Validation of the MBT paleotemperature proxy in lakes

温度是最关键的气候参数之一，但仍然很难重建。地球表面温度对其他气候因素有巨大的影响，比如水文变化。此外，最近全球变暖的趋势表明，我们需要了解温度，以及它对子孙后代气候变化的影响。政府间气候变化专门委员会最近的一份报告指出，地球在20世纪变暖了0.6摄氏度，预计在21世纪将再变暖2-6摄氏度。此外，最近的一个NRC委员会得出结论，在许多记录中观察到的近期变暖是真实的，但是在公元1600年之前的温度重建中可信度较低，在公元900年之前就更不可信了。根据NRC委员会的说法，对温度重建缺乏信心的主要原因是精确年代的替代证据相对缺乏。他们提出，生成额外的温度记录将提高我们对从2000年前到今天的全球温度重建的信心。此外，NRC委员会指出，通过使用新的发展代理来提高新温度重建的可靠性的努力也很有意义。古地温在大陆系统中很难测量，特别是在湖泊沉积物等古档案中。最近的工作强调了在湖泊沉积物中应用新的微生物脂质替代温度的潜力。细菌来源的支状GDGT脂质已经在土壤、泥炭和湖泊沉积物中被发现，这些GDGT的分支程度似乎与温度有关，这可以用Weijers等人（2007）的“MBT”指数来量化。本提案的目标是通过(a)确定湖泊沉积物中分支GDGT分布是否确实反映了流域年平均气温，以及(b)特定流域内的季节偏差和亚环境等其他因素在多大程度上影响了这些细菌膜脂保存的表观温度信号，从而验证MBT古温度代理在湖泊沉积物中的使用。我提出了一系列分析，旨在测试MBT和CBT代理作为从湖泊沉积物中重建温度和pH值的工具的有效性，遵循涉及三种不同调查途径的方法。这三种分析方法的结合将针对与MBT指数重建温度有关的一些主要问题，包括重建的准确性、季节性和环境变化的偏差以及与仪器记录的一致性。具体而言，拟议的研究将包括三个主要目标。1)建立湖泊表层沉积物与流域年平均气温（MAT）之间的CBT和MBT全球定标。2)对3个站点不同亚环境土壤的年周期MBT进行分析，找出影响MBT的环境因子和潜在的季节偏差。3)近100年来3个站点的仪器温度数据与湖泊沉积物重建的MBT温度的比较。更广泛的影响包括培训研究生和本科生，并通过州立公园的展览向公众传播有关这项研究的信息。对科学界的更广泛影响包括急需验证MBT古温度代理在湖泊系统中的应用。现代全球气候变化预测的气温上升将在未来一个世纪对自然系统和人口产生重大影响。更好地了解现代系统过程以及它们如何反映现代气候条件，可以为了解过去气候和模拟未来趋势提供有用的工具。适当应用经过严格调查的代用物，如MBT，提供了目前在仪器记录之外的时间尺度上的古温度值的最佳信息，但只有在我们充分理解与之相关的所有警告并适当应用这些代用物的情况下，这些代用物的使用才是有效的。

EAR-0745658WERNE, Josef P.Temperature is one of the most critical climate parameters to understand, yet remains difficult to reconstruct. Earth's surface temperature has a tremendous impact on other climate factors, such as hydrological variability. Furthermore, the recent trend of global warming illustrates our need to understand temperature, and its influence on climate change for future generations. A recent report by the IPCC stated that the Earth warmed by 0.6 degrees C during the 20th century, and is projected to warm by an additional ~2-6 degrees C during the 21st century. In addition, a recent NRC Committee has concluded that the recent warming observed in many records is real, but that there is less confidence in temperature reconstructions prior to A.D. 1600, and much less prior to A.D. 900. The primary reason for a lack of confidence in temperature reconstructions, according to the NRC committee, is the relative scarcity of precisely dated proxy evidence. They propose that the generation of additional temperature records would improve our confidence in global temperature reconstructions during the period from 2,000 years before present to today. Furthermore, the NRC committee indicates that efforts to improve the reliability of new temperature reconstructions through use of new developing proxies are also of great interest.Paleotemperature is difficult to measure in continental systems, particularly paleoarchives such as lake sediments. Recent work has highlighted the potential for new, microbial lipid based proxies for temperature to be applied in lake sediments. Bacterial-sourced branched GDGT lipids have been identified in soils, peats, and lake sediments and it appears that the degree of branching in these GDGTs is related to temperature, which can be quantified in the "MBT" index of Weijers et al. (2007). The goal of this proposal is to validate the use of the MBT paleotemperature proxy in lake sediments by (a) determining whether the branched GDGT distribution identified in lake sediments do indeed reflect watershed mean annual air temperature, and (b) to what extent other factors such as seasonal bias and sub-environments within a given watershed are influencing the apparent temperature signal preserved by these bacterial membrane lipids.I propose a series of analyses designed to test the validity of the MBT and CBT proxies as tools to reconstruct temperature and pH from lacustrine sediments, following an approach involving three different avenues of investigation. The combination of these three analytical approaches will target some of the major questions related to reconstructing temperature with the MBT index, including issues related to accuracy of the reconstruction, biases from seasonality and environmental variability, and coherence with the instrumental record. Specifically, the proposed study will be comprised of three major objectives. 1) Development of a global calibration of CBT and MBT between lake surface sediment and watershed mean annual air temperature (MAT). 2) Analysis of MBT in soils from different sub-environments from three selected sites over an annual cycle to identify environmental factors affecting MBT and potential seasonal biases. 3) Comparison of instrumental temperature data from three selected sites with MBT temperatures reconstructed from lake sediments over the past ~100 years. Broader impacts include training graduate and undergraduate students and disseminating information on this research to the public through displays at state parks. Broader impacts to the scientific community include a much-needed validation of the application of the MBT paleotemperature proxy in lacustrine systems. Increasing temperatures predicted by modern global climate change will significantly impact natural systems as well as human populations in the coming century. Gaining a better understanding of modern system processes and how they reflect modern climatic conditions can provide a useful tool for understanding past climate and modeling future trends. Appropriate application of rigorously investigated proxies such as the MBT provides the best information about paleotemperature estimates currently available on timescales beyond the existence if instrumental records, but the use of such proxies is only valid if we fully understand all of the caveats associated with them and apply them appropriately.