Validation of the MBT paleotemperature proxy in lakes

温度是需要理解的最关键的气候参数之一，但仍难以重建。地球表面温度对其他气候因素有巨大影响，例如水文变异性。此外，最近全球变暖的趋势表明，我们需要了解气温及其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称，地球在20世纪变暖了0.6摄氏度，预计21世纪将额外变暖约2-6摄氏度。此外，NRC最近的一个委员会得出结论，在许多记录中观察到的最近的变暖是真实的，但人们对公元1600年之前的温度重建缺乏信心，对公元900年之前的温度重建的信心要小得多。根据NRC委员会的说法，人们对温度重建缺乏信心的主要原因是相对缺乏准确确定日期的代理证据。他们提出，更多温度记录的产生将提高我们对从现在到现在的2000年期间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也是非常有意义的。在大陆系统中很难测量古温度，特别是湖泊沉积物等古档案。最近的工作突出了新的基于微生物脂类的温度替代指标在湖泊沉积物中应用的潜力。已在土壤、泥炭和湖泊沉积物中发现了细菌来源的分枝GDGT脂类，这些GDGT中的分枝程度似乎与温度有关，这可以用Wejers等人的“MBT”指数来量化。(2007)。这项建议的目的是验证MBT古温度代用品在湖泊沉积物中的使用，方法是：(A)确定在湖泊沉积物中确定的GDGT分支分布是否确实反映了分水岭的年平均气温，以及(B)季节偏差和给定分水岭内的亚环境等其他因素在多大程度上影响这些细菌膜脂保存的表观温度信号。我提出了一系列分析，旨在测试MBT和CBT代用品作为从湖泊沉积物中重建温度和pH的工具的有效性，遵循三种不同研究途径的方法。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、季节性和环境变异性的偏差以及与仪器记录的一致性等问题。具体地说，拟议的研究将包括三个主要目标。1)建立了湖面沉积物与流域年平均气温(MAT)之间CBT和MBT的全球定标。2)分析三个选定地点不同亚环境土壤中MBT的年周期，以确定影响MBT的环境因素和潜在的季节偏差。3)三个测点的测温数据与近百年来由湖泊沉积物重建的MBT温度进行了比较。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示向公众传播这项研究的信息。对科学界更广泛的影响包括对MBT古温度指标在湖泊系统中的应用进行亟需的验证。现代全球气候变化预测的气温上升将对下个世纪的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及其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。适当应用经过严格调查的替代物，如MBT，提供了关于目前可用时间尺度上的古温度估计的最佳信息，而不是现有的仪器记录，但只有当我们充分理解与它们相关的所有警告并适当地应用它们时，这种替代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.