Quaternary Environments Ice Cores

1. Quaternary EnvironmentsIce Cores

2. Records From Ice Cores • Precipitation • Air Temperature • Atmospheric Composition • Gaseous composition • Soluble and insoluble particles • Volcanic Eruptions • Solar Activity

3. Records From Ice Cores

4. Extent of Ice Core Sampling • 15 Ice cores extend into the last glaciation • Greenland • Antarctica • China • Few Mid-Latitude high elevation cores

8. Paleoclimatic Information From Ice Cores • Stable isotopes of water and the atmospheric O2 • Other gases from air bubbles in the ice • Dissolved and particulate matter in firn and ice • The physical characteristics of the firn and ice

9. Definitions • Snow Crystals – Form of snow as it falls • Firn – Snow that has survived the summer ablation season • Ice – The produce of metamorphosis as firn is buried by subsequent snow accumulation • Depth varies depending upon surface temperature and accumulation rate • i.e 68m at Camp Century, Greenland and 100m Vostok, Antarctica

10. Stable Isotope Analysis • Basic Premise – Molecules with heavier isotopes will stay at the source during evaporation • HD16O or H218O • Various things control isotopic concentration • Temperature • Evaporation • Distance from source • Compared to the Standard Mean Ocean Water (SMOW) • Equivalent to water collected from 200-500m depth in the Atlantic, Pacific, and Indian Oceans

12. Complications • 18O content of precipitation depends on: • 18O content of water vapor from the source • Amount of moisture in the air at source • Evaporation en route to deposition • Source of land evaporation • Temperature at which evaporation and condensation takes place • Extent to which clouds become supersaturated

13. Empirical Evidence • Studies show that despite the complications geographical and temporal variations in isotopes do occur, reflecting temperature effects due to changing • latitudes, • altitude, • distance from moisture source, • season, • long-term climatic fluctuations.

14. Dating of Ice Cores • Determine the age-depth relationship • Very accurate time scales for at least 10,000 to 12,000 years • Radioisotopic Methods • 10Be • 14C* • 39Ar • 81Kr • 210Pb*

15. Dating of Ice Cores • AMS 14C Dating • CO2 from air bubbles • 10kg of sample • Equivalent to 1.5m length of ice core • Problems • CO2 exchange with the atmosphere is an open system until the air bubbles are cut off from the surface

25. Annual Layers • Can count visual annual fluctuation in the ice caused by melt and thaw layers • Various Markers • Visual stratigraphy • Electrical conductivity measurements (ECM) • Laser light scattering (from dust) • Oxygen isotopes • Chemical variations • GISP2 and GRIP match back to 15,000 years with 200 year precision

26. Resolution • <1% error back to 2,000 BP, • 2% by 40,000 BP, • 10% by 57,000 BP, • up to 20% by 110,000 BP

27. Seasonal Variations • Microparticulate matter and ice chemistry • Major ions • Trace elements • High Spring values and low Autumn values produce seasonal variations • Sodium, Calcium, Nitrate, Chloride • Electrical Conductivity Measurements (ECM) • Continuous record of acidity • Volcanic eruptions – high • Alkaline dust – low

28. Changing resolution back in time from the Camp Century ice core from Greenland

29. Site A, Central Greenland

30. Electrical Conductivity Measurements

31. Acidity of annual layers from A.D. 553 to A.D. 1972

32. Accumulation at Summit, Greenland

33. Theoretical Models • Calculated ice-age at depth by means of a theoretical ice-flow model • Depend upon • Past changes in ice thickness • Temperature • Accumulation rates • Flow patterns • And ice rheology • Problems minimized at ice divides (Grip core at Summit, Greenland) or deep cores that are still well above ground level (Vostok, Antarctica)

34. Schematic Diagram of Isotopic Depletion

35. Stratigraphic Correlations • Correlation of multiple proxy records from ice cores against records with better chronological control (i.e. δ18O from benthic foraminifera) • Danger of correlating events and onset of circular reasoning

36. Vostok Core, Antarctica • Longest well-resolved ice-core record on Earth and a yardstick for comparison with other paleoclimatic records • Deuterium records compared with SPECMAP δ18O records suggest that the Vostok core extend back 426,000 years spanning the last four glacial events • SPECMAP Data • (1) quantitative data on planktonic species and assemblages which reflect conditions in the surface waters of the Atlantic ocean; • (2) measurements of 180, 13C difference (planktonic and benthic), and Cd/Ca.

38. Climate Changes • The rate and cause of climatic changes is of great interest • Resolution is an important factor in determining rates of change

40. Shear in Ice Records • Differential forces at depth in the glaciers cause the ice to flow distorting the record • Boudinage – Pinching of a layer that is less likely to flow compared to the surrounding layers • Ice strength is dependent upon dust content

41. Atmospheric Composition • Ice cores are archives of atmospheric composition • Contain records of greenhouse gases • Carbon Dioxide, Methane, Nitrous Oxide • Air mass Characteristics • Volcanic Eruptions • Changes in Dust content

44. Greenhouse Gases • Methane is 220% greater today than 250 years ago • Carbon Dioxide is 130% pre-industrial levels • Nitrous Oxide is 110% greater than 250 years ago • All levels are far higher than anything seen in the last 220,000 years

45. Volcanic Eruptions from Ice Cores