Keywords: 
• west pacific ocean /
• methane /
• concentration /
• carbon isotope

Abstract: The oceans are proved to be a source for atomospheric methane, while in different sea area, the concentration of methane dissolved in seawater and the methane flux injected ints the atmosphere from the ocean surface vary greatly. In this study, the concentration and carbon isotopic composition of methane dissolved in the upper seawater of west Pacific Ocean were analysed, the methone evasion flux in this area was computed, additionally, the source of marine methane was also disscassed according to its carbon isotopic characteristics. The reslts of this study show that marine dissolved in the upper seawater in this region is extremly over saturated, while there are great disparities among the sorface methane concentrations in different locations, the values of which vary from 13 nmol/L to 169mol/L, methane concentration of the surface water are higher in the open sea zone than in the near shore zone, which is different from the formerly studied area; mathane dissolved in the deeper part of the uppor water (200 to 300 m), is more than that dissolved in the shallower part (0 to 100 m). Carbon isotopic composition pattern of methane, ethane and propane proves the biogenic formation of these light hydrocarbons dissolved in the upper sea water. Flux of methane across the seawater-atmosphere interface varies between 0.7 and 10.4 nmol ^－１m in the studied area, which is considerably high compared with the values of other open seas, while our results still proved that oceans are not animportant source for methane.