Lecture 3- Milankovitch cycles etc. Flashcards
Sapropels
Organic rich black muds- layers of high carbon concentrations
Sapropels- low salinity lids
Prevent oxygen rich water being formed as low salinity fresh water sits on the surface
Sapropels and precession
Sapropels sit on precession spikes (strong indication insolation and rainfall at source of the Nile)
Urbain Leverrier
Applied Newton’s gravitational laws to orbits/masses of planets
Eccentricity change- 100,000 years
1-6%
Obliquity change (tilt)- 41,000 years
24.5 to 22.1 degrees
When tilt is decreased…
Polar regions receive less sunlight
When tilt is increased…
Polar regions receive more sunlight…
Precession of the equinoxes
Caused by the ‘wobble’ of the earth’s axis
Cause of decrease in summer radiation
Caused by a decrease in axial tilt
Tilt cycle (41,000)
Predominates at poles, gets smaller at equator
Precession (22,000)
Is small at poles, larger at equator
Eccentricity cycle (100,000)
Amount of energy change involved in the eccentricity
cycle is small
Problem with dating glaciers
Morraine of previous glaciers are bulldozed- only evidence of the most recent glacier
Carbonate ooze (depth)
<4000m
2 types of info found from carbonate ooze:
- Species distribution of foraminifera reflects temperature and
nutrients - Shells lock isotopic (C & O) concentrations from water
of formation
Carbonate compensation depth
More carbonate can be dissolved in Atlantic ocean as CCD is deeper
Why is CCD deeper in Atlantic
Organic matter rains down and oxidised carbonates move down the water column and make the water more acidic
Atlantic cores
Faster sedimentation: more resolution
Assumptions made when tuning
- An orbital signal is present
- Time lag
- Which component of orbital change the
record responds to - Continuous and complete record
Issues with using magnetic susceptibility for global changes
Only useful for regional changes
The further you go back in time
The more difficult it is to use ice sheet models as your main measure
What is the relationship between obliquity and glaciation?
Higher obliquity tends to reduce glaciation, while lower obliquity tends to favour glacial growth, as it results in milder summer temperatures and more ice accumulation over time.
