1. CHAPTER 6: GEOCHEMICAL CYCLES Most abundant elements: oxygen (in solid earth!), iron (core), silicon (mantle), hydrogen (oceans), nitrogen, carbon, sulfur… The elemental composition of the Earth has remained essentially unchanged over its 4.5 Gyr history –Extraterrestrial inputs (e.g., from meteorites, cometary material) have been relatively unimportant –Escape to space has been restricted by gravity Biogeochemical cycling of these elements between the different reservoirs of the Earth system determines the composition of the Earth’s atmosphere and oceans, and the evolution of life THE EARTH: ASSEMBLAGE OF ATOMS OF THE 92 NATURAL ELEMENTS

2. BIOGEOCHEMICAL CYCLING OF ELEMENTS: examples of major processes Physical exchange, redox chemistry, biochemistry are involved Surface reservoirs

3. HISTORY OF EARTH’S ATMOSPHERE Outgassing N 2 CO 2 H 2 O oceans form CO 2 dissolves Life forms in oceans Onset of photosynthesis O2O2 O 2 reaches current levels; life invades continents 4.5 Gy B.P 4 Gy B.P. 3.5 Gy B.P. 0.4 Gy B.P. present

4. COMPARING THE ATMOSPHERES OF EARTH, VENUS, AND MARS VenusEarthMars Radius (km)610064003400 Surface pressure (atm)9110.007 CO 2 (mol/mol)0.963x10 -4 0.95 N 2 (mol/mol)3.4x10 -2 0.782.7x10 -2 O 2 (mol/mol)6.9x10 -5 0.211.3x10 -3 H 2 O (mol/mol)3x10 -3 1x10 -2 3x10 -4

5. EVOLUTION OF O 2 AND O 3 IN EARTH’S ATMOSPHERE

6. Source: EARLY EARTH Oxygen for heavy-metal fans: Lyons TW, Reinhard CT NATURE Volume: 461 Issue: 7261 Pages: 179-181 SEP 10 2009

7. OXIDATION STATES OF NITROGEN N has 5 electrons in valence shell  9 oxidation states from –3 to +5 -30+1+2+3+4+5 NH 3 Ammonia NH 4 + Ammonium R 1 N(R 2 )R 3 Organic N N2N2 N 2 O Nitrous oxide NO Nitric oxide HONO Nitrous acid NO 2 - Nitrite NO 2 Nitrogen dioxide HNO 3 Nitric acid NO 3 - Nitrate Decreasing oxidation number (reduction reactions) Increasing oxidation number (oxidation reactions) radical

8. THE NITROGEN CYCLE: MAJOR PROCESSES ATMOSPHERE N2N2 NO HNO 3 NH 3 /NH 4 + NO 3 - orgN BIOSPHERE LITHOSPHERE combustion lightning oxidation deposition assimilation decay nitrification denitri- fication biofixation burial weathering

9. Oceanic Nitrogen Processes

13. BOX MODEL OF THE NITROGEN CYCLE Inventories in Tg N Flows in Tg N yr -1

14. N 2 O: LOW-YIELD PRODUCT OF BACTERIAL NITRIFICATION AND DENITRIFICATION Important as source of NO x radicals in stratosphere greenhouse gas IPCC [2007] NH 4 + +3/2O 2  NO 2 − + H 2 O + 2 H + NO 3 − + Org-C  N 2 + … N2ON2O

15. PRESENT-DAY GLOBAL BUDGET OF ATMOSPHERIC N 2 O SOURCES (Tg N yr -1 )18 (7 – 37) Natural10 (5 – 16) Ocean3 (1 - 5) Tropical soils4 (3 – 6) Temperate soils2 (1 – 4) Anthropogenic8 (2 – 21) Agricultural soils4 (1 – 15) Livestock2 (1 – 3) Industrial1 (1 – 2) SINK (Tg N yr -1 ) Photolysis and oxidation in stratosphere 12 (9 – 16) ACCUMULATION (Tg N yr -1 )4 (3 – 5) Although a closed budget can be constructed, uncertainties in sources are large! (N 2 O atm mass = 5.13 10 18 kg x 3.1 10 -7 x28/29 = 1535 Tg ) IPCC [2001]

17. Vertical and Horizontal Distributions of nutrients and dissolved oxygen in the sea Summary Nutrients (N, P; Si) and trace elements (Cu, Zn, Fe [!]) used by plants and animals) are stripped from surface ocean and carried into the deep ocean by sedimentation. Re-mineralization creates excess concentrations of these elements, and depletion of oxygen, in deep water. The mean ratios of elements evolved during re-mineralization ("Redfield ratios") appear to be very uniform over the ocean, and possibly over geologic time, even though the ratios are not fixed in individual organisms. N 2 O is evolved during re-mineralization with a consistent ratio to O 2 uptake. (Yield = ~3% N 2 O : NO 3 - )(mole/mole; 6% as N)

18. Atlantic Ocean Deep Vertical Profile (Bermuda time series station)

19. Pacific: Average vertical distribution of temperature, salinity, and nutrients (nitrate+nitrite) at Ocean Station Aloha: 1988 to 1995. (World Ocean Circulation Experiment, Hawaii Ocean Time Series Project, University of Hawaii. Units: degrees Celsius, part-per-thousand of salt, and μmole/kg of nutrients). http://www.soest.hawaii.edu/hioos/oceanatlas/verstructure.htm

20. GEOSECS WOCE WOCE Pacific O 2 min

21. Figure 2 Vertical profiles of first-row transition metal ions and other elements in the N. Pacific. A Butler Science 1998;281:207-209

22. ( )

23. 3.4e-3 moleN 2 O/mole O 2 ; 0.03=N 2 O / NO 3 −

24. N 2 O and nutrients in the sea

25. GV launch in the rain, Anchorage, January, 2009 (HIPPO-1) HIPPO boat: NCAR Gulfstream V "HIAPER"

26. HIPPO_2 Nov 2009 HIPPO_3 Apr 2010 HIPPO_1 Jan 2009 preHIPPO Apr-Jun 2008 HIPPO itinerary

27. HIPPO-1 Atmospheric Structure (Pot'l T K): January, 2009, Mid-Pacific (Dateline) Cross section

28. CO 2 CH 4 CO HIPPO sections, January 2009 0 5 10 15 km -60 -40 -20 0 20 40 60 80 -60 -40 -20 0 20 40 60 80 -60 -40 -20 0 20 40 60 80 LATITUDE -60 -40 -20 0 20 40 60 80 -60 -40 -20 0 20 40 60 80 -60 -40 -20 0 20 40 60 80 N2ON2OSF 6 O3O3 0 5 10 15 km

29. Nov 2009 CO 2 CH 4 CO Jan 2009 CO 2 CH 4 CO 0 5 10 15 km -60 -40 -20 0 20 40 60 80 -60 -40 -20 0 20 40 60 80 -60 -40 -20 0 20 40 60 80 LATITUDE

30. January 2009 November 2009 -60 -40 -20 0 20 40 60 80 -60 -40 -20 0 20 40 60 80 LATITUDE -60 -40 -20 0 20 40 60 80 -60 -40 -20 0 20 40 60 80 N2ON2OO3O3 0 5 10 15 km

31. Other tracers confirm N 2 O variable layers arise from different air origins CO 2 CH 4 CO

32. Observed vs Model (ACTM) Prabir Patra, Kentaro Ishijima (JAMSTEC) Eric Kort (Harvard) HIPPO_1 Jan 2009 HIPPO Nitrous Oxide (N 2 O)

33. ACTM Eric Kort (Harvard); Prabir Patra, Kentaro Ishijima (JAMSTEC)

34. ACTM model (optimized for ground stations) Excellent fit to surface observations 64 surface stations, monthly means (courtesy K. Ishijima)

35. ObservedACTM Prior Jan., S-bound Jan., N-bound Nov., S-bound Nov., N-bound

36. SF 6 CH 4 N2ON2O N 2 O HIPPO-2

37. Global Totals (Tg N in N 2 O, over 63 days) 6.4 Posterior 4.8 3.2 Prior 3.15 Global Distribution of N 2 O emissions: HIPPO cross sections, ACTM Model Eric Kort (Harvard); Prabir Patra, Kentaro Ishijima (JAMSTEC)

38. Inversion results by region HIPPO-1 HIPPO_2

40. BOX MODEL OF THE NITROGEN CYCLE Inventories in Tg N Flows in Tg N yr -1

41. Inventories in Tg N Flows in Tg N yr -1 BOX MODEL OF THE N 2 O CYCLE 36 8 1.53 10 3 N 2 O

42. PRESENT-DAY GLOBAL BUDGET OF ATMOSPHERIC N 2 O SOURCES (Tg N yr -1 )18 (7 – 37) Natural10 (5 – 16) Ocean3 (1 - 5) Tropical soils4 (3 – 6) Temperate soils2 (1 – 4) Anthropogenic8 (2 – 21) Agricultural soils4 (1 – 15) Livestock2 (1 – 3) Industrial1 (1 – 2) SINK (Tg N yr -1 ) Photolysis and oxidation in stratosphere 12 (9 – 16) ACCUMULATION (Tg N yr -1 )4 (3 – 5) Although a closed budget can be constructed, uncertainties in sources are large! (N 2 O atm mass = 5.13 10 18 kg x 3.1 10 -7 x28/29 = 1535 Tg ) IPCC [2001]

43. Short Questions 1.Denitrification seems at first glance to be a terrible waste for the biosphere, jettisoning precious fixed nitrogen back to the atmospheric N 2 reservoir. In fact, denitrification is essential for maintaining life in the interior of continents. Can you see why? 2.We showed that industrial fertilizer application and fossil fuel combustion have significantly increased the global nitrogen pool in the land biota and soil reservoirs over the past 200 years. Did it also significantly increase the global nitrogen pool in the surface ocean biota? 3.What might the be effects of a warmer climate on turnover rates for nitrogen in the environment ? For denitrification ?

44. FAST OXYGEN CYCLE: ATMOSPHERE-BIOSPHERE Source of O 2 : photosynthesis nCO 2 + nH 2 O  (CH 2 O) n + nO 2 Sink: respiration/decay (CH 2 O) n + nO 2  nCO 2 + nH 2 O O2O2 CO 2 orgC litter Photosynthesis less respiration decay O 2 lifetime: 6000 years vs Photosynthesis ~200 PgO/yr 1.2x10 6 Pg 4x10 3 Pg 8x10 2 Pg

45. SLOW OXYGEN CYCLE: ATMOSPHERE-LITHOSPHERE O2O2 CO 2 Compression subduction Uplift CONTINENT OCEAN FeS 2 orgC weathering Fe 2 O 3 H 2 SO 4 runoff O2O2 CO 2 Photosynthesis decay orgC burial SEDIMENTS microbes FeS 2 orgC CO 2 orgC: 1x10 7 Pg C FeS 2 : 5x10 6 Pg S O 2 : 1.2x10 6 Pg O O 2 lifetime: 3 million years

46. …however, abundance of organic carbon in biosphere/soil/ocean reservoirs is too small to control atmospheric O 2 levels

47. The heavier temperature lines 160,000 BP to present reflect more data points, not necessarily greater variability. Source: Climate and Atmospheric History of the past 420,000 years from the Vostok Ice Core, Antarctica, by Petit J.R., Jouzel J., Raynaud D., Barkov N.I., Barnola J.M., Basile I., Bender M., Chappellaz J., Davis J. Delaygue G., Delmotte M. Kotlyakov V.M., Legrand M., Lipenkov V.M., Lorius C., Pépin L., Ritz C., Saltzman E., Stievenard M., Nature, 3 June 1999. Antarctic Ice Core Data CO 2 varies over geologic time, within the range 190 – 280 ppm for the last 420,000 years. The variations correlate with climate: cold  low CO 2. Is CO 2 driving climate or vice versa?

48. GLOBAL PREINDUSTRIAL CARBON CYCLE Inventories in Pg C Flows in Pg C a -1 6 8 PgC/yr

49. 1950 1960 1970 1980 1990 Year History of consumption of fossil fuels. Emissions have increased by more than 2X since 1970. There rise in the last 5 years has been really dramatic. But there has not been a corresponding rise in the annual increment of CO 2. In 1970 ~75% of the emitted CO 2 stayed in the atmosphere, but only ~40% in 2000. 3800 6500 Global Fuel Use 7800 in 2005! 8200 in 2007!

50. Antarctic ice cores compared with modern data for CO 2

51. Arrows indicate El Nino events Atmospheric increase ~57% of fossil fuel emissions Interannual variability correlated with El Niño CO 2

52. The rate of CO 2 accumulation in the atmosphere has risen on a decadal time scale, from 0.7 ppm/yr in the 1960's to 1.8 ppm/yr in the 2000's. The 1980's and 1990's were(slightly) anomalous.

53. 0.57

54. SHORT QUESTIONS Comparison of the rates of CO 2 atmospheric accumulation vs. global fossil fuel emission indicates that only 57% of the CO 2 emitted by fossil fuel combustion remains in the atmosphere. 1.Does this mean that inputs of fossil fuel CO 2 have a residence time in the atmosphere of only 2 years? 2. Does this mean that CO 2 would start declining if fossil fuel emissions were to stop tomorrow? …or if they were to level off immediately and become constant ?

55. Composition of Sea Water "alkalinity" defines Σ' Z i [i] : response of H + and OH - to addition of CO 2 Charge balance in the ocean: [HCO 3 - ] + 2[CO 3 2- ] = [Na + ] + [K + ] + 2[Mg 2+ ] + 2[Ca 2+ ] - [Cl - ] – 2[SO 4 2- ] – [Br - ] The alkalinity [Alk] ≈ [HCO 3 - ] + 2[CO 3 2- ] = 2.3x10 -3 M

56. UPTAKE OF CO 2 BY THE OCEANS CO 2 (g) CO 2. H 2 O HCO 3 - + H + HCO 3 - CO 3 2- + H + K H = 3x10 -2 M atm -1 K 1 = 9x10 -7 M K 2 = 7x10 -10 M pK 1 Ocean pH = 8.2 pK 2 CO 2. H 2 O HCO 3 - CO 3 2- OCEAN ATMOSPHERE

57. LIMIT ON OCEAN UPTAKE OF CO 2 : CONSERVATION OF ALKALINITY Equilibrium calculation for [Alk] = 2.3x10 -3 M pCO 2, ppm 100 200 300 400 500 8.6 8.4 8.2 2 3 4 1.4 1.6 1.8 1.9 2.0 2.1 Ocean pH [CO 3 2- ], 10 -4 M [HCO 3 - ], 10 -3 M [CO 2. H 2 O]+[HCO 3 - ] +[CO 3 2- ], 10 -3 M Charge balance in the ocean: [HCO 3 - ] + 2[CO 3 2- ] = [Na + ] + [K + ] + 2[Mg 2+ ] + 2[Ca 2+ ] - [Cl - ] – 2[SO 4 2- ] – [Br - ] The alkalinity [Alk] ≈ [HCO 3 - ] + 2[CO 3 2- ] = 2.3x10 -3 M is the excess base relative to the CO 2 -H 2 O system It is conserved upon addition of CO 2  uptake of CO 2 is limited by the existing supply of CO 3 2- : Increasing Alk requires dissolution of sediments: …which takes place over a time scale of thousands of years CO 2 (g) + CO 3 2 + H 2 O 2HCO 3 - Ca 2+ + CO 3 2- CaCO 3

58. N CO 2 atm =P CO 2 N atm N CO 2aq = P CO 2 K H V oc (1 + K 1 /[H + ] + K 1 K 2 / [H + ] 2 ) | | | [CO 2 aq ] [HCO 3 − ] [CO 3 = ] 1 : 140 : 16 CO 2  H 2 O  HCO 3 - + H + K 1 = [ HCO 3 - ][ H + ] / [ CO 2  H 2 O ] HCO 3 -  H + + CO 3 = K 2 = [ CO 3 = ][ H + ] / [HCO 3 - ] [ HCO 3 - ] = ( K 1 /[ H + ] ) [ CO 2  H 2 O ] ; [CO 3 = ] = ( K 2 K 1 /[ H + ] 2 ) [ CO 2  H 2 O ]

59. EQUILIBRIUM PARTITIONING OF CO 2 BETWEEN ATMOSPHERE AND GLOBAL OCEAN Equilibrium for present-day ocean:  only 3% of total inorganic carbon is currently in the atmosphere But CO 2 (g)  [H + ]  F  … positive feedback to increasing CO 2 Pose problem differently: how does a CO 2 addition dN partition between the atmosphere and ocean at equilibrium (whole ocean)?  28% of added CO 2 remains in atmosphere!

60.  (buffer factor) Sundquist et al. 1979

61. FURTHER LIMITATION OF CO 2 UPTAKE: SLOW OCEAN TURNOVER (~ 200 years) Inventories in 10 15 m 3 water Flows in 10 15 m 3 yr -1 Uptake by oceanic mixed layer only (V OC = 3.6x10 16 m 3 ) would give f = 0.94 (94% of added CO 2 remains in atmosphere)

62. comp to ~300  moles/kg CO 3 = Observed penetration of fossil fuel CO 2 into the oceans

63. CYCLING OF CARBON WITH TERRESTRIAL BIOSPHERE Inventories in PgC Flows in PgC a -1

64. EVIDENCE FOR LAND UPTAKE OF CO 2 FROM TRENDS IN O 2, 1990-2000

65. NET UPTAKE OF CO 2 BY TERRESTRIAL BIOSPHERE (1.4 Pg C yr -1 in the 1990s; IPCC [2001]) is a small residual of large atm-bio exchange Gross primary production (GPP): GPP = CO 2 uptake by photosynthesis = 120 PgC yr -1 Net primary production (NPP): NPP = GPP – “autotrophic” respiration by green plants = 60 PgC yr -1 Net ecosystem production (NEP): NEP = NPP – “heterotrophic” respiration by decomposers = 10 PgC yr -1 Net biome production (NBP) NBP = NEP – fires/erosion/harvesting = 1.4 PgC yr -1

66. GLOBAL CO 2 BUDGET IN 1980s AND 1990s (Pg C a -1 ) IPCC [2001]

67. HUMAN INFLUENCE ON THE CARBON CYCLE Natural fluxes in black; anthropogenic contribution (1990s) in red

68. 1950 1960 1970 1980 1990 Year History of consumption of fossil fuels. Emissions have increased by more than 2X since 1970. There rise in the last 5 years has been really dramatic. But there has not been a corresponding rise in the annual increment of CO 2. In 1970 ~75% of the emitted CO 2 stayed in the atmosphere, but only ~40% in 2000. 3800 6500 Global Fuel Use 7800 in 2005! 8200 in 2007!

69. 2007

71. China is projected to have exceed US emissions in 2009. slide from the previous offering of EPS 133….

72. China did exceed US emissions, in 2007... USA China India Emissions (Pg C/yr) 0.5 1 1.5 2

73. Per Capita Fossil Fuel Use since 1950, selected countries USA China India UK

74. PROJECTIONS OF FUTURE CO 2 CONCENTRATIONS [IPCC, 2001]

75. PROJECTED FUTURE TRENDS IN CO 2 UPTAKE BY OCEANS AND TERRESTRIAL BIOSPHERE IPCC [2001] Feedbacks…

77. SHORT QUESTIONS 1.The conventional scientific view is that fossil fuel CO 2 injected to the atmosphere will affect the atmosphere for ~100 years before transfer to the deep ocean and that it represents therefore a long-term environmental problem. This view has been challenged by a skeptic from U. Virginia on the basis of bomb 14 CO 2 data. Above-ground nuclear tests in the 1950s injected large amounts of 14 CO 2 in the atmosphere, but atmospheric observations following the nuclear test ban in 1962 showed an exponential decay of 14 CO 2 back to background values on a time scale of 5 years. This shows, according to our skeptic, that if we were to shut down fossil fuel emissions then CO 2 would return to natural background values within 5 years. What do you think of this reasoning?

78. SHORT QUESTIONS 1.You wish to fly from Boston to California on a commercial flight that consumes 100,000 lbs of jet fuel for the trip. The company offers - as an extra charge on your ticket - to make your personal trip carbon- neutral by planting trees. Does this seem practical, in terms of the number of trees that would need to be planted? And is this a reasonable long-term proposition for mitigating your personal “carbon footprint”? 2.The U.S. presently emits 1.5 Pg C a -1 of CO 2. It is proposed to sequester this carbon underground as calcium carbonate (density 2 g cm -3 ). Assuming that the sequestered carbon is spread out over the whole U.S. area (7x10 6 km 2 ), by how much would it raise the surface of the U.S. every year? Suppose instead that it was sequestered in a cavern, a large hole with cross section 1 km 2. How deep would we have to dig the hole each year ?