Organic sulfur compositions and their relationships with iron sulfides in Antarctic lake sediments

Abstract

本文利用有机硫硫同位素组成（δ³⁴S_org）及活性铁的黄铁矿化度（DOP）和硫化度（DOS）研究了南极阿德雷岛受企鹅活动影响的Y2湖和未受影响的菲尔德斯半岛燕鸥湖YO沉积物中有机硫的来源组成及其与铁硫化物的联系.结果表明，Y2沉积物1~15 cm较低的δ³⁴S_org指示有机质硫化形成的贫³⁴S成岩有机硫（S_diag）占比较高，其中在8~15 cm较高的DOS指示铁硫化物形成和有机质硫化同时发生，源于该层位高含量的活性铁供给.Y2剖面48~56 cm沉积物有机硫富集³⁴S显著，对应于企鹅数量高峰期，表明大量企鹅粪的外部输入使沉积物中富³⁴S的生物有机硫（S_bio）快速增加，并超过了内部硫转化过程中成岩有机硫的增加.YO沉积物在28 cm处δ³⁴S_org显著降低，主要是由于该层位硫酸盐异化还原强，有机质硫化形成的大量S_diag成为有机硫的主要成分，同位素质量平衡计算结果显示该层位S_diag占比高达95.4%；同时，28 cm处较高的DOP指示沉积物黄铁矿的形成与有机质硫化同时发生，主要源自沉积物中高硫酸盐还原强度产生了足够多的硫化氢前体.本研究表明，有机硫组分的来源转化与有机质、活性铁紧密耦合，对区域湖泊有机质成岩埋藏及潜在的气候环境效应具有重要的指示意义.;Sulfur isotope ratios of organic sulfur (δ³⁴S_org), degrees of pyritization (DOP) and sulfurization (DOS) in sediments were analyzed to reveal the organic sulfur compositions and their relationships with iron sulfides in a penguin-affected lake Y2 and a pristine Yanou Lake (YO) at Ardley Island and Fildes Peninsula, Antarctica, respectively. The depleted δ³⁴S_org values in Y2 sediments of 1-15 cm indicated a high proportion of ³⁴S-depleted diagenetic organic sulfur (S_diag) in total sulfur. Meanwhile, the high DOS in Y2 sediments of 8-15 cm indicated a concurrent sulfurization of iron and the organic matter, likely due to the high availability of active iron in this layer. The observed much enriched δ³⁴S_org in Y2 sediments of 48-56 cm corresponding to the period of high penguin populations, which indicated that large external inputs of penguin guanos result in a rapid increase in ³⁴S-enriched biological organic sulfur (S_bio) in the sediments, and exceeds the S_diag that from the internal sulfur transformations. The depleted δ³⁴S_org in YO sediment of 28 cm indicates a high proportion (95.4%) of ³⁴S-depleted S_diag which was from strong sulfurization of organic matter, corresponding to the strongest sulfate reduction in this layer. Meanwhile, the high DOP in YO sediment of 28 cm indicated a concurrent formation of pyrite sulfur and the sulfurization of organic matter in this layer, due to the high available precursors of hydrogen sulfide and/or intermediate species of sulfur from the sulfate reduction. Our study indicates that the components of organic sulfur are coupled tightly with organic matter and reactive iron and provides a direct implication for the depositions of organic matter and thus the potential climatic and environmental effects in regional aquatic ecosystems.