Deep-Sea Sediments

Two types of sediment cover most of the deep ocean floor: Abyssal clay covers most of the deep ocean floor accumulates at a rate of about 1mm every 1000 years mostly lithogenic sediment carried by ocean currents and wind. Biogenous Oozes must be composed of more than 30% biogenic material (skeletal fragments) may be calcareous or siliceous rate of deposition of oozes depends on biological activity and dissolution of the skeletal fragments.

Calcareous Ooze Made mostly of the calcite (calcium carbonate, CaCO3) shells of foraminifera and coccolithophores These planktonic organisms are dominant in warm surface waters in the world’s oceans They make up 48% of deep ocean sediments

Carbonate Compensation Depth At depths greater than 4500 m, the dissolved carbon dioxide (CO2) concentration is so high that it causes calcite to dissolve. This is called the Carbonate Compensation Depth. The CCD varies with temperature, salinity and atmospheric carbon dioxide.

Siliceous Ooze Made mostly of silica (SiO2) shells of diatoms and radiolarians These planktonic organisms are dominant in cold surface waters and in upwelling areas. They make up 14% of deep ocean sediments.

Carbonate Compensation depth and Biogenous ooze accumulation

Abyssal Clays Made mostly of clay minerals, and very fine grained, less than 0.002 mm Can be carried by winds to all parts of the world They do not dissolve in water. Dominant in the deep ocean in areas where oozes are absent Especially dominant below CCD in warmer oceans Make up about 40% of deep ocean sediment.

Distribution of Deep ocean sediment Calcareous ooze is the dominant deep ocean sediment in warm water above the CCD, and along the mid- ocean ridges, seamounts and other peaks. Siliceous ooze is dominant in cold water below the CCD, and where deep ocean currents upwell to the surface. Abyssal clays are dominant below the CCD in warm water and wherever biogenous oozes are absent.

Distribution of Marine Sediment Types