1Ocean 421 Your Name___________________ Chemical Oceanography Spring 2000 Final Exam (Use the back of the pages if necessary)(More than one answer may be correct.) 1. Due to the water molecule's (H2O) great abundance in seawater: (10 pts) a) Seawater has a high heat capacity b) The activity of H2O is 1 in all equilibrium calculations c) Salts dissolve easily in seawater d) The activity coefficients of all dissolved constituents are equal e) The activity of Ca2+ is greater than its concentration. 2. Due to the great abundance of dissolved salts in seawater: (10 pts) a) sea water has a higher density than freshwater b) sea water has a higher molar volume than freshwater c) sea water has a higher boiling point than freshwater d) sea water has a high ionic strength e) sea water has a higher sound absorption than freshwater 3. Some elements in seawater are considered to be conservative. a) What is the definition of a conservative element? (5 pts) b) There are statements in the literature that uranium (U) is a conservative element in seawater. How would you design a study to show this is true or not true? (5 pts)24. Both equilibrium and kinetic (dynamic) models have been proposed for the composition of seawater. What arguments can be given favoring the kinetic model relative to the equilibrium approach? (10 pts) 5. As deep water flows from the North Atlantic to the North Pacific the carbonate alkalinity increases from 2350 µEq to 2475 µEq while total CO2 (e.g., DIC) increases from 2200 µM to 2375 µM. Estimate the average contributions of CaCO3 dissolution and organic carbon respiration that create this increase in DIC. (15 pts) 6. CaCO3 is added to water and it dissolves. How will the following parameters vary? (10 pts) pH alkalinity total CO2 Ca2+ PCO237. 238U (t1/2 = 4.5 x 109 yr) decays to 234Th (t1/2 = 24.1 d) a) Define, and give the conditions for, secular equilibrium (5 pts) b) Assuming the activity of 238U = 2.3 dpm kg-1 what is the molar concentration of 234Th? (10pts) c) Assume there has been an extreme bloom period with intensive scavenging that removes most of the 234Th from the water column in the euphotic zone. Suddenly the bloom stops. How long will it take for 234Th to reach secular equilibrium with 238U? (5 pts) 8. Which of the following is a first order process? (10 pts) a) River input b) Downwelling c) Biological Production, with respect to DIC d) Biological Production, with respect to N,P, Fe or another biolimiting element e) Radioactive decay 9. The Redfield (or RKR) ratio represents (10 pts) a) C:N:P content of organic matter formed during photosynthesis b) C:N:P content of nutrients released during respiration c) C:N:P of preformed nutrients in the surface ocean d) C:N:P of nutrient uptake during photosynthesis e) C:N:P of organic matter found in sediments410. Relative to the Atlantic, Pacific deepwater (10 pts) a) pH is higher b) PCO2 is higher c) Alkalinity is higher due to a larger organic C respiration: CaCO3 dissolution rate ratio d) Alkalinity is higher due to a smaller organic C respiration: CaCO3 dissolution rate ratio e) Total CO2 is higher than alkalinity 11. In which situations is it advantageous to use K’, the apparent equilibrium constant (10 pts) a) Ion activites (but not concentrations ) can be measured and free energies are known b) Trace metal speciation calculations c) At ionic strength, I=0 d) Carbonate system equilibria in seawater e) When Q > K. 12. Due to the input of radionuclides during bomb testing in the 1960s, which information has been gained? (10 pts) a) Water mass ventilation using chlorofluorocarbon (CFC) tracers b) N-S mixing across the equator using 3H as a tracer c) Export production using C/234Th ratios d) Stagnant boundary layer thickness using a 14C steady state box model e) The rate of turbulent mixing in the bottom boundary layer. 13. The oxidation of organic matter (10 pts) a) produces dissolved organic carbon b) produces dissolved inorganic carbon c) consumes energy d) provides bacteria with energy for growth and function e) is not possible in the absence of oxygen 14. Trace elements with nutrient-like distributions, such as barium and copper (10 pts) a) show a linear relationship with salinity and [Cl-] b) are depleted at the surface c) are enriched at the surface d) are regenerated (i.e. increase) with depth e) have fixed stoichiometric ratios to P515. CO2 and climate. There is evidence that the ocean's circulation varied in a regular way during the past glacial periods. This has to do with the different sources and strengths of bottom water formation. a) Broecker (1997) used a conservative geochemical tracer called PO4* to determine the intensity of the northern and southern sources, where waters of southern origin are described by: PO4* = PO4 + O2 / 175 - 1.95 mmol kg-1 and waters of northern origin by: PO4* = PO4 + O2 / 175 - 0.73 mmol kg-1 Explain the origin of these equation and how it can be used for this purpose and why they are different for the norther and southern sources.(5 pts) b) What were the reorganizations in ocean circulation that occurred in the past and what was their origin?(5 pts) c) If there are ocean reorganizations in the future, will they be caused by the same mechanism? If not what will be the cause? (5 pts)616. Acantharian protozoa use strontium to form celestite, SrSO4(s) skeletons. Is the formation of celestite thermodynamically favorable in seawater? The solubility of celestite is written as: SrSO4 (s) = Sr2+ + SO42- a) Calculate the equilibrium constant for this reaction at 25oC given the following free energies of formation (∆Gfo) and using (∆Gro)=-2.3RT log K=-5.708 log K at 25oC. Species ∆Gfo (kJ mol-1) SrSO4(s) -1340.9 Sr2+(aq) -563.83 SO42-(aq) -744.53 b) What is the equilibrium expression? c) If seawater has [Sr2+]T=0.0928 mmol/L and [SO42-]= 28.93 mmol/L and the total activity coefficients are γSr=0.25 and γSO4= 0.065, what is ∆Gr? Is the formation of celestite thermodynamically favorable in seawater?7 17. A recent paper reported data for the gas nitrous oxide (N2O) in the surface waters of the Arabian Sea (Lal and Patra, 1998, Global