Creating an Orbitally Tuned
Chronology
Overview
A Brief History of Orbital Theory
Geomorphological
evidence of past
glaciations - orbital
changes suspected
Louis Agassiz- first proposed
past ice age
“This is the work of Ice!”
1837
Joseph Adhemar- first to
suggest precession control
James Croll- linked reduced
winter sunlight to increased
snow accumulation
Developed theory and
predicted multiple glaciations
A Brief History of Orbital Theory
Milutin Milankovitch
- First hypothesized that summer
insolation at 65oN as most important
control on ice sheets
- Detailed calculations of insolation
Orbital Cycles
Precession and Eccentricity
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Eccentricity
Only orbital cycle to
change the total
insolation
Precession
Effect of precession
depends on ellipticity of
orbit
Precession has greatest influence at low
latitudes
Anti-phased across hemispheres
i.e. Eccentricity
modulates precession
Obliquity
Obliquity has greatest influence at high
latitudes
In phase across hemispheres
Incoming Solar Radiation - Insolation
Obliquity
- Largest effect at high
latitudes
- In phase across
Precession
- Largest effect at low latitudes
- Anti-phased across
hemispheres
Orbital Signal in Climate Records
Signal vs
Noise
Signal
- original forcing recorded in
proxy record
Noise
- distortion of signal
- additional signal not related
to orbital forcing
orbital forcing - climate
response
Understanding of how climate works
Tool for creating chronologies
Ingredients for understanding
orbital climate change
• Proxy of climate change
• Continuous record
• Absolute age dating technique
Emiliani 1955- Pleistocene
temperatures
Climate Proxy & Continuous Record
Absolute Age Dating Techniques
C14 dating in foraminifera
U234 - Th230 dating coral reefs
Ar40 - Ar39 dating palaeomagnetic reversals
Hays, Imbrie & Shackleton, 1976
Continuous climate proxy records
Independent chronology
Hays, Imbrie & Shackleton, 1976
Spectral analysis shows significant
peaks at orbital frequencies
Shackleton et al., 1990
Placed Brunhes-Matuyama magnetic
reversal 5-7% older than accepted
radiometric dates
Ingredients for creating an
orbitally tuned chronology
• Assumptions
• Tuning target
• Tuning parameter
Assumptions
• Orbital signal is present
• Time lag
• Nature of orbital forcing - climate
response
• Continuous and complete record
Tuning Target
Tuning Parameter
Sapropels
d18O
Magnetic
Susceptibility
Simple Ice Sheet Model
y = ice volume
t = time
b = nonlinearity
coefficient
Tm = time lag
x = forcing
Simple Ice Sheet Model
y = ice volume
t = time
b = nonlinearity
coefficient
Tm = time lag
x = forcing
Lisiecki & Raymo 2005 - LR04 Stack
Combined 57 d18O records to make “global” record
Lisiecki & Raymo 2005 - LR04 Stack
Distribution and number of records vary through time
Lisiecki & Raymo 2005 - LR04 Stack
Lisiecki & Raymo 2005 - LR04 Stack
Alignment to the LR04 Stack
Alignment to the LR04 Stack
LR04
Site 1267
The early Pliocene problem
Conclusions
• Characteristics of orbital cycles
• Ingredients needed to understand
orbital scale climate change
• Importance of chronology & stratigraphy
• How to use our understanding of orbital
climate change to create age models