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Chemistry of polar ice (part II)

Chemistry of polar ice (part II). S & N cycles from ice core studies Robert DELMAS . YESTERDAY. Chemical information is located in the ice matrix itself Basic features of glaciochemistry soluble vs insoluble ion balance Primary aerosol species

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Chemistry of polar ice (part II)

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  1. Chemistry of polar ice (part II) • S & N cycles from ice core studies Robert DELMAS

  2. YESTERDAY • Chemical information is located in the ice matrix itself • Basic features of glaciochemistry • soluble vs insoluble • ion balance • Primary aerosol species • Sea salt. May be modified in ice records. Strong interaction with secondary sulfate aerosol • Continental dust: very high in glacial conditions

  3. Sulfur cycle at high southern latitudes

  4. MAJOR COMPONENT OF THE GLOBAL AEROSOL LOAD CLIMATIC ROLE: Direct & indirect DEPOSITED AS AN AEROSOL AFFECTED BY « DRY DEPOSITION » EFFECT SULFATE Excess-sulfate or nssSO4 : [nssSO4 ] = [SO4] - 0.25 [Na]

  5. MARINE BIOGENIC ACTIVITY (gaseous DMS emission) together with MSA VOLCANIC ACTIVITY Continuous or sporadic Stratospheric pathway Tropospheric pathway (South America) Antarctic volcanoes nssSULFATEORIGINS FOR CENTRAL ANTARCTICA In glacial conditions: an additional source (e.g. gypsum: CaSO4)? A tool to differentiate origins: S & O isotope measurements

  6. About Antarctic nsssulfate… • H2SO4is formed from SO2 in gaseous or in liquid phase (see next) • H2SO4 may be scavenged by sea salt aerosol • Are sea salt and sulfate aerosol transported separately or internally mixed?

  7. Oxidation ways of SO2 (investigated by O isotope measurements) 1 Heterogeneous phase: SO2 + O3/H2O2 growth of existing aerosol particle, in particular sea salt 2 Gas-phase: SO2 + OH  new aerosol particle Alexander, B., J. Savarino, N.I. Barkov, R.J. Delmas, and M.H. Thiemens, 2002 Alexander, B., M.H. Thiemens, J. Farquhar, A.J. Kaufman, J. Savarino, and R.J. Delmas,2003

  8. Two kinds of sulfate in the Antarctic 10Be is attached to background aerosol

  9. Methanesulfonic acid (HCH3SO3) • Directly derived from DMS • Aerosol or gas? • Specific tracer of marine biogenic activity (from DMS) • Tracer of El Niño events? • Ratio MSA/nssSO4 commonly used • Strong post-deposition effect • Concentrations generally high in glacial conditions

  10. Volcanic sulfate

  11. ECM: ElectroConductometric Measurement • Sulfuric acid peaks • Sulfuric acid peaks Tambora period (1800-1820)

  12. Volcanic eruptions recorded at various Antarctic sites 1259 AD South Pole 1964-65

  13. Volcanism recorded at Vostok Ash layers 1259 AD eruption: sulfate and fluoride

  14. Sulfate in Antarctica

  15. Sulfate in Greenland

  16. The turn of the century in Greenland

  17. Volcanic eruptions in the Northern Hemisphere

  18. Sulfate and MSA in Antarctic coastal regions Antarctic Peninsula • In James Ross Island snow

  19. Seasonal variations in South Pole snow • MSA is labile in the upper firn layers

  20. MSA at South Pole El Niño events ?

  21. MSA: importantloss in the upper firn layers • VOSTOK

  22. MSA is released to the interstitial air but remains stored in the firn layers • It is then entrapped again by ice below close-off

  23. MSA in Antarctic ice cores Are this data reliable?

  24. In Greenland

  25. Isotope measurements related to the sulfur cycle • S-isotopes in SO4 • O isotopes in SO4

  26. Years AD Dronning Maud Land (german core) Depth

  27. Fluctuation of S-isotopic composition over 2 centuries Annual mean

  28. Continental source only volcanic Dronning Maud Land 1990 1800 A continental source + a volcanic source

  29. NITROGEN CYCLE • UP TO NOW, NOT UNDERSTOOD • There are two major species in polar ice related to this cycle: NO3 and NH4 • MAY EXIST in the ATMOSPHERE as a GAS (HNO3) or an AEROSOL • VERY COMPLEX TRANSFER FUNCTION for HNO3 • IMPORTANT ENVIRONMENTAL ISSUES like O3 hole, biomass burning or photochemistry (in-situ production)

  30. Strong decrease in upper firn layers

  31. During ice ages, nitrate is attached to dust

  32. NITRATE IN ANTARCTIC CORES EPICA Biomass burning? Dome F

  33. Anthropogenic pollution in Greenland

  34. Lead pollution in Greenland

  35. N-isotope measurements in NO3-

  36. Greenland Ammonium • Samples easily contaminated • Extremely weak in central Antarctic snow (<1 ppb) • In coastal regions higher concentrations linked to penguins

  37. Carboxylic acids at Summit

  38. Conclusions (1) • Glaciochemical work is much more sophisticated and difficult than water stable isotope measurements and gas measurements • Prioritiy recently given to aerosol research could give a boost to glaciochemistry • It can be envisaged to investigate in the future viruses, bacteria, microorganisms … which are attached to aerosol particles, in particular in non-polar regions • More ice cores in tropical and mid-latitude mountains to understand continental aerosol and source regions of polar dust

  39. Conclusions (2) • Glaciochemistry is still a very open domain • Processes occurring in firn have to be confirmed in particular for NO3, Cl and MSA • The interaction between sea salt and sulfate aerosol has to be taken into account • The role of glacial dust on atmospheric chemistry has to be investigated • Na as an indicator of sea ice extent in the past • CaNO3 as a tracer of biomass burning in Antarctica

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