EAE 14 - Other climate proxies Flashcards
Dendroclimatology
What is Dendroclimatology?
Using tree rings to reconstruct climate
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Dendroclimatology
Why is Dendroclimatology useful?
3 points.
- Understand recent and ongoing changes
- Put change into pre-industrial context
- Help model the future
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Dendroclimatology
Why are Dendroclimatology’s benefits?
4 points.
- Annual (even seasonal) resolution
- Absolute dating to calendar year
- Long record relative to instrumental data
- Widespread
EAE 17ac
Dendroclimatology
What are the approaches for dendroclimatology?
4 points.
Tree corer:
- fast, portable and nondestructive tool
- Samples living and dead trees
Full discs
- Helpful for dead wood
- Sampling needs licenses / approvals from authorities
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Dendroclimatology
How are vessels distributed in wood?
Ring porous: The diameter of the pores in early wood is muh larger than latewood
Semi ring porous: The pores are more numerous in earlywood
Diffuse porous: The size of pores and distribution is more regular
EAE 17ae
Dendroclimatology
What is Ecological Amplitude?
2 points.
- A tree species will be more sensitive to changes in environmental conditions at the margins of its ecological distribution
- Includes: Latitude, longitude, elevation, topographical position
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Dendroclimatology
What are the climatic constrains to plant growth?
3 points.
- Temperature
- Radiation
- Water
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Describe
Important principle in dendrochronology: Replication
3 points.
- Reduce variability in measurements within a single tree and between trees
- Maximise environmental signal and reduce error
- Usually want >30 samples per site
The growth of each ring in each tree is influenced by its immediate surroundings (e.g. trees nearby, moisture sources, soil structure), its individual genetics/biology, the specific impacts on the tree during its life (e.g. damage/fire/insect attack/canopy openings, called “releases”), as well as the broader climate. As dendroclimatologists, we are usually interested in extracting the climate signal only.
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Dendroclimatology
What is Cross-dating?
4 points.
Matching ring width patterns among cores
Various sources of samples:
- Recently alive trees
- Trees felled for lumber (may be 100’s of years old)
- Long dead timber
- Burried timber (or drowned in the construction of a dam)
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Dendroclimatology
What is detrending?
Identifying and removing the age trend
Young trees grow faster than old trees.
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Dendroclimatology
What other factors can be examined in Dendroclimatology?
3 points.
- (Quantitative) wood anatomy
- Stable isotope composition
- Wood density
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Dendroclimatology
What proxies do we measure in corals?
3 points.
- Oxygen isotopes (δ¹⁸O)
- Trace elements
- Luminescence
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Coral dating
What do oxygen isotopes reveal?
2 points.
- Proxy for ocean temperature
- Influenced also by precipitation
EAE 17am
Coral dating
What do trace elements reveal?
4 points.
- Geochemical proxies for Temperature/Salinity/Precipitation
- Sr/Ca widely used as an excellent proxy for sea surface temperature (SST)
- Mn/Ca and Ba/Ca also used occasionally as a proxy for precipitation
- Sub-annual resolution and annual cycles in geochemical tracers if measured at high enough resolution!
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Coral dating
What does luminescence reveal?
Proxy for precipitation/runoff/flood due to incorporation of soil-derived humic acids transported to the reef during major flood events
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Coral dating
How is luminescence investigated?
By scan under UV/visible light
Luminescence intensity or ratios of luminescence in colour bands
Provides very high resolution!
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What is a reconstruction?
Approach to and result of “piecing together” or building a picture of the past temporal and spatial characteristics of a climate variable from one or more predictors
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What can we can reconstruct?
7 points.
- Past temperature
- Precipitation
- Vegetation
- Streamflow
- Sea surface temperature
- Climate “modes”
- Other climatic or climate-dependent conditions.
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What is the New Global Temperature Reconstruction?
4 points.
- New database
- Multiple methods
- Same input data
- Strong agreement between methods esp. at multidecadal frequencies
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What are Diatoms?
Diatoms are unicellular microscopic algae (Bacillariophyta) which have been widely used to reconstruct depositional environments throughout the Quaternary and Holocene
(Vos & de Wolf, 1993; Lowe & Walker, 1997; Zong & Horton, 1999).
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Why is diatom analysis useful?
2 points.
- Diatom analysis facilitates the reconstruction of the water conditions in which the sediment was derived (freshwater, brackish water, marine water or a mix).
- Such interpretations can be achieved because individual species are sensitive to ecological conditions such as salinity, trophic status and pH and can consequently only survive within certain thresholds of each environmental parameter.
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How are diatoms preserved?
2 points.
- Diatom preservation is good in most sediments due to the siliceous composition of the diatom frustule.
- They are found in most water-lain deposits, but preserved in abundance in finer sediments such as silts and clays which experience much lower-energy depositional environments (and thus favour frustule accumulation with minimal fragmentation).
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What assumptions are made in diatom analysis?
Analysis of present day species provides the means by which environmental characteristics are identified for the fossil diatom frustules within sediments.
It is assumed that diatoms employ uniformitarian principles; species present in today’s subaquatic environments require the same conditions (such as salinity, temperature and nutrient supply) as in the past.
In marine contexts, attempts to infer specific depositional environments from diatom assemblages (e.g. saltmarsh environments around/above Mean High Water, non-tidal lagoons).
EAE 17aw
How can pollen be used as a proxy?
5 points.
- Transportation takes pace through a number of mechanisms (wind, insect etc.).
- Different plants produce differing amounts of pollen to ensure successful pollination.
- The results of these factors mean that much more pollen is produced and released than is actively used in reproduction.
- Much of this falls to the ground and becomes preserved within sedimentary deposits.
- It is therefore possible to use the pollen preserved within sedimentary archives to understand the type of vegetation that existed at that location in the past.
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What are the problem with using pollen as a proxy?
3 points.
Concerns re is the pollen diagram a reliable, accurate and quantifiable reconstruction of the vegetation community that was present in the past?
Issues such as:
- variations in pollen production
- distribution mechanisms
- post depositional preservation
must be taken into account
Consequently such palaeoenvironmental / palaeoecological interpretations must be undertaken with caution.
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What are plankton?
Diatoms that float through the upper part of the water column
Term comes from Greek work planktos = wanderer, drifter
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What are benthos?
Diatoms that live on or in substrates.
Benthos are classified into different types according to the substrate to which they are attached.
Can live to depths limited primarily by light penetration.
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Where are diatom particularly important.
Especially important in oceans where they are estimated to contribute up to 45% of the total oceanic primary production.
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What are the 2 main types of diatoms?
CENTRIC - those that are circular with essentially radial symmetry PENNATE - those that are more elongate, with primarily bilateral symmetry.
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How are Diatoms contained?
3 points.
Diatom cells are contained within a unique silicate cell wall (SiO₄) comprised of two separate valves.
The cell wall is distinctive
- provides rigidity
- provides taxonomic characters
- allows preservation in sediments
EAE 17bd
Why are lakes important in studying climate change?
Lakes are important sentinels of climate change
pH is an indicator of humidity
Runoff and weathering
Atmospheric deposition
Organic acids by vegetation
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What are ‘Transfer functions’?
aka inference models
Quantitative Inference Model based on modern material
Widely available to infer past environmental conditions from biostratigraphic indicators from sediments
Collected at a range of locations with different conditions
CORRELATION! Not experiment based
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How is pollen represented in ‘diagrams’ vs Vegetation?
5 points.
- Both production & dispersal of polen is very variable
- Site representation depens on size & nature of sampling locality
- The importance of genera on a ‘diagram’ is complex & difficult to quantify
- Many local factors are relevant
- Some generalizations are possible.
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How is radiocarbon dating useful?
- Radiocarbon is widely used in palaeoecological records.
- Can date material back to about 50,000 years ago
- ¹⁴C formed by bombardment of ¹⁴N by cosmic rays and then like stable ¹²C forms CO₂ that is incorporated into living organisms.
- After death ¹⁴C decays to ¹⁴N and ratio of ¹²C to ¹⁴C determines the age of the fossil material assuming a s a balance between ¹⁴C production and decay.
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