Chemical Oceanography

Chemical oceanography is a fundamental scientific domain seeking to understand the distribution of chemical elements in the marine environment and the factors that control it, as well as the various phenomena occurring in the oceans by means of chemical methodologies. Today, many global environment issues, such as global warming enhanced by greenhouse gases like carbon dioxide, and chemical pollution, are increasing and there are requirements to quickly forecast the future global environment. The main objectives of chemical oceanography research are to understand the matter characteristics, including marine organisms, to clarify the material flux mechanisms of the oceans, and to determine the role of oceans in the preservation of the global environment from a chemical standpoint. This page seeks to explain those global warming and oceanic material flux issues that attract much attention today and where research is rapidly progressing.

Since the 1980’s, abnormal weather conditions have bad significant impacts worldwide, such as deluges, droughts, and mild winters. Global warming due to emissions of greenhouse gases such as carbon dioxide released through human activities release, is assumed to cause these phenomena. An accurate estimate of the amount of carbon dioxide that the oceans can absorb is necessary for forecasting the evolution of the Earth’s climatic environment. Many oceanographers worldwide have therefore recently been working on how and what amount of increasing carbon dioxide the oceans can absorb and release, to quantitatively clarify a material flux focused on the carbon involved in biological and physical processes.

Carbon on the Earth’s surface is known as one of the most important elements since it preserves the living organisms and their environment. Carbon exists not only as carbon dioxide but also as carbon monoxide, methane, carbonic ion, bicarbonate ion, free carbon dioxide, carbonate minerals, and organic matter which includes organisms. The oceans and atmosphere of carbon dioxide are assumed to exchange about 90 billion tons of carbon dioxide per year. Oceans are said to currently absorb two billion extra tons a year of carbon dioxide, based on the difference between carbon dioxide released from fossil fuel and shale burning, and its increase in the atmosphere. The amount of carbon dioxide that the oceans and atmosphere exchange is believed to depend on the difference of carbon dioxide partial pressures, water temperature and salinity, which determine solubility, and the speed of gas exchanges. Because are winds stronger in winter in the southern oceans and high-latitude regions of the northern hemisphere, surface waters are mixed more deeply and better than in summer. The exchange of gas thus intensifies and equilibrium is reached quickly. The principle is equivalent to shaking a soda to extract its gas all at once instead of leaving it quietly. In equatorial regions, upwelling of deep water with high carbon dioxide partial pressure release carbon dioxide to the atmosphere. In sea regions characterized by active phytoplankton photosynthesis, however the carbon dioxide partial pressure of the sea-surface layer decreases as it is transformed into organic matter, so that abortion from the atmosphere increases. During these transfer processes, physical factors such as surface-water circulation, temperature, and wind speed, and biochemical factors such as those involved in the activity of the organisms, play major roles.

Within sea-surface layers reached by light, and as long as nutrient salts (nitrogen, phosphorus, etc.) are supplied, phytoplankton photosynthesizes organic matter from water and carbon dioxide (this is called primary production). Nearly 90 percent of this organic matter is decomposed in the surface layer into water and carbon dioxide again but, unrecompensed remains and fragments sink into medium and deep layers. These remains, which are transported to the abyss as organic precipitate particles, are removed from the surface layer, and the missing amount is supplied as inorganic carbon dioxide from the atmosphere. Such transfer processes from the sea surface to deep layers involved in the carbon cycle are called the Biological Pump.

Therefore, oceans are essential buffers of carbon dioxide that is the main cause of global warming, within the carbon absorption processes, the transformation of inorganic carbon into organic matter through photosynthesis, as well as the transportation of this organic matter to the deep layers through the biological Pump, play determinant roles. The GLI sensor on board ADEOS-II (scheduled to be launched soon) will provide multi channel data acquisition and 250m high-resolution capabilities inherited from the successful OCTS, and measure phytoplankton concentration, primary production, and their fluctuations. GLI is expected to contribute greatly to research on the carbon Cycle as it relents to global warming.

Bibliography: Ocean and environment (Compilation of the Oceanographic Society of Japan, 2001)

Earth Obserbation Research Center

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