1. “The Science Behind Media Reports”
Reminders
Midterm Exam 10/19 – in class. Material through 10/14
. Review Sessions: Fri. 14th, 4-5 pm, Angell C
Mon. 17th, 4-5pm, 1040 Dana
No lab meeting next week, instead…there is a TAKE HOME ASSIGNMENT:
“The Science Behind Media Reports”
Remember that your project proposal is due the week of Oct. 25th before your lab section

2. General Lab Comments Questions about last week’s lab Lecture questions
Read over your writing

3. Goal of Today’s Lab Using Excel, analyze data from the Vostok Ice Core
Perform paleoclimate calculations using isotope ratios and greenhouse gas concentrations
Understand mechanisms behind climate change and the magnitude of past changes

4. Some background on… Vostok and Glacial Ice Isotope Hydrology
Milankovitch Theory

5. Vostok, Antarctica A “two-mile time machine”
Source: LDEO, Columbia University

6. Subglacial Lake Vostok Sealed from atmosphere for 15 My
Evolutionary implications?
Possible location for X-Files alien mothership

7. Ice accumulates
in annual layers
Source: Earth’s Climate, Ruddiman

8. Snow Sintering Source: Raynaud, 1992 ~100y in Greenland
~2600y in Antarctica
Source: Raynaud, 1992

9. Bubbles in the Ice
Small bubbles appear as round inclusions – see the orange crystal in center
Fossil air!

11. Hydrogen Isotopes
Hydrogen has two stable isotopes
1H and 2H

12. Three stable isotopes: 16O, 17O, 18O
Oxygen Isotopes
Three stable isotopes: 16O, 17O, 18O

13. Hydrogen & Oxygen Isotopes
D = 8*18O + 10

14. What happens to the ratios?

15. Oxygen Isotopes and Climate
Interglacial
Glacial
16O
16O
16O, 18O
18O
(Stanley, Earth System History)

16. Milankovitch Cycles
Past changes in climate have often been triggered by changes in orbital characteristics.
Variations in earth’s eccentricity, obliquity, and precession alter the seasonality of solar radiation.
It is the seasonality and location of insolation that impact the contrast between the seasons (not total solar energy).
Serbian mathematician Milutin Milankovitch

17. Eccentricity
Deviation of the shape of the Earth’s orbit around the Sun from a perfect circle.
Varies between:
-0.03 and +0.02
Cyclicity:
100ka & 413ka
Source: Earth’s Climate, Ruddiman

18. Obliquity (a.k.a, Axial Tilt)
Inclination of the Earth’s axis in relation to its plane of orbit around the Sun
Source: Earth’s Climate, Ruddiman
Varies between 22.5° and 24.5°
Cyclicity: 41ka

19. How is the distribution of insolation affected in each case?
Source: Earth’s Climate, Ruddiman

20. Precession Earth’s slow wobble as it spins on axis
Varies between 22.5° and 24.5°
Cyclicity: 23ka
Source: Earth’s Climate, Ruddiman

21. Milankovitch theory of climate change
Glacial
Ice Growth Configuration:
• Low eccentricity
• Low Tilt
• Large Earth-Sun Distance in NH Summer
Net Effect: Less seasonal contrast

22. Milankovitch theory of climate change
Inter-Glacial
Ice Growth Configuration:
• High eccentricity
• High obliquity (tilt)
• Small Earth-Sun Distance in NH Summer
Net Effect: More seasonal contrast

23. Cyclicities Eccentricity Obliquity Precession
Adding cycles creates new cycles!
Cyclicities
Source: Earth’s Climate, Ruddiman

24. CO2, CH4, and Temperature T
CH4
CO2

25. CO2, CH4, and Temperature
Both CO2 and CH4 are greenhouse gases. Warmer temperatures are associated with higher levels of greenhouses gases and vice versa.
What could affect the levels of CO2 in the atmosphere?
Burning of fossil fuels (Anthropogenic effects)
Uptake of CO2 from the oceans via the “biological pump” – feedback loop
Weathering reactions (break down of granites consumes CO2)

26. Dust and Temperature Change vs. Age
During glacial times, sea level was lower, exposing the continental shelves. What consequences does this have for dust concentrations?

27. Now it’s your turn!