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Introduction to Marine Sediment

Oceans are considered as the single largest ecosystem which covers most of the area of the Earth and ocean sediments cover more than 70% of the surface of the Earth. These sediments cover most of the areas of the oceans and create a great impact on marine life, for example, you will find minimum biodiversity at the continental slope, but on the other hand, you will find a lot of minerals at the bottom. In this article, we will be talking about marine sediment and all its related concepts which will help you to understand this important topic of Oceanography. 


Sediments are something that is collected at the bottom of a liquid by some sources. According to Collins dictionary, " Sediment is a solid material that settles at the bottom of a liquid, especially earth and pieces of rock that have been carried along and then left somewhere by water, ice, or wind." Usually, these are pieces of rocks, or sand, dust, ashes, etc. that are deposited by some agents in one place.


If we talk about marine sediment, the sediments which are associated with marine life and can be found at the seafloor or in the oceans can be termed as marine sediments. Systematic study of marine deposits actually began from 1872 to 1876 with HMS Challenger expeditions. After that, no research has been done. In 1968, the collaboration of various scientists from America, the United Kingdom,  the Soviet Union and various other countries recovered various sedimentary deposits samples with the use of drilling vessels i.e Glomar Challenger from the Atlantic and the Pacific Ocean. These sediments that are collected near the continents cover around 25% of the seafloor but as per the volume they cover around 90% of marine deposits.


Marine Sediments/Deposits

Any kind of insoluble material which is being transferred or transported by various sources from land into the water are called marine sediments. Mostly these sediments are in the form of rocks or soil particles that reach the ocean bodies from the continents. Usually, because of the erosion of the continents these sediments occur and get deposited at the surface of the ocean floor. Besides erosional activities, debris from volcanic eruptions or biological productivity and cosmic debris also got collected at the seafloor. The contributions of wind, depth of the ocean as well as ocean circulation play a great role in carrying these sediments or in their transportation, deposition as well as preservation. Alterations also affect the final ocean deposits found on the floor.

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The ocean deposits found on the continental shelves as well as continental rises are known as hemipelagic sediments which usually get collected and accumulated here too rapidly in order to chemically react with the seawater. These sediments also get collected near the coral reefs in the tropical regions containing carbonate materials whereas near volcanoes it consists of ashes. The deposits which get collected and accumulated slowly are around 75% and are known as pelagic sediments. Abyssal plains are away from the continental shelf and there are no turbidity currents, thus coarse-grained deposits are found here. At the bottom of the ocean, because of seafloor spreading the bottom is continually renewed. It can be said that the bottom is younger and no sediments older than 150,000,000 years can be found here, but on the other hand, the sediments get thicker and older with time as well.


Types of Marine Deposits

There are various types of ocean deposits that can be found in the oceans and these types are mentioned below:


Lithogenous Deposits 

Lithogenous composed of small fragments. It is also known as terrigenous sediments. The small fragments are the part of preexisting sediments that have made their way into the ocean. These sediments can contain an entire range of particle sizes, from microscopic to clay to large boulders. They are found normally everywhere on the ocean floor. These sediments are created on land by the process of weather. Here rocks and minerals are broken down into tiny particles through the action of wind, rain, water flow, temperature or ice-induced cracking, and other erosive processes. Then these particles are transferred into the oceans.


Lithogenous sediments usually reflect the composition of whatever materials they were derived from. They are dominated by the main material that makes up most terrestrial rocks. Quartz, feldspar, clay minerals, iron oxides, and terrestrial organic matter. Quartz which is also known as silicon dioxide is one of the most common minerals found in all rocks. That's why it is the dominant component of the lithogenous sediments including sand.

  • Various forms of deposits are found in oceans. About 90% of the lithogenous sediment in the oceans have come from rivers, particularly from Asia.

  • Most of the sediments, mainly the larger particles, will be deposited and remain closer to the coastline.

  • On the other side, small particles may be suspended in the water column for longer periods and may be transported a big distance from the source.

  • The wind is such a fact which can transport small particles like dust and sand to the ocean and move to thousands of kilometres from the source.

  • These small particles can fall into the ocean when the wind dies down or serve as the nuclei around which raindrops or snowflakes.

  • Glaciers also have lots of soil and rock particles and large boulders which they get carried by the ice.

  • When the glacier breaks out and melts and it meets with the ocean then these particles get deposited in the ocean.

  • Landslides, mudslides, avalanches and other gravity-driven events can deposit large amounts of materials into the ocean.

  • Wave action along a coastline will erode rocks and will push loose particles into the ocean and seashore.

  • Volcanic eruptions emit large amounts of ash and other particles into the surroundings and are then transported to the oceans through the wind.

Biogenous Deposits

Biogenous sediments are sediments that are made from the skeletal remains of living organisms. These sediments include a wide variety of microscopic organisms, coral fragments, sea urchins and pieces of mollusc shells. Algae and protozoans are the sources of biogenous sediments. The biogenous sediments come from the tests of these one-celled organisms. They are living in the surface waters of the oceans. When these tests comprise greater than 30% of the particles then these particles are known as ooze. There are two types of oozes on the ocean floor are calcareous sediment and siliceous sediment. Oozes that are dominated by diatom or radiolarian tests are called siliceous oozes and calcareous sediment are produced from the tests of microscopic algae and protozoans.


Hydrogenous Deposits

Seawater contains many different types of dissolved substances. Sometimes, chemical reactions occur that cause these types of substances to precipitate out as solid particles, which accumulate as hydrogenous sediment. All these occur by the change in conditions such as a change in temperature, pressure or pH which reduces the amount of substance that can remain in a dissolved state. These kinds of sediment are normally found near hydrogenous vents. In these systems, seawater percolates into the seafloor where it becomes superheated by magma before being expelled by the vent. This water contains many dissolved substances and when it mixes with cold seawater after leaving the vent then these particles precipitate out mostly as metal sulfides. These particles make smoke that flows from the vent and eventually settle on the bottom as hydrogenous sediments.


Cosmogenous Sediments

Cosmogenous sediments are derived from extraterrestrial sources. These have mainly come in two primary forms - microscopic spherules and larger meteor debris. Spherules mostly consist of silica or iron and nickel and are thought to be ejected as meteors burn up after entering the atmosphere. Meteors come from the collision of meteorites with the earth. These types of collisions have a great impact on the earth's atmosphere that eventually settle back down to earth and contribute to the sediments. Meteor debris consists of mainly silica and nickel. One of the main forms of this debris from collisions are tektites which are small droplets of glass. They are composed of terrestrial silica that was ejected and melted during a meteorite impact. It forms solid after it becomes cool upon returning to the surface. Cosmogenous sediments are fairly rare in the ocean and it does not usually accumulate in large deposits. It comes from space dust which is present in the atmosphere which is continuously raining down on the earth.


Marine Soil

Soil deposits on ocean beds are known as marine soils. Though oceans are very violent the seabeds are very calm for the most part. A very small particle would deposit on the seabeds. The texture and composition depend on the proximity to the land and biological matter. The ocean floor is composed of three different types of soil also known as pelagic sediments or marine sediments. The names of the soils are calcareous ooze, red clay, and siliceous ooze.


Calcareous Ooze

It is the most common soil of the three soils. It covers approximately 48% of the whole ocean floor. It consists of the shells of foraminifera, coccolithophores, and pteropods. They are the tiny organisms that are living in the ocean.


Red Clay

It is the second soil that is found in the ocean. It covers approximately 38% of the ocean floor. It is brown in color. It is made up of quartz, clay minerals, and micrometeorites which are rocks that weigh less than a gram and have fallen to earth from the outer surface.


Siliceous Ooze

Siliceous Ooze is the least common of the three soils. It covers 15% of the ocean floor and is composed of plankton debris and silica shells.


Ocean Minerals

Oceans are a great source of minerals and also considered as the future of the Earth which has tons of possibilities. The resources which have been extracted from it for many years are sand, gravel, oil, gas and salt. Various other resources are also found here such as Magnesium,  Sulphur, Potassium, Calcium, Bromine, Silicon, Boron, lithium, zinc, iodine, Aluminium, Fluorine, Copper, Barium, Lead, Carbon, etc. This list is endless as we know that the ocean and its minerals are the greatest gift of nature and contain endless opportunities for development as well.


Conclusion

Thus, we can conclude that sediments are the debris that gets collected at the bottom of any liquid, especially in terms of Earth, these are the debris that gets collected at the bottom of the sea or ocean by some agents from their origin point. These sediments create a difference as well as leave a great impact on marine life. On the other hand, it leads to the formation of various kinds of landforms on the ocean floor such as abyssal plains, submarine canyons, etc. Various resources or minerals are also found at the seafloor which is the future of the Earth and the human world for development. 

FAQs (Frequently Asked Questions)

Question 1. What Do You Mean by Marine Sediment?

Answer. According to Merriam-Webster, " sediments are the matter that settles to the bottom of a liquid." If we talk about the marine sediments, these are the deposits that are found in the marine bodies of the Earth such as Oceans. Various agents such as wind, water, etc. play their vital role in depositing and transporting these sediments from their source of origin to the ocean floors. In the form of sand, dust, soil, ashes, and rock particles these sediments are collected by the agents from the continents to the oceans which cause various impacts on the marine life and ecosystem of the water.

Question 2. What Are the Four Types of Marine Sediments?

Answer. There are four types of marine sediments mainly are lithogenous, biogenous, hydrogenous, and cosmogenous sediments. Lithogenous sediments come from land via rivers, ice, wind, volcanic eruptions, gravity, and other processes. Biogenous sediments come from a test of the organisms like algae and protozoans. Hydrogenous sediments come from the chemical reactions that cause the substance to precipitate out as solid particles which are hydrogenous sediments. It occurs due to change in conditions like changes in temperature, winds, pressure, or pH which reduce the number of substances that can remain in a dissolved state. While cosmogenous sediments come from extraterrestrial sources. It is fairly rare in the ocean and does not usually accumulate in large deposits.

Question 3. What Does Sedimentation Affect Marine Life?

Answer. Sedimentation affects marine life in various ways. It disturbs and damages the habitats of the oceanic species and also disturbs the food chain. Not only this, sediments attract warmness from the sun and increase the temperature of the water whereas the chemicals associated with certain sediments also affect the ocean water and degrade the quality. A new form of sediment pollution can be seen because of these sediments which affect the water depth and naturality of the region.  

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