早更新世帝汶海碳酸盐埋藏和陆源输入记录的古气候变化

Early Pleistocene records of carbonate burial and terrestrial input in the Timor Sea and their paleoclimatic implications

  • 摘要: 深海碳酸盐埋藏作为地球表层碳库的重要碳汇,在地质历史时期与大气二氧化碳浓度变化息息相关。古记录重建显示,大气二氧化碳浓度并不总是与全球平均气温具有较好的对应关系,其他因素可能在过去全球变化中起到了重要的作用。本文以澳大利亚西北岸外帝汶海IODP U1482站钻孔2~1.07 Ma沉积物为研究材料,测试其碳酸盐和主微量元素含量,探讨深海碳酸盐埋藏的影响因素。结果显示,碳酸盐含量与指示河流输入的钾元素含量、指示生产力的铀元素含量和底栖有孔虫δ13C以及指示风尘输入的log(Zr/Rb)等记录在2~1.63 Ma、1.63~1.31 Ma和1.31~1.07 Ma等3个阶段性均呈现长期变化趋势,可能与沃克环流和哈德莱环流调控的印尼—澳洲地区的干湿条件有关。1.31 Ma之后钾元素含量的持续降低和碳酸盐含量的增加可能揭示哈德莱环流的加强导致了澳洲西北内陆的干旱化趋势。早更新世U1482站碳酸盐含量在轨道时间尺度上主要受以河流输入为主的陆源沉积物稀释的影响;频谱分析显示其具有显著的19ka和约29ka变化周期,可能指示该研究时段内除了岁差周期外,以斜率周期为主导的冰期-间冰期旋回对区域降水和陆源沉积物输入的调控作用。

     

    Abstract: Deep-sea carbonate burial is an important carbon sink of the Earth’s surface carbon reservoir. Its variations are closely related to that of atmospheric carbon dioxide. Paleo-environment reconstructions show that changes in atmospheric CO2 concentration do not always correlate well with past temperature changes, implying that other factors may contribute to the past global change. We examined deep-sea sediments spanning the interval of 2~1.07 Ma retrieved from IODP Site U1482 located offshore northwestern Australia in the Timor Sea. Carbonate and elemental contents were analyzed to investigate the factors that influenced carbonate burial. The early Pleistocene records at Site U1482 indicate that all of our records including carbonate content, potassium content (a proxy of regional precipitation), log(Zr/Rb) (a proxy of aeolian dust input), benthic foraminiferal δ13C, and uranium content (proxies of paleoproductivity) show long-term changes punctuated at 1.63 Ma and 1.31 Ma, possibly related to the precipitation pattern over Indonesia-Australia modulated by Walker and Hadley circulations. The continuous decrease in carbonate content and increase in potassium content after 1.31 Ma likely implicate that the intensified aridification in the northwestern Australian hinterland was caused by strengthening of the Hadley circulation. Dilution by terrestrial sediments, mainly of riverine origin, is the predominant factor modifying carbonate content on orbital timescales. Spectral analysis shows that the carbonate record was dominated by 19 ka and 29 ka cycles, likely suggesting the effect of the obliquity-paced glacial/interglacial cyclicity on the regional precipitation and terrestrial input in addition to the precessional control.

     

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