All you wanted to know about glaciochemistry…

1. All you wanted to know about glaciochemistry… Robert J. DELMAS Laboratory of Glaciology and Environmental Geophysics Grenoble, France

2. A glaciochemist! • I am not a chemist • I am not a glaciologist • I am not an atmospheric chemist • I am not a climatologist • I am not a geologist • What am I?

3. The task of a glaciochemist is to analyze ice cores and to interprete the data in terms of global atmospheric changes • I have been asked to change the order of my presentations and to speak first about glaciochemistry, but logically, it would be better to have first some knowledge about the global biochemical cycles before looking at ice core data • Polar regions are not isolated. They are part of the global climatic system

4. Advantages of glacier ice • Natural ice is an extremely clean material • Nearly all parameters are recorded together limited time lags • High temporal resolution

5. What environmental information is recorded in ice cores ? • Water stable isotopes  Paleotemperature • Entrapped air bubbles  Greenhouse gases + .. • Trace impurities located in the ice matrix  Soluble and insoluble aerosols + acid trace gases like HCl, HNO3, …

6. General remarks about polar snow and ice chemistry • In principle, snow chemistry is similar to rain chemistry but… • Central Greenland and Antarctic regions (where deep ice cores are drilled) are located at very high elevation, i.e. in the free troposphere • Concentrations are extremely low in comparison to our regions

7. Geographical position of Antarctica and Greenland Many continents close to Greenland Eurocore, GRIP, GISP2... The Antarctic is surrounded by oceans Vostok, EPICA,DF, Taylor Dome…

8. Principles Snowflakes scavenge atmospheric impurities at cloud level, gases being entrapped at the firn to ice transition

9. Deposition mechanisms • Wet deposition is in principle dominant, but… • Dry deposition is very important in very low accumulation areas like the central Antarctic Plateau • In fact, deposition mechanisms of atmospheric impurities in polar regions are poorly documented

10. Snow vs rain Wind pumping

11. Post-deposition phenomena and the so-called transfer function • Question: ice records  atmosphere • Novel research domain • A key for deep ice core interpretation • All compounds are not equally affected • Affected : nitrate, chloride, MSA, carboxylic acids (in general acid gaseous species) • Not affected : insol. material, sodium, sulfate (in general particulate matter)

12. Two kinds of post-deposition phenomena • 1. Surface photochemical reaction: in the first centimeters of snow, solar radiation is capable of triggering chemical reactions. This is a new research domain. HNO3, carboxylic acids, etc… could be affected. Note that gases formed and adsorbed could be released to the troposphere. • 2. Processes linked to firnification

14. Processes linked to firnification • The transformation of snow into firn is a slow process which occurs by internal distillations and grain sintering • During this process, occluded gases are released to the interstitial phase • Between 0 and 10m, firn is very porous and gases communicate easily with the free atmosphere • Released gases can escape … • From 10m to pore close-off, there is no more exchange with the atmosphere

15. Strong post-depositional effect for NO3, Cl and MSA

16. Insoluble vs soluble • Insoluble material is essentially made of continental dust, in the form of microparticules. This fraction is very minoritory (<10%) • Most impurities are soluble : sea salt constituents, secondary aerosol…

17. Ion balance (soluble fraction) [cations] = [anions] (in µEquiv./l) [H+] + [NH4+] + [Ca2+] + [Na+] + [Mg2+] + [K+] = [SO42-] + [NO3-] + [Cl-] • Generally reduced to: [H+] + [Na+] = [SO42-] + [NO3-] + [Cl-] or even to: [H+] = [SO42-] + [NO3-] This relationship is essentially valid for Holocene snow in central regions

18. Acidity or alkalinity? • A major issue linked to the question of carbonates, which may affect the determination of CO2 in ice: carbonate may either consume or produce CO2 , depending on meltwater pH EliminationCO3-- + CO2 + H2O  HCO3- or ProductionCO3-- + 2H+  CO2 + H2O • Acidity is an excellent indicator for studying past volcanic activity • Alkalinity is typical of glacial periods

19. Northern and Southern hemispheres are different Ice age Interglacial

20. The true story of the first CO2 measurement in polar ice • Changing the extraction method of CO2 improved considerably measured concentrations No more ice melting! Crushing the ice

21. Some simple chemical calculations • Assuming a 0.03% CO2 content in the gas extracted, 1 Kg of ice contains about 30µl of CO2 • 1 µEquiv. of bicarbonate (HCO3- releases through decomposition 22.4 µl of CO2 CO2 measurements are very sensitive to the possible presence of trace amounts of carbonate in the ice lattice

22. FIRST DATA ON PALEO CO2 CONCENTRATIONSFROM POLAR ICE CORES Nature 284 (5752) 155-157 1980

23. Alkaline contamination of ice samples Low CO2 concentrations for the LGM

24. Analytical precautions Clean air bench Laith

25. Analytical precautions IC analysis

26. Atmospheric aerosols (in short) • Primary : sea salt and continental dust • Secondary (or gas derived) : sulphur cycle +…. • Natural or anthropogenic Today: primary aerosol Tomorrow: secondary aerosol

27. Sea salt species • Major component of the Antarctic aerosol • Na and Cl are the two major chemical species related to SS • SS is essentially produced by the sub-antarctic ocean and transported inland by winds • SS may also be produced from fresh sea ice areas (frost flowers) • There is a paradox: SS concentration over Antarctica is higher in winter (large sea ice extent) than in summer (minimum extent) • Strong chemical modification (Cl/Na > or < 1.8, reference value) • Marked interaction with sulfur cycle • Strong increase during glacial periods

28. Sea ice extent in both polar regionsCurrent trends NH SH And in the past?

29. Sea salt in the Antarctic • What is the origin of sea salt for ice ages? VK

30. Sea salt in EPICA Sea salt, an indicator of sea ice extent? HCl loss from firn in Holocene Climatic conditions

31. In the Northern Hemisphere Sea salt, a climatic parameter cold warm

32. Sea-salt aerosol in the Antarctic : several recent papers • Sea salt and sulfate interaction, Presented at EGS Nice 2004 • Dechlorination of sea salt in Antarctica Snow chemistry measurements on James Ross Island (Antarctic Peninsula) showing sea-salt aerosol modifications, Aristarain, A.J., and R.J. Delmas, 2002, Atmosph. Envir., 36 (4), 765-772. Bomb-test 36Cl measurements in Vostok snow (Antarctica) and the use of 36Cl as a dating tool for deep ice cores, R.J. Delmas, J. Beer, H.-A. Synal, R. Muscheler, J.-R. Petit and M. Pourchet, TellusB, in press • Sea salt and climate at JRI Ice-core study of the link between sea-salt aerosol, sea-ice cover and climate in the Antarctic Peninsula area, Aristarain, A.J., R.J. Delmas and M.Stiévenard, Clim. Change, in press

33. The SS-S-cycle interaction: Preliminary Statements • Sea salt species (Na and Cl) and SO4 are frequently determined in Antarctic snow and ice. • Aerosol measurements are scarce • Both species originate mainly from the subAntarctic ocean • Recent studies at other latitudes show that sea salt and sulfur cycle are closely linked in the MBL • Glaciochemical data need to be revisited • Important for paleochemical studies

34. Sulfate and sea salt cycles are strongly linked in the southern atmosphere 50% 100% 0% Part of SO4 attached on sea salt aerosols (modeling by Gong & Barrie, 2003)

35. ABOUT SEA SALT DECHLORINATION…

36. Just an example along a traverse…

37. Studied Antarctic sites

38. CONCLUSIONS • No dechlorination of Antarctic sea salt aerosol during transport • Dechlorination is a post deposition phenomenon. Only in central regions. • Interaction between sea salt (SS) and S-cycle (S is driven by SS, rather than the contrary) • Ice core interpretation has to take these observations into account • Formation of Na2SO4 and possibly NaHSO4

39. Insoluble dust • The ice age was a dusty world…

40. Insoluble dust

41. About the origin of antarctic dust

42. Origin of Antarctic dust over climatic periods

43. About the origin of dust Lunt and Valdes (modelling)

44. A link between CO2 and dust?

45. A link between CO2 and dust? • Iron is the active agent in continental dust for marine biological activity