Collaborative Research: Reconciling conflicting Arctic temperature and fire reconstructions using multi-proxy records from lake sediments north of the Brooks Range, Alaska

阿拉斯加布鲁克斯山脉以北地区的温度重建表明，末次冰期极大期（LGM, 26,500至19,000年前）比现在更温暖。全球气候模型对这一地区的模拟差异很大，一些模型显示气候变暖，另一些模型显示气候变冷。这个地区几乎没有高分辨率的温度记录。因此，为了检验气候模式的输出并了解区域对气候强迫的敏感性，需要对LGM至今的温度进行稳健的重建。与模糊的温度历史相关的是区域火灾历史的不确定性，正如在过去150年中意外发现的三次阿拉斯加冻土带大火所揭示的那样。这些火灾与传统观念相矛盾，传统观念认为冻土带生态系统很少（如果有的话）燃烧并激发了一个关键问题：自LGM以来，气候变化、火灾和植被之间的关系是什么？该项目将利用从湖芯获得的记录，对该地区的温度进行仔细的重建。然后将所得数据与各种气候模式输出进行比较。该项目将通过支持培训两名研究生来促进劳动力发展。学生和他们的导师将利用布朗大学STEM外展办公室的活动，在罗德岛普罗维登斯的K-12教室里，那里的教室人口主要由STEM领域代表性不足的少数民族组成。该项目将在夏季培训一名K-12教师到实验室，并支持该教师参加一个重要的区域科学会议。该小组将参加卡克托维克海洋学项目，这是一个在阿拉斯加卡克托维克因纽特村为K-12学生开设的项目。收集到的数据将被公开，并作为阿拉斯加冻土带科学的参考。最后，主要研究人员将把现有的项目博客扩展为一个专门的网站，以向公众宣传该项目。pi将使用一套有机地球化学和传统的古生态代理，从阿拉斯加北坡的四个湖泊的沉积物岩心中生成自LGM以来的高分辨率、多代理的温度和火灾记录。这些数据将与来自完全耦合气候模式的预测进行检验，以评估ipcc级模式模拟过去温度变化的能力，并评估调节区域温度的潜在强迫和反馈。这项工作建立在初步研究的基础上，这些研究表明：1)这些湖泊的烯酮分布与初夏温度之间存在强烈的、可量化的关系，北极湖泊沉积物中的植物叶蜡D/H比记录了夏季平均温度；2)湖泊沉积物中多环芳烃（PAH）记录了区域火灾历史；3)多代理分析可以确定夏季早、中、平均温度的变化，并允许对季节温度变化及其相关反馈和强迫的影响进行严格审查。多环芳烃方法补充了木炭记录，并允许在更广泛的区域范围内检测古火灾。研究地点位于Toolik野外站北极长期生态研究（LTER）站点内，该站点自1975年以来才开始提供连续的、具有战略意义的监测数据。这项研究将提供基础的、高质量的温度和火灾数据，将过去40年的仪器监测置于全新世和晚更新世的大背景下。

Temperature reconstructions from the region north of the Brooks Range in Alaska suggest a warmer-than-present Last Glacial Maximum (LGM, 26,500 to 19,000 years ago). Global climate models differ strongly in their simulations of this region, with some suggesting a warmer and others a colder cliamte. There are virtually no high-resolution temperature records from this region. Robust temperature reconstructions spanning the LGM to present are therefore needed to test the outputs from climate models and to understand regional sensitivity to climate forcing. Associated with the ambiguous temperature history is uncertainty in the regional fire history, as revealed by the unexpected discovery of three major Alaskan tundra fires in last 150 years. These fires contradict the conventional notion that tundra ecosystems rarely, if ever, burn and stimulate a key question: What are the relationships between climate change, fire, and vegetation since the LGM? This project will develop careful reconstructions of temperatures in the region using records obtained from lake cores. The resulting data will then be compared with a variety of climate model outputs.The project will contribute to workforce development by supporting the training of two graduate students. The students and their mentors will leverage activities of the Brown STEM Outreach Office to K-12 classrooms in Providence, RI, where the classroom population is composed largely of under-represented minorities in the STEM fields. The project will entrain a K-12 teacher into the laboratory during the summer and support the teacher's participation in a major regional science meeting. The team will participate in the Kaktovik Oceanography Program, a project in the Inupiat village of Kaktovik, Alaska for K-12 students. The data collected will be made public and serve as a reference for Alaskan tundra science. Finally, the principal investigators will expand an existing project blog into a dedicated website for public outreach concerning the project.The PIs will generate high resolution, multiproxy records of temperature and fire since the LGM from sediment cores of four lakes on the North Slope of Alaska using a suite of organic geochemical and traditional paleoecological proxies. These data will be tested against predictions from fully coupled climate models to evaluate the ability of IPCC-grade models to simulate past temperature changes, and to evaluate potential forcings and feedbacks that regulate regional temperatures. The work is built upon initial studies that indicate that: 1) strong, quantifiable relationships exist between alkenone distributions and early summer temperature in these lakes, and plant leaf wax D/H ratios in Arctic lake sediments record mean summer temperatures; 2) polycyclic aromatic hydrocarbons (PAH) in lake sediments record the regional fire history; and 3) multiproxy analysis can determine temperature changes in early, middle and mean summer temperatures and will permit critical examination on the impacts of seasonal temperature change and its associated feedbacks and forcing. The PAH approach complements charcoal records and allows detection of paleo-fires across a broader regional scale. Study sites are located within the Toolik Field Station Arctic Long Term Ecological Research (LTER) site, which only began to provide continuous, strategically important monitoring data since 1975. The study will provide fundamental, high quality temperature and fire data, placing the past 40 years of instrumental monitoring in the grand context of the Holocene and late Pleistocene.