Siliceous ooze

Tiny living things live in the sea.

They use glass to build shells. These shells fall to the deep ocean floor. They make a soft layer called ooze.

Some shells come from tiny plants. Other shells come from tiny animals. These shells can take many years to sink. They can even turn into hard rock. This happens over a very long time.

The ocean floor is full of these tiny shells.

Deep on the ocean floor, there is a soft layer called siliceous ooze.

This ooze makes up about 15% of the ocean floor. It is made of tiny skeletons. These skeletons come from small living things in the sea. Most of these parts come from diatoms and radiolarians.

Diatoms are tiny plants. Radiolarians are tiny animals.

These tiny creatures use a process called biomineralization. This is a way they build hard parts. They take silica from the water to make shells. These shells are made of opal silica. As the creatures die, their shells sink. Some shells sink inside small pellets from larger animals. This helps them reach the bottom faster. It can take 20 to 50 years to sink in some places.

Over a very long time, the ooze can change. If it builds up fast, it can turn into a hard rock called chert. This can take tens of millions of years. In the Southern Ocean, the ooze builds up very quickly. This is because many tiny organisms live there.

Deep on the ocean floor lies a special type of sediment called siliceous ooze.

This soft layer covers about 15% of the ocean floor. To be called an ooze, the sediment must contain at least 30% skeletal remains from tiny living things. These tiny creatures live in the upper parts of the sea. Most of the ooze is made of skeletons from diatoms and radiolarians. These microscopic organisms use silica to build their hard shells. This material is called opal silica. This process is important because it helps move nutrients through the ocean.

Tiny organisms build their shells through a process called biomineralization. This is a way they turn dissolved materials into hard parts. Diatoms and radiolarians take in silicic acid from the water. They move this acid into special tiny containers inside their bodies. There, the acid is transformed into solid opal silica.

Specialized proteins help them move the acid without making it turn hard too early. Once the organism dies, the skeleton begins to sink toward the bottom. Sometimes, these shells get wrapped in organic matter called fecal pellets. This packaging helps the shells sink faster and protects them from dissolving.

Scientists have studied how these materials move for a long time. They know that the Southern Ocean is a very busy place for silica. In this area, the ooze builds up much faster than in other spots. It can take 20 to 50 years for a skeleton to sink to the bottom.

If the skeletons pile up very quickly, they can turn into a hard rock. This rock is called marine chert. The change from soft ooze to hard chert can take tens of millions of years. This process permanently removes the silica from the ocean's cycle.

Different parts of the world have different kinds of ooze. Diatomaceous oozes are mostly made of diatom skeletons. You can find these near land in places like the North Pacific Ocean.

Radiolarian oozes are mostly made of radiolarian skeletons. These are usually found in warmer, tropical parts of the ocean. The Southern Ocean has a huge, connected layer of ooze. This happens because deep water keeps rising to the surface in that area. This rising water brings the nutrients that help these tiny creatures grow.

Siliceous ooze is also linked to how our planet handles carbon dioxide. Diatoms are primary producers that use photosynthesis to grow. This means they take carbon dioxide from the water to make food. Because they have heavy silica shells, they sink quickly to the deep sea. This helps move carbon away from the surface of the ocean. Some scientists even use iron to try and help more diatoms grow. They want to see if more diatoms can help remove more carbon from the air. It is a big, natural system that keeps the ocean healthy.

Siliceous ooze is a specific type of biogenic pelagic sediment found on the deep ocean floor. It is a vital component of the marine environment, though it is relatively rare. These oozes cover approximately 15% of the entire ocean floor. To be scientifically classified as an ooze, a sediment must consist of at least 30% skeletal remains from pelagic microorganisms. These are organisms that live in the open water column rather than on the sea floor.

Most siliceous oozes are composed of the silica-based skeletons of microscopic creatures. The two most important groups are diatoms and radiolarians. These organisms use opal silica, which has the chemical formula SiO2·nH2O, to build their protective structures. This distinguishes them from calcareous oozes, which are made of calcium carbonate skeletons.

The creation of these skeletons happens through a complex biological process called biomineralization. Diatoms and radiolarians must extract silica from the seawater in the form of silicic acid, or Si(OH)4. Once the organism takes in these molecules, they are moved into its cytoplasm. Specialized proteins called silicon transporters manage this movement. These proteins are essential because they prevent the silica from hardening too early during transport. The silicic acid is then moved into silica deposition vesicles. Inside these tiny containers, the molecules are transformed into solid opal silica.

Once these organisms die, their remains begin a long journey to the seafloor. This process is influenced by the opal silica saturation state of the ocean. As opal particles sink, they dissolve, which actually increases the silica concentration at greater depths. This makes the formation of new opal silica thermodynamically unfavorable in deep water. To reach the bottom, the silica must sink faster than it dissolves. One way this happens is through re-packaging. This occurs when opal particles are encased in larger pieces of organic matter, such as fecal pellets. This organic coating acts like a protective shield against dissolution.

This packaging allows more material to reach the seafloor successfully.

Siliceous oozes are generally categorized into two distinct types based on their biological makeup. Diatomaceous oozes are predominantly composed of diatom skeletons. These are typically found in higher latitudes near continental margins. Examples include the North Pacific Ocean and the Southern Ocean.

In contrast, radiolarian oozes consist mostly of radiolarian skeletons. These are primarily located in tropical equatorial and subtropical regions. You can find these in the subtropical Pacific and the Indian Ocean. The Southern Ocean is unique because it features a massive, contiguous band of siliceous ooze. This is caused by the constant upwelling of deep water, which provides the nutrients needed for massive biological growth.

The accumulation of these sediments happens over very long timescales. In the open ocean, the rate is roughly 0.01 mol Si m−2 yr−1. However, the Southern Ocean sees much faster accumulation at 0.1 mol Si m−2 yr−1. In these productive waters, it can take 20 to 50 years for a skeleton to sink to the bottom.

Once the ooze is deposited, it can undergo a transformation called diagenesis. If the silica accumulates faster than it can dissolve, it may turn into a hard rock called marine chert. This recrystallization and cementation process can take tens of millions of years. When chert forms, it permanently removes silica from the oceanic cycle.

Siliceous ooze plays a massive role in the global silica cycle and carbon sequestration. The deposition of this ooze is the largest long-term sink for silica in the ocean. On average, only 4% of the opal silica produced at the surface reaches the seafloor. The other 96% is recycled back into the water column. On a biological timescale, a single molecule of silica might be recycled 25 times. Each molecule stays in the cycle for about 400 years before it is finally buried. This cycle is balanced by the weathering of silicates on land and river inputs.

Diatoms are also crucial for managing atmospheric carbon dioxide through the biological pump. As primary producers, they use photosynthesis to convert carbon dioxide into organic carbon. Because diatoms are relatively large, they can absorb significant amounts of carbon. Their heavy opal silica shells also act as ballast, helping them sink rapidly to the deep sea. This carries carbon away from the surface. Scientists have even conducted iron fertilization experiments to see if increasing nutrients can trigger diatom blooms. The goal is to see if more diatoms can increase the rate of carbon sequestration in the deep ocean.