Geomicrobiology and biogeochemistry of gas hydrates and cold seeps
1. Introduction
This special issue grew out of a topical session organized for the 2001 Fall Meeting of the American GeophysicaI Union in San Francisco, CA, USA. The goal was to provide a synthesis of a rapidly expanding research area: geomicrobiology and biogeochemistry of gas hydrates and cold seeps. We have attempted to include the most up-to-date research possible; therefore, while the focus is on review of this field, most of the papers include some previous ly unpublished data, and some papers are describing new research.
Gas hydrates are ice-like crystalline deposits in which hydrocarbon and non-hydrocarbon gases are held within rigid cages of water molecules. It is currently estimated that 2100-3600 Gt (1Gt= 1015g) of methane resides in marine gas hydrates (Milkov et al., 2003a). In addition, mud volcanos and seeps may emit 6-13 Tg (1 Tg=1012g) year-1 of CH4 to the atmosphere from onshore and shallow offshore oceans (Dimitrov, 2002; Milkov et al., 2003b). These estimates emphasize the potential importance of methane hydrates, mud volcanos, and cold hydrocarbon seeps for the global carbon cycle.
Most gas hydrates are found in marine sediments. Marine gas hydrates are formed at high pressure and low temperature on continental slopes/rises and are often associated with hydrocarbon vents, seeps, or mud volcanoes. Modern gas hydrates and seeps have been found globally at deep-sea spreading centers, convergent plate boundaries, and passive continental margins (Fig. 1). Relic hydrate- and seep-locations have been identified around the world in geologic formations ranging from Quaternary to Devonian (e.g., Beauchamp et aI., 1989; Peckmann and Thiel, this issue).
This
special issue is organized according to geo-graphic regions where gas
hydrates and cold seeps have been found (Fig. 1); some of the hydrate
or seep locations have been studied in significant detail, while others
have only preliminary descriptions. The first four papers describe the
geochemistry and microbiology of the Gulf of Mexico (Sassen et al., Joye
et al., Orcutt et aI., and Formolo et aI.). These are followed by studies
in the Hydrate Ridge (Boetius and Suess) and Eel River Basin (Orphan et
al.) on the western coast and the Blake Ridge (Borqwski) on the eastern
coast of the North America. This first group of papers addresses the best
known and studied sites of gas hydrates, hydrocarbon vents, or cold hydrocarbon
seeps. The next five papers describe gas hydrates and seeps in modern
oceans or seas outside the North America; some of tl1ese sites are less
well studied. These include the Mediterra- nean Sea (Werne et al.), the
Norwegian Sea (Hakon . Mosby) (Milkov et aI.), the Nankai Trough (Colwell
et al.), the Congo-Angola Basin (Charlou et al.), and tl1e Black Sea and
Cariaco Basin (Wakeham et al.) (Fig. 1). The final two papers describe
ancient seep environments (Peckmann and Thiel; Pierre and . Rouchy), which
extend the importance of hydrate- or seep-associated biogeochemical processes
to the geological past.
SREL Reprint #2849
Zhang, C. L. and B. Lanoil. 2004. Geomicrobiology and biogeochemistry of gas hydrates and cold seeps. Chemical Geology 205:187-194.
