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Ice Cores
• Very important paleoclimatic archives.• Records of past atmospheric conditions.
– Temperature– Humidity– Snow accumulation– Atmospheric composition– Volcanic activity– Tropospheric turbidity– Wind speed, wind direction– Atmospheric circulation
Stable Isotopes-Concepts
• Name Symbol Definition
• Atomic number Z # protons (p+)
• Neutron number N # neutrons (n)
• Mass number A # p+ + n
Abundance of stable isotopes of water
Isotope Z A Abundance (%)
Atomic wt.
(amu)
H 1 1 99.985 1.007825
D 1 2 0.015 2.014102 16O 8 16 99.762 15.994915 18O 8 18 0.200 17.999160
17O* 8 17 0.038 16.999131
Physical properties of water
H216O H2
18O
Density (g/cm3 at 20°C ) 0.997 1.1106
Melting point (°C at 760 torr) 0.00 0.28
Boiling point (°C at 760 torr) 100.00 100.14
Vapor pressure (torr at 100°C) 760.00 758.07
Viscosity (centipoise at 20.2°C) 1.002 1.056
Isotope effect and fractionation
• Isotopes undergo the same chemical and physical reactions.
• The rate of these reactions, however, could be different (isotope effect), resulting in the partitioning of isotopes (fractionation).
Terminology=1000(Rsample/Rstandard – 1)where R=heavy isotope/lighter isotope
18O= 1000(18Rsample/18Rstandard – 1)where 18R=18O/16O
D= 1000(2Rsample/2Rstandard – 1)where 2R=D/H
Standard is V-SMOW (Vienna-Standard Meteoric Ocean Water). 18OV-SMOW = DV-SMOW = 0‰
d-excess
• Meteoric Water Line: D=8*18O+10
d-excess under“normal” conditions
d= D-8*18O
Increased relative humidity or lower sea-surface temperature (reduced evaporation rates) produces lower d-excess values.