IMS W7 Paleo-oceanography

Question 1

Paleo oceanography

Answer 1

Generating reconstructions of the past for temperature, climate and ecosystems.

Question 2

3 main ingredients paleo

Answer 2

Archives
Timescales
Proxies
(Locations)

Question 3

Types of archives (7)

Answer 3

Historical archives
Lake sediments
Coral reefs
Continental coastal sediments
Ocean sediments (very slow accumulation)
Ice cores
Phenological observations

Question 4

Why look at ice?

Answer 4

The bubbles in the ice can tell something about the atmosphere.

Question 5

Proxy

Answer 5

Approximation of the conditions in the past with indirect indicators.
- Fossil remains –> adapted to environmental conditions
- Chemical compositions

Question 6

Taking sediment steps

Answer 6

1. Sample the marine sedimentary archive
2. Determine time in sediments
3. Extract information using proxies
4. Interpret data
5. Correlation
6. Generalization

Question 7

Which archive?

Answer 7

Core repository: all deep ocean sediment cores ever recovered.
Marine archive: last 100 years (coastal marine sediments)

Question 8

Where to drill?

Answer 8

Look at location: type of sediment
Timescale: how quickly does sedimentation take place
Which scientists: for every type of sediment at least one

Question 9

Sediment thickness

Answer 9

Neritic sediments:
- Rivers: 800-1000cm/1000 yr
- Bays: 500 cm/1000 yr
- Shelf: 40cm/1000 yr
Pelagic sediments:
- 0.1-1 cm /1000 yr

Question 10

Biases sediment

Answer 10

sediment erosion, deposition, bioturbation, bio irrigation

Question 11

How to determine time of sediment cores?

Answer 11

Radioactive dating (up to mlns yrs)
Magneto stratigraphy (up to mlns yrs)
Tephrochronology (up to 10,000s yrs)
Biostratigraphy (100 mlns yrs)
Chemostratigraphy (up to blns yrs)
Cyclostratigraphy (up to mlns yrs)

Question 12

Isotope

Answer 12

atoms of the same chemical element that contain equal number of protons but different numbers of neutrons in their nuclei. Hence they differ in relative atomic mass but not in chemical properties.

Question 13

Radioactive dating

Answer 13

Looking at the decay of radioactive isotopes. Looking at halftimes. Problems: contamination, reservoir, unable to look further than 10 half times.

Question 14

Problems radioactive dating

Answer 14

• Contamination
• 14C variations in the ocean reservoir
• Different species in different habitats
• Reworking (bioturbation)
• Diagenesis (skeleton is coated with younger CaCO3/biochemical alterations)

Question 15

Magneto stratigraphy

Answer 15

Susceptibility reversal: looking at the polarisation of the earth.

Question 16

Tephrochronology

Answer 16

Looking at volcanic eruptions and the ashes.

Question 17

Biostratigraphy

Answer 17

looking at micro fossils –> great visualization of the K-T layer.

Question 18

Chemo stratigraphy

Answer 18

Looking at stable isotopes: Oxygen (16 and 18) and Carbon (12 and 13). Shows changes in temperature and ice formalization in time.

Question 19

Shifting to heavier oxygen isotopes

Answer 19

glacier time: the lighter isotope oxygen-16 tends to be incorporated in the ice sheets leaving oxygen-18 in the sediments.

Question 20

Shifting to lighter oxygen isotopes

Answer 20

change in sea level as the ice melts. The oxygen-16 is released. Signature becomes lighter.

Question 21

Carbon isotope

Answer 21

Tells something about the source of carbon and environmental conditions. Plants like to take up C12 as it is lighter. When they take up C13 it could potentially mean an increase in primary productivity.

Question 22

Cyclostratigraphy

Answer 22

Looking at the solar radiation on a location of the earth as it changes through time.

Question 23

Ideal proxy

Answer 23

dependence on only one environmental parameter.

Question 24

Thing to consider with proxy

Answer 24

Applicability for past times
Range of estimates, error limits
Modification with time

Taphonomic issues: process leading to fossilization
Preservation and alteration issues: transport, bringin in invasive species/molecules

Question 25

Type of proxies

Answer 25

• Biological
• Inorganic geochemical proxies
• Organic geochemical proxies

Question 26

Biological proxies

Answer 26

Microfossils:
- Ostracods (origin of the water)
- Foraminifers (seafloor oxygen and productivity)
- Dinoflagellates and their cysts (sea surface productivity)
- Diatoms (sea ice)

Question 27

Why microfossils as proxies

Answer 27

• high densities
• cosmopolitan occurrences
• high preservation potential
• highly diverse
• occur over long timescales

Question 28

Inorganic geochemical proxies

Answer 28

• Oxygen isotopes on foraminifer shells (temperature and latitudinal variation)
• Carbon isotopes (productivity and water age)
• Magnesium calcium ratio

Question 29

Organic geochemical proxies

Answer 29

Biomarkers for temperature
UK 37: unsaturated ketones on coccolithophores.
TEX (tetra ether index) 86: carbon items in lipids of thaumarchaeota