A clathrate source for Black Sea Basin methane?
William S. Reeburgh, Ph.D.
University of California, Irvine
Wednesday, January 13, 1999
3:00 p.m.Pacific Forum
Following a brief summary of methane biogeochemistry, this seminar focuses on methane
data obtained during the 1988 U.S.-Turkish Black Sea Expedition. The water column data
consists of methane concentration profiles, oxidation rate profiles measured using two
independent radioactive tracers, C3H4
and 14CH4, and a
recently measured stable isotope (d 2H-CH4 and d 13C-CH4) profile from a central station. Sediment methane profiles
were measured on cores collected at a shelf and deep-basin station.
The water column profiles show uniform and high methane concentrations and oxidation
rates at depths below 500 m, suggesting a methane residence time on the order of decades.
Although shelf sediments are a source of methane, the deep basin sediments consume methane
and cannot supply the deep-water column. Because there is no way to maintain the uniform
deep-water column methane distribution with a shelf source, our problem is to find a deep
The recent carbon and hydrogen stable isotope measurements offer insights into the
"missing" methane source. The deep basin methane is isotopically heavy below 500
m, indicating that it is either the most extensively oxidized biogenic methane observed to
date, or that dissociating clathrates might be the source. A clathrate source appears to
be the most reasonable possibility for maintaining the uniform deep methane concentration
and isotope distributions.
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Last updated: December 19, 2000