creating an orbitally tuned chronology. overview
TRANSCRIPT
Creating an Orbitally Tuned Chronology
Overview
Geomorphological evidence of past
glaciations - orbital changes
suspectedLouis Agassiz- first
proposed past ice age
Joseph Adhemar- first to suggest precession control
James Croll- linked reduced winter sunlight to increased
snow accumulation
A Brief History of Orbital Theory
“This is the work of Ice!”1837
Developed theory and predicted multiple
glaciations
A Brief History of Orbital TheoryMilutin Milankovitch
- First hypothesized that summer
insolation at 65oN as most important
control on ice sheets
- Detailed calculations of insolation
Orbital Cycles
Precession and Eccentricity
Eccentricity Only orbital cycle to change
the total insolation
PrecessionEffect of precession depends
on ellipticity of orbit
i.e. Eccentricity modulates precession
Precession has greatest influence at low latitudes
Anti-phased across hemispheres
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 hemispheres
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
Climate Proxy & Continuous Record
Emiliani 1955- Pleistocene temperatures
C14 dating in foraminiferaU234 - Th230 dating coral reefs
Ar40 - Ar39 dating palaeomagnetic reversals
Absolute Age Dating Techniques
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 18OMagnetic
Susceptibility
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
Simple Ice Sheet Model
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
LR04
Site 1267
Alignment to the LR04 Stack
The early Pliocene problem
•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
Conclusions