1. Climate archives, data, models (Ch. 2) climate archives dating of climate archives timespan & time resolution GCMs

2. Climate archives -- a climate archive is a source of climate data types include: sediments glacial ice tree rings & corals historical records instrumental records

3. Sediments -- loose material produced by the disintegration of rocks -- transported by wind or water near Earth’s surface -- tend to accumulate in layers in low spots (sedimentary deposition in low areas) examples: sand or silt grains at beaches, or in streams mud / clay particles in lake & ocean bottoms shells of dead organisms in oceans sediments

4. Sediments -- often trap biologic material -- can record temperatures (e.g., inferred from O-isotope data) -- sediments accumulate in low areas, most recent at top -- get time record by taking a core sample pollen

5. Sedimentary deposition in lakes, seas, ocean:

6. Some lake core sample locations time records for as long as deposition in lake persists; can be ~1000 years

7. Ocean core sample locations time records for as long as deposition in ocean persists; can be ~1 - 10 million years

8. Glacial ice -- ice in glaciers or ice sheets -- deposited in annual layers -- ices trap gases in bubbles & record temperatures (O-isotope data) -- get time sequence by taking ice cores in areas that are experiencing ice accumulation

9. Mountain glaciers time records up to ~1000 years _____________ Ice sheets (e.g., Antarctica, Greenland) time records up to ~100,000 years

10. Tree rings -- annual growth of wood layers time records of ~ 100 - 10,000 years Corals -- organisms that live in shallow ocean water -- secrete annual carbonate layers time records of ~ 10 - 1,000 years

11. Some tree ring, coral, and ice core sample locations

12. Historical records -- info about climate that was recorded by people time records over ~ 1000 years Instrumental records -- info on climate (e.g. temperature) recorded by direct measurement time records over ~ few hundred years

13. Dating of climate archives to understand how climate has varied over time, one needs to be able to determine relative or absolute (actual) ages use one or all of the following techniques: (1) radiometric dating (2) correlation (3) counting annual layers

14. (1) Radiometric dating -- absolute dating technique -- depends on the decay of radioactive isotopes -- usually applied to rocks that solidified from magma (molten rock), but radiocarbon dates can be obtained for organic material in sedimentary materials

15. What are isotopes? -- atoms that vary in mass but have the same chemical behavior (i.e., same element, different isotopes) 8 protons 8 neutrons 8 protons 9 neutrons 8 protons 10 neutrons 16 O 17 O 18 O Example: there are 3 stable oxygen isotopes

16. But not all isotopes that exist in nature are stable (some undergo radioactive decay) This changes the number of neutrons or protons in the nucleus of the atom (can get different element as result) Example: Carbon has 3 isotopes 12 C - contains 6 protons, 6 neutrons - stable 13 C - contains 6 protons, 7 neutrons - stable 14 C - contains 6 protons, 8 neutrons - unstable (radioactive)

17. Carbon-14 decays to Nitrogen-14 Parent isotope 14 C has decayed to daughter isotope 14 N. 14 C (6 protons, 8 neutrons) --> 14 N (7 protons, 7 neutrons)

18. So: how do we use radioactive decay to date something?

19. So: how do we use radioactive decay to date something? Answer: If we know the rate of decay and can measure the amount of parent and daughter isotopes, we can calculate the time elapsed. Half-life = the amount of time needed to transform 1/2 of the parent into the daughter isotope

20. Radioactive decay

21. D/P = 0/24 = 0 12/12=1 18/6=3 21/3=7 the ratio of daughter to parent is unique at any given time, and gives us the number of half-lives that have passed

22. Some half-lifes:

23. (2) Correlation -- relative dating technique -- goal is to understand time sequence of events even if absolute age not known -- use in geologic outcrops where cross-cutting relationships or distinctive features are seen

24. in sedimentary rock layers, the layer on top is the youngest, the layer at bottom is the oldest in order for a rock unit to cut across other rocks, it has to be younger than the other rocks Geologic principles

25. Relative ages (oldest to youngest): igneous 1 sed layer A igneous 2? sed layer B igneous 3 sed layer C igneous 4?

26. lava flow dated at 3.8my -> To get ages of rocks that cannot be radiometrically dated, use combination of correlation & radiometric dating The circle below represents a point of interest (say a fossil) found in an undatable rock unit that is bounded above and below by datable lava flows. How old is the green dot?

27. lava flow dated at 3.8my -> 3.9 + 0.3 m.y.3.7 + 0.1 m.y. The date on the right hand side is a more precise date.

28. (3) Counting annual layers -- relative dating technique -- can be turned into an absolute age if additional info known (e.g., if one knows when layers started or stopped forming)

30. Timespan & time resolution -- different climate archives give info on different timespans timespan: largest time unit we can measure -- vary also in time resolution time resolution: smallest time unit we can measure

31. archive resolution related to the time span: longer time span archives tend to have worse (larger) time resolution...and vice versa

32. sediments give us our oldest record of climate: oldest sedimentary rocks are ~ 3.5 b.y. old oldest ice core layers from Antarctica: ~400,000 years old

33. General circulation models (GCMs) these are 3-d computer models that provide a complete numerical simulation of the climate system they simulate response of climate to various forcings useful for: -- understanding climate archives -- predicting future climate can be tested by comparing simulated to real responses

34. Steps in models:

35. subdivide climate system into smaller pieces analyze how these interact

36. Observed Model January surface temperature