Ti content in Huguangyan maar lake sediment as a proxy for monsoon‐induced vegetation density in the Holocene
Ti content in Huguangyan maar lake sediment as a proxy for monsoon‐induced vegetation density in the Holocene
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DOI：
10.1002/grl.50740
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发表时间：
2013-11
影响因子：
5.2
通讯作者：
Ji Shen;Xudong Wu;Zhaohui Zhang;Weiming Gong;T. He;Xiaomei Xu;Hailiang Dong
中科院分区：
文献类型：
--
作者：
Ji Shen;Xudong Wu;Zhaohui Zhang;Weiming Gong;T. He;Xiaomei Xu;Hailiang Dong
自Yancheva等（）提出湖光岩玛珥湖沉积物中Ti元素的来源于中国黄土高原（CLP）并将其作为亚洲冬季风的代用指标以来，关于湖光岩玛珥湖沉积物中Ti元素的来源一直存在争议。我们对CLP的湖泊沉积物、围岩和黄土中的载钛矿物和钛通量进行了全面的研究。研究表明，HGY表层沉积物中最重要的钛载体磁铁矿的化学成分和形态特征与湖周围岩中的相同，但与CLP黄土样品中的有很大差异。我们计算的CLP的现代风成Ti通量与HGY的平均总Ti通量相比可以忽略不计，并且来自流域侵蚀的Ti通量可以提供足够的Ti，表明HGY沉积物中的Ti主要来自围岩侵蚀。全新世总有机碳（TOC）（植被密度）和Ti/Ca比值（陆地输入）之间的负相关表明，季风引起的植被密度在控制Ti输入到HGY中的作用优于径流。S比代表TOC直接介导的氧化铁还原成岩作用（磁铁矿保存），而不是冬季季风引起的底层水缺氧/好氧条件。我们的记录显示，在夏季季风减弱的推动下，整个全新世植被密度下降、Ti输入增加、还原成岩作用减弱。
The provenance of element Ti in Huguangyan maar lake (HGY) sediment has been under debate since Yancheva et al. ( ) proposed its eolian source from the Chinese Loess Plateau (CLP) and applied it as a proxy for Asian winter monsoon. We performed a comprehensive study on Ti‐carrying minerals and Ti fluxes in lake sediments, wall rocks, and loess from the CLP. Here we show that the chemical compositions and morphological features of magnetite, the most important Ti carrier in HGY surface sediments, are identical to those in wall rocks around the lake, but substantially different from those in CLP loess samples. Our calculated modern eolian Ti flux from the CLP is negligible compared to the average total Ti flux to HGY, and Ti flux from catchment erosion can provide enough Ti, indicating Ti in HGY sediment are predominantly from wall rock erosion. Inverse correlation between total organic carbon (TOC) (vegetation density) and Ti/Ca ratio (terrestrial input) in the Holocene suggests monsoon‐induced vegetation density predominates over runoff in controlling Ti input to HGY. S‐ratio represents TOC directly mediated reductive diagenesis of iron oxides (magnetite preservation), rather than anoxic/oxic condition at the bottom water induced by winter monsoon. Our record shows a decreased vegetation density, increased Ti input and weakened reductive diagenesis through the Holocene driven by a weakened summer monsoon.