Collaborative Research: Chemical Weathering and Organic Carbon Export From Arctic Watersheds, North Slope, AK

最近的气候变化对北极产生了巨大的影响，模型表明，随着二氧化碳在大气中继续积累，未来的影响将会加速。了解这个问题很重要，因为北极的环境变化可能会在人类的时间尺度上产生全球范围的影响。特别是，永久冻土中有机碳的氧化可能会对全球变暖产生积极的反馈。虽然许多研究都集中在北极变暖和碳循环之间的关系上，但大气中二氧化碳水平上升对化学风化过程的具体影响以及有机碳动态的耦合变化相对较少受到关注。该项目有两个综合目标：确定矿物风化反应和水文过程，这些反应和水文过程控制着水在土壤和溪流中运输过程中无机溶质地球化学的演变方式和速度，并建立化学风化现象与有机碳输出之间的联系。这项工作将集中在阿拉斯加北坡的源头溪流和小溪的主要离子和同位素地球化学上。基于初步数据，本工作的指导假设是碳酸盐/硅酸盐风化比随流量和多年冻土活土层深度的季节变化而波动，其中基流条件下碳酸盐/硅酸盐风化比最高，活土层深度最大；峰流条件下碳酸盐/硅酸盐风化比最低，活土层深度最小。为了验证这一假设及其对理解有机碳输出的影响，该团队将：1)量化碳酸盐和硅酸盐风化作用下主要阳离子释放、二氧化碳消耗和溶解有机碳（DIC）产生的速率；2)评价河流和土壤中Ca、Sr和C （DIC）同位素组成的控制因素；3)建立这些示踪剂与其他河流水组分的关系，包括水的H和O同位素、有机质浓度以及有机质的同位素组成（C和N）。他们将收集水、沉积物、基岩和土壤样本。从春季解冻到秋季冻结，将进行水样采集。在实验室，他们将进行浸出和消化实验，以量化矿物风化端元。他们将使用质量平衡模型、碳酸盐平衡计算、水线分离以及元素和同位素混合方程来综合数据。这项研究是阐明北极阿拉斯加河流的同位素和有机地球化学之间的基本联系的第一个综合努力之一。由于变暖可能会通过几种反馈机制改变碳酸盐与硅酸盐风化的比例，因此本研究将建立一种在流域尺度上监测北极环境变化的新方法。

Recent climate change has dramatically impacted the Arctic, and models suggest that accelerated effects will occur in the future as CO2 continues to accumulate in the atmosphere. Understanding this problem is important because arctic environmental change could have planetary-scale repercussions within human timescales. In particular, oxidation of organic carbon stored in permafrost might create a positive feedback to global warming. While numerous studies have focused on the relationship between warming and carbon cycling in the Arctic, specific effects of rising atmospheric CO2 levels on chemical weathering processes and coupled changes in organic carbon dynamics have received relatively little attention.This project has two integrated goals: to identify mineral weathering reactions and hydrologic processes that control how and at what rate the inorganic solute geochemistry of water evolves during transport within soils and streams and to establish linkages between chemical weathering phenomena and organic carbon export. The work will focus on the major ion and isotope geochemistry of headwater streams and creeks draining the North Slope of Alaska. Based on preliminary data, the guiding hypothesis of the work is that the ratio of carbonate to silicate weathering fluctuates in response to seasonal changes in discharge and permafrost active layer depth, with the highest ratios observed during base flow conditions and maximum active layer depth and the lowest ratios observed during peak flow conditions and minimum active layer depth. To test this hypothesis and its implications for understanding organic carbon export, the team will: 1) Quantify rates of major cation release, CO2 consumption, and dissolved organic carbon (DIC) production by carbonate and silicate weathering; 2) Evaluate controls on the Ca, Sr, and C (of DIC) isotope composition of rivers and soils; and 3) Establish relationships between these tracers and other river water constituents, including H and O isotopes of water, organic matter concentrations, and the isotope composition of organic matter (both C and N). They will collect water, sediment, bedrock, and soil samples. Water sampling will occur from spring thaw through fall freeze-up. In the laboratory, they will conduct leaching and digestion experiments to quantify mineral weathering end members. They will synthesize data using mass-balance modeling, carbonate equilibria calculations, hydrograph separations, and elemental and isotope mixing equations.This study represents one of the first integrative efforts to elucidate fundamental linkages between the isotope and organic geochemistry of Arctic Alaskan rivers. Because warming will likely alter the ratio of carbonate to silicate weathering via several feedback mechanisms, this study will establish a novel method for monitoring Arctic environmental change at the watershed scale.