Weathering of western Greenland: Influences on oceanic fluxes of radiogenic isotopes

这一提议解决了这样一种假设，即随着格陵兰冰盖(GRIS)的消退，暴露和风化的增加将改变海洋中放射性同位素的通量。在冰川地区新鲜基岩和沉积物的初始风化过程中，放射性成因的锶(锶)和铅(铅)同位素以及非放射性成因的钕(ND)优先被淋溶。随着风化时间和风化强度的增加，径流的同位素组成接近母岩的值。因此，水和基岩的锶、钕和铅同位素值之间的偏移量提供了有关风化程度的信息。需要检验的具体假设是：(1)与未与冰盖相连的冰川退化流域相比，来自GRIS的水中放射性成因的锶和铅更多，放射性成因的ND更少，(2)同位素比值的值取决于冰川退化流域的暴露年龄和每种环境的风化强度，(3)大陆冰川的放射性成因同位素的总通量取决于冰川和冰川退化流域的相对空中范围。这些假设将在格陵兰岛西部靠近Kangerlussuaq的地方得到验证，自上一次冰盛期以来，GRI的撤退暴露了大约175公里宽的狭长地带。水、沉积物和冰河物质将从罗素冰川和莱弗里特冰川出口流出的冰下溪流、沃森河的前冰川分水岭和四个冰川消融的分水岭中采集样本，这些分水岭没有连接到GRIS，这些分水岭的年龄从大约600到18,000年不等。将测量水样中主要元素和微量元素的浓度，以模拟潜在的矿物溶解和对同位素通量的贡献，并测量锶、钕和铅的同位素比率，以评估它们来自冰下、冰期和冰川消融流域的通量。这项工作将把大陆冰川环境中的陆地风化产物与放射性同位素的海洋通量联系起来，从而提高解释海洋记录的能力。这项工作很重要，因为它位于北大西洋深水地层区域附近，它应该有助于规划拟议中的格陵兰附近的海洋钻探探险。这项工作将通过吸收4名从本科生到博士水平的学生来影响人力资源，所有这些学生都将参与实地工作，并将合作完成实验室和数据分析。这项工作的成果将用于几个研究生和本科生课程，并将在国家和国际科学会议上以及通过出版物介绍。外展活动将包括在当地学校演讲，作为学院和大学的特邀演讲者，以及佛罗里达自然历史博物馆的年度开放日。

This proposal addresses the hypothesis that as the Greenland Ice Sheet (GrIS) retreats, increased exposure and weathering will alter fluxes of radiogenic isotopes to the oceans. Radiogenic strontium (Sr) and lead (Pb) isotopes, and non­radiogenic neodymium (Nd) are preferentially leached during initial weathering of fresh bedrock and sediments in glacial terrains. With increased duration and intensity of weathering, isotopic compositions of runoff approach parent rock values. Therefore, magnitudes of offsets between Sr, Nd and Pb isotope values of water and bedrock provide information about the extent of weathering. Specific hypotheses to be tested are (1) more radiogenic Sr and Pb and less radiogenic Nd discharge in water originating from the GrIS than from deglaciated watersheds without connections to the ice sheet, (2) values of isotope ratios depend on the exposure age of the deglaciated watersheds and the intensity of weathering in each environment, and (3) the total flux of radiogenic isotopes from continental glaciers depends on the relative aerial extents of glaciated and deglaciated watersheds. These hypotheses will be tested in western Greenland near Kangerlussuaq, where retreat of the GrIS since the Last Glacial Maximum has exposed an approximately 175 km wide strip of land. Water, sediment, and moraine material will be sampled from subglacial streams discharging from the outlet portals of the Russell and Leverett Glaciers, in the proglacial watershed of the Watson River, and in four deglaciated watersheds, not connected to the GrIS that drain moraines ranging in age from about 600 to 18,000 years. Water samples will be measured for major and trace element concentrations to model potential mineral dissolution and contributions to isotope fluxes, and for Sr, Nd, and Pb isotope ratios to assess their fluxes from subglacial, proglacial, and deglaciated watersheds. This work will link terrestrial weathering products in a continental glacier setting to oceanic fluxes of radiogenic isotopes, thereby improving the ability to interpret marine records. The work is important because of its location near the formation regions of North Atlantic Deep Water and it should contribute to planning for a proposed ocean drilling expedition off Greenland. The work will impact human resources through incorporation of 4 students from undergraduate to Ph.D. level, all of whom will participate in field work and will work collaboratively to complete laboratory and data analyses. Results of the work will be used in several graduate and undergraduate courses and will be presented at national and international scientific meetings and through publications. Outreach will include lectures at local schools, as invited speakers at colleges and universities, and in the annual open house at the Florida Museum of Natural History.