Scientists at Sea / Fast Facts  
Hydrogeological setting
    This figure depicts the ocean crust (basement plus overlying sediments) of the mid-ocean spreading ridge (zone I) and ridge flank (zones II-III). The basement (mauve color) becomes covered in increasingly thick sediments (yellow) with age. Bottom ocean water exchanges with basement fluids only in zone I & II or at seamounts that penetrate through the sediments (zones IVa and IVb).