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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) • 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 • Sea salt. May be modified in ice records. Strong interaction with secondary sulfate aerosol • Continental dust: very high in glacial conditions
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]
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
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?
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
Two kinds of sulfate in the Antarctic 10Be is attached to background aerosol
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
ECM: ElectroConductometric Measurement • Sulfuric acid peaks • Sulfuric acid peaks Tambora period (1800-1820)
Volcanic eruptions recorded at various Antarctic sites 1259 AD South Pole 1964-65
Volcanism recorded at Vostok Ash layers 1259 AD eruption: sulfate and fluoride
Sulfate and MSA in Antarctic coastal regions Antarctic Peninsula • In James Ross Island snow
Seasonal variations in South Pole snow • MSA is labile in the upper firn layers
MSA at South Pole El Niño events ?
MSA is released to the interstitial air but remains stored in the firn layers • It is then entrapped again by ice below close-off
MSA in Antarctic ice cores Are this data reliable?
Isotope measurements related to the sulfur cycle • S-isotopes in SO4 • O isotopes in SO4
Years AD Dronning Maud Land (german core) Depth
Fluctuation of S-isotopic composition over 2 centuries Annual mean
Continental source only volcanic Dronning Maud Land 1990 1800 A continental source + a volcanic source
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)
NITRATE IN ANTARCTIC CORES EPICA Biomass burning? Dome F
Greenland Ammonium • Samples easily contaminated • Extremely weak in central Antarctic snow (<1 ppb) • In coastal regions higher concentrations linked to penguins
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
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