THE BEAUFORT SEA CONTINENTAL-SHELF AS A SEASONAL SOURCE OF ATMOSPHERIC METHANE

Methane concentrations in the Beaufort Sea under the winter ice canopy offshore from northern Alaska are 3 to 28 times greater than they are in late summer when the ice is absent in a similar region offshore fr om northern Canada where methane is in approximate equilibrium with th e atmosphere. These observations suggest that methane concentrates in the water under the sea-ice cover during winter and ventilates rapidly in late summer as the ice melts and retreats. Conditions similar to t hose on the Beaufort Sea shelf likely exist on the much larger Siberia n shelf, making the Arctic Ocean margin a possible seasonal, high-lati tude, marine source of about 0.1 Tg yr-1 atmospheric methane. The smal l addition of methane likely contributes to the late-summer increase i n atmospheric methane that is observed each year particularly in the n orthern hemisphere.