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1. Cenozoic Record of global cooling Transition from: Cretaceous Warmth (no ice or small ephemeral ice sheets) to Pleistocene (ice caps in both hemispheres)

2. Cenozoic Time Scale

3. Cenozoic Cooling Stepwise cooling of high latitudes and deep waters Recorded by oxygen isotopes Record of global ice volume and temperature

4. d18O d18O to temperature T = 16.9 – 4.38(dc – dw) + 0.10 (dc – dw)2 (Shackleton, 1974) dc= d18O in foram calcite dw = d18O in seawater (varies with ice volume) 1 equations- 3 variables

5. d18O Record of the Cenozoic Isolating the ice volume effect Shackleton (mid 1970s) Bottom waters stayed cool during glacial/interglacials, near freezing Assume benthic record = ice volume Both planktic and benthic change = ice volume Unequal change = temperature

7. d18O Isolating the ice volume effect Prentice and Matthews (1988) Change in benthic d18O values larger than those of corals, tropical planktonics- includes a temperature component as well (Cretaceous warm bottom water) Total change in benthics greater than change anticipated from ice free to bipolar ice sheets Equatorial surface waters changed little (or predictably) with glaciations (CLIMAP, isotopes data), thus equatorial planktonics record ice volume

9. Cenozoic Record Miller et al., 1987 and Zachos et al., 2001 Improved data sets New ways to view the record

10. Cenozoic Record Series of cooling +/or ice volume events Transition from Cretaceous/Paleocene greenhouse to bipolar ice house Overshoots (Zachos)

15. Cenozoic Record Cenozoic forcing factors Not a unidirectional change (multiple factors) Tectonics- paleogeography, mountain building, gateway events CO2 Orbital forcing

16. Paleoclimate Data DSDP = Deep Sea Drilling Program (1968 – 1985) ODP= Ocean Drilling Project (1985-2004) International consortium, US primary financial and scientific participant (22 nations participated) IODP= Integrated Ocean Drilling Project (2004 - 2013) Multiplatform, 3 part division Non riser drilling- Operated by US Riser Drilling- Operated by Japan Mission Specific Platform- Operated by European consortium

39. Earth’s Orbit

40. Orbital Theory Orbital Theory- idea that orbitally driven changes in Northern Hemisphere insolation drive the glacial/interglacial oscillation Also known as the Milankovitch theory

41. Don’t need to make the entire planet cooler Find that cool summers in the NH high latitudes allow ice to be maintained through the year and accumulate Milankovitch’s contribution Others had similar idea but believed cold winters were necessary Orbital Theory

42. 3 Orbital Parameters Eccentricity- shape of the Earth’s orbit around the sun Obliquity- tilt angle of the Earth Precession- Position of the Earth on its elliptical orbit relative to seasons Orbital Theory

43. Orbital Parameters Eccentricity Change in the shape of the Earth’s orbit around the sun 100 ky through minimum and maximum 400 ky from 0 to 0

44. Orbital Parameters

45. Eccentricity

46. Eccentricity

47. Eccentricity Total range = 0 ? 0.06 Affects total insolation by 0.2% (~0.5°C) only parameter to affect total insolation- others redistribute insolation More important role = modulation of precession

48. Orbital Parameters Obliquity Tilt of Earth’s axis Affects seasonality- distribution of solar radiation No tilt = no seasons Extreme tilt = extreme seasonality 41 ky – min to min Total range 22.1° - 24.5° (currently 23.5° and dec.)

49. Obliquity

50. Obliquity Hemispheres in phase Increases or decreases seasonality in both hemispheres Greatest effect at high latitude

51. Obliquity

52. Orbital Parameters Precession of the equinox Determines where the Earth is on its elliptical path around the sun when the equinoxes occur (relative to perihelion and apheion) Made up of two components Axial precession – wobble in the Earth’s axis- 19 ky Precession of the ellipse- 23 ky

53. Precession

54. Precession

55. Precession Measured by the “precession index” = the Earth – sun distance on June 21st Incorporates the eccentricity component

56. Precession Modulated by eccentricity Irrelevant when eccentricity = 0 Maximum effect at low latitudes Two hemispheres are out of phase Warmer summers in one hemisphere correlate with cooler summers in the other hemisphere

58. Precession Effect

60. Glacial Configuration Pleistocene glacial intervals coincide with cool, high northern latitude summers Tilt? Precession? Northern Hemisphere summer at aphelion or perihelion? Eccentricity?

62. Where are we now?

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