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

Ice Core drilling

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‰

Temperature

Altitude

Distance from the source

Latitude

IAEA (2001).  GNIP Maps and Animations.

IAEA (2001).  GNIP Maps and Animations

IAEA (2001).  GNIP Maps and Animations

Fricke and O’Neil, 1999

Edwards et al., 2004

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.

Dating Ice Cores

• Radio-isotopes

• Ice layers

• Ice flow models

• Reference horizons

Volcanic markersprovide additional time control

Seasonal variations can be detected with microparticles and glacio-chemical data

Antarctic Ice Cores

Vostok Ice Core

Epica Group, 2004

Epica Group, 2004

Epica Group, 2004

Greenland

MIS-5MIS-3MIS-1 MIS-4

Blunier and Brook, 2001, Science

Warmer/Wetter?

Colder/Drier?

Range of18O values in the Kilimanjaro

ice core