Download Ice-core Chemistry

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
Sulfur cycle at high southern latitudes
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]
nssSULFATE
ORIGINS FOR CENTRAL ANTARCTICA
• MARINE BIOGENIC
ACTIVITY (gaseous
DMS emission)
• together with MSA
In glacial conditions:
an additional source
(e.g. gypsum: CaSO4)?
•
•
•
•
VOLCANIC ACTIVITY
Continuous or sporadic
Stratospheric pathway
Tropospheric pathway
(South America)
• Antarctic volcanoes
A tool to differentiate origins:
S & O isotope measurements
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?
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
Volcanic sulfate
ECM: ElectroConductometric
Measurement
• Sulfuric acid peaks
•Sulfuric acid peaks
Tambora period (1800-1820)
Volcanic eruptions recorded at
various Antarctic sites
1259 AD
1964-65
South Pole
Volcanism recorded at Vostok
Ash layers
1259 AD eruption:
sulfate and fluoride
Sulfate in Antarctica
Sulfate in Greenland
The turn of the century in
Greenland
Volcanic eruptions in the
Northern Hemisphere
Antarctic Peninsula
Sulfate and MSA in
Antarctic coastal regions
• 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: important loss in the upper
firn layers
• VOSTOK
• 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?
In Greenland
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
A
100%
Continental source only
volcanic
% Sources
80%
fter/volc
60%
fbm
fsm
40%
20%
0%
FB1
FB2
FB3
FB4
FB5
FB6
1990
FB8
1800
B
100%
Dronning
Maud Land
% Sources
80%
fcont
60%
fbm
A continental source +
a volcanic source
fsm
40%
20%
0%
FB1
FB2
FB3
FB4
FB5
FB6
FB8
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)
Strong decrease in upper firn layers
During ice ages, nitrate is
attached to dust
NITRATE IN ANTARCTIC CORES
EPICA
1.2
1
Biomass burning?
EPICA
0.8
2
NO3 µEq/l
Accumulation cm/yr
1.5
2.5
0.4
3
3.5
0
4
0
400
200
METERS
600
Dome F
Anthropogenic pollution in
Greenland
Lead pollution in Greenland
N-isotope measurements in NO3
-
Greenland
Ammonium
• Samples easily contaminated
• Extremely weak in central
Antarctic snow (<1 ppb)
• In coastal regions higher
concentrations linked to
penguins
Carboxylic acids at Summit
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 nonpolar 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