春季西北太平洋水体中甲烷和氧化亚氮的分布及海气交换通量

DISTRIBUTION AND FLUXES OF METHANE AND NITROUS OXIDE IN THE WESTERN NORTH PACIFIC OCEAN IN SPRING

于2010年5—6月搭乘日本KH10-1航次,对西北太平洋两个不同深度站位甲烷(CH4)和氧化亚氮(N2O)的垂直分布及海气交换通量进行了研究。结果显示:研究海域表层海水中CH4和N2O浓度分别为(2.55±0.22)nmol/L和(7.50±1.11)nmol/L,饱和度分别为126%和116%,均处于轻度过饱和状态。在垂直方向上,CH4浓度分布呈现次表层极大的特征,次表层以下CH4浓度随深度增加逐渐减小。CH4次表层极大值可能是由于细菌利用甲基化合物进行好氧产生和在悬浮颗粒物、浮游动物或其他海洋生物肠道内厌氧微环境产生的综合作用造成的。N2O浓度随深度的增加而增大,在跃层下部达到最大值,N2O与溶解氧的垂直分布呈镜像关系。水体中N2O主要通过硝化过程产生。利用LM86和W92公式计算得到CH4的海气交换通量分别为(0.76±0.57)μmol/(m2·d)和(1.57±0.67)μmol/(m2·d),N2O的海气交换通量分别为(1.96±0.24)μmol/(m2·d)和(3.08±0.38)μmol/(m2·d),因此西北太平洋是大气CH4和N2O的净源。

We investigated vertical profiles and atmospheric fluxes of methane(CH4) and nitrous oxide(N2O) in two stations in the northwestern Pacific in May/June during KH10-1 cruise in 2010. CH4 and N2 O concentrations in the surface waters were(2.55±0.22)nmol/L and(7.50±1.11)nmol/L, in saturation of 126% and 116%, respectively. On vertical profile, CH4 maximum occurred in the subsurface layer and then decreased with depth. CH4 maximum in the subsurface may be due to aerobic CH4 production as a byproduct of methylphosphonate decomposition and the anaerobic production by methanogenic bacteria in anaerobic microenvironments in suspended particles or the guts of zooplankton. N2 O concentrations increased with depth, and reached a broad maximum at the base of thermocline, which reflected the vertical profiles of dissolved oxygen. N2 O in the water column was mainly produced by nitrification. The air-sea CH4 fluxes estimated by the Equations of Liss and Merlivat in 1986 and Wanninkhof in 1992 were(0.76±0.57)μmol/(m2·d) and(1.57±0.67)μmol/(m2·d); and N2 O fluxes(1.96±0.24)μmol/(m2·d) and(3.08±0.38)μmol/(m2·d), respectively. Therefore, the northwestern Pacific is a net source of atmospheric CH4 and N2 O.