slide1 n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Lecture 34: Orbital (Milankovitch) Theory of the Ice Ages PowerPoint Presentation
Download Presentation
Lecture 34: Orbital (Milankovitch) Theory of the Ice Ages

Loading in 2 Seconds...

play fullscreen
1 / 45

Lecture 34: Orbital (Milankovitch) Theory of the Ice Ages - PowerPoint PPT Presentation


  • 322 Views
  • Uploaded on

Lecture 34: Orbital (Milankovitch) Theory of the Ice Ages. warmer, less ice. Holocene. Last glaciation. colder, more ice. Interglacial. Glacial. Orbital forcing of Earth’s climate. Changes in Earth’s orbital geometry (eccentricity, tilt, precession).

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Lecture 34: Orbital (Milankovitch) Theory of the Ice Ages' - kirk-moon


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide2

warmer, less ice

Holocene

Last glaciation

colder, more ice

Interglacial

Glacial

orbital forcing of earth s climate

Orbital forcing of Earth’s climate

Changes in Earth’s orbital geometry

(eccentricity, tilt, precession)

Changes in the seasonal distribution of

Insolation (heat) as a function of latitude

Amplified by other processes

CO2, albedo

feedback

Glacial-interglacial climate change

james croll
James Croll
  • Scottish (1821-1890)
  • Millwright, carpenter, tea shopkeeper, electrical sales, hotelkeeper, insurance salesman, janitor, Geologic Survey, Fellow of the

Royal Society

decreases in winter radiation would favor snow accumulation, coupled this to the idea

of a positive ice-albedo feedback to amplify the solar variations.

slide5

Milutin Milankovitch,

  • Serbian mathematician
  • (1879-1958)
  • 1941, “Canon of Insolation of the Earth and Its Application to the Problem of the Ice Ages,” 626 pages
  • improved upon Croll's work by making more precise calculations of solar insolation (all done by hand!)
  • Emphasized the importance of decreases in summer radiation which favors snow accumulation and glacial advance
slide6

The equilibrium line of a glacier is the location where

accumulation equals ablation

If accum>ablation, glacier advances

If ablation>accum glacier retreats

Decreased summer insolation

lowers the equilibrium line

and glacier advances.

slide7

Cool summers

in northern hemisphere

60

65

70

Latitude of equivalent insolation

75

250

200

150

100

0

300

50

550

500

450

400

350

300

600

slide9

Eccentricity grossly exaggerated

Today’s orbital parameters

152.5 x 106 km

July

147.5 x 106 km

slide10

Obliquity is responsible for seasons

Dec 21

June 21

Mar 21

Sept 21

slide11

Obliquity

  • Current value: 23.5o
  • Range: 22o-24.5o
  • Period: 41,000 yrs
slide12

Effect of Obliquity on Insolation

difference in obliquity from 22 to 24.5o with other parameters held at present values

Boreal summer

W m-2

summer

austral

Effect on insolation is greatest at high latitudes

Same sign for respective summer season (hemispheric response is in phase).

slide13

varies at a period of

41 kyrs.

Obliquity

frequency [1/ky] Period [ky] Amplitude

0.02439 40.996 0.011168

0.02522 39.657 0.004401

0.02483 40.270 0.003010

0.01862 53.714 0.002912

0.03462 28.889 0.001452

slide14

Eccentricity

a

a

p

  • Current value: 0.017
  • Range: 0-0.06
  • Period(s): ~100,000 yrs

~400,000 yrs

a - p

Eccentricity =

a + p

a = aphelion distance

p = perihelion distance

slide15

Eccentricity changes

the total insolation

received by the

Earth but the

difference is small!

0.5 W m-2/ 1370 W m-2

= 0.04%

Dominant periods are

at ~400 and near 100 kyrs

Eccentricity

frequency [1/ky]Period [ky]Amplitude

0.00246406.1820.010851

0.0105594.8300.009208

0.00807123.8820.007078

0.0101498.6070.005925

0.00769130.0190.005295

slide16

Precession

(axial)

precession of the ellipse
Precession of the Ellipse
  • Elliptical shape of Earth’s orbit rotates
    • Precession of ellipse is slower than axial precession
    • Both motions shift position of the solstices and equinoxes relative to

Earth-Sun distance

slide19

The effect of axial and elliptical precession is the change the

timing during the year of perihelion and aphelion

152.5 x 106 km

July

147.5 x 106 km

precession of the equinoxes
Precession of the Equinoxes

July 4

a

  • Earth’s wobble and rotation of its elliptical orbit produce precession of the solstices and equinoxes
    • One cycles takes 23,000 years
  • Simplification of complex angular motions in three-dimensional space

p

Jan 4

p

a

a

p

a

p

extreme solstice positions
Extreme Solstice Positions
  • Today June 21 solstice is near aphelion (July 4)
    • Solar radiation a bit lower making summers a bit cooler
  • Configuration reversed ~11,500 years ago
    • Precession moves June solstice to perihelion
    • Solar radiation a bit higher, summers are warmer
    • Assumes no change in eccentricity

Cool summers

Warm summers

slide22

Effect of precession from its minimum value (boreal winter at perihelion) to its

maximum value (boreal summer)

Boreal summer

summer

austral

Precession affects insolation at both high and low latitudes.

Opposite sign in northern and southern hemispheres for respective season

(out of phase)

slide23

Dominant periods

at ~19, 22 and 24 kyrs

Precession

frequency [1/ky]Period [ky]Amplitude

0.0422123.6900.018839

0.0446722.3850.016981

0.0527518.9560.014792

0.0523619.0970.010121

0.0432623.1140.004252

slide26

Last

Ice

Age

Difference in Northern Hemisphere insolation at summer solstice relative to today

Holocene

interglacial

slide27

Ice Growth (glacial) Configuration

  • (cool summers)
  • Low obliquity (low seasonal contrast)
  • NH summers during aphelion (cold summers in the north)
  • High eccentricity
slide28

Ice Decay (Deglaciation) Configuration

  • High obliquity (high seasonal contrast)
  • NH summers during perihelion (hot summers in the north)
  • High eccentricity
milankovitch theory revived
Milankovitch Theory Revived

The measurement of long, continuous oxygen isotope variations in deep-sea were instrumental in providing evidence for the Milankovitch theory of the ice ages.

Pacific deep core V28-238

Shackleton & Opdyke, 1972

slide31

Variations in the Earth's Orbit: Pacemaker of the Ice Ages

J. D. Hays, John Imbrie, N. J. Shackleton

Science, 194, No. 4270, (Dec. 10, 1976), pp. 1121-1132

(eccentricity)

(obliquity)

(precession)

Marine oxygen isotope record shows

the same periodicities predicted by

orbital forcing.

slide32
Marine isotope record provides support for the Milankovitch Theory but there are still some unanswered questions

So many

problems

1. 100,000-year problem

Milutin Milankovitch

1879-1958

2. The Mid Pleistocene transition problem

3. Stage 11 (Termination V) problem

4. Causality Problem:

Timing of Term II

slide33

I

II

III

IV

V

VI

Ice

decay

5

1

11

9

7

13

14

8

4

10

2

6

12

Ice

growth

slide34

100 ky

41 ky

23 ky

Insolation

65oN

Benthic

18O

slide35

1. The 100-kyr Problem

Classic Milankovitch forcing

(might consider alternatives)

Forcing

small

?

big

Response

Why does the climate system have so much 100-kyr power when the forcing is so weak?

but recall that eccentricity also modulates amplitude of the precession cycle

slide36

2. The Middle Pleistocene Transition

32

16

Schulz and Zeebe (2006)

slide37

Insolation (June 65oN ) Milankovitch Forcing

Schulz and Zeebe (2006)

100 kyr

100 kyr

slide38

18O

100-kyr world

41-kyr world

Insolation (forcing)

?

slide39

3. Stage 11/Termination V Problem

I

II

III

IV

V

VI

Ice

decay

11

Strong

Response

12

Weak

Forcing

Ice

growth

slide40

4. Causality Problem

sea level begins to rise before

boreal summer insolation

Termination II/Stage 5 Problem

A. L. Thomas, G. M. Henderson, et al., 2009. Penultimate Deglacial Sea-Level Timing from U/Th Dating of

Tahitian Corals. Science doi:10.1126/science.1168754 (23 April) 2009

slide41

NATURE|Vol 451|17 January 2008|

Milutin Milankovitch (1879-1958)

slide42

Non-linear ice volume models invoking threshold response

How to

explain the

100-kyr

power?

Ice Sheet Growth Lags Summer Insolation

model 1 calder 1974
Model 1: Calder (1974)

18O

Ice

volume

V = ice volumei = summer insolation at 65°N

i0 = insolation threshold

k = kA (accumulation) if i < i0

k = kM (melting) if i > i0

18O (observed)

Ice

Volume model

Model produces some

100-kyr power

model 2 imbrie and imbrie 1980
Model 2: Imbrie and Imbrie (1980)
  • Written in dimensionless form (i.e., variables are divided by a scaling value)

18O

Ice

volume

dV/dt = (i-V)/

Not observed

In climate record

(time series might

be too short)

V = ice volume

i = summer insolation at 65°N

t = tM if V > i (melting)

t = tA otherwise

Ice

Volume model

18O

slide45

Hypothesis:

Roy et al. (2004)

  • 41 kyr world
  • Less ice volume
  • Smaller, thinner ice sheet
  • Ice sheets responded linearly to
  • obliquity forcing
  • 100-kyr world
  • New source of low-frequency variability:
  • Ice volume and thickness increases
  • Ice sheet mass is capable of surviving
  • weak summer insolation maxima
  • Deglaciations begin to skip precession
  • and/or obliquity cycles
  • Lenthens duration of glacial cycle
  • New source of high-frequency variability:
  • Large, thick ice-sheet begins behaving
  • dynamically (non-linearly)
  • 100-kyr cycle driven by internal ice
  • sheet dynamics (paced by insolation)