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CHAPTER 6: GEOCHEMICAL CYCLES

CHAPTER 6: GEOCHEMICAL CYCLES. THE EARTH: ASSEMBLAGE OF ATOMS OF THE 92 NATURAL ELEMENTS. Most abundant elements: oxygen (in solid earth!), iron (core), silicon (mantle), hydrogen (oceans), nitrogen, carbon, sulfur…

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CHAPTER 6: GEOCHEMICAL CYCLES

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  1. CHAPTER 6: GEOCHEMICAL CYCLES THE EARTH: ASSEMBLAGE OF ATOMS OF THE 92 NATURAL ELEMENTS • 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 cyclingof 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

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

  3. HISTORY OF EARTH’S ATMOSPHERE N2 CO2 H2O O2 O2 reaches current levels; life invades continents oceans form CO2 dissolves Life forms in oceans Onset of photosynthesis Outgassing 4.5 Gy B.P 4 Gy B.P. 0.4 Gy B.P. 3.5 Gy B.P. present

  4. COMPARING THE ATMOSPHERES OF EARTH, VENUS, AND MARS

  5. EVOLUTION OF O2 AND O3 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 NITROGENN has 5 electrons in valence shell a9 oxidation states from –3 to +5 Increasing oxidation number (oxidation reactions) radical radical Decreasing oxidation number (reduction reactions)

  8. THE NITROGEN CYCLE: MAJOR PROCESSES combustion lightning ATMOSPHERE N2 NO oxidation HNO3 denitri- fication biofixation deposition orgN decay NH3/NH4+ NO3- BIOSPHERE assimilation nitrification weathering burial LITHOSPHERE

  9. Oceanic Nitrogen Processes

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

  11. NH4++3/2O2NO2−+ H2O + 2 H+ NO3−+ Org-C  N2 + … N2O N2O: LOW-YIELD PRODUCT OF BACTERIAL NITRIFICATION AND DENITRIFICATION • Important as • source of NOx radicals in stratosphere • greenhouse gas IPCC [2007]

  12. PRESENT-DAY GLOBAL BUDGET OF ATMOSPHERIC N2O IPCC [2001] Although a closed budget can be constructed, uncertainties in sources are large! (N2O atm mass = 5.13 1018 kg x 3.1 10-7 x28/29 = 1535 Tg )

  13. 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. • N2O is evolved during re-mineralization with a consistent ratio to O2 uptake. (Yield = ~3% N2O : NO3- )(mole/mole; 6% as N)

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

  15. http://www.soest.hawaii.edu/hioos/oceanatlas/verstructure.htmhttp://www.soest.hawaii.edu/hioos/oceanatlas/verstructure.htm 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).

  16. GEOSECS WOCE WOCE Pacific O2 min

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

  18. ( )

  19. 3.4e-3 moleN2O/mole O2 ; 0.03=N2O / NO3−

  20. N2O and nutrients in the sea

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

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

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

  24. HIPPO sections, January 2009 CO CO2 CH4 0 5 10 15 km 0 5 10 15 km 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 N2O SF6 O3 0 5 10 15 km 0 5 10 15 km 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

  25. CH4 CO CO2 Jan 2009 0 5 10 15 km CO CO2 CH4 Nov 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

  26. N2O O3 January 2009 0 5 10 15 km -60 -40 -20 0 20 40 60 80 -60 -40 -20 0 20 40 60 80 November 2009 0 5 10 15 km -60 -40 -20 0 20 40 60 80 -60 -40 -20 0 20 40 60 80 LATITUDE

  27. Other tracers confirm N2O variable layers arise from different air origins CO2 CH4 CO

  28. HIPPO Nitrous Oxide (N2O) Observed vs Model (ACTM) Prabir Patra, Kentaro Ishijima (JAMSTEC) Eric Kort (Harvard) HIPPO_1 Jan 2009

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

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

  31. Observed ACTM Prior Jan., S-bound Jan., N-bound Nov., S-bound Nov., N-bound

  32. SF6 CH4 N2O HIPPO-2 N2O

  33. Global Distribution of N2O emissions: HIPPO cross sections, ACTM Model Global Totals (Tg N in N2O, over 63 days) 6.4 Posterior 4.8 3.2 Prior 3.15 Eric Kort (Harvard); Prabir Patra, Kentaro Ishijima (JAMSTEC)

  34. Inversion results by region HIPPO-1 HIPPO_2

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

  36. 1.53 103 N2O 6 8 3 Inventories in Tg N Flows in Tg N yr-1 BOX MODEL OF THE N2O CYCLE

  37. PRESENT-DAY GLOBAL BUDGET OF ATMOSPHERIC N2O IPCC [2001] Although a closed budget can be constructed, uncertainties in sources are large! (N2O atm mass = 5.13 1018 kg x 3.1 10-7 x28/29 = 1535 Tg )

  38. Short Questions • Denitrification seems at first glance to be a terrible waste for the biosphere, jettisoning precious fixed nitrogen back to the atmospheric N2 reservoir. In fact, denitrification is essential for maintaining life in the interior of continents. Can you see why? • 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? • What might the be effects of a warmer climate on turnover rates for nitrogen in the environment ? For denitrification ?

  39. FAST OXYGEN CYCLE: ATMOSPHERE-BIOSPHERE • Source of O2: photosynthesis nCO2 + nH2O g (CH2O)n + nO2 • Sink: respiration/decay (CH2O)n + nO2 g nCO2 + nH2O 8x102 Pg O2 lifetime: 6000 years vs Photosynthesis ~200 PgO/yr CO2 1.2x106 Pg Photosynthesis less respiration O2 orgC orgC decay litter 4x103 Pg

  40. SLOW OXYGEN CYCLE: ATMOSPHERE-LITHOSPHERE O2 lifetime: 3 million years O2: 1.2x106 Pg O CO2 O2 Photosynthesis decay runoff Fe2O3 H2SO4 weathering CO2 O2 orgC FeS2 OCEAN CONTINENT orgC Uplift burial CO2 orgC: 1x107 Pg C FeS2: 5x106 Pg S microbes FeS2 orgC SEDIMENTS Compression subduction

  41. …however, abundance of organic carbon in biosphere/soil/ocean reservoirs is too small to control atmospheric O2 levels

  42. Antarctic Ice Core Data CO2 varies over geologic time, within the range 190 – 280 ppm for the last 420,000 years. The variations correlate with climate: cold  low CO2 . Is CO2 driving climate or vice versa? 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.

  43. 6 8 PgC/yr GLOBAL PREINDUSTRIAL CARBON CYCLE Inventories in Pg C Flows in Pg C a-1

  44. 7800 in 2005! 8200 in 2007! 6500 1990 Global Fuel Use 1980 1970 3800 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 CO2. In 1970 ~75% of the emitted CO2 stayed in the atmosphere, but only ~40% in 2000. 1960 1950 Year

  45. Antarctic ice cores compared with modern data for CO2

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