OCN400 - Problem Set #2 Jim MurrayAutumn 2001 (10/12/01)1. Box Model, residence time.Element “X” is at steady state in the contemporary ocean with a concentration of1.0 x 10-3 mol L-1 (M). The main input is from rivers and the main removal is by thestripping of X from seawater during hydrothermal circulation (concentration of X in thereturn flow from the vents to the ocean is zero). The following information is available:Volume of ocean 1.4 x 1021 LRiver Flow: 3.2 x 1016 L year-1Concentration of X in rivers 1.0 x 10-4 MConcentration of X in seawater 1.0 x 10-3 Ma. Calculate the residence time of X with respect to total (e.g. river) inputs.b. Set up the mass balance equation (sources = sinks) for X. Calculate the rate of waterflow through the hydrothermal circulation that would have to exist for this to be a steadystate system.A change in climate patterns results in a new significant source of X to the ocean in theform of atmospheric deposition. Some phytoplankton in the surface ocean biota respondto the enhanced input by building their shells out of X, resulting in a new sedimentationflux as a sink of X from the ocean. The rate of water flow in the hydrothermal system isunchanged.Rate of atmospheric deposition of X 2.0 x 1012 mol year-1Rate of burial of X in sediments 0.5 x 1012 mol year-1c. Set up the new mass balance equation for X. Calculate the concentration of X inseawater once the ocean reached its new steady state.d. Calculate the new residence time of X with respect to total inputs.2. Siegenthaler and Sarmiento (1993) have presented box models of the global carboncycle for pre-industrial (PI) times and the present (1980-89). These are shown below.Answer the following questions and show all your work and calculations.a) Was atmospheric CO2 in steady state in pre-industrial times?b) Is atmospheric CO2 in steady state at present (1980-1989)?c) What is the residence time of atmospheric CO2 for PI conditions?d) What was the residence time of carbon in biota in the surface ocean in PI time?e) How has the residence time of carbon in marine biota changed as a result of increasedfossil fuel CO2?3. Sodium (Na) is the highest concentration cation in seawater. What controls theconcentration of Na in seawater?4. Only one of the following is the essential approximation made when assuming steadystate:a. ocean inputs from rivers equals the particle flux out of the euphotic zoneb. the concentration does not change with timec. the removal flux must be proportional to how much is there.d. the river input must equal the atmospheric input.5. Gypsum solubility is written as:CaSO4.2H2O(s) = Ca2+ + SO42- + 2H2O pK = 4.58a) If we added gypsum to distilled water (with no other salts present) and let it come toequilibrium, what would the equilibrium concentration of total Ca be? Use the Daviesequation to calculate γi.b) If the total sulfate concentration of seawater is 25.0 x 10-3 mol kg-1, what would be theconcentration of total Ca if gypsum was at solubility equilibrium? How does thiscompare with the actual concentration of
View Full Document
Unlocking...