Page 32 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 1. General introduction
of carbon (Fig. 6) (Janowiak et al. 2017). Oceanic carbon provides a large stock with 37,100 Pg C, of which over 95% is present in the form of inorganic dissolved carbon. Soils store approximately 1,325 Pg C in the top meter, and potentially up to 3,000 Pg C when including the deep biosphere (Köchy, Hiederer and Freibauer 2015). Permafrost contains up to 1,600 Pg C that is stored under frozen conditions (Tamocai et al. 2009; Hugelius et al. 2014). Fossil fuel stocks, which are present in the form of coal, oil, and natural gas, store 10,000 Pg C, which is gradually released into the atmosphere due to human activity. However, the atmosphere only contains a fraction of the released carbon in the form of CO2.
Atmosphere 839
Permafrost 1,600
Soils and Vegetation 2,400
Fossil Fuels 10,000
Deep and Intermediate Oceans 37,100
Figure 6. Global carbon stocks in petagrams of carbon (Pg C). Adapted from the Climate Change Resource Center and data from the United States Department of Agriculture, Forest Service (Janowiak et al. 2017).
Plant biomass deposits comprise major carbon stocks on the planet (Fig. 6). These stocks mainly occur in the form of peat and coal deposits. Coal is consecutively formed when peat layers are exposed to high temperature and pressure over millions of years. By being the most abundant fossil fuel, coal deposits also provide an important long-term carbon reservoir.
Coal deposits comprise the major fossil carbon stock
Coal is the most available fossil fuel on the planet, comprising 70% of the total fossil fuel stocks (Iram, Akhtar and Ghauri 2017). The current coal stocks originate mainly from the
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