Towards century-timescale simulation of the response of ocean sediment methane hydrates to climate change
Abstract
We show preliminary results from SpongeBOB, a new two-dimensional model of the accumulation, compaction (Sponge), and geochemistry (Beneath-Ocean Biosphere) of a deep continental margin sediment lens from the coast to the abyss, applied to the passive margin on the East coast of the United States. The model tracks the 200 million-year life history of the sediment mass from initial rifting to the present, with specified rates of subsidence and sediment accumulation to match inferences from seismic sections and deep drilling data. Gas migration is controlled by the gas volume, which allows the gas phase to become interconnected at a critical value. The present-day distribution of methane as hydrate and gas in sediments, and pore fluid tracers such as delta-13C of methane and DIC, are used to ground truth the rates of processes such as methanogenesis and gas and pore fluid migration. We subject the model to transient forcing of the glacial / interglacial cycles and of anthropogenic climate change. Most of the methane is in the stratigraphic type deposits, distributed widely at low concentrations, tending also to be found near the base of the stability zone hundreds of meters below the sea floor. The time scale for atmospheric warming to reach and melt these deposits would generally be thousands of years. The structural deposits could melt more quickly. These are controlled by subsurface gas migration through geological structures such as faults and permeable layers. Hydrate concentrations can be much higher in structural deposits, and much closer to the sea floor. We make a preliminary attempt to resolve these two parts of the hydrate methane reservoir by explicitly incorporating representative geological features into the two-dimensional model, such as extensional faulting in the crust and overlying sediments and the effects of permeable layers associated with turbidites.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.U34A..01A
- Keywords:
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- 0714 Clathrate;
- 1050 Marine geochemistry (4835;
- 4845;
- 4850);
- 1622 Earth system modeling (1225);
- 4255 Numerical modeling (0545;
- 0560);
- 4806 Carbon cycling (0428)