Quantifying Surface Area in Muds from the Antarctic Dry Valleys: Implications for Weathering in Glacial Systems

当冰川在陆地上爬行时，它们可以充当推土机，将岩石拔起并研磨成细小的沉积物。 冰川在数千年至数百万年的时间里穿越南极地貌，留下了这些磨碎的沉积物。这项研究建立在调查人员的试点发现的基础上，这些发现揭示了在麦克默多干谷（MDV）中发现的冰川衍生细粒沉积物中的表面积非常大和可变的测量值，这是南极大陆目前未被冰覆盖的少数景观之一。 表面积是化学风化的关键，化学风化是岩石转化为土壤的过程，因为离子被溪流和地下水带走。这些化学风化过程也是地球系统自然地从大气中去除二氧化碳的主要手段之一。因此，在沉积物中观察到的高表面积意味着高“耐候性”，这反过来又意味着更多的二氧化碳可能从大气中清除。因此，高表面积冰川沉积物中的化学风化可能对地球的碳循环产生重大影响。研究人员将测量先前从干旱山谷收集的沉积物的化学和物理性质，以了解哪些因素导致产生具有高表面积和潜在“天气能力”的沉积物，并调查这些冰川系统中产生的沉积物如何最终影响地球的碳预算。这项研究的结果将帮助科学家（包括模型制作者）完善对冰川融化影响的预测--以及随之而来的冰川沉积物的暴露？大气中的碳含量这些结果也可能有助于利用岩石风化原理开发二氧化碳去除技术的应用研究工作。除了科学上的好处，这项研究还将涉及多名本科生、研究生和博士后，包括科学教育本科生，从而有助于培养下一代STEM劳动力。物理风化产生新鲜的表面，大大提高了原生矿物的比表面积（SSA）和反应表面积（RSA）。定量SSA和RSA的沉积物是关键，以确定在自然风化过程中的溶解和浸出率，但很少有数据存在的沉积物SA的分布，特别是在冰川和河流系统。从泰勒谷和赖特谷（位于MDV）冰川流系统的试点数据表现出显着的高和变量值在SSA和RSA，值，在某些情况下大大超过从泥在温带冰川系统的值。这一发现激发了目前的研究，其目的是调查的假设，即高和可变SA的泥浆在赖特和泰勒谷反映纹理和/或成分的遗传，从不同的沉积环境内MDV，生物控制，灰尘添加，和/或成壤过程。这些假设将通过沉积学、矿物学和地球化学表征沉积在各种环境（冷与湿基冰川作用;河流、湖泊、灰尘和漂流沉积物）和不同年龄（中新世到现代）的冰川沉积物中的泥浆进行测试，并从MDV和SA和反应性的定量变化。与来自温带冰川系统的分析泥浆进行比较将能够进行极地-温带比较。分析将侧重于先前从MDV收集的沉积物的泥浆。将分别通过激光分析和N2吸附BET测量粒度和SSA。碳酸盐去除后，将对样品进行SSA重新分析，并对泥浆进行地球化学表征。矿物学和整体化学也将评估共同出现的砂馏分，并记录纹理属性。将使用SSA标准化溶解实验来比较从沉积物释放的溶质，以确定RSA。结果将与各种沉积学和地球化学分析相结合，以检验所提出的假设。最终，这项研究应该揭示南极系统的风化如何促进全球碳循环。

As glaciers creep across the landscape, they can act as earthmovers, plucking up rocks and grinding them into fine sediments. Glaciers have moved across the Antarctic landscape over thousands to millions of years, leaving these ground-up sediments in their wake. This study builds on pilot discoveries by the investigators that revealed remarkably large and variable measurements of surface area in glacially-derived fine-grained sediments found in the McMurdo Dry Valleys (MDV), one of the few landscapes on the Antarctic continent not currently covered by ice. Surface area is key to chemical weathering, the process by which rock is converted to soils as ions are carried away in streams and groundwater. These chemical weathering processes are also one of the primary means by which the Earth system naturally removes carbon dioxide from the atmosphere. Hence, high surface areas observed in sediments implies high "weatherability" which in turn translates to more potential carbon dioxide removed from the atmosphere. Therefore, chemical weathering in high surface area glacial sediments may have significant impacts on Earth's carbon cycle. The researchers will measure the chemical and physical properties of sediments previously collected from the Dry Valleys to understand what factors lead to production of sediment with high-surface area and potential "weather ability" and investigate how sediment produced in these glacial systems could ultimately impact Earth's carbon budget. Results from this research will help scientists (including modelers) refine predictions of the effects of melting glaciers- and attendant exposure of glacial sediment? on atmospheric carbon levels. These results may also contribute to applied research efforts on development of carbon-dioxide removal technologies utilizing principles of rock weathering. In addition to the scientific benefits, this research will involve several students at the undergraduate, graduate, and post-doctoral levels, including science education undergraduates, thus contributing to training of the next-generation STEM workforce.Physical weathering produces fresh surfaces, greatly enhancing specific surface area (SSA) and reactive surface area (RSA) of primary minerals. Quantifying SSA and RSA of sediments is key to determining dissolution and leaching rates during natural weathering, but few data exist on distribution of sediment SA, particularly in glacial and fluvial systems. Pilot data from glacial stream systems in Taylor Valley and Wright Valley (located in the MDV) exhibit remarkably high and variable values in both SSA and RSA, values that in some cases greatly exceed values from muds in temperate glacial systems. This discovery motivates the current research, which aims to investigate the hypothesis that high and variable SAs of muds within Wright and Taylor Valleys reflect textural and/or compositional inheritance from the differing depositional settings within the MDV, biologic controls, dust additions, and/or pedogenic processes. These hypotheses will be tested by sedimentologically, mineralogically, and geochemically characterizing muds from glacially derived sediment deposited in various environments (cold vs. wet based glaciation; fluvial, lacustrine, dust, and drift deposits) and of varying age (Miocene to Modern) from the MDV and quantifying variation of SA and reactivity. Comparisons with analyzed muds from temperate glacial systems will enable polar-temperate comparisons. Analyses will focus on muds of previously collected sediment from the MDVs. Grain size and SSA will be measured by Laser Analysis and N2 adsorption BET, respectively. After carbonate removal, samples will be re-analyzed for SSA, and muds characterized geochemically. Mineralogy and bulk chemistry will also be assessed on co-occurring sand fractions, and textural attributes documented. SSA-normalized dissolution experiments will be used to compare solutes released from sediments to determine RSAs. Results will be integrated with the various sedimentologic and geochemical analyses to test the posed hypotheses. Ultimately, this research should shed light on how weathering in Antarctic systems contributes to global carbon cycling.