Oceanography, Chemical

Oceanography, Chemical

Oceanography is the scientific discipline that studies Earth's oceans. Chemical oceanography is concerned with the study of the dissolved elements in sea water and the ocean's numerous chemical and biochemical cycles. Topics of study include the origin and evolution of sea water, the origin of the sediment that covers the seafloor, the relationships between the myriad of chemical constituents of sea water, and the significance of changes in ocean chemistry (i.e., the influence of changing geology, including biological activity, and human-induced pollution).

Chemical oceanography can be further divided into focused areas of study. For example, marine chemistry is concerned with the composition of sea water. Marine geochemistry is additionally concerned with the chemistry of the precipitated rocks and sediment found on the ocean floor. Additionally, marine biogeochemistry is concerned with the role of organisms (particularly microorganisms) in the alteration or formation of geological features in the oceans.

The study of pollutants holds a high priority among many chemical oceanographers. Runoff of sewage, oil, fuel, and agricultural chemicals into the oceans decreases sea-water quality, particularly along the coast. At a local scale (i.e., beach or ocean/estuary interface), the decreasing water quality is more easily detected. In contrast, the global effect of ocean pollution is more difficult to determine. The full scope and the significance of the pollution-related changes are currently not clear, although chemical oceanographers are involved in clarifying the interaction between the ocean water with various pollutants, and with the ocean surface and the sea floor.

Another increasingly important aspect of chemical oceanography research concerns the study of the role of oceans in the global carbon cycle. The oceans are a major source and reservoir of carbon dioxide. Too much carbon dioxide in the atmosphere traps the escape of heat, leading to increasing global temperatures ("greenhouse effect"). The role of the oceans in potential global warming remains to be clarified.

Many elements are soluble in sea water, the oceans are major reservoirs of these elements. The study of trace elements (such as mercury and arsenic that are usually present in nature at very low levels) in sea water is important in the understanding of cycling of these elements between inorganic and organic processes. For example, naturally occurring elements such as mercury and arsenic are toxic to humans in high concentrations, and a deeper understanding of how the oceans contribute to potential human exposure (e.g., through consumption of mercury-laden fish) is gaining research importance.

Precise elemental studies may require sophisticated equipment and ultraclean sampling containers. Obtaining high-quality results can be timeconsuming and difficult, but the results have proved significant. Chemical oceanographers, for example, were among the scientists who first discovered and unraveled the unique ecosystem of hydrothermal vents that are present at the extremely cold, lightless bottom of the ocean floor.

A related area of chemical oceanography is concerned with the speciation of trace metals in ocean water. Some metals exist in a number of different forms, or species. Metals such as manganese, iron, nickel, and zinc form certain chemical species when organisms utilize the metals. Thus, the discovery of an abundance of such metal species is a clue to the presence of life in the ocean system under study.

see also Carbon Dioxide in the Ocean and Atmosphere; Hot Springs on the Ocean Floor; Ocean Biogeochemistry; Oceanography, Geological; Radionuclides in the Ocean; Tracers of Ocean-Water Masses.

Brian D. Hoyle

and K. Lee Lerner

Bibliography

Donat, John R., and Kenneth W. Bruland. "Trace Elements in the Oceans." In Trace Elements in Natural Waters. Boca Raton, FL: CRC Press, 1995.

Libes, Susan M. An Introduction to Marine Biogeochemistry. New York: John Wiley & Sons, 1992.