The quantification of methane fluxes from the sediment into the sea water (sediment-water-transition-zone) and the subsequent dispersal of methane in the hydrosphere are necessary to contribute to the knowledge of benthic biogeochemical cycles. Presently, typical studies about benthic biogeochemical cycles rely on bottom water and sediment sampling for subsequent ex situ water and pore water analysis as well as for ex situ incubations (on board the ship or land based laboratory). Furthermore, in situ measurements are taken at the seafloor applying benthic chamber systems or micro-electrode profilers. Some of the advantages of in situ methods referring to flux measurements are the low impact on the hydrodynamic regime, no depressurization, no influence of larger areas and the minimal effect on the benthic biota with respect to bioirrigation intensity. Additionally, the sampling rate of in situ sensors is up to 750 times higher compared to established methods and enables important high resolution measurements. Therefore, in situ techniques are preferred for sensitive investigations such as flux measurements or quantification of dissolved gases above gas seeps. Using a unique underwater mass spectrometer (UWMS, Inspectr200-200, Applied Microsystems Limited™) it became possible for the first time to obtain dissolved methane concentrations and other gases in the hydrosphere in high resolution. In this talk I will present first results of methane flux measurements (Baltic Sea) as well as the detection, mapping and inventory calculation of submarine released methane (North Sea and Arctic Ocean) by novel in situ mass spectrometry.