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

Robert DELMAS

yesterday
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
sulfate
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]

nsssulfate origins for central antarctica
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
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?
slide7

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

slide8

Two kinds of sulfate in the Antarctic

10Be is attached to background aerosol

methanesulfonic acid hch 3 so 3
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
ECM: ElectroConductometric Measurement
  • Sulfuric acid peaks
  • Sulfuric acid peaks

Tambora period (1800-1820)

volcanism recorded at vostok
Volcanism recorded at Vostok

Ash layers

1259 AD eruption: sulfate and fluoride

sulfate and msa in antarctic coastal regions
Sulfate and MSA in Antarctic coastal regions

Antarctic Peninsula

  • In James Ross Island snow
seasonal variations in south pole snow
Seasonal variations in South Pole snow
  • MSA is labile in the upper firn layers
msa at south pole
MSA at South Pole

El Niño events ?

slide23
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
MSA in Antarctic ice cores

Are this data reliable?

isotope measurements related to the sulfur cycle
Isotope measurements related to the sulfur cycle
  • S-isotopes in SO4
  • O isotopes in SO4
slide27

Years AD

Dronning Maud Land

(german core)

Depth

dronning maud land

Continental source only volcanic

Dronning Maud Land

1990

1800

A continental source +

a volcanic source

nitrogen cycle
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
NITRATE IN ANTARCTIC CORES

EPICA

Biomass burning?

Dome F

ammonium

Greenland

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