OCN400-Problem Set #5 Jim MurrayAutumn 2001 11/19/011. Box Models: Atmospheric CO2 and the Biological PumpAs water upwells from the deep ocean to the surface water, it equilibrates with theatmosphere. Biological activity in the surface ocean effects the oceanic carbonate systemand the resulting PCO2 in the atmosphere.Calculate atmospheric PCO2, deep water O2 and AOU for the following four cases.a) an abiogenic oceanb) a productive ocean with preformed phosphate [PO4]° = 0.90 µmol kg-1.c) a productive ocean with no surface PO4.d) a productive ocean with preformed phosphate [PO4]° = 0.90 µmol kg-1 if all biologicalproduction is in the form of siliceous organisms (e.g. no CaCO3 shells or alkalinitychange)Useful info:DICd = 2250 µmol kg-1Alkd = 2365 µeq kg-1K1' = 10-6.0K2' = 10-9.1KH' (CO2) = 10-1.53 mol kg-1 atm-1Vmix = 300 cm y-1PO4deep = 2.2 µmol kg-1 PO2 = 0.2095 atm(hints: First set up a PO4 balance for the surface. Use the RKR ratios to calculate thesurface DIC and Alk. Calculate the alkalinity flux based on the Ca/P ratio in the lecturenotes. Calculate PCO2 from DIC and Alk using the equations in the OCN421 notes. Deriveor find the equation to calculate PCO2 from DIC and Alk and then do these calculations inan Excel spreadsheet.)2. Box Models: 234Th as a Tracer for Particulate Export FluxThe surface ocean almost invariably shows a radioactive disequilibrium of 234Th from238U due to the export of particulate material from the surface ocean to which 234Th isadsorbed. This is one approach for estimating the flux of carbon from the euphotic zone.Consider the 2-box model: By knowing the activity of 238U, we know the sourceof 234Th into the surface box. By knowing the activity of 234Th, we know the particulateflux out of the surface box for a steady state ocean.a) If the total activity of 234Th in the surface box is 1.8 dpm l-1 and 238U is 2.4dpm l-1, what is the magnitude of the export flux of 234Th (in moles m-2 y-1). The decayconstant for 234Th is λ = 0.0288 d-1.b) How does this flux compare with the flux due to mixing? Is vertical mixingimportant for 234Th cycling?c) If the global average sinking material has an average value of 0.20 dpm 234Thper µmol organic carbon, what is global new production?d) How does this value compare with global values of primary production givenin Lecture? Calculate the global average ratio of export flux to primary production. Is thisa reasonable value? Explain.3. Oxidation-Reduction reactionsThe Black Sea is the world’s largest permanently anoxic water body. It is a semi-enclosed marginal sea with a physical and chemical structure that is determined by itshydrological balance. Seawater flows in through the Bosporus to the deep layer of thebasin. Freshwater inflow from European rivers keeps the salinity low in the surface layer.As a result the water column is strongly stratified with respect to density. A consequenceis that the surface layer (about 0 to 50m) is well oxygenated while the deep layer (100mto 2000m) has no oxygen and high sulfide concentration. At the boundary between theoxic surface and anoxic deep layers there is a suboxic zone (from approximately 50m to100m depth) where O2 and HS- are essentially both absent. The distributions of nutrients(e.g. NO3-, NH4+ , PO4) and metals (e.g. Mn, Fe) and the absence of O2 and HS– suggestthe occurrence of unique or unusual metabolic processes within the suboxic zone (e.g.,anaerobic Mn(II), Fe(II), NH4+, HS–, and S(0) oxidation and the possibility for unusualphotosynthetic reactions).Thor has proposed that nitrate reacts with ammonia to produce N2 (g). Using the half-reactions in Table 15-1 of the Chapter 15 notes do the following:a) Write a balanced reaction for NO3 + NH4+ to produce N2 (g)b) What is the equilibrium constant for this reaction?c) How much free energy would be available from this reaction given the followingconcentrations at the point of reaction at σt = 15.90?N2 (g) = 0.80 atmpH = 7.5NO3- = 0.1 µMNH4+ = 0.1