- © The Mineralogical Society Of America
Carbon is highly important for our biosphere, not just because it forms organic compounds; it also creates atmospheric greenhouse gases, pH buffers in seawater, and redox buffers virtually everywhere. Carbon species can stabilize metamorphic minerals and they can affect plutonism and volcanism. These various C constituents all interact via the biogeochemical C cycle, an array of C reservoirs linked by a network of physical, chemical and biological processes. The overall C cycle actually consists of multiple nested cyclic pathways that differ with respect to some of their reservoirs and processes (Fig. 1⇓). However, all pathways ultimately pass through the hydrosphere and atmosphere, and it is this common course that unites the entire carbon cycle and allows even its most remote constituents to influence our environment and biosphere.
The history of the biogeochemical C cycle has been at least partially recorded in the C isotopic composition (δ13CPDB) of carbonate (δcarb) and reduced C (δorg) in ancient sedimentary and metamorphic rocks. To the extent that sedimentary rocks avoided deep burial and alteration, they have preserved information that indicates the status of the C cycle at the time of their deposition.
THE PRESENT-DAY CARBON CYCLE
The C cycle can be represented as an …