Sea level

Question 1

Ways to reconstruct sea level changes e.g. ancient coastlines

Answer 1

Corals - utilises the fact that coral reefs adjust due to changing sea level

Question 2

Factors controlling sea level change

Answer 2

• Tectonic movements ( local scale)
• Temperature cycles
• Global warming
• Glacial melt

Question 3

Consequences on ocean of waxing and waning of the continental ice masses

Answer 3

A lot of O16 was extracted from the ocean and stored in ice leading to higher oxygen isotopes in ocean waters and lower sea level

Question 4

What processes impact global sea level?

Answer 4

• Amount of ice on the continent
• Temperature of seawater
• Seafloor spreading rates (shape of the ocean basins )
• Amount of continental margin (mega-continent or lots of continental fragments
• On a local level additional effects like regional tectonic movement may play a role

Question 5

Impact of sea level on climate

Answer 5

Change of albedo when sea level covers or exposes continental shelves
- With LESS continental shelf exposed, MORE sunlight is absorbed- by the surface of the earth. E.g. HIGH sea level absorbs more sun light (warmer)

Question 6

Sea floor spreading rate

Answer 6

Faster sea floor spreading rate= a hotter crust and a more elevates mid ocean ridge- continues elevated even on the ridge flanks.

Question 7

Slower sea floor spreading=

Answer 7

Less elevated crust and a lower sea level

Question 8

Continental margins

Answer 8

Have a lot of volume and displace large amounts of seawater

Question 9

Most promising result for reconstructing sea level changes

Answer 9

Corals

Question 10

Why can we use corals to reconstruct sea level change?

Answer 10

Some coral species only occur in a very narrow depth interval in the ocean- coral reefs adjust to changing sea levels

Question 11

Acropora Palmata

Answer 11

Only survived within top 5m of ocean

Question 12

Isostatic Pressure

Answer 12

The Earth’s crust responds to the weight above it by exerting an equalizing pressure (isostatic pressure) in all directions, helping to maintain balance between continents and the ocean floor

Question 13

Hudson Bay- isostatic rebound

Answer 13

Needs to rebound 150m to compensate for pressure applied by ice sheets

Question 14

Weight applied to the crust:

Answer 14

Dispersed throughout the lithosphere

Question 15

Consequence of the lithosphere being ridgid

Answer 15

Weight is transferred across the crust resulting in a peripheral depression and a forebulge

Question 16

Extent of depression beyond ice margin 150-180km

Answer 16

Can record relative sea level change

Question 17

Lateral displacement of mantle material from below the center of the ice sheet loading:

Answer 17

Results in the formation of an area of slight uplift (10-20m) beyond the peripheral depression (forebulge)

Question 18

Isostatic rebound in Scotland

Answer 18

• Emergence at a modest rate
• Outpaced by sea level rise

Question 19

Processes impacting global sea level:

Answer 19

• Amount of ice on the continent
• Temp of seawater
• Sea floor spreading rate (shape of basin)
• Amount of continental margin (mega-continent or lots of continental fragments)
• Regional tectonic movement may play a role

Question 20

Estimates of sea level further back in time

Answer 20

Suffer from a growing uncertainty

Question 21

Sea water albedo

Answer 21

0.06

Question 22

Soil Albedo

Answer 22

0.25

Question 23

Sand albedo

Answer 23

0.40

Question 24

Less continental shelf exposed=

Answer 24

MORE sunlight absorbed- by the surface of the earth

Question 25

Faster sea floor spreading

Answer 25

Produces a hotter crust and a more elevates mid ocean ridge

Question 26

Slower sea floor spreading

Answer 26

Produces less elevates crust and a lower sea level

Question 27

Continental margins ...

Answer 27

have a large volume and displace large amounts of seawater

Question 28

Lots of continental fragments

Answer 28

= lots of margins therefore sea level=high

Question 29

Effect of the break up of Pangea on global sea level?

Answer 29

High sea level flooded MOST continental interiors

Question 30

Oceanic plateaus (large igneous provinces)

Answer 30

Can be very big and displace large volumes of water

Question 31

Factors contributing to sea level fall in the last 80 million years

Answer 31

- Decrease in ocean ridge volume - Collision of India and Asia - Decrease in volcanic plateau volume - Water stored in ice sheets -Thermal contraction of seawater

Question 32

The Messinian Event

Answer 32

The Mediterranean Sea dried up due to continental movement

Question 33

Why did the Messinian event occur?

Answer 33

5.9 mya Water exchange with the Atlantic Ocean via the Strait of Gibraltar was interrupted

Question 34

Evidence for the Messinian event

Answer 34

Evaporite minerals, soils and fossil plants

Question 35

2 scenarios used to explain the salinity crisis

Answer 35

- Uplift Model - Drying- out model

Question 36

Uplift Model

Answer 36

1. Large-scale regional uplift 2. Draining of the basin into the Atlantic Ocean 3. Large-scale regional sinking of crust

Question 37

Drying Out Model

Answer 37

1. Small-scale local uplift and evaporation 2. Drying out of basin 3. Small-scale local sinking of sill