Earth.Parts #23 - Carbon cycling and Earth's carbon reservoirs
Channel: Earth.Parts
Date: 2017-03-21

We've learned a lot about the carbon cycle by studying how climate operates, based initially on concerns regarding anthropogenic climate change but the payoff from that research has been a vastly improved understanding about how climate-controlling processes function.

The carbon cycle, as we've learned in the last few decades, is an extensive and complicated business that tracks where the atoms of carbon (C) go and where they spend their time, in the atmosphere, at Earth's surface and in the rocky depths beneath our feet. 

Carbon is a required chemical element for life, and builds the architecture of our cells and the organic mass of all life on Earth. Organic chemical compounds are those that include a C-H bond, such as methane, glucose or petroleum.

On Earth carbon continuously cycles through a variety of different chemical forms, or reservoirs. Limestone is the hugest reservoir of carbon stored in Earth's crust, laid down over hundreds of millions of years by life forms in the oceans. Second to limestone is organic carbon in sediments, kerogen found in black shale, and fossil fuels.

The atmospheric reservoir of carbon is one of the smallest, and human activities have contributed waste CO2 to specifically that one small reservoir, which has resulted in a modification in atmospheric chemistry that leads to enhanced thermal retention.

In general cyclic processes on Earth can be better understood in terms of geochemical reservoirs that at any time hold a certain mass of material, and geochemical fluxes that move material from one reservoir to another. The residence time of an element in a given reservoir can be expressed in terms of reservoir size divided by input or output flux over time. 

For example, the atmospheric CO2 reservoir is about 760 Gigatons (Gt) of C, and the annual drawdown of CO2 by world photosynthesis is about 60 Gt, dividing the two gives us an estimate of about 12.7 years as the residence time of C in the atmosphere with respect to only photosynthesis alone, ignoring other influences for the purpose of the exercise. 

If a geochemical reservoir is changing or unstable over time the concept of residence time shifts instead to a description of a reservoir's characteristic response time, which assesses how long a system takes to respond to perturbation. 

If you like these videos please subscribe & share!