1. (20 points) The figure below (adapted from: Rauch, J.N. and T.E. Graedel (200
ID: 1002890 • Letter: 1
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1. (20 points) The figure below (adapted from: Rauch, J.N. and T.E. Graedel (2007) Earth's anthrobiogeochemical copper cycle, Global Biogeochemical Cycles, 21, 2, doi 0028500 depicts the global copper cycle prior to human perturbation. a. What is the flux of copper into, and out of, freshwater? And the ocean? b. What is the residence time of copper in freshwater and the ocean and does this figure depict freshwater and the ocean in steady-state? If either is not in steady state, by how much is the inventory (stock changing each year in percent per year? c. From the same paper, the authors note that currently an extra 1396 Gg of Cu enter freshwaters each year, an extra 1230 Gg of Cu leave freshwaters each year, that extra amount leaving freshwaters enters the ocean as an additional flux along with an additional 19 Gg (for a total additional entering the ocean of 1249 Gg Cu per year). If these additional fluxes are kept constant, what will the ultimate steady state inventories of Cu in freshwaters and the ocean be, and how long will it take to approach (95%) the new steady-state? 1.3 31 13 Natural Freshwater 770 oceans 780 0.2 Biomass 2500 Cont. Regolth 8.7E9 Consolidated 9.5E11 4700 2.7 Mantle Rock 1.0E14Explanation / Answer
a. incoming flux of fresh water = 2600 Gg/year
outgoing flux of fresh water = 2370 Gg/year
incoming flux of ocean = 22+770= 792 Gg/year
outgoing flux of ocean = 780+13 = 793 Gg/year
b.
residence time of copper in fresh water (steady state)= 6.3*10^4 / (2600-2370)= 273.91 years
residence time of copper in oceans(steady state) = 1.9*10^5 /(793-792) =1,90,000 years
if they are not in steady state then stock changes according to the percentage of inflow and outflow.
percentage retained varies accordingly.
c.
ultimate steady state of freshwater
incoming flow = 2600 + 1396 = 3996 Gg/year
outgoing flow = 2370 +1230 = 3600 Gg/year
total retained = 3996 - 3600 = 396 Gg/year
ultimate steady state of oceans
incoming flow = 770 + 1249 = 2019 Gg/year
outgoing flow = 793 Gg/year
total retained = 2019- 793 = 1226 Gg/year
time taken to approach 95% of steady state(fresh water) = 0.95 *6.3*10^4 /(396) = 151.136 years
time taken to approach 95% of steady state(ocean) = 0.95 * 1.9*10^5/(1226) = 147.226 years
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