Gas Hydrate Deposits below the Arctic Ocean: Response to Glacial Cycles and Global Warming

科学价值：全球变暖将不可避免地破坏未来天然气水合物矿床的稳定。然而，任何甲烷释放的规模和后果目前尚不清楚。解决对天然气水合物的担忧之所以困难，是因为对天然气水合物如何应对气候变暖的理解不全面。一个关键因素是应对的时间尺度。缓慢的甲烷扩散损失主要被与硫酸盐的反应消耗，并在沉积物中以CaCO3的形式沉淀，对气候影响很小。更快速的反应可能会将甲烷直接释放到海洋和大气中，在那里它可能会扰乱气候和碳循环。区分这些可能性是这项研究的首要目标。首席调查员将对北冰洋浅层大陆架下的天然气水合物进行建模研究。这些沉积物被认为是冰川时期的遗迹，当时较低的海平面使大陆架暴露在零度以下的温度下。自上一次冰川盛期以来，海平面的上升淹没了大陆架，并带来了地表温度的变化，从+10度到+15摄氏度。在过去的10年里，底层沉积物中的天然气水合物一直在对这种变暖做出反应。升温的持续时间和幅度为研究天然气水合物沉积的响应提供了一个独特的自然实验。首席调查员将使用来自波弗特海的温度和孔压的测井观测来约束和测试天然气水合物形成和解离的机制模型。观察结果和模型的比较将被用来解决两个具体问题。天然气水合物对气候变暖的响应时间尺度是多少？水合物沉积物中有多少部分能够将甲烷释放到海洋和大气中？这项研究的预期结果将是更好地理解控制甲烷从水合物沉积物中释放的基本物理过程。这项工作与北极未来变暖特别相关，尽管所获得的知识应该可以转移到其他海洋地点。更广泛的影响：这项研究的一个重要成果超出了项目的直接目标，它将能够在预测未来大气中二氧化碳和甲烷的浓度时更可靠地考虑天然气水合物。强调机械论模型的动机是希望避免基于当前条件的临时假设。首席调查员将应用这里开发的模型来研究过去和未来的情况。对北冰洋下面的天然气水合物的关注与未来对全球变暖的预测特别相关，因为北极的变化预计将是最剧烈的。北极地区也可能与古新世-始新世最热时期水合物过去释放的甲烷有关。这项研究将支持对一名女研究生开发和使用定量物理模型的培训。在本研究期间汇编的电子数据库(包括测井数据和陆架沉积物有机碳浓度的测量)将通过一个网站提供。首席调查员将向感兴趣的研究人员提供模型源代码

ABSTRACTBuffettOPP-0713742Scientific Merit: Global warming will inevitably destabilize gas hydrate deposits in the future. However, the magnitude and consequence of any methane release is not presently known. The difficulty in addressing concerns about gas hydrate is due to an incomplete understanding of how gas hydrate responds to warming. A crucial factor is the time scale for the response. Slow, diffusive loss of methane is largely consumed by reactions with sulfate and precipitated as CaCO3 within the sediments, with little effect on climate. A more rapid response may release methane directly into the ocean and atmosphere, where it can perturb both climate and the carbon cycle. Distinguishing between these possibilities is an overarching goal of the research. The Principal Investigator will undertake a modeling study of gas hydrate below shallow continental shelves in the Arctic Ocean. These deposits are thought to be a relic of the glacial period when lower sea level exposed the shelves to sub-zero temperatures. Rising sea level since the last glacial maximum has inundated the continental shelves and brought a temperature change to the surface of +10o to +15 oC. Gas hydrates in the underlying sediments have been responding to this warming for the past 10 kyr. The duration and magnitude of the warming provides a unique natural experiment to investigate the response of a gas hydrate deposit. The Principal Investigator will use well-log observations of temperature and pore pressure from the Beaufort Sea to constrain and test mechanistic models for gas hydrate formation and dissociation. A comparison of observations and models will be used to address two specific questions. What is the time scale for gas hydrate to respond to warming? What fraction of the hydrate deposit is capable of releasing methane into the ocean and atmosphere? The expected outcome of the research will be an improved understanding of the basic physical processes that control the release of methane from hydrate deposits. The work is specifically relevant to future warming in the Arctic, although the knowledge gained should be transferable to other marine locations. Broader Impacts: An important result of this research that extends beyond the immediate goals of the project will be an ability to account more reliably for gas hydrate in predictions of future atmospheric concentrations of CO2 and CH4. The emphasis on mechanistic models is motivated by the desire to avoid ad hoc assumptions based on present-day conditions. The Principal Investigator will apply the models developed here to investigate conditions in the past and future.The focus on gas hydrate below the Arctic Ocean is particularly relevant for future predictions of global warming because the changes in the Arctic are expected to be most dramatic. The Arctic region may also be relevant for past release of methane from hydrates during the Paleocene-Eocene Thermal Maximum. The research will support the training of a female graduate student in the development and use of quantitative physical models. The electronic databases compiled during this study (including well-log data and measurements of organic carbon concentration in shelf sediments) will be made available through a web site. The Principal Investigator will provide model source codes to interested researchers