Chemistry of polar ice (part II)

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Chemistry of polar ice (part II)

• S N cycles from ice core studies
• Robert DELMAS

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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

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Sulfur cycle at high southern latitudes
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SULFATE

• MAJOR COMPONENT OF THE GLOBAL AEROSOL LOAD
• CLIMATIC ROLE Direct indirect

• DEPOSITED AS AN AEROSOL
• AFFECTED BY  DRY DEPOSITION  EFFECT

Excess-sulfate or nssSO4 nssSO4 SO4 -
0.25 Na
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nssSULFATEORIGINS FOR CENTRAL ANTARCTICA

• VOLCANIC ACTIVITY
• Continuous or sporadic
• Stratospheric pathway
• Tropospheric pathway (South America)
• Antarctic volcanoes

• MARINE BIOGENIC ACTIVITY (gaseous DMS emission)
• together with MSA

In glacial conditions an additional source
(e.g. gypsum CaSO4)?
A tool to differentiate origins S O isotope
measurements
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About Antarctic nsssulfate

• H2SO4 is 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?

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

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Volcanic sulfate
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ECM ElectroConductometric Measurement

• Sulfuric acid peaks

• Sulfuric acid peaks

Tambora period (1800-1820)
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Volcanic eruptions recorded at various Antarctic
sites
1259 AD
South Pole
1964-65
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Volcanism recorded at Vostok
Ash layers
1259 AD eruption sulfate and fluoride
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Sulfate in Antarctica
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Sulfate in Greenland
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The turn of the century in Greenland
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(No Transcript)
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Volcanic eruptions in the Northern Hemisphere
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Sulfate and MSA in Antarctic coastal regions
Antarctic Peninsula

• In James Ross Island snow

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Seasonal variations in South Pole snow

• MSA is labile in the upper firn layers

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MSA at South Pole
El Niño events ?
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MSA important loss in the upper firn layers

• VOSTOK

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

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MSA in Antarctic ice cores

• Are this data reliable?

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In Greenland
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Isotope measurements related to the sulfur cycle

• S-isotopes in SO4
• O isotopes in SO4

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Years AD
Dronning Maud Land (german core)
Depth
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Fluctuation of S-isotopic composition over 2
centuries
Annual mean
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Dronning Maud Land
Continental source only volcanic
1800
1990
A continental source a volcanic source
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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)

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Strong decrease in upper firn layers
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During ice ages, nitrate is attached to dust
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NITRATE IN ANTARCTIC CORES
EPICA
Biomass burning?
Dome F
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Anthropogenic pollution in Greenland
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Lead pollution in Greenland
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N-isotope measurements in NO3-
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Ammonium
Greenland

• Samples easily contaminated
• Extremely weak in central Antarctic snow (lt1 ppb)
• In coastal regions higher concentrations linked
  to penguins

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Carboxylic acids at Summit
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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

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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