Chemical Oceanography 14 March 2012 Points are in parentheses (show all your work) Final Exam

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Ocean 400 Name: Chemical Oceanography 14 March 2012 Winter 2012 Points are in parentheses (show all your work) (give as much detail as you can) (use back if necessary) Final Exam 1.

1 Ocean 400 Name: Chemical Oceanography 14 March 2012 Winter 2012 Points are in parentheses (show all your work) (give as much detail as you can) (use back if necessary) Final Exam 1. Sarmiento and Gruber (2002) The Global Carbon Cycle Remember the box model for the carbon cycle from Figure 1 of Sarmiento and Gruber (2002). a) Calculate the residence time (in years) of C in the atmosphere for the present (black plus red arrows) accounting for all sources or sinks. You don t need to see this one in color! (10) b) Calculate the preindustrail residence time of C in the surface ocean. (5) c) Calculate the present residence time of C in the surface ocean. (5) d) Is the residence time of C in the surface ocean at steady state? (5)

2 2. Doney et al (2009) Ocean Acidification The surface ocean is becoming more acidic due to addition of anthropogenic CO 2. The ph of preindustrial surface seawater was The ph of surface seawater is projected to reach 7.60 by the year 2100 if we continue to add anthropogenic CO2 to the atmosphere at the same rate (business as usual). a) Calculate the numerical molar concentration of [H + ] that was present in preindustrial seawater. (5) b) By what percentage will the [H + ] concentration have changed if the ph reaches 7.60 in the year (10)

3 3. Major and Trace Elements a) What is the main criteria that determines if an element is a major element in seawater? (10) b) Below is a plot of Sr versus PO 4 in seawater. What does this plot tell you about the distribution (vertical profiles and interocean) of Sr in seawater? (10)

4 4. Ocean carbonate reactions We have learned the following equilibrium reactions and constants for seawater. 1. CO 2 (g) + H 2 O H 2 CO 3 K H = H 2 CO 3 H HCO 3 K 1 = HCO 3 H CO 3 K 2 = H 2 O OH - + H + K w = CaCO 3 (calcite) Ca CO 3 SW K sp = 5.9 x 10-7 = CaCO 3 (calcite) Ca CO 3 FW K sp = 5.0 x 10-9 = CaMg(CO 3 ) 2 (dolomite) = Ca 2+ + Mg CO 3 K sp = 2 x = You can assume the solubility of dolomite is the same in FW and SW. 4a) If we know the DIC and ph of surface seawater what is the equilibrium concentration of bicarbonate (HCO 3 - )? Assume DIC = 2.0 x 10-3 and ph = (10) 4b) If we know the DIC and ph of surface seawater what is the equilibrium concentration of P CO2? Assume DIC = 2.0 x 10-3 and ph = (10)

5 4c) At the Hawaii Ocean Time Series (HOT) Calcite is supersaturated by a factor of 5.5 (Ω calcite = 5.5). What would the Ca 2+ have to be for Ω calcite = 1.0? (10) Assume ph = 8.0 Assume DIC = 2.0 x 10-3 M 4d) Calcite is the form of carbonate solid most often found in modern marine sediments. However rocks from the Paleozoic have much more Dolomite than Calcite Calcite ( CaCO 3 ) can be converted to Dolomite (CaMg(CO 3 ) 2 ) by the following reaction: 2 CaCO 3 (s) + Mg 2+ = CaMg(CO 3 ) 2 (s) + Ca 2+ i) Calculate the value of the equilibrium constant for the conversion of calcite to dolomite given above. Use the fresh water (FW) solubility product for calcite. (10) ii) In a Florida groundwater aquifer geochemists measured a dissolved ratio of Ca/Mg = Are calcite and dolomite at equilibrium in this environment? (10)

6 5. Radioactive Decay and Secular Equilibrium In the 238 U decay series, 210 Pb with a half-life of 22.3 yrs decays to 210 Po which has a half-life of 138 days. a) What are the criteria for determining if secular equilibrium exists between any two isotopes in the ocean? (10) b) What would be the relationship between the activity of 210 Pb (i.e., A 210Pb ) and 210 Po (i.e., A 210Po ) if secular equilbrium existed? (10) c) 210 Po is a very toxic isotope (about 106 times more toxic than cyanide). The main hazard is its intense alpha radiation (half-life = 138 days) which, if ingested, does serious damage to internal tissues. Imagine that you are an undercover spy and you want to poison some critic of your government by slipping some 210 Po into their margarita. The maximum safe body burden of 210 Po is = 16.7 dpm. To make sure your deadly poison works you want to increase the body burden by >10 times to >167 dpm. Hint: 1 Becquerel (Bq) = 1 dps = dpm i) Your chemical lab at UW knows how to separate 210 Po from 210 Pb. You just have to get them the material. You have 200 dpm of pure 210 Pb. How long do you have to let the 210 Pb decay so that you have 190 dpm of of 210 Po? (190 dpm is 95% of 200 dpm). (10) ii) Your lab chemists do their job well and now you have a sugar cube containing 200 dpm of 210 Po. You get ready to meet your victim in a bar in Fremont but suddenly he is out of the country (gone to Britain) for 138 days. Finally you meet and while his back is turned you slip the sugar cube into his drink. Will your poison work? Explain why. (10)

7 6. Oxidation-Reduction Can ammonia (NH 4 + ) be oxidized to nitrate (NO 3 - ) by MnO 2 in sediments? Hulth et al (1999, Geochimica et Cosmochimica acta, 63, 49-66) proposed this reaction based on data from hemipelagic sediments. 9a) What is the oxidation state of N in NH 4 +? (5) 6b) Write a coupled oxidation-reduction reaction of MnO 2 reacting with NH 4 + to produce NO 3 -. From the lecture notes we have the two half reactions written below. Give the equilibrium constant for the reaction. (10) 1/2MnO 2 (s) + 2 H + + e - = ½ Mn 2+ + H 2 O log K = /8 NO /4 H + + e - = 1/8 NH /8 H 2 O log K = c) Hulth et al (1999) reported the following representive conditions for pore water in sediments. Can the reaction of MnO 2 + NH 4 + proceed for these conditions? (10) ph = 7.5, Mn 2+ = 100 x 10-6 M, NO 3 - = 10 x 10-6 M, NH 4 + = 100 x 10-6 M 6d) How will the alkalinity change if the reaction proceeds to the right? (5)

8 7. Oxygen in seawater Falkowski et al (2011, EOS, 92, p. 409) summarized data for Ocean Deoxygenation: Past, Present and Future. The data shown here show a decadal trend and oscillations on four different density surfaces. The blue x are for the density of σ t = 26.5 (~150m) at Ocean Station P in the subarctic North Pacific. 7a) Explain what controls the concentration of oxygen in seawater at any given depth and time? (10) 7b) On the density of 26.5 the oxygen appears to be decreasing systematically since Explain how that could occur. There are at least two options. Explain well. (10) 7c) How might the distributions of O 2 in seawater change in the future with an increase in surface water warming? (10)

9 8. Nutrient ratios The classic Redfield model for plankton production and respiration is written as: 106 CO HNO 3 + H 3 PO H 2 O (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) O2 (Algal Protoplasm) How accurate is this model? 8a) Explain how the N/P ratio might vary in phytoplankton as they change from survivalist to bloomer modes (Arrigo, 2005). What is the origin of this variability? (10) 8b) Different values have been used for the amount of O 2 produced during primary production. Explain how these different stoichiometries have been determined. (10)

10 8c) A tracer used to describe the ocean nitrogen system is called N*. N* is defined as: N* = [NO 3 - ] - 16 [PO 4 3- ] In the Southern Ocean the N* of upwelled water is initially negative (blue = -4) (Weber and Deutsch, 2010, Nature, 467, p.550). After the water is upwelled it is transported at the surface to the north and the N* increases to less negative values (red = -2). Propose a plausible explanation(s) based on what you know about ocean N cycling. (10)

Mid-Term #1 (125 points total)

Mid-Term #1 (125 points total) Ocean 520 Name: Chemical Oceanography 20 October 2009 Fall 2009 Points are in parentheses (show all your work) (use back if necessary) MidTerm #1 (125 points total) 1. Doney et al (2008) Ocean Acidification