Estimation of pore space methane hydrate in marine sediments of Cascadia Margin

Abstract

The first key controlling factor to estimate the methane yield is the percentage of organic carbon that can be utilized by methanogenic bacteria. Total Organic Carbon (TOC) analysis is one of the most common proxies which provide clues for methane rich seep zones. Bacteria and bacterial activity play a vital role in the degradation of organic matter. It has been revealed that the presence of sulphate reducing bacteria at bottom layers of the core, suggests the presence of methane from the subsurface layers where methanogenesis process takes place. The present study is resulted from Integrated Ocean Drilling Program (IODP), Hole 1325B, during the Pleistocene sequence of North-Eastern Pacific Ocean and further supporting results for entire 311 transect obtained from published records of Shipboard Scientific Party. The total carbon (TC), inorganic carbon (IC) and TOC content is examined individually for 357 samples from various depths, measures the rate of deposition of total organic carbon. The average values of TC, IC and TOC shows quite fluctuating trends in the study region with 0.67 wt%, 0.11 wt% and 0.56 wt% respectively. Many published results suggest that 0.5 wt% TOC is required for hydrate formation by determining the average TOC content at hydrate bearing sediments. The outcome of proposed study put forward that the TOC content is an important aspect for the formation of methane hydrate in marine sediment. The rate of methane generated, dissolved methane are also estimated in order to calculate the pore space methane hydrate in the study area. This accumulation can roughly explain the average amount of hydrates as 0.85% in the sediments at the study region and 0.88% particularly from Hole 1325B where the amount of methane generated at 146.48 mM.