CH4 in the ocean is released from the sediments, where it can be produced by microorganisms or it is of geological origin. It is oxidized in the water column, so that the majority of the methane released from the sediment does not reach the surface ocean. However, in shallow shelf areas, methane emissions to the atmosphere can be very high. In the open ocean, a persistent methane maximum at the depth of the chlorophyll maximum is observed, which can feed emissions to the atmosphere. These are much lower than in the coastal areas, but due to the huge open ocean area they constitute a large part of the oceanic methane emissions. CH4 measurements in the oceans are quite sparse (see Figure below). Particularly in the open ocean, more data are needed to create a reliable estimate of the methane distribution in the global ocean.

Location of surface and depth profile measurements of CH4 included in MEMENTO (2014); large dots indicate available depth profiles. 

We are continously looking to expand the CH4 database, and would strongly encourage scientists to contribute their data to MEMENTO.  If you wish to contribute your data, then there are data submission templates where you could fill in all the required information and send it directly to us.