Lecture 20 Flashcards
Biogeochemical Cycles
Relates to the transformations of nutrient elements on the earth. A global biogeochemical cycle relates to the total global flow of the element, and as such it is a description of a materially closed system.
Estimation of Reservoir Amounts
Reservoir amounts for an element are usually estimated from some knowledge of its concentration in the reservoir and the size of the reservoir itself. [you should know how to derive these numbers]
The short-term carbon cycle
Refers to that part of the cycle that operates independently of the lithosphere.
Is the natural cycle balanced on seasonal timescales?
Not balanced. But, on the longer time scales (multi-year-decadal): the cycling of carbon between the biosphere and CO2 is extremely stable and very nearly always in balance. If there is excess net organic carbon production, the excess is readily processed by organisms before it can be stored in deep ocean or soils.
What is the relevant CO2 transfer rate?
~8 Gtons ~100 years
The Airborne Fraction
The fraction of CO2 emitted into the atmosphere that remains in the atmosphere.
Missing Sink
The missing 90 Gtons. Called missing because we can’t account for it.
Terrestrial biosphere
For reasons that are not entirely understood has been stimulated to grow by 90 Gtons C since preindustrial times.
Long-term response
Once the biosphere is depleted, the loss of O2 via respiration and decay ceases, but there is still a small sink for O2… the decay of organic sediments.
Fain Sun Paradox
When Earth formed 4.6 bya solar luminosity was about 70% of its present value. However the T is below freezing until ~2 bya. No ocean and no life at Earth’s surface before 2 bya.
