Deep-Sea SedimentsCBGS

2012

3 types of sediment cover most of the deep ocean floor:

• Abyssal clay- covers most of the deep ocean floor, accumulates at <1mm/1000yr. Source is continent and cosmogenic, carried by ocean currents and aeolian transport.

• Oozes- must be composed of >30% biogenic material (tiny skeletons of plants and animals) mixed with clay.

Rate of deposition of oozes depends on:– Productivity of area

– Destruction by chemical dissolution

– Physical dilution- mixing with other sediments

Calcareous Ooze

• Composed predominantly of CaCO3 shells of Foraminiferans and Coccolithophores

• These plankton are dominant in warm surface waters

• They compose 48% of deep ocean sediments

Coccolithophores and Foraminifera-calcareous tests

Coccolithophores can bloom over massive areas

• Coccolithophore species Emiliania huxleyi can overproduce in blooms and often sheds excess coccoliths, these tiny particles act like sequins in the water and are very reflective, they make the sea surface “glitter”.

Carbonate Compensation Depth• At depths of >4,500m, the

dissolved CO2 concentration is so high it causes CaCO3 to dissolve. As a result, calcareous shells are not found below ~5,000m.

• The depth where carbonate supply is equal to the rate of dissolution is the Carbonate Compensation Depth.

• This occurs around 6000m in Atlantic and 3500-4000 m in parts of the Pacific.

The depth of the CCD varies as a function of the chemical composition of the seawater and its

temperature. Furthermore, it is not constant over time, having been globally much shallower in the Cretaceous

through to Eocene. If the atmospheric concentration of carbon dioxide

continues to increase, the CCD can be expected to rise, along with the ocean's acidity.

CaCO3(s) + H2O + CO2 → Ca2+(aq) + 2HCO3-(aq).

Siliceous Ooze

• Composed predominantly of SiO2 shells of Diatoms and Radiolarians

• These plankton are dominant in cold surface waters or areas of upwelling near equatorial landmasses

• They compose 14% of deep ocean sediments

Diatoms and Radiolarians- glass frustules

Sedimentary processes in the open ocean

From J. Noyes El Camino College

Calcareous Ooze

Calcareous ooze

• The dominant deep ocean sediment in low latitudes above the CCD.

• Along the mid-ocean ridges, seamounts and other peaks

From J. Noyes El Camino College

Siliceous Ooze

Siliceous Ooze

• The dominant deep ocean sediment in high latitude regions, below the CCD and surface current divergences near the equator (where cold water is upwelling)

From J. Noyes El Camino College

Red Clay

Abyssal Clays

• Dominant in deep ocean basins in areas where oozes are absent

• Especially below CCD in warmer oceans

Global Distribution of Marine Sediment Types

On Thursday: Short test on deep ocean (HTV’s, life and

sediments)

• ……and Cookie Contest! I’ll bring the milk! Ho Ho Ho!!!!