Ocean Floor Sediments

The main types of sediment found on the seafloors globally are, siliceous, carbonate, red clay, red clay-siliceous and terrigenous/ice-rafted.  

Siliceous sediments are found in areas of high productivity where upwelling of nutrient rich deep waters happens, they cover 15% of the sea floor and accumulate at a fairly slow rate of 0.2-1 cm per 1000 years. This happens along the equator, along coast lines and around the south pole. These are all places of upwelling, the equatorial upwelling happens by trade winds meeting at the equator and then diverging which pulls the equatorial surface water apart leaving a space for deep waters to rise and take place bringing nutrients with them. The upwelling along the coasts, specifically the East Pacific, occur because of winds travelling along the coast causing Ekman transport which creates a net transport movement of surface water away from the coast, allowing deep waters to up well. Finally, upwelling occurs around the Antarctic because of winds blowing in an eastward direction which pushes the surface water northwards due to Ekman transport therefore allowing upwelling to take place. Nutrients provide energy for primary productivity of phytoplankton which in turn deposit there siliceous shells which sink to the ocean floor to create a siliceous ooze.  

Carbonate sediments are made up from calcareous ooze which is another biogenic sediment, it makes up 48% of the sea floor and accumulates at a faster rate of 0.3-5cm per 1000 years. It is composed of the CaCO3 shells of primary productivity plankton such as foraminifera and coccoliths which sink to the sea floor. However, under certain conditions, these shells will dissolve and not make it to the seafloor, this level is called the Carbonate Compensation Depth (CCD). It occurs at certain depths, at a certain acidity and a certain temperature. The Pacific ocean deep waters are generally more acidic than the Atlantic deep waters and deeper therefore carbonate sediments are more common in the Atlantic than the Pacific. It also won’t be found at the pole because of the low water temperatures causing it to dissolve. Carbonate ooze is particularly common along the Mid Atlantic ridge.

Red clay sediments are not biogenic, containing less than 30% organic material. It is composed of very fine clay and quartz which normally arrive as dust blown from land by the wind which lands on the sea surface and gradually sinks to the bottom. It accumulates at a very slow rate of 0.1-0.5 cm per 1 000 years therefore will only be found where there is no other sediment accumulating at a faster rate. It covers the deepest and remote sea floors where no other sediments collect. Red Clay can mix with siliceous sediment which makes a mix of Siliceous/Red Clay.

Finally Terrigenous and Ice rafted sediments are found near coastlines and consist of river and glacial eroded material. They are transported to the oceans by river, by wind or by ice bergs containing sediments which are then dropped at sea when the berg melts. This sediment consists of gravels, sands, silts and clays and will be deposited on continental shelves. Ice Rafted sediments are found particularly around the polar waters. 

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