Transcript Quaternary Environments Ice Cores Records From Ice Cores Precipitation  Air Temperature  Atmospheric Composition   Gaseous composition  Soluble and insoluble particles Volcanic Eruptions  Solar Activity 

Quaternary Environments
Ice Cores
Records From Ice Cores
Precipitation
 Air Temperature
 Atmospheric Composition

 Gaseous
composition
 Soluble and insoluble particles
Volcanic Eruptions
 Solar Activity

Records From Ice Cores
Extent of Ice Core Sampling

15 Ice cores extend into the last glaciation
 Greenland
 Antarctica
 China
 Few
Mid-Latitude high elevation cores
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

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
Stable Isotope Analysis

Basic Premise – Molecules with heavier isotopes
will stay at the source during evaporation


Various things control isotopic concentration




HD16O or H218O
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
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
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.
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*
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
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
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

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
eruptions – high
 Alkaline dust – low
 Volcanic
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

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)
Schematic Diagram of Isotopic
Depletion
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

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.

Climate Changes

The rate and cause of climatic changes is
of great interest
 Resolution
is an important factor in
determining rates of change
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
Atmospheric Composition

Ice cores are archives of atmospheric
composition
 Contain
records of greenhouse gases
 Carbon
 Air
Dioxide, Methane, Nitrous Oxide
mass Characteristics
 Volcanic Eruptions
 Changes in Dust content
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

Volcanic Eruptions from Ice Cores