期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：44
页码：15669-15674
DOI：10.1073/pnas.1405237111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceLipid biomarkers in geological samples are important informants regarding past environments and ecosystems. Conventional biomarker analysis is labor intensive and requires relatively large sediment or rock samples; temporal resolution is consequently low. Here, we present an approach that has the potential to revolutionize paleoenvironmental biomarker research; it avoids wet-chemical sample preparation and enables analysis of biomarkers directly on sediment cores at submillimeter spatial resolution. Our initial application to a sediment core deposited during the Holocene climate optimum in the Mediterranean Sea reveals a new view of how small-scale variations in lipid distribution are integrated into commonly reported signals obtained by conventional analysis and demonstrates a strong influence of the [~]200-y de Vries solar cycle on sea-surface temperatures and planktonic archaeal ecology. Marine microorganisms adapt to their habitat by structural modification of their membrane lipids. This concept is the basis of numerous molecular proxies used for paleoenvironmental reconstruction. Archaeal tetraether lipids from ubiquitous marine planktonic archaea are particularly abundant, well preserved in the sedimentary record and used in several molecular proxies. We here introduce the direct, extraction-free analysis of these compounds in intact sediment core sections using laser desorption ionization (LDI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). LDI FTICR-MS can detect the target lipids in single submillimeter-sized spots on sediment sections, equivalent to a sample mass in the nanogram range, and could thus pave the way for biomarker-based reconstruction of past environments and ecosystems at subannual to decadal resolution. We demonstrate that ratios of selected archaeal tetraethers acquired by LDI FTICR-MS are highly correlated with values obtained by conventional liquid chromatography/MS protocols. The ratio of the major archaeal lipids, caldarchaeol and crenarchaeol, analyzed in a 6.2-cm intact section of Mediterranean sapropel S1 at 250-{micro}m resolution ([~]4-y temporal resolution), provides an unprecedented view of the fine-scale patchiness of sedimentary biomarker distributions and the processes involved in proxy signal formation. Temporal variations of this lipid ratio indicate a strong influence of the [~]200-y de Vries solar cycle on reconstructed sea surface temperatures with possible amplitudes of several degrees, and suggest signal amplification by a complex interplay of ecological and environmental factors. Laser-based biomarker analysis of geological samples has the potential to revolutionize molecular stratigraphic studies of paleoenvironments.
