GEL 1 Lecture Notes - Lecture 25: Axial Tilt, Oxygen-18, Thermal Expansion
Oxygen isotope composition obtained from microfossils
During glacial periods: more 18O in the ocean water as 16O is stored in the glaciers
During interglacial periods
ice cores as archives of climate
● darker layers are winter
● records go back only 1 million years
Milankovitch Cycles
● climate variation predicted by cyclic changes in Earth's orbital geometry
Eccentricity: measure of how circular or elliptical Earth's orbit is around the sun
● 100,000 and 400,000 year time scale
● change in amount of energy earth gets during summer and winter times is not
that big
Obliquity (Tilt)
● 41,000 year time scale
● 22.5-24.5 degrees
● greater tilt: more solar radiation at the poles during the summer
Precession
● 23,000 years
● wobble of axis
● changes when the north/south hemispheres are facing the sun (summer)
summer solar insolation
winter solar radiation not well preserved
Last 1Ma, cycles have gone through huge change
● Lisiecki and Raymo, 2005
○ much smaller scale variations
■ frequency of variation changed too
○ earth's cycles (glacial vs interglacial) have changed
■ used to be influenced by obliquity cycle, but eccentricity has
become the dominant influence
Document Summary
During glacial periods: more 18o in the ocean water as 16o is stored in the glaciers. During interglacial periods ice cores as archives of climate. Records go back only 1 million years. Climate variation predicted by cyclic changes in earth"s orbital geometry. Eccentricity : measure of how circular or elliptical earth"s orbit is around the sun. Change in amount of energy earth gets during summer and winter times is not that big. Greater tilt: more solar radiation at the poles during the summer. Changes when the north/south hemispheres are facing the sun (summer) summer solar insolation winter solar radiation not well preserved. Last 1ma, cycles have gone through huge change. Earth"s cycles (glacial vs interglacial) have changed. Used to be influenced by obliquity cycle, but eccentricity has become the dominant influence. Track this variation by measuring temperature and co2 from antarctic ice cords. In last 150 years, co2 concentration has skyrocketed bc industrial revolution.
