The last 600ky…LGMLast GlacialMaximum18Ky

Paleoclimataology

Lecture notes from Ellen Druffel

1. Eccentricity

• 3% range ofvariation of E-Sdistance due to elipticalorbit around Sun,Pull of large planets

• Now, perihelion occurs during northernWinter (3 January)

• 100ky and 413kyperiods

• Now, e =.0167(relatively circular)

2. Tilt - Reason for Seasons

• Now tilt is 23.5°, andis decreasing.

• Higher the tilt, higherthe seasonal differences

• Has gone from 24.5°-22.2°, varied by pullof large planets

• 41 ky period

3. Precession - WobbleVaries E-S distance with

season

• Variation of the direction in which the E axis leans.

• Caused by the pull of Sun and moon on Earth

• Now Earth’s axis points to Polaris

• 23 ky stronger period - combined wobble and slow turning of eliptical orbit.

Now

11Kya

On the long term…the precessional index

Eccentricity variations at 100Ky and 413Kymodulate the amplitude of the precession cycle.This is why we have the 100Ky ice age cycle!

How orbital theory, climate records (18O)and northern hemisphere insolation (i.e. melting in N. Atlantic) compare over the past 600ky.

Cold warm

now

LGM18ky

BLAG invokes chemical weathering

Molnar & England, 1990

Molnar & England, 1990