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Lecture 3. Terrestrial Biogeochemical Cycling and Climate Elena Shevliakova & Chip Levy. UNITS. 1 Tg = 1 Terragram = 10 12 grams 1Mt = 1 Megaton = 10 6 tons = 10 9 kilograms = 10 12 grams 1 Pg = 1 Pedagram = 10 15 grams 1 Gt = 1 Gigaton = 10 9 tons = 10 12 kilograms = 10 15 grams.
1 Tg = 1 Terragram = 1012 grams
1Mt = 1 Megaton = 106 tons = 109 kilograms = 1012 grams
1 Pg = 1 Pedagram = 1015 grams
1 Gt = 1 Gigaton = 109tons = 1012 kilograms = 1015 grams
GB Bonan 2002, Ecological Climatology
The phosphorus cycle is “simple” because it does not involve the atmosphere.
Phosphate from rock dissolves very slowly (unless we intervene. The dissolved phosphate is used by plants, which may pass it to animals. Some of the phosphate is excreted by animals and goes immediately into the dissolved pool. When plants or animals die, phosphate is released by bacteria decomposition of organic compounds (like nucleic acids). Large quantities of dissolved phosphate are carried into the sea by runoff. The formation of new rocks from marine sediments, where the phosphorus eventually comes to rest, is very slow. However, it is unlikely that we will soon run out of phosphate rock - the known reserves are large. Nevertheless, supplies in soils are readily depleted, so phosphorus is often a limiting nutrient.
Although photosynthesis and respiration used to be in balance globally, fossil fuel combustion (roughly 10% of NPP) now means that emissions of CO2 exceed surface uptake.
Assuming fossil fuel combustion adds carbon to the atmosphere as CO2, 6.3 Gt of carbon is 3 CO2 molecules extra added to every 106 molecules of air or 3 more ppmv of CO2. [Bad News]We are now transferring between 6 and 7 Gt(C) per year from below ground to the atmosphere, but the increase seen is about 1.5 ppmv per year. We conclude that the combined net rate of transfer of carbon outof atmospheric to terrestrial and ocean sinks is currently about half the rate of carbon transfer intothe atmosphere from fossil fuels. [Good News, for now]
X (7.2/6.4) = 4.1/3.2
X >1.0 means ?
Is this good or bad?
Ocean: 67484 observations
(Pg C yr-1)
Well known sources
Fossil fuel emissions 6.3 + 0.4
Where CO2 has been observed
Remains in atmosphere 3.2 + 0.1
Dissolved in ocean 2.1 + 0.2
Net terrestrial uptake (inferred) 1.0 + 0.4
1Pg/yr sink if pan-tropical
Northern Forest Sink = 0.7 GTC y –1 Goodale et. al. (2002)
Although a net missing sink of 1.0 + 0.4 sounds pretty good, uncertain land use compromises our ability to predict the future of the sink:
1. Tropical deforestation (a big source).
2. Temperate land use change (a big sink).
Missing Sink = Residual Net Flux
+Tropical Deforestation Source
– Temperate Land Use Sink
Annual tree basal area increment
(standardized by pre-treatment mean)
Korner et al. 2005