Collaborative Research: Environmental Fluctuations during the Arctic Eocene Growing Seasons: Stable Isotope Analysis of Plant Fossils from Axel Heiberg Island

这是由约翰霍普金斯大学、马萨诸塞州理工学院和迈阿密大学的主要研究人员共同提出的一项合作建议。 北极地区的化石记录在始新世（5780 - 3660万年前）的热带时期是惊人的，包括广泛的落叶针叶林和生活在北纬80度左右的大型爬行动物。特别令人感兴趣的是北极地区降水类型和数量、相对湿度和温度的季节性波动。利用植物化石的形态特征对始新世北极地区阿克塞尔海伯格岛的古温度特征进行了研究，发现年平均温度和冷月平均温度之间存在很大差异（差异高达15摄氏度），这表明该地区具有极端的季节性，每年的相对湿度变化很大，生长季节早期融雪对生态系统的贡献很大。主要研究人员将使用阿克塞尔海伯格岛植物化石材料作为相对湿度和植物可用水的同位素组成的替代品来测试这一假设。这项工作是他们以前的地球化学研究的延伸，旨在利用植物化石中的氧、氢和碳稳定同位素来量化始新世中期北极的陆地古气候。 本文提出的工作包括两个互补的方法：1）氧和氢稳定同位素分析的亚采样的水杉木材生长轮的时间分辨率接近每月的间隔;和2）GC-IRMS分析的植物生物标志物提取的树脂和沉积物的阿克塞尔海伯格岛。利用植物化石纤维素和树脂的稳定同位素分析，主要研究人员将测试早期水是否相对于后期水被同位素耗尽，这与融雪对早期植物可用水的贡献是一致的。这些分析还将使他们能够计算始新世北极生长季节期间相对湿度的变化;多雪的冬季和温暖的生长季节之间的过渡将带来相对湿度的增加。使用植物萜类化合物的分类分析将打开一个新的窗口，通过许多有机轴承层的阿克塞尔海伯格岛的植物群的相对丰度;生物标志物分析的树脂岩和他们的碳，氢和氧同位素组成将揭示始新世和本pCO 2和其长期之间的差异？13 C，以及地下水的同位素特征。该项目的学术价值集中在其对北极始新世季节性的新解释上，可以与以前的研究进行比较，其中大多数研究都集中在始新世期间中纬度低季节性的证据上。1）三名研究生和三名本科生的参与（在麻省理工学院少数民族学生资源办公室和巴尔的摩环境生物学合作项目的帮助下确定）; 2）通过几个NSF资助的教育中心传播结果，包括体验南极和北极网站的教师;和3）增强迈阿密大学的仪器基础设施，因为高压液相色谱（HPLC）系统被添加到永久性分析设施中。

AbstractJahrenOPP-0323877SternbergOPP-0322364Summons OPP-0324276 This is a collaborative proposal by Principal Investigators at Johns Hopkins University, Massachusetts Institute of Technology, and the University of Miami. The fossil record in Arctic regions is striking during the Eocene (57.8 - 36.6 million years ago) tropical interval, and includes extensive deciduous conifer forests and large reptiles living at ~80 degreesN latitude. Of particular interest is the seasonality of the Arctic with respect to fluctuations in type and amount of precipitation, relative humidity, and temperature. Paleotemperature characterizations of the Eocene Arctic on Axel Heiberg Island using morphological features of plant fossils have revealed large differences between Mean Annual Temperature and Cold Month Mean estimates (up to 15degreesC difference) suggesting extreme seasonality with large annual changes in relative humidity and an early growing-season contribution of snowmelt into the ecosystem. The Principal Investigators will test this hypothesis by using Axel Heiberg Island fossil plant materials as proxies for relative humidity and the isotopic composition of plant-available water. This work is extension of their previous geochemical studies toward quantifying the terrestrial paleoclimate of the middle-Eocene Arctic using oxygen, hydrogen, and carbon stable isotopes in plant fossils. The work proposed here consists of two complementary approaches: 1) Oxygen and hydrogen stable isotope analyses of sub-sampled growth rings of fossilized Metasequoia wood at a temporal resolution approaching monthly intervals; and 2) GC-IRMS analyses on plant biomarkers extracted from fossilized resin and sediments of Axel Heiberg Island. Using stable isotope analyses of plant-fossil cellulose and resin, the Principal Investigators will test whether early-season water was isotopically depleted relative to late-season water, which would be consistent with snowmelt contributing to early-season plant-available water. These analyses will also allow them to calculate changes in relative humidity during the Eocene Arctic growing season; the transition between a snowy winter and a warm growing season would carry with it an increase in relative humidity. Taxonomic analysis using plant terpenoids will open a new window on the relative abundance of plant groups through the many organic-bearing strata of Axel Heiberg Island; biomarker analyses of resinites and their carbon, hydrogen and oxygen isotope compositions will shed light on secular differences between Eocene and present pCO2 and its ?13C, as well as the isotopic signature of groundwater. The intellectual merit of this project centers around its new account of Arctic Eocene seasonality that can be compared to prior studies, most of which focused upon evidence for low seasonality at middle latitudes during the Eocene.Broader impacts resulting from this proposed project include: 1) the involvement ofthree graduate and three undergraduate students (identified with help from the M.I.T.Minority Student Resource Office and the Baltimore Collaborative in EnvironmentalBiology Project); 2) the dissemination of results via several NSF-funded educational centers, including the Teachers Experiencing Antarctica and the Arctic Website; and 3)enhancement of the instrumentation infrastructure at the University of Miami as a highpressure liquid chromatography (HPLC) system is added to the permanent analyticalfacilities.