Fire-induced shifts in stalagmite organic matter mapped using Synchrotron infrared microspectroscopy

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Organic Geochemistry Pub Date : 2024-07-25 DOI:10.1016/j.orggeochem.2024.104842

Liza K. McDonough , Micheline Campbell , Pauline C. Treble , Christopher Marjo , Silvia Frisia , Jitraporn Vongsvivut , Annaleise R. Klein , Viktoria Kovacs-Kis , Andy Baker

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引用次数: 0

Abstract

Understanding organic matter (OM) in cave mineral deposits (speleothems) is essential for interpreting land use and climatic changes, and the incorporation of trace elements associated with organic compounds. However, the sources and composition of OM in speleothems are poorly understood due to challenges associated with measuring OM at low concentrations and the destructive nature of most speleothem OM analysis techniques. Synchrotron Fourier-transform infrared (FTIR) microspectroscopy is a promising non-destructive technique that can be used to investigate stalagmite OM composition. We use FTIR to analyse vegetation, soil, calcium carbonate and ash end-members and demonstrate the use of Synchrotron infrared microspectroscopy (IRM) mapping to detect temporal changes in the OM composition of a stalagmite from a shallow cave in south-west Western Australia. Our analysis reveals predominant FTIR peaks in the stalagmite linked to amides and CH₂ groups, suggesting potential microbial contributions, with smaller proportions of aromatic, CH₃ and CO groups. High-resolution transmission electron microscopy revealed that this OM is likely hosted in sets of nanopores spaced hundreds of nanometers apart, aligned along calcite crystallographic orientations. Furthermore, we assess the impact of known wildfire events as discrete short term environmental changes on the stalagmite’s OM composition. The temporal variability in OM functional group composition after fires implies complex fire-soil-vegetation-microbial interactions. This research demonstrates the effectiveness of Synchrotron IRM mapping in providing insights into the short and long-term environmental influences on stalagmite OM composition. Expanding this research to other regions and climates could further enhance the interpretation of OM changes in speleothem-based palaeoclimate reconstructions.

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利用同步辐射红外微光谱绘制石笋有机物的火灾诱变图

了解洞穴矿床（speleothems）中的有机物（OM）对于解释土地利用和气候变化以及与有机化合物相关的微量元素的加入至关重要。然而，由于低浓度 OM 测量的挑战和大多数岩浆 OM 分析技术的破坏性，人们对岩浆中 OM 的来源和组成知之甚少。同步辐射傅立叶变换红外（FTIR）微光谱技术是一种很有前途的非破坏性技术，可用于研究石笋的 OM 成分。我们使用傅立叶变换红外光谱分析植被、土壤、碳酸钙和灰烬的末端成分，并展示了同步加速器红外微光谱（IRM）制图技术在检测西澳大利亚西南部浅洞穴石笋的 OM 成分的时间变化方面的应用。我们的分析表明，石笋中的傅立叶变换红外光谱峰主要与酰胺和CH2基团有关，表明可能有微生物的贡献，而芳香族、CH3和CO基团所占比例较小。高分辨率透射电子显微镜显示，这种 OM 很可能存在于间隔数百纳米、沿方解石晶体学方向排列的纳米孔中。此外，我们还评估了已知野火事件作为离散的短期环境变化对石笋 OM 成分的影响。火灾后 OM 功能群组成的时间变化意味着火灾-土壤-植被-微生物之间复杂的相互作用。这项研究证明了同步加速器 IRM 测绘在深入了解石笋 OM 组成的短期和长期环境影响方面的有效性。将这项研究扩展到其他地区和气候条件下，可以进一步加强对基于古气候重建的石笋OM变化的解释。

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来源期刊

Organic Geochemistry 地学-地球化学与地球物理

CiteScore

5.50

自引率

6.70%

发文量

100

审稿时长

61 days

期刊介绍： Organic Geochemistry serves as the only dedicated medium for the publication of peer-reviewed research on all phases of geochemistry in which organic compounds play a major role. The Editors welcome contributions covering a wide spectrum of subjects in the geosciences broadly based on organic chemistry (including molecular and isotopic geochemistry), and involving geology, biogeochemistry, environmental geochemistry, chemical oceanography and hydrology. The scope of the journal includes research involving petroleum (including natural gas), coal, organic matter in the aqueous environment and recent sediments, organic-rich rocks and soils and the role of organics in the geochemical cycling of the elements. Sedimentological, paleontological and organic petrographic studies will also be considered for publication, provided that they are geochemically oriented. Papers cover the full range of research activities in organic geochemistry, and include comprehensive review articles, technical communications, discussion/reply correspondence and short technical notes. Peer-reviews organised through three Chief Editors and a staff of Associate Editors, are conducted by well known, respected scientists from academia, government and industry. The journal also publishes reviews of books, announcements of important conferences and meetings and other matters of direct interest to the organic geochemical community.