In this blog post, we will explore how deep-sea sediments can provide scientific clues about past marine environments and climate change.
Among the various sediments found on the deep seabed, those created by the skeletons and fragments of organisms are called biogenic sediments. The most common biogenic sediment on the deep seabed is ooze. It is mainly formed by the shells and skeletons of dead plankton mixed with clay carried far from land by wind and water currents. While clay that does not form ooze on the deep seabed accumulates at a rate of about 2 mm per 1,000 years, ooze accumulates at a rate of about 1 to 6 cm per 1,000 years. This suggests that biological activity has a significant impact on the formation of deep-sea sediments.
The more plankton there is in the surface water, the slower the dissolution rate of laminae after they are formed on the seafloor, and the more laminae are deposited. This deposition process is related to the marine ecosystem, and the formation rate and composition of laminae are important indicators of changes in the marine environment. For example, changes in sea temperature and ocean currents can directly affect the deposition of laminae.
This is an important factor in the distribution and proliferation of marine organisms, and by analysing laminae, we can infer the marine environment of the past. Analysing the composition and distribution of laminae found in the deep sea can lead to various scientific discoveries.
For example, areas where certain types of benthic organisms are found in large numbers may indicate changes in ocean current patterns or marine habitats in that area. This is important information for understanding the dynamics of marine ecosystems. Benthic organisms also play an important role in the exploration and development of marine resources. The mineral components contained in benthic organisms help predict the type and quantity of marine resources, providing important data for future resource management.
Sediments containing at least 30% calcareous remains of organisms composed of carbonates, such as coccolithophores and foraminifera, are called ‘calcareous plankton,’ while sediments containing at least 30% siliceous remains of organisms composed of siliceous components are called ‘siliceous plankton.’ Calcareous plankton are found in relatively warm and shallow areas. This is because cold seawater contains more carbon dioxide, which dissolves carbonates, so the skeletons and remains of organisms composed of carbonates dissolve at depths greater than the carbonate compensation depth. The carbonate compensation depth is the depth at which the supply and dissolution of carbonates are equal, and is approximately 4,500 metres on average. Calcareous ooids, which cover about 48% of the deep sea surface, are concentrated in the central Atlantic Ocean and the eastern Pacific Ocean. This suggests that calcareous plankton are actively living in specific areas of the marine ecosystem.
On the other hand, siliceous ooids, which account for about 14% of the deep sea surface, are found even at depths deeper than the carbonate compensation depth. Siliceous ooze is particularly abundant in areas where nutrients-rich water rises to the surface due to upwelling, because the plankton that make up siliceous ooze tend to inhabit areas where upwelling occurs. For example, siliceous ooze is most commonly found on the deep seabed near Antarctica, where upwelling occurs and cold currents flow, because diatoms tend to inhabit areas where upwelling occurs.
In addition, siliceous laminaria is also found in large quantities in upwelling areas that extend along the equator in the Pacific Ocean because they are home to large numbers of radiolarians, which are siliceous organisms. Scientific analysis of the formation, distribution, and composition of laminaria provides a wealth of information about the paleoceanographic environment and the distribution of organisms at the time the sediments were deposited.
For example, analysing the types and proportions of radiolarians contained in ooids allows us to estimate the water temperature, salinity, and nutrient status at the time. This provides important data for paleoceanographic research and greatly aids our understanding of past climate change and the evolution of ecosystems. The study of deep-sea ooids plays an important role not only in modern oceanography but also in earth science as a whole.
By analysing the ratio and types of organic matter contained in deep-sea sediments, it is possible to track past atmospheric carbon dioxide concentrations and climate fluctuations. This provides important information for predicting current and future climate change and can contribute to the protection of the global environment. For example, by analysing changes in the distribution of diatoms contained in deep-sea sediments, it is possible to estimate past ocean temperatures and nutrient conditions, which can then be compared with current changes in the marine environment.
Furthermore, such research provides important information for the exploration and management of marine resources, contributing to the maintenance of sustainable marine ecosystems. Marine sediments are key to studying the marine environment of the past and will play an important role in marine management in the future. Through this, we will be equipped with better tools for understanding the history and future of the Earth.
