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The last 600ky…. LGM Last Glacial Maximum 18Ky. Paleoclimataology. Lecture notes from Ellen Druffel. 1. Eccentricity. • 3% range of variation of E-S distance due to eliptical orbit around Sun, Pull of large planets • Now, perihelion occurs during northern Winter (3 January) - PowerPoint PPT Presentation
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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