Lectures 2-3 - Uplift: What does it mean?

Question 1

What is the Moho?

Answer 1

The discontinuity between the crust and the mantle (seismic wave increases velocity). A chemical discontinuity.

Question 2

At what temperature is the separation between the lithosphere and the asthenosphere?

Answer 2

1200 degrees celsius

Question 3

What is the difference between relative sea level change and eustatic sea level change?

Answer 3

Relative sea level change - the sea appears to have moved up or down but may be the land Eustatic sea level change - the volume of water in the ocean changes

Question 4

What is eustatic sea level change?

Answer 4

Changing the total mass of the ocean. E.g. melting of ice on land and the melt water runs off into the ocean

Question 5

What is steric sea level change?

Answer 5

Changing the density of the ocean. E.g. heating up the seawater, warm water takes up more volume

Question 6

What global change dictates eustatic sea level change?

Answer 6

More ice on land = lower sea level: - Global warming and loss of ice sheets and land glaciers (over decades to centuries) - Glacial cycles (100k years)

Question 7

How are corals used for palaeo-sea reconstruction?

Answer 7

Question 8

Why is seawater higher during steric sea level change?

Answer 8

Warmer ocean = Higher sea level:

• Heating up the ocean makes the seawater less dense and it expands to take up more volume

Question 9

What three factors can influence the shape of ocean basins?

Answer 9

1. Relative sea level change:
   - A change in local sea level with respect to a land reference point, e.g. land uplift
2. Changes in plate tectonics:
   - Changing thickness of ocean crust and sediments
   - Changing land crust and distribution

> Up to a few hundred metres of sea level change (>10 million years)

3. Local tectonic effect
   - Land uplift => lower relative sea level
   - Land sinking => Higher relative sea level

Question 10

What happens effect does slow mid-ocean ridge spreading have?

Answer 10

Oceanic crust cools and contracts

Question 11

What effect does fast mid-ocean ridge spreading have on sea level?

Answer 11

Rises as sea water displaced onto continental shelves.

More hot buoyant oceanic crust occupies more space in the ocean basin

E.g. Upper Cretaceous (90 Mya) MSL > 300m

Question 12

Summarise the spatial-temporal scale of processes contributing to mean sea level

Answer 12

Question 13

What process complicates the study of mean sea level?

Answer 13

Post glacial isostatic rebound. Scandanavia and Scotland are still bouncing back up from glaciers that melted 10,000 years ago.

Question 14

How is post isostatic rebound measured in the British Isles?

Answer 14

(Shennan et al., 2006)

British isostatical rebound is very variable. Equation to work out is

Question 15

Describe three ways that we can find relative sea level from the past

Answer 15

1. We can look for beach sediments, record their present elevation and date them (usually ¹⁴C in organic material within the sediments)
2. We can look for constructive marine terraces (corals) and date them (U-Th series)
3. We can date the destructive marine terraces IF they have not been buried subsequently (cosmogenic isotopes)

Question 16

What are the three components used in the modelling of the Glacial Isostatic Adjustment (GIA)?

Answer 16

• An Earth model to simulate the isostatic processes
• A model of ice thickness and distribution in the Late Quaternary
• A model to compute the distribution of ocean relatively to land-masses