Origin and Morphology of Ocean Basins

Abstract

The obvious question to ask about the seafloor is how deep it is and why. The overall depth distribution largely became known through the voyage of HMS Challenger in the ninteenth century, and it could then be combined with available information from the land surface (Fig. 2.1). We see that there are two most common elevations on the solid planet: an upper one just above sea level and a lower one centered near the average depth of the ocean. The higher of the two main levels presumably mainly represents the action of erosion to sea level (base level), as well as uplift of continental crust. The lower one, one assumes, reflects the volume of seawater along with the availability of space to put the water (i.e., the room that is left after making the continents). The seafloor between the two elevation modalities, that is, the part connecting shelves and deep ocean floor, is a transition consisting largely of the continental slopes and rises. A portion of this intermediate category of elevations also must be assigned to the worldwide mid-ocean ridge and its flanks. In addition, there is a special (small) portion of seafloor that is more than twice deeper than the average: such great depths only occur in narrow trenches, mainly in the subduction ring around the Pacific Ocean.