Deep-Sea Sediments CBGS 2012. 3 types of sediment cover most of the deep ocean floor: Abyssal clay-...
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Transcript of Deep-Sea Sediments CBGS 2012. 3 types of sediment cover most of the deep ocean floor: Abyssal clay-...
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!!!!