What are the changes occuring on the Orbital Time Scale?
- Axis Tilt (currently 23.5)
- Shape of earths revolution around the sun
- Shift of the seasons (precession)
How often do Orbital scale Changes occur
23,000 and 413,000 year cycles
What proxie data allows us to observe these cycles?
- 3 Myrs - 800Kyrs (marine sediments)
- 800 Kyrs (Ice cores)
what major characteristics of our climate does orbital scale effect?
- Monsoons
- Polar Ice Sheets
- GHGs concetrations
Describe earths Eccentric orbit
elliptical ,with the perihelion being 153 Mkm away and the Aphelion being 158 Mkm away
What are the 3 main components that drive orbital climate change? describe them and their timescales.
- Earths tilt, 41,000 year cycle, fluctation from 22.2-24.5 degrees
- Earth’s eccentricity
becomes more elliptical (or less), 2 cycles which occur at 100,000 and 413,000 years - Precession
changes in solstice and equinox positions. 23,000 year cycle
How does the earths tilt effect the climate?
- Larger tilt angle means warmer summer at poles and colder winter at the poles. Smaller angles means more neutral seasons.
What is Precession, how does it effect climate.
The slow rotation of the elliptical orbit of the earth around the sun.
Difference between poles and equator with respect to response to orbital cycles
Poles are affected more by long term cycles where as equator is effected by short term cycles
Variability between NH and SH with respect to orbital scale cycles
if NH and SH react in the same manner, it is either precession or eccentricity, if they have opposite reactions, it is the earths tilt.
List the Three orbital scales in order from shortest cycle period to longest.
- Precession
- Earths tilt
- Long, short eccentricity
If all cycles are occuring simultaneously, how can one detangle them from climate data?
Through spectral analysis requiring a time series.
What is the relation of monsoons to orbital scale cycles?
Varying orbital scale cycles result in increased insolation, and increased insolation is associated with stronger monsoons (specifically summer) due to great uplift overland.
What cycle does the disappearing of the sahara follow
the 23,000 year precession based cycle.
What causes lakes like the sahara to exist?
Increase in solar radiation, therefore more precipitation
What are some evidence of heavy monsoons in the sahara. Give brief descriptions of each
- Sapropels, lack organic rich sediment deposited in lakes at times of monsoons, shows up as black sections in sediment cores. (use O18 for dating)
- Paleoriver beds satellite evidence that riverbed sediment is under sand in desert.
- Freshwater diatoms found in the atlantic sediments off the coast of africa
Accumulation Vs. Ablation
- Accumulation = + mass balance
- Ablation = - mass balance
Equilibrium : Accumulation = Ablation
Specify the Milankovich theory and how it relates to ice growth
Ice grows during low summer insolation (less ablation)
lowest summer insolation
- is when earth has the lowest tilt angle, - Solstice is farthest from the sun (Preccesion)
- Max eccentricity
How does orbital time scale cycles relate to ice development (and the study of it).
We know when the lowest insolation will occur in the summer therefore we know when there will be max ice growth.
Give paleoclimate evidence of Orbital scales control over Ice development (3 archives, detail as to how their used)
- Marine Foraminifera
- made shells which were used for O18, ocean sediments! - Coral Reef Terraces
- showed the height of the ocean, this showed how much water was stored in ice, used radiometric dating. - Tree-Grass pollen
Todays orbital scale positioning
Tilt = 23.5 Precession = 0.8+ Eccentricity = Close to min
All is headed toward the coldest summer!
