Cycles Flashcards
What is dendrochronology?
the study of tree rings to date past events and areas
What do tree rings represent?
Annual growth/ seasons/ growth conditions
How ill tree rings reflect the seasons?
Less dense in summer due to better growth conditions
Dense in winter with worse conditions
How long can trees be used to date?
~14,000 years
What do ice cores record?
CO2 and temperature
What is the length of glacial seasons?
~100,000 years
What was the climate 20,000 years ago in europe?
Glacial
How do ice cores represent time?
Will creating banding of snow layers which trap gas bubbles of that atmosphere at that time
How far back can ice cores be used to date?
~1 million years
What can be seen with in the Mediterranean rock record which shows cycles?
Prominent rhythmic alterations in rock type in marine and lake sediments
What does the presence of high frequency switches of sediment colour and bundling show?
Multiple cycles occurring at once
Why are lakes and river sediments less likely to show signs of cycles?
Lakes affected by uplift and tectonics
Rivers are highly dynamic
What other type of core can cycles be seen in?
Marine cores
What did Luis Agassiz propose?
extinction of the Pleistocene megafauna was due to widespread and deep “winter”
What gave evidence in glacial environments that glaciers had once been larger?
Erratic’s and moraines being seen at higher elevations
What did the realisation of greater glacial extent provide a new explanation for?
Erratic’s and other glacial features across N. Europe and N. America
Who was Milutin Milankovitch?
A Serbian engineer and meteorologist who worked on a mathematical theory of climate
What did Milankovitch calculate?
Seasonal variations in the amount of solar radiation received by the Earth were dependent on variations in the Earth’s orbit
What did Milankovitch propose?
summer insolation (solar radiation) at high northern latitudes was critical in melting ice from the previous winter
What feedback was produced by Milankovitch based on his summer insolation theory?
Cooler summers
Less ice melt
Year-on-year build up of ice
Glacial advance
What was the initial focus of the orbital theory?
Explain why periodic glaciations occurred
What criticism was there about the orbital theory?
George Simpson reported large summer and large winter temperature changes, but concluded that these extremes cancelled in the annual average
What 3 things did Milankovitch proposed dominated the amount of solar radiation at earths surface was dominated by?
Eccentricity
Obliquity
Precession
What is the cycle length of eccentricity?
100 and 400 thousand years
What is the cycle length of obliquity?
41,000 years
What is the cycle length of precession?
23,000 years
What marine records show that proves Milankovitch’s theory?
Marine records show glacial and interglacial cycles which show his cycle periods
What are Earths orbital variations caused by?
Mutual gravitational interactions between the sun, planets and satellites
What can be done to see how the orbital cycles would have been affected in the past?(Laskar solutions)
Can be back calculated using supercomputer to show relative positions of planets in the past useful to around 55 Mya
What is the range for obliquity?
21.5 to 24.5
What are perihelion and apehelion?
Perihelion point on earths orbit closest to the sun
Apehelion point of earths rotation furthest from the sun
What are the relative distances of perihelion and apehelion?
A = 158 million km
P = 153 million km
What is an equinox?
Point where day and night are equal
How many equinoxes are there?
2 (~20 March / 22 September)
What are the solstices?
When sun appears to reach highest (summer) / lowest (winter) point (& longest / shortest days)
What does eccentricity relate to?
The shape of earths orbit being roughly elliptical
When is the NH closest to the sun?
In winter (milder winter)
What does low eccentricity cause?
More variability in seasonal cycles
What does obliquity relate to?
The tilt of earths axis
What does a tilted axis give earth?
Seasons as no tilt there would be equal conditions or 90* tilt = extreme seasons)
What is precession?
The wobble of earth on its axis
What can precession alter?
The position of perihelion
What are the complex dynamics of identifying orbital variation?
They act in unison to determine insolation and seasonality
How can oscillation’s be presented in the frequency domain? (with example)
As spectra as 1/Period (frequency) so 20,000 yrs = 0.00005 years
What will a perfect oscillation of orbital data be like?
infinite duration will give a spectrum peak that
is infinitely narrow at the central frequency
How will signals with a finite strength be presented?
Smeared out spectrum
What does power relate to with orbital cycles in data?
coherence and strength of cycles at given frequency
