Abyssal Zone

The abyssal zone is the deep open-ocean depth band from roughly 4,000 to 6,000 meters, lying below the bathyal slope and above the hadal trenches. Temperatures stay near 0 to 4 degrees Celsius, pressure exceeds 400 atmospheres at 4,000 m, and no sunlight penetrates. It overlies the abyssal plain and is filled mainly by Antarctic Bottom Water and North Atlantic Deep Water, the densest water masses formed by surface cooling at high latitudes. Flow here is slow and steered by topography and the planetary vorticity gradient, forming the lower limb of the meridional overturning circulation.