Pelagic sediment

Tiny bits fall to the deep ocean floor.

These bits come from many places. Some are shells from tiny sea life. Other bits are dust from the wind. Some bits are ash from volcanoes.

This soft layer is called sediment. It builds up very slowly. It can take a long time to grow. Some parts are red or brown. This color comes from iron.

Some bits fall from the sky too. These are tiny pieces from space. The deep sea is a very quiet place. It is full of these small treasures.

Deep in the ocean, tiny bits fall to the floor. This layer is called pelagic sediment. It builds up very slowly over many years.

Most of this sediment comes from tiny sea life. These small creatures leave behind shells. When the shells pile up, we call it ooze. There are two main kinds of ooze. Calcareous ooze comes from shells made of calcium. It covers 48% of the ocean floor. Siliceous ooze comes from shells made of silica. This type is found in cold polar waters.

Other parts of the floor have red clay. This clay is not made of shells. It is mostly dust blown by the wind. It can also come from volcanic ash. This clay is often bright red or brown. That color comes from iron. Red clay is the slowest to grow. It covers 38% of the ocean floor. Many tiny things fall through the water to reach the bottom. This includes bits of bone or even dust from space.

Deep in the open ocean, far from the land, tiny particles fall to the floor. This layer of material is called pelagic sediment. It is made of many different things. Some parts are tiny shells from living things. Other parts are small bits of clay or dust from the wind. Even bits of volcanic ash and space dust can fall down. This sediment is important because it tells us about the ocean's history.

How this sediment builds up is a very slow process. Tiny organisms live in the surface waters. When they die, their hard parts sink toward the bottom. Some parts are made of calcium. Others are made of silica, which is a type of glass. These sinking bits can take a long time to reach the floor. Some fine clays stay floating for a hundred years or more. They finally settle by sticking together in small clumps.

Scientists group these sediments into three main types. The first type is called calcareous ooze. This ooze is made of at least 30% calcium shells. It is the most common type. It covers 48% of the world ocean floor. The second type is siliceous ooze. This is made of at least 30% silica shells. It covers only 15% of the ocean floor. It is often found in cold polar oceans.

The third type is red clay, also called pelagic clay. This is the least common type of ooze. It covers 38% of the ocean floor. Red clay has less than 30% from living things. Most of it is actually dust blown by the wind. It can also contain fish bones or whale ear bones. This clay is often bright red or chocolate brown. That color comes from iron and manganese on the particles.

You can think of the ocean floor like a giant collector. It catches everything that falls from above. The distance from land changes what settles there. Deep water also changes which shells stay intact. Some shells dissolve before they reach the bottom. This is why different types of sediment sit in different places. The ocean floor is a quiet place where history piles up.

Pelagic sediment, also known as pelagite, is a fine-grained material that settles on the floor of the open ocean. It forms far away from land through a slow process of accumulation. These sediments are composed of many different particles. They include the microscopic shells of tiny organisms called phytoplankton and zooplankton. They also contain clay-sized siliciclastic sediment and organic detritus, which is often called marine snow. Even trace amounts of volcanic ash and meteoric dust from space can be found within these layers.

Three main factors control what kind of sediment forms in a specific area. The first factor is the distance from major landmasses. Being far from land prevents the sediment from being diluted by terrigenous sediment, which comes from the land. The second factor is water depth. Depth affects whether biogenic particles, or remains from living things, are preserved as they sink. The final factor is ocean fertility. This determines how many biogenic particles are produced in the surface waters above.

Scientists use a specific term called ooze to describe certain pelagic sediments. An ooze is a sediment that consists of at least 30% microscopic remains from planktonic organisms. These remains are either calcareous or siliceous. The rest of the ooze is usually made of clay minerals. This creates a bimodal grain size, meaning it has two distinct sizes. One size is the biogenic silt or sand, and the other is the fine siliciclastic clay. Oozes accumulate extremely slowly, often at rates of only a few centimeters per millennium.

Calcareous ooze is the most common type of pelagic sediment. It covers 48% of the world ocean floor. This ooze is composed of at least 30% calcareous microscopic shells, which are also called tests. These tests come from organisms like foraminifera, coccolithophores, and pteropods. This sediment accumulates at depths above the carbonate compensation depth. It is the fastest-growing pelagic sediment, with rates between 0.3 and 5 cm per 1,000 years.

Siliceous ooze is another type of biogenic sediment. It is composed of at least 30% siliceous microscopic shells from plankton like diatoms and radiolaria. It may also contain sponge spicules or silicoflagellates. This type of ooze accumulates at depths below the carbonate compensation depth. Its distribution is limited to areas with high biological productivity, such as upwelling zones near the equator or polar oceans. It is the least common ooze, covering only 15% of the ocean floor. It accumulates at a rate of 0.2 to 1 cm per 1,000 years.

Red clay, or pelagic clay, is the third main type of sediment. It is found in the deepest and most remote parts of the ocean. This sediment covers 38% of the ocean floor. It contains less than 30% biogenic material. This is because the calcareous and siliceous particles dissolve as they settle through the water column. The remaining material consists of aeolian quartz, clay minerals, and volcanic ash. It also contains authigenic minerals, which are minerals formed in place, such as zeolites, limonite, and manganese oxides.

The distinct red or chocolate brown color of these clays comes from coatings of iron and manganese oxide. In areas without organic carbon, these elements remain in their oxidized states. When buried deeply, brown clay can change into red clay as iron-hydroxides convert to hematite. Red clay accumulates in areas with very little planktonic production. The particles are transported thousands of kilometers by wind and ocean currents. Fine clays can stay suspended in the water for over a hundred years before they settle.

Understanding these sediments helps scientists map the history of the Earth. The distribution of these materials relates to many different systems. For example, the thickness of sediments varies greatly across the ocean. Continental shelves hold about 9% of the ocean area but contain 15% of the total sediment volume. The deep-ocean floor covers 78% of the area but only 13% of the volume. By studying these layers, researchers can learn about past ocean fertility and climate changes.