Development of a New Terrestrial Palaeotemperature Proxy Based on dD Values of Lipid Biomarkers of Peat Bog Vegetation

基于泥炭沼泽植被脂质生物标志物 dD 值开发新的陆地古温度代理

• 批准号: NE/E010989/1
• 负责人: Richard Evershed
• 金额: $ 6.13万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE010989%2F1
• 关键词: Development; New; Terrestrial; Palaeotemperature; Proxy

Peat bogs, or more specifically ombrotrophic mires, are extremely sensitive to climate change. Precipitation is the only source of water and nutrients to the bog and so therefore the dominant vegetation is strongly influenced by the local climatic conditions. Peat forms from the partial decay of plants growing on the surface of the bog and over time this accumulates into peat deposits. Results from radiocarbon dating of these peat layers reveal the build up of the peat quite rapid and can be up to the order of 10 mm every ten years. Contained within peat layers are various indicators of past climatic conditions, also known as palaeoclimate proxies, which can be used to study climate changes in the past. For example, macrofossils, i.e. the remains of the plants, and pollen reflect the abundance of the plants originally growing at the bog surface. These plants are very sensitive to climate and so changes such factors as rainfall or temperature are reflected in the macrofossil records inferred. However, peat records have up to now been unable to provide information on regional temperatures. There is obviously a need for more exact reconstruction of past temperatures given the current debates on global warming. Where macrofossils are unidentifiable in the peat record then the study of past climates becomes difficult. However, advances in environmental sciences have lead to the discovery of new molecular tools which bridge these gaps in palaeoclimate reconstruction. Chemical analysis of lipids in modern major peat forming plants growing on the peat bog surface, such as the Sphagnum mosses, sedges and heathers, has revealed they contain distinct chemical characteristics, or lipid biomarkers. For example, the lipid biomarker n-C23 alkane which is a component of leaf wax, is found in high concentrations in Sphagnum species where as in other peat vegetation such as heathers the n-C23 is either absent or present in very low abundance. Further work has revealed that n-C23 alkane abundances can track the contribution of Sphagnum mosses to the peat records. A notable feature of lipids is their hydrophobic nature which means they are immobile in peat bog and so remain at their point of deposition. In addition to lipid biomarkers, other molecular tools which have been used in palaeoclimate reconstruction are stable isotopes. Bulk stable isotope values measured in macrofossil remains in peat have been used to infer relative changes in wetness, however, bulk isotope techniques require well preserved macrofossils. A new molecular approach known as compound-specific isotope analysis can measure isotopes of specific compounds such as lipids. For example, work carried out at Bristol has shown that the dD values of the lipid biomarker n-C23 alkane from peat bogs, measured using the new technique of gas chromatography-thermal conversion-isotope ratio mass spectrometry (GC-TC-IRMS), correlate with vegetation changes in the past. Furthermore n-C23 alkane dD values strongly correlate with recorded temperature variations during the 19th and 20th century so suggests compound-specific dD values of this, and perhaps other lipid biomarkers, have potential value as a new terrestrial-based palaeotemperature proxy (akin to a geological thermometer) in the peat bogs. The overall aim of the proposed work is to develop a new terrestrial palaeotemperature proxy based on dD values of biomarkers of peat bog vegetation. This will be achieved by measuring the dD values of the n-C23 alkane extracted from 4 peat bogs across Europe on a west-east latitudinal transect. These dD records will then be correlated with other peat proxies, and temperature data collected over the past 200 years, which will allow us to calibrate the biomarker-specific dD records so we can then develop the palaeotemperature proxy. This proposed work could provide us with an invaluable tool in which we could study past regional temperature variations.

泥炭沼泽，或者更具体地说是富雨沼泽，对气候变化极其敏感。降水是沼泽水和养分的唯一来源，因此主要植被受当地气候条件的强烈影响。泥炭是由生长在沼泽表面的植物部分腐烂而形成的，随着时间的推移，这些植物积累成泥炭沉积物。这些泥炭层的放射性碳测年结果显示，泥炭的形成相当迅速，每十年可以达到10毫米的量级。泥炭层中含有过去气候条件的各种指标，也称为古气候代用指标，可用于研究过去的气候变化。例如，大型化石，即植物的遗骸和花粉反映了最初生长在沼泽表面的植物的丰度。这些植物对气候非常敏感，因此降雨或温度等因素的变化反映在推断的宏体化石记录中。然而，泥炭记录到目前为止还无法提供区域温度的信息。鉴于目前关于全球变暖的辩论，显然需要更精确地重建过去的温度。如果在泥炭记录中无法辨认出宏体化石，那么对过去气候的研究就变得困难了。然而，环境科学的进步导致了新的分子工具的发现，弥补了古气候重建的这些差距。对生长在泥炭沼泽表面的现代主要泥炭形成植物（如泥炭藓、莎草和石南）中的脂质进行化学分析，发现它们含有独特的化学特征或脂质生物标志物。例如，作为叶蜡组分的脂质生物标志物n-C23烷烃在泥炭藓属物种中以高浓度存在，而在其他泥炭植被如石南中，n-C23要么不存在要么以非常低的丰度存在。进一步的研究表明，n-C23烷烃丰度可以追踪泥炭藓对泥炭记录的贡献。脂质的一个显著特征是它们的疏水性质，这意味着它们在泥炭沼泽中是固定的，因此保持在它们的沉积点。除了脂类生物标志物外，稳定同位素也已被用于古气候重建。在泥炭中的宏体化石残留物中测量的大量稳定同位素值已被用来推断湿度的相对变化，然而，大量同位素技术需要保存完好的宏体化石。一种新的分子方法被称为化合物特异性同位素分析，可以测量特定化合物（如脂质）的同位素。例如，在布里斯托进行的工作表明，使用气相色谱-热转换-同位素比值质谱法（GC-TC-IRMS）新技术测量的泥炭沼泽中脂质生物标志物n-C23烷烃的dD值与过去的植被变化相关。此外，n-C23烷烃dD值与19和20世纪期间记录的温度变化强烈相关，因此表明该化合物的特定dD值以及可能的其他脂质生物标志物具有作为泥炭沼泽中新的基于陆地的古温度代理（类似于地质温度计）的潜在价值。建议的工作的总体目标是开发一个新的陆地古温度代理的基础上dD值的泥炭沼泽植被的生物标志物。这将通过测量从横跨欧洲的4个泥炭沼泽中提取的n-C23烷烃的dD值来实现。然后，这些dD记录将与其他泥炭代理和过去200年收集的温度数据相关联，这将使我们能够校准生物标记特定的dD记录，这样我们就可以开发古温度代理。这项拟议的工作可以为我们提供一个宝贵的工具，我们可以研究过去的区域温度变化。