Methane in the western part of the Sea of Okhotsk in 1998-2000

Abstract

We measured oceanic methane in the western part of the Sea of Okhotsk in 1998, 1999, and 2000. An anomalously high methane concentration was found in near-bottom water above the shelfbreak (∼200 m) off northeast Sakhalin every year: up to 488 nmol kg-1 in 1998, 981 nmol kg-1 in 1999, and 556 nmol kg-1 in 2000. This anomalously high concentration can be used to trace the water with density range 26.6 to 26.8 σθ in the upper Dense Shelf Water. In the shelf off east Sakhalin, a strong stratification caused by freshwater from Amur River controlled the upward transport of methane through the suppression of vertical convection. The calculated methane flux was largest in the northeastern shelf region of Sakhalin (88 mol CH4 km-2 d-1). In the western part of the Sea of Okhotsk (0.73 × 106 km2, 51% of total Sea of Okhotsk area), the emission rate of methane was 11 Gg CH4 yr-1. Copyright 2004 by the American Geophysical Union.