What is Biogeochemistry?

Development of a “New” Scientific Field

Life on our planet is made up of an incredible variety of carbon molecules, and, in essence, life processes are carbon chemistry. Conversely, the carbon cycle, which can be viewed as the movement of carbon atoms through various places of storage on Earth, called “reservoirs,” is intimately tied to life processes. In the study of the carbon cycle, biology and geochemistry merged to form a new scientific discipline called “biogeochemistry.” (See Glossary for more information). Biogeochemists study the carbon cycle and its interconnections with the cycles of other elements involved in life processes, mainly nitrogen, oxygen and phosphorus, but also sulfur and iron and certain trace metals. In addition, the water cycle helps drive the carbon cycle, and this is where climate and the carbon cycle are most intimately connected.

Biogeochemistry includes the history of the great carbon reservoirs in the crust of the Earth, like limestone rocks and the coal deposits, as well as the distribution of nitrate and phosphate in the ocean. It seeks to explain the composition of the atmosphere (consisting mainly of nitrogen and oxygen, as well as other trace gases) as a result of bacterial action and photosynthesis. And biogeochemistry records the exchange of matter at the interfaces: the decay of organic matter in soils and resulting gases released into the air; the uptake of oxygen by the ocean and its utilization at depth; and the leaching of nutrients from the soil and their transport into the sea.

The all-important role of life processes in maintaining Earth's environments was stressed early in the 20th century by the Russian mineralogist, Vladimir Vernadsky (1863-1945), who may be considered the father of biogeochemistry. The American limnologist and geochemist G. Evelyn Hutchinson (1903-1991) led the way and first outlined the broad scope and principles of this new field. More recently, the basic elements of the discipline of biogeochemistry have been restated and popularized by the British engineer and science writer, James Lovelock (born 1919), under the label of the “Gaia Hypothesis.” Lovelock emphasizes a concept that life processes regulate the radiation balance of Earth to keep it habitable.

Biogeochemistry and the Carbon Cycle

At the core of biogeochemistry is the carbon cycle, which describes the movement of carbon atoms through the life-support systems on the surface of the planet. Models of the carbon cycle, based on mathematical formulations, consist of "reservoirs" of carbon and the "fluxes" between these reservoirs. Examples of reservoirs are the "ocean", the "atmosphere," the "biosphere," the "soil carbon," the "carbonate sediments," and the "organic carbon sediments." The "fluxes" between them describe the rate at which atoms move from one reservoir into another. For example, a flux could be the rate of movement of carbon between organic matter produced in ocean surface waters and the sediments of the ocean floor.

Simple sketch of the carbon cycle, illustrating fluxes and reservoirs. (From: SeaWIFS project)

The crucial questions concern the mechanisms that control the fluxes, and how these controls change as the planet warms up. For example: What controls the productivity of the ocean, and what controls the proportion of the matter produced that reaches the ocean sediment? And how does the amount of plankton change with warming of the ocean, and how does the flux of organic matter to the seafloor change as a result? This is all part of the prediction game. But if we wish to predict what will happen, we first have to understand what has happened in the past and what has happened so far.