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

AbstractJahrenOPP-0323877SternbergOPP-0322364Summons OPP-0324276这是约翰霍普金斯大学、麻省理工学院和迈阿密大学的首席研究人员共同提出的建议。北极地区的化石记录在始新世(5780万年前)热带间期是惊人的，包括广泛的落叶针叶林和生活在北纬80度的大型爬行动物。特别令人感兴趣的是北极在降水类型和数量、相对湿度和温度方面的季节性波动。利用植物化石的形态特征对阿克塞尔海贝格岛始新世北极的古温度进行了表征，显示出年平均温度与冷月平均估计值之间的巨大差异(高达15摄氏度的差异)，这表明了极端的季节性，相对湿度的年变化很大，生长季节较早，融雪对生态系统的贡献。首席调查人员将使用阿克塞尔·海贝格岛的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物来检验这一假设。这项工作是他们之前的地球化学研究的延伸，目的是利用植物化石中的氧、氢和碳稳定同位素来量化中始新世北极的陆地古气候。这项工作由两种互补的方法组成：1)水杉木材化石生长轮的氧和氢稳定同位素分析，时间分辨率接近月间隔；2)从阿克塞尔海贝格岛的化石树脂和沉积物中提取的植物生物标志物的GC-IRMS分析。使用植物化石纤维素和树脂的稳定同位素分析，首席调查员将测试早期水相对于后期水是否同位素耗尽，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期间相对湿度的变化；从多雪的冬季到温暖的生长季的过渡将带来相对湿度的增加。利用植物萜类化合物进行的分类分析将打开一扇新的窗口，了解阿克塞尔海贝格岛许多有机地层中植物群的相对丰度；树脂及其碳、氢和氧同位素组成的生物标志物分析将有助于揭示始新世与现代PCO2及其~(13)C之间的长期差异，以及地下水的同位素特征。这个项目的学术价值集中在它对北极始新世季节性的新描述上，可以与以前的研究相比较，大多数研究集中在始新世中纬度季节性较低的证据上。这个拟议项目产生的更广泛的影响包括：1)涉及三名研究生和三名本科生(在麻省理工学院少数族裔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，包括体验南极洲的教师和北极网站；以及3)加强迈阿密大学的仪器基础设施，因为在永久性分析设施中增加了高压液相色谱(HPLC)系统。

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 15 degreesC 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.