EAGER: Collaborative Research: Development of an isotope-enabled reactive transport tool to simulate carbon transformations in karst environments

EAGER：合作研究：开发同位素反应运输工具来模拟喀斯特环境中的碳转化

• 批准号: 1600931
• 负责人: Jennifer Druhan
• 金额: $ 4.53万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-05-01 至 2018-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1600931&HistoricalAwards=false
• 关键词: EAGER; Collaborative; Research; Development; isotope

Understanding the processes that control the storage and transformation of carbon near Earth's surface -- the zone encompassing the vegetation canopy, through the soil, to ground water -- is essential for predicting the long-term impacts of climate change on Earth's carbon cycle. Cave minerals are capable of recording these processes because as they grow they record the chemistry of groundwater seeping into the cave through time. Carbon isotope ratios in cave minerals have the potential to provide essential clues as to how Earth's carbon cycle responded to past climate changes. However, though carbon isotope ratios in cave minerals are easily measured, they can be difficult to interpret given the number of factors that influence cave systems. The goal of this research is to use observations of water chemistry variability from the surface through the soil and into a Tennessee cave system to construct and verify a computer model that simulates the transport and reaction of carbon in the Earth's surface. This software can be used to question the environmental factors that are most important for controlling carbon isotopes in cave systems. Through this research, a new and versatile computational capability will emerge to help determine how climate is recorded in cave minerals. This will provide a deeper understanding of carbon cycle response to past climate changes and thus help to make critical predictions for the future. This project is led by two early career female scientists and will involve the training of two new Ph.D. students and at least two undergraduate students.Carbon isotope records of speleothem hold great potential for reconstructing past changes in the Earth's surface response to climate change, such as transient vegetation, soil respiration, carbon stabilization in deep soils, and/or chemical weathering in the epikarst. Yet, because of their inherent complexity, these data often go unpublished and un-interpreted, despite being regularly collected during more common oxygen isotope investigations. By sampling waters from soils and drip sites within a cave on a multi-year timescale, it is possible to observe how seasonal environmental signals are translated and modified along heterogeneous flow paths in the soil and epikarst. However, interpreting time-averaged speleothem records representing climate changes occurring over years to centuries requires integration of observational data and simulation studies that provide a temporal bridge between long and short-term processes. The current research tackles this problem through the development of a carbon isotope enabled reactive transport model that is calibrated and tested in a karst system, providing a novel tool for the investigation and interpretation of speleothem carbon isotope records. This will be accomplished through modification of the reactive transport model CrunchTope to accommodate three-isotope systems to simulate stable and radioactive carbon isotope fractionation and decay within a multicomponent reaction network. Validation of the model for karst settings will be accomplished using data from an ongoing environmental monitoring program at Blue Spring Cave in Tennessee. Once functionality of the CrunchTope model has been demonstrated for the Blue Spring karst environment, this approach can be expanded to investigate carbon isotope systematics and speleothem carbon isotope records from a variety of cave settings and climate regimes. Looking beyond carbon, this model will provide a versatile tool for evaluating the partitioning and resultant distribution of numerous isotope systems in karst settings (e.g. Calcium, Magnesium, Strontium, Uranium), and thus the model will facilitate development and interpretation of a variety of cutting-edge paleoclimate proxy records from cave environments.

了解控制地球表面附近碳储存和转化的过程-这一区域包括植被冠层，通过土壤转化为地下水-对于预测气候变化对地球碳循环的长期影响至关重要。洞穴矿物能够记录这些过程，因为随着它们的生长，它们记录了地下水渗入洞穴的化学过程。洞穴矿物中的碳同位素比率有可能为地球的碳循环如何应对过去的气候变化提供重要线索。然而，尽管洞穴矿物中的碳同位素比率很容易测量，但由于影响洞穴系统的因素众多，因此很难解释。这项研究的目标是利用从地表到土壤的水化学变化的观测，并进入田纳西州的洞穴系统，以构建和验证一个计算机模型，模拟地球表面碳的运输和反应。该软件可用于质疑对控制洞穴系统中碳同位素最重要的环境因素。通过这项研究，将出现一种新的通用计算能力，以帮助确定气候如何记录在洞穴矿物中。这将使人们更深入地了解碳循环对过去气候变化的反应，从而有助于对未来做出关键性的预测。该项目由两名早期职业女性科学家领导，将培训两名新的博士。洞穴沉积物的碳同位素记录对于重建地球表面对气候变化的响应具有很大的潜力，例如瞬时植被，土壤呼吸，深层土壤中的碳稳定性和/或表层岩溶的化学风化。然而，由于其固有的复杂性，这些数据往往去未发表和未解释，尽管定期收集在更常见的氧同位素调查。通过对洞穴内土壤和滴水点的沃茨进行多年时间尺度的采样，可以观察到季节性环境信号是如何沿着土壤和表层岩溶中的异质流动路径进行翻译和修改的。然而，解释时间平均的洞穴沉积物记录，代表气候变化发生在几年到几个世纪，需要综合观测数据和模拟研究，提供一个长期和短期过程之间的时间桥梁。目前的研究解决了这个问题，通过开发一个碳同位素启用的反应性运输模型，在岩溶系统中进行校准和测试，提供了一个新的工具，调查和解释的洞穴沉积物碳同位素记录。这将通过修改反应性传输模型CrunchTope来实现，以适应三同位素系统，模拟多组分反应网络内的稳定和放射性碳同位素分馏和衰变。岩溶环境的模型验证将使用正在进行的环境监测计划在田纳西州蓝泉洞的数据。一旦CrunchTope模型在蓝泉喀斯特环境中的功能得到证明，这种方法就可以扩展到研究各种洞穴环境和气候状况的碳同位素系统学和洞穴沉积物碳同位素记录。展望未来的碳，这个模型将提供一个多功能的工具，用于评估岩溶环境中的许多同位素系统（如钙，镁，锶，铀）的分区和由此产生的分布，因此，该模型将有助于开发和解释各种尖端的古气候代理记录从洞穴环境。