The importance of nutrients for Earth’s carbon cycle
Chris Reinhard, Georgia Institute of Technology
The global carbon cycle links together the biosphere, planetary climate, and the chemistry of the oceans and atmosphere. The cycling of carbon at Earth’s surface is in turn governed by feedbacks linking it with the oxygen and sulfur cycles, the cycling of major and trace nutrients, and the exchange of volatiles with Earth’s interior. In particular, life on Earth requires ~30 chemical elements for the synthesis of structural compounds, enzymes, and nucleic acids. The cycling of these biological essential elements – nutrients – is a critical factor regulating the productivity of Earth’s biosphere. On arbitrarily long timescales, it is thought that the cycling of phosphorus (P) provides the ultimate limitation on biospheric fertility, making the global phosphorus cycle critical for the long-term transfer of organic carbon into Earth’s sedimentary reservoirs and, through attendant impacts on Earth’s oxygen cycle, the recycling of carbon from Earth’s crust back into the ocean-atmosphere system. Earth’s rock record suggests that these processes and linkages depend strongly on the amount of oxygen in Earth’s ocean-atmosphere system, in ways that are at times counterintuitive. For example, while local anoxia can enhance the burial of carbon in marine sediments, pervasive anoxia can dramatically decrease the productivity of the biosphere. In this light, it is the dynamics of nutrient cycling at Earth’s surface that to a considerable extent modulate the activity level of the biosphere and thus global carbon fluxes.