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

当冰川缓缓穿过这片土地时，它们可以扮演推土机的角色，将岩石拉起，碾磨成细小的沉积物。几千年到几百万年来，冰川穿过了南极的地形，留下了这些被地面覆盖的沉积物。这项研究建立在研究人员的试验性发现的基础上，这些发现揭示了麦克默多干谷(MDV)中发现的冰川来源的细粒沉积物中的表面积的巨大和可变的测量结果，MDV是目前南极大陆上为数不多的没有被冰覆盖的景观之一。表面积是化学风化的关键，化学风化是指当离子在溪流和地下水中被带走时，岩石转化为土壤的过程。这些化学风化过程也是地球系统从大气中自然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”，这反过来又意味着从大气中去除更多潜在的二氧化碳。因此，高表面积冰川沉积物中的化学风化可能会对地球的碳循环产生重大影响。研究人员将测量以前从干燥山谷收集的沉积物的化学性质和物理性质，以了解哪些因素导致产生具有高表面积和潜在“气候能力”的沉积物，并调查这些冰川系统产生的沉积物最终可能如何影响地球的碳收支。这项研究的结果将帮助科学家(包括建模人员)完善对冰川融化影响的预测-以及随之而来的冰川沉积物暴露？大气中的碳含量。这些结果还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，这项研究还将涉及几名本科生、研究生和博士后，包括科学教育本科生，从而有助于培训下一代STEM工人。物理风化产生新鲜的表面，极大地提高原生矿物的比表面积(SSA)和反应表面积(RSA)。定量测定沉积物的SSA和RSA是确定自然风化过程中溶解和淋溶速率的关键，但关于沉积物SA分布的数据很少，特别是在冰川和河流系统中。来自泰勒谷和莱特谷(位于MDV)的冰川河流系统的试点数据显示，SSA和RSA的值都非常高且可变，在某些情况下，这些值远远超过温带冰川系统的泥浆的值。这一发现推动了目前的研究，旨在调查以下假设：莱特谷和泰勒山谷中泥浆的高和可变SA反映了MDV、生物控制、粉尘添加和/或成土过程中不同沉积环境的结构和/或成分遗传。这些假说将通过沉积学、矿物学和地球化学学的方法进行验证，这些泥浆来自不同环境(冷冰期和湿冰期；河流、湖泊、尘埃和漂流沉积)和不同时代(中新世到现代)的冰川沉积，并量化SA和反应性的变化。与来自温带冰川系统的分析泥浆进行比较将使极地-温带比较成为可能。分析将重点放在以前从MDV收集的沉积物的泥浆上。晶粒度和比表面积将分别用激光分析和氮气吸附BET进行测量。碳酸盐去除后，样品将重新分析SSA，并对泥浆进行地球化学表征。矿物学和大宗化学也将根据共生砂级分进行评估，并记录纹理属性。SSA归一化溶解实验将用于比较从沉积物中释放的溶质以确定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，这项研究应该会阐明南极系统的风化如何有助于全球碳循环。

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.