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

点击翻译按钮获取中文摘要

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