Quaternary Environments Ice Cores

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Quaternary EnvironmentsIce Cores
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Records From Ice Cores

• Precipitation
• Air Temperature
• Atmospheric Composition
• Gaseous composition
• Soluble and insoluble particles
• Volcanic Eruptions
• Solar Activity

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Records From Ice Cores
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Extent of Ice Core Sampling

• 15 Ice cores extend into the last glaciation
• Greenland
• Antarctica
• China
• Few Mid-Latitude high elevation cores

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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

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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

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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

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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

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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.

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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

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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

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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

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Resolution

• lt1 error back to 2,000 BP,
• 2 by 40,000 BP,
• 10 by 57,000 BP,
• up to 20 by 110,000 BP

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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

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Changing resolution back in time from the Camp
Century ice core from Greenland
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Site A, Central Greenland
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Electrical Conductivity Measurements
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Acidity of annual layers from A.D. 553 to A.D.
1972
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Accumulation at Summit, Greenland
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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)

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Schematic Diagram of Isotopic Depletion
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Stratigraphic Correlations

• Correlation of multiple proxy records from ice
  cores against records with better chronological
  control (i.e. d18O from benthic foraminifera)
• Danger of correlating events and onset of
  circular reasoning

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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 d18O
  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.

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Climate Changes

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

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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

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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

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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

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Volcanic Eruptions from Ice Cores
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