## 4 Results  
### Hydrate-Related Information Stored in GARAHydrates  
The hydrate-related information is structured in four levels inside GARAHydrates: (i) geological and geochemical evidence and indicators, (ii) geophysical indicators, (iii) seabed fluid flow structures, and (iv) oceanographic variables (Figure 2). Four types of items describe the information: location items, property metadata, geo-descriptors and references/comments (Table 1). Location items describe the geographical location (coordinates, geological setting, etc.). Property-reference metadata store the owner of the data and contact information. Geo-descriptors describe the geological, geochemical and geophysical characteristics of the evidence or indicator. Finally, references/comments store bibliographic references and other comments of interest of each item of evidence or indicator. The level of information \"geological and geochemical evidence and indicators\" stores evidence (e.g., crystals of gas hydrates) and indicators (e.g., degassing structures and pore water anomalies) of gas hydrates acquired by direct sampling. The level \"geophysical indicators\" stores seismic or electric features of gas hydrate presence in the sediment column, such as high resistivity, BSR levels, bright spots, acoustic blanking facies and gas chimneys. The level \"seabed fluid flow structures\" stores structures related to fluid migration in areas where evidence or indicators of marine gas hydrates have been observed. Finally, the level \"oceanographic variables\" stores information about seafloor temperature, geothermal gradient and bathymetry. More than 136,000 records of hydrate samples, seismic indicators and seabed fluid flow structures have been stored (Table 2). In west Greenland, no hydrates were recovered; there are only six indirect items of evidence or indicators, such as pore water anomalies of chloride. However, BSR levels (\(\sim\)9400 km\({}^{2}\)) and gas flares and seepage (\(\sim\)3500 km\({}^{2}\)) have been mapped. West Greenland-Svalbard-Barents Sea is, together with the Black Sea, one of the most extensive hydrate regions in the study area, with more than 2100 km\({}^{2}\) and 26,300 km\({}^{2}\) of mapped hydrates and BSR levels (58), respectively, as well as numerous gas flares and seepage. Although the mid-Norwegian margin is a very localized hydrate region, it is the only site where hydrates have been recovered on the northwest Atlantic European margins. Here, gas hydrates are linked to the old slumped slope (Storegga), BSR levels and seepage area. On the southern Iberian and northwest African margins and in the Mediterranean Sea, hydrates have only been recovered on mud volcanoes (in the Gulf of Cadiz and eastern Mediterranean Sea). A high number of hydrate samples have been recovered in these regions as a result of many oceanographic cruises by scientific groups. The Black Sea is the hydrate region that has most gas hydrate surfaces mapped (more than 3650 km\({}^{2}\)), with more than 80 mud volcanoes on the seafloor, 91% of them inside the GHSZ. Finally, three information layers are stored in the oceanographic variable group: seafloor temperature (5896 records), geothermal gradient (4332 records) and bathymetry (composite raster dataset with a cell size \(\sim\)100 \(\times\) 100 m).