CAS ES 107 Chapter Notes - Chapter 8: Methanogenesis, Photic Zone, Primary Production
7 Jun 2018
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Chapter 8: Recycling of the Elements
-earth is able to maintain liquid water because of our natural recycling systems for the elements
essential to life including carbon, nitrogen, phosphorus, and sulfur
-the link between tectonic activity and the carbon cycle is important to the regulation of
atmospheric CO2 concentrations and thus climate as well
-these elements are released to the biosphere as rocks weather, volcanoes erupt, and nitrogen is
made available from the atmosphere by chemical transformations stimulated by lightening
discharge
-nutrients→ substances normally obtained in the diet
-the carbon in CO2 is inorganic carbon and is not associated with compounds formed by living
organisms
A journey through the Terrestrial Organic Carbon Cycle
-after spending decades in the troposphere, the CO2 will pass through an opening in a leaf,
becoming an organic carbon
-the leaf is digested by animals and released back into the atmosphere by the animals’ respiration
-a leaf that has not been eaten falls to the ground, now the carbon atom is a part of the soil, where
it will remain for the next 50 years
-bacteria and fungi will have decomposed the organic matter that contains the atom and chemical
reactions that result transform the carbon atom again into a gaseous CO2 molecule, which
escapes to the atmosphere
-this cycle is repeated nearly 500 times before a “leak” occurs
-once ina while, before the organic matter containing the carbon decomposes, the soil erodes and
goes to the rivers and oceans
-it settles on the seafloor, or is carried with its underlying oceanic plate deep into a subduction
zone
-under pressures and temps, the carbon atom may be converted into a gaseous carbon atom and
escape to the surface
-the carbon may spend millions of years in sedimentary/metamorphic rock reservoir
-weathering will cause the carbon in the sedimentary rock to disintegrate, letting the carbon
escape as CO2 into the atmosphere
-the weathering process is the connecting link
-the inflow to the atmospheric CO2 reservoir is the combo of respiration and decomposition
-the outflow is photosynthesis
Steady state→ the state of a system is constant with time
-it could not be achieved if no inflow and no outflow existed (if both stopped)
-because of humans, the CO2 level is not at a steady state
-when inflow exceeds outflow, CO2 levels rise, like what happens in the Northern
Hemisphere during the winter
-steady state can be maintained over time only if the rates of inflow and or outflow are
sensitive to changes in reservoir size
-CO2 fertilization→ as CO2 levels go up, plants photosynthesize more rapidly
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