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The 100 Kyr cycle

The 100 Kyr cycle. Agnes Barszcz. Who wants to be a climatologist?. 2 teams: The Aphelions The Perihelions Rules Joker. What I am going to talk about. Various hypotheses for 100 kyr cycle Why Milankovich is wrong Suggest a new hypothesis See if it is reasonable

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The 100 Kyr cycle

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  1. The 100 Kyr cycle Agnes Barszcz

  2. Who wants to be a climatologist? • 2 teams: • The Aphelions • The Perihelions • Rules • Joker

  3. What I am going to talk about • Various hypotheses for 100 kyr cycle • Why Milankovich is wrong • Suggest a new hypothesis • See if it is reasonable • Look at it’s sensitivity to different parameters • Its flaws • What is the right theory • FUN: Giving out the price!!!

  4. What is the 100 kyr cycle?

  5. What is causing it? • Many hypothesies: • The milankovitch cycle • Isostatic adjustmets of the litosphere under the weight of the glacier • Feedback between atmosphere ocean and Co2 • ….. • WE ARE STILL MISSING A SOLUTION!

  6. Question 1: • Who can tell me in less then 2 minutes what the Milankovich theory is ?

  7. Milankovich and and why it is wrong! • 3 components • Eccentricity • Precession • Axial tilt

  8. Which one was key for us?

  9. Milankovich and and why it is wrong! • 3 components: Eccentricity would be the one we are interested in! -> Top five reasons that we should NOT……

  10. Eccentricity changes are small • Orbital calculation when caried out with greater presision show a major cycle of 400 Kyr Spectrum of 100-kyr glacial cycle: Orbital inclination,not eccentricity. By RICHARD A. MULLER* AND GORDON J. MACDONALD http://www.pnas.org/cgi/reprint/94/16/8329.pdf , 1995 • Well dated climate proxies show a 100 kyr cycle only over the last million of years • Double peak in frequency domain • Causality problem

  11. Suggested solution: • Changes in the orbital inclination

  12. Find a suitable solution…

  13. Methods • Use simple or complex models

  14. Pros and cons • Complex models: Global circulation models • Pro: They take into account many parameters. They are more realistic • Cons: Require large computers $$$$$ • -> Used to simulate equilibrium responses to various initial conditions

  15. Pros and cons • Simple models: • Pro: Require less computer power, and run faster.. • Con: Yield less realistic results. We do not see the influence of all the small parameters that we have neglected

  16. What was used • A simple model

  17. Claim • Hezi Gildor and Eli triperman say the 100 kyr cycle is NOT related to the milankovich cycle!!!!!!!!

  18. The answer! • Their hypothesis is: • The variation of the ice-albedo between glacial and interglacial periods • Variant of the precipitation-temperature feedback

  19. What the autors used • A simple zonaly averaged box

  20. The components of the model • Ocean meridional thermohaline circulation • Atmospheric temperature-humidity feedback • Land glaciers • Sea ice

  21. What,where,how? • The ocean model • 4 surface boxes (400 m) • 2 polar: • Water may be covered with sea ice of variable extent • Land may be covered with land ice of variable extent • 2 midlatitude boxes • 4 Deep water boxes (4000 m) • ** Important to note that the ablation rate of glacier stays constant with time….

  22. What,where,how? • The atmosphere model: • Each box can have 4 types of lower surfaces: • Land • Ocean • Land Ice • Sea ice • -> All have different albedos

  23. The technicalities • What is a leapfrog scheme?

  24. Leapfrog

  25. Why leapfrog? • Time reversible • Assures energy conservation • A better accuracy http://www.lifelong-learners.com/pde/SYL/s2node4.php http://einstein.drexel.edu/courses/CompPhys/Integrators/leapfrog/

  26. How it goes… The crux of the problem

  27. How it goes: Ocean is ice free • Temperatures are mild • More precip then melting and carving ->->Land ice sheet grows

  28. How does that affect the temperature?

  29. As ice sheet grows slowly • The albedo of the earth decrease • The sea temperature are below zero only in the polar boxes. ->->-> At year 90 kyr, the global SST reaches zero degrees

  30. What’s special about the moment that the SST reaches zero?

  31. Ice sheet rapidly grows • As the SST attained a critical value, sea ice grows very rapidly! • In 20 year all polar box is covered in sea ice. ->->-> Sea ice switch is ON

  32. When the switch is on.. • Sea Ice Stop growing!!! Why????

  33. Self-limitation of sea ice • The sea cools by giving out heat to the atmosphere • When it is covered by ice, there is no more exchange • The warm midlatitude waters mix with the polar waters ->->-> No more sea ice growth

  34. The ice age! • The glacier is at it’s maximum • The atmosphere is at it’s coldest How do we get out of an ice age??

  35. Moisture feedback • There is less moisture captured by cold air, so less northward moisture transport • Because of the ice cap, there is also less evaporation in the polar region ->->-> Less moisture present in polar regions

  36. We are loosing the icesheet • The precipitaion rate is reduced by ½ • The ablation rate stays constant ->->-> The glaciers retract

  37. On the road to warm times • As the ice sheet retract, the albedo is decreasing. • Atmospheric and ocean temperatures rise slowly. • As long as there are ice sheets in polar region the ocean temperature in the region in below zero :sea ice is present. -> How does that affect the land ice sheet?

  38. Further down, on the road to warm times.. • As long as the ice sheet is there, the land glaciers retreat fast • The sea ice, does melt by sloooowly… • The meltdown is slow because the SSt is close to zero.. -> What is causing it to melt anyways?

  39. Close to interglaciation.. • The sea ice melts down because of the heat advected and diffused by the ocean, that is coming from the midlatitudes. ->What will cause the abrupt acceleration of the melt down of sea ice?

  40. Deep Ocean • Because the deep ocean heats up: But Why?

  41. The deep ocean • Because of the melt down of the land ice sheet • The switch is OFF

  42. Switch is “off” • All the ice melts down in about 40 years • Atmosphere and ocean temperatures rise again

  43. And back… • The temperatures are maximum • The ice sheet is minimum • The amount of precipitation is at it’s maximum ->We are back at the starting point!

  44. The Results • Simulated years from 170 kyr to 70 kyr

  45. Theoretically it makes sense… Ok so we have a scheme… Does it practically?

  46. So what about the THC?!? • THC = Thermohaline circulation • It was included in the model • It is rather an effect the a cause of the 100 kyr cycle What changes the strength of the THC?

  47. The THC strength • When glaciers melt, there is a lot of fresh water relised: minimal THC (12Sv) • At interglacial periods, there is a lot of evaporation: Salier water: strong THC(16Sv) • When glaciers form: less evaporation: weaker THC(13Sv)

  48. Is it an ok resolution to have only 4 boxes? • How many did we use in the model we made in class?? • It is only the upper part of the ocean that has to cool significantly for glaciation. (The lower part’s role is to provide delayed responses to various forcing) • It was already demonstrated in previous papers that this can be achieved in only a few tens of years

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