Quaternary Environments Ice Cores Records From Ice Cores
- Slides: 49
Quaternary Environments Ice Cores
Records From Ice Cores T Precipitation T Air Temperature T Atmospheric Composition T Gaseous composition T Soluble and insoluble particles T Volcanic Eruptions T Solar Activity
Records From Ice Cores
Extent of Ice Core Sampling T 15 Ice cores extend into the last glaciation T Greenland T Antarctica T China T Few Mid-Latitude high elevation cores
Paleoclimatic Information From Ice Cores Stable isotopes of water and the atmospheric O 2 l Other gases from air bubbles in the ice l Dissolved and particulate matter in firn and ice l The physical characteristics of the firn and ice l
Definitions T T T 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 T i. e 68 m at Camp Century, Greenland 100 m Vostok, Antarctica T
Stable Isotope Analysis T Basic Premise – Molecules with heavier isotopes will stay at the source during evaporation T T HD 16 O or H 218 O Various things control isotopic concentration Temperature T Evaporation T Distance from source T T Compared to the Standard Mean Ocean Water (SMOW) T Equivalent to water collected from 200 -500 m depth in the Atlantic, Pacific, and Indian Oceans
Complications T 18 O content of precipitation depends on: 18 O content of water vapor from the source T Amount of moisture in the air at source T Evaporation en route to deposition T Source of land evaporation T Temperature at which evaporation and condensation takes place T Extent to which clouds become supersaturated T
Empirical Evidence T Studies show that despite the complications geographical and temporal variations in isotopes do occur, reflecting temperature effects due to changing T latitudes, T altitude, T distance from moisture source, T season, T long-term climatic fluctuations.
Dating of Ice Cores T Determine the age-depth relationship T Very accurate time scales for at least 10, 000 to 12, 000 years T Radioisotopic T 10 Be T 14 C* T 39 Ar T 81 Kr T 210 Pb* Methods
Dating of Ice Cores T AMS 14 C Dating T CO 2 from air bubbles T 10 kg of sample T Equivalent to 1. 5 m length of ice core T Problems T CO 2 exchange with the atmosphere is an open system until the air bubbles are cut off from the surface
Annual Layers T Can count visual annual fluctuation in the ice caused by melt and thaw layers T Various Markers T Visual stratigraphy T Electrical conductivity measurements (ECM) T Laser light scattering (from dust) T Oxygen isotopes T Chemical variations T GISP 2 and GRIP match back to 15, 000 years with 200 year precision
Resolution T <1% error back to 2, 000 BP, T 2% by 40, 000 BP, T 10% by 57, 000 BP, T up to 20% by 110, 000 BP
Seasonal Variations T Microparticulate matter and ice chemistry T Major ions T Trace elements T High Spring values and low Autumn values produce seasonal variations T Sodium, Calcium, Nitrate, Chloride T Electrical (ECM) Conductivity Measurements T Continuous T Volcanic record of acidity eruptions – high T Alkaline dust – low
Changing resolution back in time from the Camp Century ice core from Greenland
Site A, Central Greenland
Electrical Conductivity Measurements
Acidity of annual layers from A. D. 553 to A. D. 1972
Accumulation at Summit, Greenland
Theoretical Models T Calculated ice-age at depth by means of a theoretical ice-flow model T Depend upon Past changes in ice thickness T Temperature T Accumulation rates T Flow patterns T And ice rheology T T Problems minimized at ice divides (Grip core at Summit, Greenland) or deep cores that are still well above ground level (Vostok, Antarctica)
Schematic Diagram of Isotopic Depletion
Stratigraphic Correlations T Correlation of multiple proxy records from ice cores against records with better chronological control (i. e. δ 18 O from benthic foraminifera) T Danger of correlating events and onset of circular reasoning
Vostok Core, Antarctica T T Longest well-resolved ice-core record on Earth and a yardstick for comparison with other paleoclimatic records Deuterium records compared with SPECMAP δ 18 O records suggest that the Vostok core extend back 426, 000 years spanning the last four glacial events T SPECMAP Data (1) quantitative data on planktonic species and assemblages which reflect conditions in the surface waters of the Atlantic ocean; T (2) measurements of 180, 13 C difference (planktonic and benthic), and Cd/Ca. T
Climate Changes T The rate and cause of climatic changes is of great interest T Resolution is an important factor in determining rates of change
Shear in Ice Records T Differential forces at depth in the glaciers cause the ice to flow distorting the record T Boudinage – Pinching of a layer that is less likely to flow compared to the surrounding layers T Ice strength is dependent upon dust content
Atmospheric Composition T Ice cores are archives of atmospheric composition T Contain records of greenhouse gases T Carbon T Air Dioxide, Methane, Nitrous Oxide mass Characteristics T Volcanic Eruptions T Changes in Dust content
Greenhouse Gases T Methane is 220% greater today than 250 years ago T Carbon Dioxide is 130% pre-industrial levels T Nitrous Oxide is 110% greater than 250 years ago T All levels are far higher than anything seen in the last 220, 000 years
Volcanic Eruptions from Ice Cores
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