The geological methane budget at Continental Margins and its influence on climate change

Abstract

Geological methane, generated by microbial decay and the thermogenic breakdown of organic matter, migrates towards the surface (seabed) to be trapped in reservoirs, sequestered by gas hydrates or escape through natural gas seeps or mud volcanoes (via ebullition). The total annual geological contribution to the atmosphere is estimated as 16-40 Terragrammes (Tg) methane; much of this natural flux is 'fossil' in origin. Emissions are affected by surface conditions (particularly the extent of ice sheets and permafrost), eustatic sea-level and ocean bottom-water temperatures. However, the different reservoirs and pathways are affected in different ways. Consequently, geological sources provide both positive and negative feedback to global warming and global cooling. Gas hydrates are not the only geological contributors to feedback. It is suggested that, together, these geological sources and reservoirs influence the direction and speed of global climate change, and constrain the extremes of climate.

Bubble momentum plume as a possible mechanism for an early breakdown of the seasonal stratification in the northern North Sea

“…Based on timescale considerations, Rehder et al, 1999) proposed that the relevant process is the transport to the winter wave-mixed-layer, i.e., the deepest thermocline depth. Marine CH4 emissions occur from all global coastal oceans from biogenic and thermogenic sources (Judd et al, 2002). The latter are associated with petroleum reservoirs, which often are under production.…”

Symbioses of Methanotrophs and Deep-Sea Mussels (Mytilidae: Bathymodiolinae)

“…Hydrologic activity at cold seeps along continental margins and plate boundaries also releases sulfide-, methane-, and ammoniarich fluids from the sediment (reviewed in van Dover 2000;Judd 2003). Mud volcanoes are formed when water, mud, and gas (usually dominated by CH 4 , but may include CO 2 or nitrogen) are expelled from sedimentary sequences at zones of tectonic compression (Hedberg 1980;Brown 1990;Milkov 2000;Judd et al 2002). The methane derived from these environmental sources forms a significant proportion of the global carbon budget (Hornafius et al 1999;Judd et al 2002).…”

“…Mud volcanoes are formed when water, mud, and gas (usually dominated by CH 4 , but may include CO 2 or nitrogen) are expelled from sedimentary sequences at zones of tectonic compression (Hedberg 1980;Brown 1990;Milkov 2000;Judd et al 2002). The methane derived from these environmental sources forms a significant proportion of the global carbon budget (Hornafius et al 1999;Judd et al 2002). Methane is generated via both biogenic and inorganic processes in seabed fluids (reviewed in Judd et al 2002;Judd 2003).…”

“…The methane derived from these environmental sources forms a significant proportion of the global carbon budget (Hornafius et al 1999;Judd et al 2002). Methane is generated via both biogenic and inorganic processes in seabed fluids (reviewed in Judd et al 2002;Judd 2003). Anaerobic archaeal methanogens generate methane biologically (Huber et al 1989;Shima et al 2002).…”

“…Anaerobic archaeal methanogens generate methane biologically (Huber et al 1989;Shima et al 2002). Thermocatalytic processes deep within sediments can also degrade organic matter to yield methane (Judd et al 2002). Finally, the majority of methane at hydrothermal vents is believed to be of abiogenic origin, the result of degassing and cooling of mafic magmas and the serpentization of ultramafic rocks (Apps and van de Kamp 1993).…”