Sea Level Lecture 5- Reconstructing sea-level change Flashcards

1
Q

What are potential issues with instrumental records?

A

Biased both spatially and temporally
Only a very limited snapshot of behaviour

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2
Q

Are instrumental records most precise and accurate?

A

Yes

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3
Q

What are challenges with reconstructing sea-level change?

A

Consistent framework is needed
- Very few sea-level indicators occur exactly at mean tide level
- Need to understand modern distribution with respect to tidal levels
- Concept known as the ‘indicative meaning’

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4
Q

Can we only reconstruct relative sea level?

A

Yes

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5
Q

How can we work out RSL in terms of reconstruction?

A

RSL = sample elevation - RWL
Sample elevation - sampling error as never know the core top and depth perfectly
RWL- indicator error as sea-level indicators form over a range of elevations not just at one (indicative range)

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6
Q

What information is needed to reconstruct sea level change?

A

Age
Location
Elevation (height of where sample found today and relationship of the indicator to a tidal level - indicative meaning)
Tendency of change and abruptness of change can be useful

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7
Q

What is a sea level proxy called and what must it have?

A

Sea-level indicator
Must have a systematic and quantifiable relationship to tides

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8
Q

What are the 4 types of sea-level indicators?

A

Physical
Biological
Archaeological
Geochemical

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9
Q

What is an example of a raised shoreline?

A

Forth valley

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10
Q

Discuss the surveying of palaeoshorelines?

A

In the field, relict shorelines are surveyed along their entire length to establish altitude (mOD) and also gradient

The gradient and orientation of the shoreline relates to the amount of isostatic uplift that has occurred

The features can then be plotted and correlated with other similar features

The age can then be established using radiocarbon or luminescence methods

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11
Q

What is an example of a physical sea level indicator?

A

Surveying of palaeoshorelines

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12
Q

What is an example of a biological sea level indicator?

A

Sedimentary evidence

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13
Q

Discuss sedimentary evidence.

A

Undertake detailed stratigraphic analyses using coring methods

Survey and map the area

Collect samples and undertake detailed analysis in the laboratory

Often uses microfossils

Typically dated using radiocarbon or other isotopic methods

Corals can be used

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14
Q

Discuss geochemical indicators

A

Bulk sediment ->
Sediment fraction ->
Compund specific

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15
Q

What are the three main groups of archaeological dating methods?

A

Age estimation techniques
Age equivalent techniques
Relative chronology

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16
Q

Discuss age estimation techniques.

A

Radiometric methods - based on rate of decay such as radiocarbon dating, uranium series dating
Incremental methods based on growth of an organism such as varves or dendrochronology

17
Q

Discuss age equivalent techniques

A

Dates extended to similar distinctive horizons elsewhere such as pollution, tephra and stratigraphy

18
Q

Discuss relative chronology.

A

Chemical reactions of weathering and organic decomposition that are time dependent
Relative dates estimated from the state of rock/sediment diagenesis

19
Q

What is radiocarbon (14C) dating?

A

Developed by Libby (1949)
Least common of three isotopes - 12C, 13C and 14C
Half life of 5730 years
Used to date very recent events

20
Q

What is the 14C principle?

A

Organisms take up 14C while they are alive, in a known proportion to other isotopes

When organism dies 14C is lost through radioactive decay

Time since death can be determined by 14C content

21
Q

What can 14C be used to date?

A

Can be used to date wood, charcoal, bones, shells and pottery

Oldest dates around 50000 years

Calibration required as rate of production hasn’t been constant

Ages relative to 1950 AD

22
Q

What are sources of error in 14C dating?

A

Problems of sample selection and contamination

Young carbon effects

Old carbon effects

Variation in 14C content in the ocean reservoir

Fractionation effects

Radiocarbon plateau

23
Q

What are the principles of luminescence dating?

A

Light emitted from a mineral crystal (usually quarts or feldspars) when exposed to heat or light

The light emitted is related to the amount of ionizing radiation that the sample has been exposed to from sediment

The clock is set to zero by heating or optical bleaching

Wind and water transported sediments are good for luminescence dating

24
Q

What are continuous cores?

A

Geologic tide gauges

25
Q

What can RSL reconstructions be used to understand?

A

A wide array of processes including changes due to climate and GIA.