HR: 16:00h
AN: OS42C-01 INVITED     [PDF]
TI: How and Why the Global Estimates of Hydrate-Bound Gas in Marine Sediments Decreased Over the Last Thirty Years, and What This Means for Resources and Global Change Evaluations
AU: * Milkov, A V
EM: alexei.milkov@bp.com
AF: BP America, EPTG, WL1 15.122 Westlake Blvd, Houston, TX 77079 United States
AB: It is often assumed that oceanic gas hydrates contain huge volume of natural gases, mainly methane. The most widely cited estimate of global hydrate-bound gas is 21$\times$10$^{15}$ m$^{3}$ of methane at STP (or $\sim$10,000 Gt of methane carbon), which is proposed as a "consensus value" from several independent estimations. This large gas hydrate reservoir is further suggested as an important component of the global carbon cycle and as a future energy source. I present a revised and updated set of relatively well-justified global estimates and analyze how and why they changed over time. It appears that the global estimates of hydrate-bound gas decreased by at least an order of magnitude from 1970s - early 1980s (estimates on the order of 10$^{17}$-10$^{18}$ m$^{3}$) to late 1980s - early 1990s (10$^{16}$ m$^{3}$) to late 1990s - present (10$^{14}$-10$^{15}$ m$^{3}$). The decrease of estimates is a result of growing knowledge of the distribution and concentration of gas hydrates in marine sediments and ongoing effort to better constrain the volume of hydrate-bearing sediments and their gas yield. These parameters appear to be relatively well constrained at present through DSDP/ODP drilling and direct measurements of gas concentration in sediments. The global estimate of hydrate-bound gas that best reflects the current knowledge of submarine gas hydrate is in the range (1-5)$\times$10$^{15}$ m$^{3}$ ($\sim$500-2,500 Gt of methane carbon). A significantly smaller global gas hydrate inventory implies that the role of gas hydrate in the global carbon cycle may be not as significant as speculated before. Gas hydrate still may be considered as a future energy resource, not because the global volume of hydrate-bound gas is large, but because some gas hydrate accumulations may contain resources significant and concentrated enough to be profitably recovered in future.
DE: 1635 Oceans (4203)
DE: 3099 General or miscellaneous
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting