ice age cycles - university of washington
TRANSCRIPT
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• Large Ice sheets covered Northwestern Europe and Northern North America
• Due to orbitally induced changes in northern hemisphere summer insolation – Ice volume changes are coordinated with CO2
changes (shift of carbon between atmosphere and oceans)
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Last Glacial Maximum Present
What does an ice age look like?
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Vocabulary: Isotopes!
atomic mass: number of protons plus neutrons H normally 1+0 = 1 C normally 6+6 = 12 O normally 8+8 = 16
an atom (or element) is defined by number of protons H(1), C(6), O(8), Pb(82)
isotope: same element, different atomic mass >> that is, different number of neutrons
1H (normal), 2H (deuterium), 3H (tritium; radioactive) 12C (normal), 13C, 14C (radioactive) 16O (normal), 18O
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16O vs 18O "light"
(normal) "heavy"
• evaporation selects for "light" • condensation (precipitation) selects for "heavy"
18O in ocean sediments records glacial ice volume: More "light" water in ice-sheets means remaining ocean water is "heavier". 18O in ice-cores indicates local temperature: Colder conditions means more precipitation en route so "lighter" snow.
Kasting et al"
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Oxygen Isotope Concentration in Shells of Organisms Growing in the Deep Ocean
TIME
"heavy" water! = more ice!
"light" water! = less ice!
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Ice-age begin
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Kasting et al"
"heavy" water! = more ice!
"light" water! = less ice!
TIME
Short (10,000 yr) Warm Episodes
Ocean sediment record !
of Global Ice Volume"
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Trigger with feedback causes ice-sheets... to grow and keep growing
or to melt and keep melting
Ice-albedo feedback
- Other feedbacks are needed to explain the magnitude of the changes. - Greenhouse gases (e.g. CO2 and CH4) seem to be involved.