Neglected fluxes: Understanding the evolution of weathering as continental ice sheets retreat

格陵兰冰盖是北方最大的冰盖。 然而，随着北极变暖，冰盖一直在退缩，结果，改变了风化的基本性质以及向海洋输送营养物质和元素的方式。 拟议的工作重点是水文，生物，地球化学，和同位素的签名的冰川前流域，这是流域输送稀释，但大量的冰川融水从顶部和下面的冰盖到海洋，和冰川消退流域，这是流域不再物理连接到冰盖和来源，只有每年的降水量和永久冻土融化。 PI认为，虽然冰消流域受到的关注较少，但初步工作表明，对于海洋和大气通量，它们可能与冰前流域同等重要或更重要。 此外，随着冰盖融化，对融水和成分通量有贡献的地区将越来越多地来自冰消流域。 从这项工作中获得的理解将为预测未来的陆-海和陆-气通量提供一个背景，以应对冰盖的持续退缩。该项目的结果有可能改变我们对全球二氧化碳，营养物质和同位素循环的理解，以应对冰盖的崩溃，并允许预测未来对全球变暖和冰盖退缩的反应。 结果还将提供一个背景下解释过去的高纬度冰盖退缩和气候变化的基础上海洋同位素记录。 该项目包括对本科生、研究生和博士后研究人员的培训，以及与格陵兰学术机构的学生和教师的合作。拟议的研究将测试以下假设：（1）冰消和冰前流域由于不断演变的风化模式而向海洋和大气贡献不同的元素、同位素和营养物通量，随着格陵兰冰盖的退缩，这些反应和相关通量将在流域内和流域之间发生变化。该项目侧重于三个实地区域：Kangerlussuaq和Narsasuaq附近的冰消期和冰前期流域以及Sisimiut附近的冰消期流域。 每个地区都有不同的水平衡，暴露年龄和风化特征，并将在两个融化季节进行三次采样，以评估季节内和年际变化。 溶质数据的质量平衡模型和PHREEQc模型将用于识别和评估风化反应的程度。风化程度也将根据矿物的比例贡献趋势以及溶解和推移质锶和铅同位素比率之间的抵消来估计，并将与磷通量和有机碳不稳定性和降解联系起来。这种整体方法将提供一个广泛的观点，相对元素，营养和同位素通量在冰前和冰消环境。 这些结果将提供强度，时间尺度和风化反应的驱动因素，目标是将通量与过去记录和未来与大陆冰盖崩塌相关的全球气候变化预测联系起来。

The Greenland Ice Sheet is the largest ice sheet in the northern hemisphere. However, as the arctic warms the ice sheet has been retreating, and as a result, altering the fundamental nature of weathering and the delivery of nutrients and elements to the ocean. The proposed work is focused on the hydrological, biological, biogeochemical, and the isotopic signatures of proglacial watersheds, which are watershed that convey dilute but high volume glacial meltwater from the top and underneath the ice sheet to the ocean, and deglacial watersheds, which are watersheds that are no longer physically connected to the ice sheet and sourced only by annual precipitation and permafrost melt. The PIs contend that while deglacial watersheds have received less attention, preliminary work suggests they may be equally or more important than proglacial watersheds for oceanic and atmospheric fluxes. Moreover, as the ice sheet melts, the area contributing to meltwater and constituent fluxes will increasingly be from deglacial watersheds. The understanding gained from this work will provide a context for the prediction of future land-ocean and land-atmosphere fluxes in response to continued ice sheet retreat. Results of the project have the potential to change our understanding of global CO2, nutrient, and isotope cycling in response to ice sheet collapse and permit predictions of the future responses to global warming and ice sheet retreat. Results will also provide a context to interpret past high latitude ice sheet retreat and climate change based on marine isotope records. The project includes training for undergraduate, graduate, and postdoctoral researchers, as well as a collaboration with students and faculty at a Greenlandic academic institution.The proposed study will test the hypotheses that (1) deglacial and proglacial watersheds contribute distinct elemental, isotopic, and nutrient fluxes to the ocean and atmosphere as a result of evolving weathering patterns, and (2) these reactions and associated fluxes will change within and between watersheds as the Greenland Ice Sheet retreats. The project focuses on three field areas: deglacial and proglacial watersheds near Kangerlussuaq and Narsasuaq and a deglacial watershed near Sisimiut. Each area has a distinct water balance, exposure age, and weathering characteristics, and will be sampled three times over two melt seasons to evaluate intra-seasonal and inter-annual variations. Mass balance models and PHREEQc modeling of solute data will be used to identify and assess extents of weathering reactions. Weathering extents will also be estimated based on trends in proportional contributions of minerals and offsets between dissolved and bedload strontium and lead isotope ratios, and will be linked to phosphorous fluxes and organic carbon lability and degradation. This holistic approach will provide a broad view of the relative elemental, nutrient and isotopic fluxes in proglacial and deglacial environments. These results will provide magnitudes, time scales, and drivers of weathering reactions, with a goal of linking fluxes to past records and future predictions of global climate change associated with continental ice sheet collapse.