标志物同位素值在第四纪晚期消冰作用期间变化约10至15‰。这些变化与iCESM的预测和南中国海的其他记录一致,最好用区域变暖和对大气pCO2增加的生物反应引起的同位素水文变化来解释。其次,保存在山脉附近的陆上沉积物中的生物标志物的δ2Hn烷烃比沉积在近海的生物标志物质多负约15至20‰,碳同位素的时间变化超过了在近海沉积物中观察到的变化。陆上岩心位置靠近造山带,其特征是平均海拔>1 km,而海上现场的平均集水区海拔为~500 m。这些数据表明,沉积环境和集水区海拔高度极大地偏离了通过河流系统输送的沉积物的地球化学特征。集水区几何形状和沉积物整合产生的同位素变化幅度大大超过了冰川消退期间与变暖相关的变化。这一结果表明,与气候因素相比,集水区整合过程在形成热带山区系统的河流地球化学记录方面可能发挥类似或更大的作用。
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来源期刊
American Journal of Science
American Journal of Science 地学-地球科学综合
CiteScore
5.80
自引率
3.40%
发文量
17
审稿时长
>12 weeks
期刊介绍: The American Journal of Science (AJS), founded in 1818 by Benjamin Silliman, is the oldest scientific journal in the United States that has been published continuously. The Journal is devoted to geology and related sciences and publishes articles from around the world presenting results of major research from all earth sciences. Readers are primarily earth scientists in academia and government institutions.
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