Validation of the MBT paleotemperature proxy in lakes

WERNE，Josef P.温度是最关键的气候参数之一，但仍然难以重建。地球表面温度对水文变化等其他气候因素有着巨大的影响。此外，最近全球变暖的趋势表明，我们需要了解温度及其对子孙后代气候变化的影响。IPCC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世纪将再变暖约2 - 6摄氏度。此外，最近的一个NRC委员会得出结论，许多记录中观察到的最近变暖是真实的，但对公元1600年之前的温度重建的信心较低，公元900年之前更是如此。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稀缺。他们提出，生成额外的温度记录将提高我们对从2,000年前到今天的全球温度重建的信心。此外，NRC委员会指出，通过使用新开发的替代物来提高新温度重建的可靠性的努力也很有意义。在大陆系统中，特别是在湖泊沉积物等古档案中，古温度很难测量。最近的工作突出了新的，微生物脂质为基础的代理温度应用于湖泊沉积物的潜力。已在土壤、泥炭和湖泊沉积物中鉴定出细菌来源的分支GDGT脂质，并且这些GDGT中的分支程度似乎与温度有关，这可以在Weijers等人（2007）的"MBT"指数中量化。本提案的目标是通过以下方式验证MBT古温度代用指标在湖泊沉积物中的使用：（a）确定湖泊沉积物中确定的分支GDGT分布是否确实反映了流域年平均气温，以及（B）在多大程度上其他因素，如季节性偏差和次给定流域内的环境正在影响这些细菌膜脂保存的表观温度信号。旨在测试的有效性MBT和CBT代理工具，以重建温度和pH值从湖泊沉积物，以下方法涉及三种不同的调查途径。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，包括与重建的准确性、季节性和环境变异性的偏差以及与仪器记录的一致性有关的问题。具体而言，拟议研究将包括三个主要目标。 1)在湖泊表面沉积物和流域年平均气温（MAT）之间发展CBT和MBT的全球校准。 2)在一个年度周期内，对三个选定地点的不同亚环境土壤中的MBT进行分析，以确定影响MBT的环境因素和潜在的季节性偏差。 3)过去~100年三个选定地点的仪器温度数据与从湖泊沉积物重建的MBT温度的比较。更广泛的影响包括培训研究生和本科生，并通过在州立公园的展览向公众传播有关这项研究的信息。对科学界更广泛的影响包括对湖相系统中MBT古温度代用指标的应用进行急需的验证。现代全球气候变化所预测的气温上升将在未来世纪对自然系统和人类人口产生重大影响。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，可以为理解过去的气候和模拟未来趋势提供有用的工具。适当应用严格调查的代理，如MBT提供了最好的信息，目前可在时间尺度上的古温度估计超出了仪器记录的存在，但只有当我们充分理解与它们相关的所有注意事项，并适当地应用它们，使用这些代理是有效的。

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.