5b only. The answer for 5a is as follows:

• 1. The residence time for carbon in a system can be calculated by using the formula

Residence time = Storage capacity/ flux rate

• Thus, for the atmosphere, the residence time is 760/60 = 12.67 years

Similarly, for the forest, we have, 600/30 = 20 years

and for soil, we have 1600/30 = 53.33 years.

2. a) In this question, we are asked to simply check for residence times for atmospheric and oceanic exchange with respect to their residence times. The question explicitly states so. Thus, the residence time for carbon in the atmosphere is 760/60 = 12.67 years.

Similarly, the residence time for oceanic carbon is 38,300/60 = 638.3 years.

b) Since the oceanic and atmospheric reservoirs are considered to be mixed into a single large reservoir, the exchange between the two can be neglected. Sedimentation accounts for 0.2 Gt of carbon exchange between this new mixed reservoir and the carbonate sediments reservoir. If we assume a steady state condition for the reservoirs, which is a necessity for residence time calculations, the sum of inputs must be equal to the outputs. Of the 0.2 Gt output required for steady state equilibrium, 0.17 Gt can be accounted for by carbonate weathering, while 0.03 Gt can be accounted for by volcanism. We must assume that volcanic CO2 is taken out of the mixed reservoir eventually by sedimentation, with a constant flux rate of 0.03 Gt.

Thus, the residence time is

(38300+760)/0.03 = 1302000 years.

5. The major flow of oxygen in and out of the atmosphere results from photosynthesis (by plants) and respiration by plants and microbes that decompose dead organic matter. a. Assuming a simple photosynthate formula (CH20), what is the atmospheric residence time of oxygen (O) with respect to this global flow? (10 pts.) b. Given your answer above, would you expect to see significant fluctuations in the stock during the course of a year? Why or why not? (10 pts.) 5. The major flow of oxygen in and out of the atmosphere results from photosynthesis (by plants) and respiration by plants and microbes that decompose dead organic matter. a. Assuming a simple photosynthate formula (CH20), what is the atmospheric residence time of oxygen (O) with respect to this global flow? (10 pts.) b. Given your answer above, would you expect to see significant fluctuations in the stock during the course of a year? Why or why not? (10 pts.)