Oceans as Sources or Sinks of Biologically Produced Gases relevant to Climatic Change

Gases may be produced in the world’s oceans largely by biological and chemical processes in sediments at the sediment water interface, water column, photic zone, surface waters and at the water atmosphere interface. Some of these gases play an important role in the forcing of global climate (e.g. CO2, CH4, (CH3)2S, COS, and N2O) [1]. Their eventual transfer to the atmosphere is driven by supersaturation of ocean waters in comparison with the water-air equilibrium concentration for each individual gas. Conversely, the oceans may act as sinks for some of these gases, under conditions of undersaturation. Tropospheric and stratospheric chemistry are influenced by these gases and the net result is either direct positive radiative forcing (e.g. CH4, CO2, N2O; “greenhouse gases”), or indirect negative radiative forcing (e.g. (CH3)2S) [2]. Increases in the concentrations of the former gases result in global warming. The oxidative products of the latter two gases form condensation nuclei which in turn form marine clouds affecting the earth’s albedo and hence resulting in a negative radiative forcing (global cooling) [3]. In relation to the ASE EUROTRAC subproject, the fluxes of all the above gases have been studied by different groups and in various contexts. Below, a short state of the art is elaborated, for the role of the oceans as sources or sinks for the above named gases.