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

这一提议提出了一个假设，即随着格陵兰冰盖（GrIS）的退缩，暴露和风化的增加将改变放射性同位素流向海洋的通量。放射性锶（Sr）和铅（Pb）同位素和非放射性钕（Nd）在冰川地区的新鲜基岩和沉积物的初始风化过程中优先浸出。随着风化时间和强度的增加，径流的同位素组成接近母岩值。因此，水和基岩的Sr，Nd和Pb同位素值之间的偏移量提供了有关风化程度的信息。有待检验的具体假设是：（1）与与冰盖无关的冰川消退流域相比，来自冰川消退流域的水中放射成因Sr和Pb排放量更多，放射成因Nd排放量更少;（2）同位素比值取决于冰川消退流域的暴露年龄和每种环境中的风化强度;（3）大陆冰川放射性同位素的总通量取决于冰川期和冰消期流域的相对空中延伸。这些假设将在格陵兰西部Kangerlussuaq附近进行测试，自末次盛冰期以来，GrIS的撤退暴露了大约175公里宽的土地。水、沉积物和冰碛物材料将从冰碛下溪流中取样，这些溪流从拉塞尔冰川和莱弗里特冰川的出口门户、沃森河的冰前流域以及四个冰川消退的流域中排出，这些流域未连接到年龄约为600至18,000年的冰碛物的GrIS。将测量水样的主要和微量元素的浓度，以模拟潜在的矿物溶解和贡献的同位素通量，并为Sr，Nd和Pb同位素比值，以评估其通量从冰下，冰前和冰川消退流域。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，因为它靠近北大西洋深水的形成区域，它应该有助于规划格陵兰岛附近拟议的海洋钻探探险。这项工作将通过纳入4名从本科到博士的学生来影响人力资源。所有这些人员都将参与实地工作，并将合作完成实验室和数据分析。研究成果将用于若干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发表。外联活动将包括在当地学校举办讲座，作为学院和大学的特邀演讲者，以及在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.