Greenhouse gas leaking from Arctic Ocean floor
KEITH HESTER, MONTEREY BAY AQUARIUM INSTITUTE
hydrate. “If this process [of hymeters (m), depending upon Scientists have reported the drate dissociation due to rising temperature, pressure, salinity, presence of previously unknown ocean temperatures] becomes and the types of gases present, sources of methanesa greenwidespread along Arctic contiaccording to Graham Westbrook house gas some 25 times more nental margins, tens of megaof the University of Birmingham powerful than CO2 at trapping tons of methane per (U.K.). However, on a research heatsbubbling up from the Arcyearsequivalent to 5 to 10% of cruise in 2008, Westbrook and tic Ocean seafloor north of Northe total amount released glocolleagues collected sonar imway. Gradual warming of a bally by natural regional current sourcesscould be has caused temperreleased into the ature-sensitive ocean,” Westbrook methane hydrate warns. Although below the seabed most, if not all, of to break down and the methane is disdischarge the gas, solving in the seathe researchers say. water, a tiny For years, scienfraction of it transtists have debated fers to the atmowhether the plansphere by et’s rising temperaequilibration. Furtures would turn thermore, the dismethane deposits Naturally occurring deposits of gas hydratesmainly methane hydrateshave solved methane in permafrost rebeen identified from borehole samples and by using seismic-reflection lowers oxygen levgions into a “tick- profiles and other tools. Oceanic deposits occur largely along continental margins. els and contributes ing bomb” that, to ocean acidificaonce detonated, ages of more than 250 plumes of tion, the researchers note. could liberate vast quantities of methane gas rising from the seaAn assessment by Matthew T. methane to the atmosphere, floor at depths ranging between Reagan and others of Lawrence possibly triggering disastrous cli150 and 400 m. They found Berkeley National Laboratory mate-feedback effects. Some pathese plumes along a section of concluded that rapid discharges leoclimate studies have argued continental margin washed by of methane are possible for shalthat such scenarios have octhe West Spitsbergen Current low-lying hydrates in both warm curred in the past, and that the (WSC), an arm of the Gulf and cold regions. If Arctic hyprocesses of hydrate formation Stream that delivers Atlantic seadrates prove as widespread as and disintegration have been a water to the Arctic. As the WSC some evidence indicates, the asprimary driver of glacial cycles. has warmed by 1 °C over the sessment suggests, this could Over the past couple of depast 30 years, the depth at pose a particular threat to recades, as the tools for oceanowhich hydrate in the area is gional or even global ecology. graphic exploration have grown stable has fallen from 360 to “The [Westbrook] study is notemore sophisticated, researchers 396 m, liberating methane, worthy in its documentation of have documented about 90 oceWestbrook says. significant methane releases ocanic locations of methane hycurring at locations correspondThe plumes averaged several drate, estimated to contain as ing to the limit of gas hydrate meters in diameter, with the much as 63,000 gigatons or stability for a system that has largest reaching within 50 m of more of carbon. Previously, Inseen documented temperature the sea surface. The researchers ternational Polar Year (2007) changes at the seafloor,” Reagan have not yet calculated the acsurveys of the East Siberian Arcsays. “This is a good example of tual volume of gas being retic shelf uncovered abundant what methane release due to clileased. However, on the basis of methane seeps and measured mate change might look like,” he previous studies of hydrate conrecord-breaking summertime contends. centrations in the area, they esconcentrations of the gas in Veteran hydrate researcher Petimate that the 30-kilometernorthern polar waters. ter Brewer of the Monterey Bay long zone of plume occurrence Hydrate usually forms in sediAquarium Research Institute could be losing about 27 kiloment beneath the seabed and is says, “The depths at which the tons per year from dissociating stable at depths below 300-500 7600 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / October 15, 2009
10.1021/es9026387
2009 American Chemical Society
Published on Web 09/16/2009
plumes have been detected [in the study] are consistent with hydrate dissolution, but it’s not proof that climate change has caused this. Modeling shows that it takes a very long time for heat to penetrate deep into
ocean sediments. So this is not yet a smoking gun.” However, Brewer points out, if widespread hydrate dissolution does happen, another ominous consequence could follow: if ocean floor sediments become increas-
ingly gas-saturated, they will likely turn highly unstable, so that earthquakes are more likely to unleash tsunami-like landslides. —NOREEN PARKS
October 15, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 7601
