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，末次冰川盛期(LGM，26,500至19,000年前)比现在更温暖。全球气候模型在对这一地区的模拟中存在很大差异，一些模型认为气候变暖，另一些模型则认为气候较冷。这一地区几乎没有高分辨率的温度记录。因此，需要从末次盛冰期到现在的强劲温度重建，以测试气候模型的输出，并了解区域对气候强迫的敏感性。与模糊的温度历史相关的是区域火灾历史的不确定性，正如过去150年来阿拉斯加苔原地区三次重大火灾的意外发现所揭示的那样。这些大火与冻土带生态系统很少(如果有的话)燃烧并激发一个关键问题的传统观念相矛盾：自末次大冰盖以来，气候变化、火灾和植被之间有什么关系？该项目将利用从湖泊岩心获得的记录，仔细地重建该地区的温度。结果数据将与各种气候模型的结果进行比较。该项目将通过支持两名研究生的培训，为劳动力发展做出贡献。学生和他们的导师将利用布朗STEM外展办公室的活动，在罗得岛州普罗维登斯的K-12教室，那里的教室人口主要由STEM领域中代表性不足的少数族裔组成。该项目将在暑假期间将一名K-12教师带入实验室，并支持该教师参加一个重要的地区性科学会议。该小组将参加卡克托维克海洋学项目，该项目位于阿拉斯加州卡克托维克的伊努皮亚特村，面向K-12学生。收集的数据将公之于众，作为阿拉斯加冻土带科学的参考。最后，主要调查人员将把现有的项目博客扩展为与该项目有关的公共宣传的专用网站。PI将使用一套有机地球化学和传统的古生态指标，从阿拉斯加北坡四个湖泊的沉积物岩芯中生成自末次盛冰期以来的高分辨率、多代理的温度和火灾记录。这些数据将根据完全耦合的气候模型的预测进行测试，以评估IPCC级模型模拟过去气温变化的能力，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，表明：1)这些湖泊中的烯烃分布与初夏温度之间存在着强烈的、可量化的关系，北冰洋湖泊沉积物中的植物叶蜡D/H比率记录了平均夏季温度；2)湖泊沉积物中的多环芳烃(PAH)记录了区域火灾历史；以及3)多指标分析可以确定初夏、中期和平均夏季温度的温度变化，并将允许对季节性温度变化的影响及其相关的反馈和强迫进行关键检查。PAH方法补充了木炭记录，并允许在更广泛的区域范围内探测古火灾。研究地点位于图利克野外站北极长期生态研究(LTER)地点内，该地点自1975年以来才开始提供具有重要战略意义的连续监测数据。这项研究将提供基本的、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 climate. 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.