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。放射性成因的锶（Sr）和铅（Pb）同位素以及非放射性成因的钕（Nd）在冰川地形新鲜基岩和沉积物的初始风化过程中优先淋滤。随着风化时间和强度的增加，径流的同位素组成逐渐接近母岩值。因此，水和基岩的Sr、Nd和Pb同位素值之间的偏移大小提供了风化程度的信息。需要验证的具体假设是：(1)来自GrIS的水的放射性Sr和Pb排放量比来自与冰盖无关的消冰流域的水的放射性Pb排放量多，而放射性Nd排放量少；(2)同位素比值的值取决于消冰流域的暴露年龄和每种环境的风化强度；(3)来自大陆冰川的放射性同位素的总通量取决于冰川和消冰流域的相对航空范围。这些假设将在靠近Kangerlussuaq的格陵兰西部得到验证，在那里，自末次冰期以来GrIS的退缩暴露出了大约175公里宽的陆地带。水、沉积物和冰碛物质将从拉塞尔和莱弗里特冰川出口流出的冰下溪流中取样，在沃森河的前冰川分水岭，以及四个与GrIS无关的冰川消融流域，这些流域的冰碛物的年龄从600年到18000年不等。将测量水样的主要和微量元素浓度，以模拟潜在的矿物溶解和对同位素通量的贡献，并测量Sr、Nd和Pb同位素比率，以评估它们在冰下、冰前和冰川消融流域的通量。这项工作将把大陆冰川环境下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，因为它的位置靠近北大西洋深水的形成区，它应该有助于规划拟议的格陵兰岛海洋钻探探险。这项工作将通过纳入4名本科生到博士学位的学生来影响人力资源，他们都将参与实地工作，并将合作完成实验室和数据分析。这项工作的结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和通过出版物提出。外联活动将包括在当地学校演讲，在学院和大学受邀演讲，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.