The hydrogen isotopic compositions of sedimentary mid-chain n-alkanes record ecological change at a Portuguese paleowetland
The hydrogen isotopic compositions of sedimentary mid-chain n-alkanes record ecological change at a Portuguese paleowetland
复制标题
DOI：
10.1016/j.quaint.2019.09.009
复制
发表时间：
2019-11
影响因子：
2.2
通讯作者：
Audrey K. Taylor;M. Benedetti;Jonathan A. Haws;C. S. Lane
中科院分区：
文献类型：
--
作者：
Audrey K. Taylor;M. Benedetti;Jonathan A. Haws;C. S. Lane
沉积档案中中链（c23和C25）和c27正构烷烃的来源可能不明确。在葡萄牙沿海，一个泥炭矿床代表了中全新世古湿地（PRC-South），最初以sphagnumum为主，为评估中链烷烃来源阐明方法提供了理想的环境。特别地，我们研究了中链烷烃（δDmid）和c29正构烷烃（ΔDmid-C29）之间δD与烷烃分子分布和化合物特异性δ13C值之间的差异的综合记录，以改进对古环境变化的解释，并评估δDmid值用于水文重建的可靠性。在sphagnumn大幅下降后，PRC-South的中链烷烃产量仍然显著，但ΔDmid-C29values的增加表明，中链烷烃主要来自沉积物上部50 cm的陆相。这种向正方向发展ΔDmid-C29values的趋势与n- c27丰度的相对增加相吻合，可能代表着sphagnummoss被产生大量中链烷烃的树种（如桦树、栎树或fagusspp）所取代。研究结果表明，ΔDmid-C29displays有望作为一种中链烷烃源归属的工具，但植物和陆生植被的氢同位素分异可能严重阻碍其应用。我们使用ΔDmid-C29at PRC-South最终证明了定性或定量解释沉积δ dn -烷烃值时考虑植被组成的重要性，特别是inSphagnumwetlands。
The origin of mid-chain (C23and C25) and C27n-alkanes in sedimentary archives can be ambiguous. In coastal Portugal, a peat deposit representing a mid-Holocene paleowetland (PRC-South) that was initially dominated bySphagnumpresents an ideal setting for assessing methods of mid-chainn-alkane source elucidation. In particular, we examine a comprehensive record of the difference in δD between mid-chain (δDmid) and C29n-alkanes (ΔDmid-C29) in relation ton-alkane molecular distributions and compound-specific δ13C values in order to improve interpretations of paleoenvironmental change and evaluate the reliability of δDmidvalues for hydrologic reconstructions. Mid-chainn-alkane production remains significant at PRC-South after a substantialSphagnumdecline, yet an increase in ΔDmid-C29values indicates a primarily terrestrial origin of mid-chainn-alkanes in the upper 50 cm of the deposit. This progression towards more positive ΔDmid-C29values coincides with a relative increase inn-C27abundance and potentially represents the replacement ofSphagnummoss by tree species that produce abundant mid-chainn-alkanes, such asBetula,Quercus, orFagusspp. According to our analysis, ΔDmid-C29displays promise as a tool for mid-chainn-alkane source attribution inSphagnumpaleoenvironments, but interspecies variability of hydrogen isotope fractionation inSphagnummosses and terrestrial vegetation could critically hinder its application. Our use of ΔDmid-C29at PRC-South ultimately exemplifies the importance of accounting for vegetation composition when qualitatively or quantitatively interpreting sedimentary δDn-alkanevalues, particularly inSphagnumwetlands.