Chapter 3 - Climate Archives Flashcards
What is the main type of climate archive?
Sedimentary debris deposited by water is the major climate archive on Earth for over 99% of geological time
Why is reconstruction of oceanic environments prior to 170 mya not possible?
As no seafloor older than this exists, due to continuous destruction via subduction. This means there is a lack of deep sea sedimentary records from this time period.
Why are plankton and pollen the most useful proxies?
wide spread (produced everywhere) and abundant In sediments. Thus relative abundance has a high degree of accuracy. Also tends to be a small number of species in different areas with defined climate preferences
What is the simplest kind of physical model?
1D column model which simulates a single vertical column of air, representing the average structure of the atmosphere. Provide info about effects of greenhouse gases, aerosols etc.
What has improved representation in climate models?
- Shrinking size of grid boxes improved coastal mapping and elevation
Increased computer power allows more aspects to be introduced e.g. soil moisture
Why does the importance of different climate archives change for different time scales?
For relatively recent history, oceanic sedimentary archives may be useful, however natural processes such as tectonic activity and erosion decrease their use and preservation as time passes. Prior to 170 mya, surviving sedentary records come from under the continents
Why are ocean sediments and ice cores especially important archives of climate?
Deep ocean sediments are important as they generally yield records of high quality. Ice cores are important as they contain many kinds of climate info, however are geographically limited. Also can be dated back extremely far (800,000 years in Antarctica)
How does the method of dating climate records vary with the type of archive?
- Radiometric dating and correlation: old sedimentary archives
- Radiocarbon dating: young sedimentary records
- Counting annual layers: tree rings, ice cores (dark/light layers), varve couplets, coral bands
- Correlation with orbital cycles: monsoon strength and ice sheets
- Internal chronometer: varves
How does the resolution from sedimentary archives vary with depositional environment?
Resolution depends on the amount of disturbance after deposition, and the rate of burial of the record.
- Best records come from low energy marine environments
- Productive coastal regions create disturbance through organisms burrowing etc.
- Deep ocean - increased pressure and loss of water caused by deep burial - high resolution
- In ice cores layering is lost below a certain depth
- High resolution where counting can be carried out
Which two major groups of organisms are most important to climate reconstructions over the past several million years?
Planktonic foraminifera (coccoliths), Diatoms and Radiolaria
Describe how the products derived from physical and chemical weathering provide different kinds of info about the climate system.
Physical:
- Ice rafted debris: eroded by ice sheets and delivered by icebergs to ocean
- Eolian sediments: lifted from continents and blown into ocean
- Fluvial sediments: microscope/geochemical analysis can give source
Chemical:
- Foraminifera shells: Chemical weathering allows for transportation of dissolved ions. Can track large scale fluxes of calcium, carbon etc over time. Also data in isotopes - record changes in global ice volume and ocean temp
Ice cores: data about gas concentrations in air trapped in ice. Proxies in ice cores include dust, snow thickness and isotopes
Describe 2 ways the performance of climate models is evaluated
Outputs can be tested against independent geologic data.
Output compared with regional instrumental measurements of temp, pressure etc. averaged out over the last several decades
Why aren’t models of the atmosphere and ocean allowed to interact continuously?
This is because the ocean and atmosphere continuously exchange heat, water vapour etc. allows continuous interaction would force the system to make short term calculations through the entire system. Back and forth allows for faster overall progression
Also air and water respond to heat at different rates due to heat capacity - overcome by asynchronous coupling
Describe two features that make the ocean most useful in geochemical mass balance models
The ocean receives almost all erosional products from the continents, interacts with all other reservoirs and eventually deposits tracers in well preserved sedimentary archives
