sea level changes

Question 1

what is relative mean sea level?

Answer 1

• Relative mean sea level: average vale of sea level measures every hour over a period of at least one year.

Question 2

what is Geoid?

Answer 2

Geoid: shape of the surface of equal gravitational potential around the earth. Shape of mean sea level in absence of winds, currents, tide variations in water density and atmospheric pressure.

Question 3

what is the shape of mean sea level?

Answer 3

The shape of mean sea level with all dynamic effects removed. The radius at the equator is larger than at the poles due to long term effects of the earths rotation. there is topography- mountains have more mass than valleys, so the pull of gravity is regionally stronger near mountains.

Question 4

what is a bench mark?

Answer 4

• Bench mark: reference land level for tide gauge

Question 5

what is isostatic?

Answer 5

• Isostatic: change in level of land/crust, due to changing load

Question 6

what is eustatic?

Answer 6

• Eustatic: change in ocean level (global) due to the change in the volume of water of change in the configuration/ age of the ocean basins.

Question 7

what is steric?

Answer 7

• Steric: change in volume mass of water relative to a volume of standard salinity and temperature (change in water volume due to changes in temperature or salinity)

Question 8

what are 2 methods of measuring sea level?

Answer 8

• Tide gauge: machine that measures the sea level.

* Satellite: radar measurement of sea surface height

Question 9

what have the most potential of sea level rise and why?

Answer 9

Have the most potential for rapid sea level rise. Water depth equivalent of main ice caps. BUT, not just as simple as glacial ice meltwater causing sea level rise- you need to take unto account loading by ice.

Question 10

what is buoyancy and isostasy?

Answer 10

Buoyancy and isostasy: floating solids displace water equal to their mass. As icebergs “sink”, until the mass of the water it displaces is equal to the total mass of the iceberg. This is isostasy, and applies to lithospheric plates. The continental flats higher, the oceanic sinks lower.

Question 11

how thick is the continental lithosphere?

Answer 11

The continental lithosphere is 150 km thick. Granitic crust. Lighter and floats higher.

Question 12

how thick is the oceanic lithosphere?

Answer 12

The oceanic lithosphere 7-100 km thick made of basaltic crust, which is heavier and less buoyant, and hence sinks lower.

Question 13

what is glacial isostacy?

Answer 13

Glacial isostasy: isostatic equilibrium. Loading by ice sheet destroys equilibrium so mantle moves to restore the equilibrium. Ice sheet melts and destroys the equilibrium, so the mantle moves to restore the equilibrium

Question 14

what happens on deglaciation?

Answer 14

On deglaciation: crustal rebound on melting of ice- results in isostatic sea level changes- lowering in sea level. Post-glacial isostatic rebound will continue for another 10,000 years. Causes raised beaches and still affects Europe.

Question 15

what is the most direct methods for determining the age of fossil corals?

Answer 15

Most direct method: determining of age and altitude/depth of fossil corals:
• Measure altitude of fossil coral relative to modern sea level
• Measure U/Th and or age of coral
• Compensate for uplift/subsidence since coral was formed.

Question 16

what is the estimated post-glacial sea level rise?

Answer 16

Estimated post-glacial sea level rise: includes rapid pulses due to ice sheet instability or collapse.

Question 17

what is sea level change liked to?

Answer 17

• Sea level change: sedimentary deposition is strongly linked to sea level.

Question 18

what is transgression?

Answer 18

• Transgression: flooding due to sea level rose. Sediment belts shift landwards, strata deepen upwards.

Question 19

how does sea level regression change?

Answer 19

Sea level changes: regression- exposure due to sea level fall. Depositional belts shift seaward, strata “shallow upwards”

Question 20

what is regression tied to?

Answer 20

• Regression tied to erosion, less likely to be preserved.

Question 21

what does regression include?

Answer 21

• Includes “seismic stratigraphy” and sequence stratigraphy”.

Question 22

how do we find evidence of subduction?

Answer 22

• Look for evidence in the plate tectonics, break up of Pangea supercontinent. Deep subducting oceanic crust replaced by a shallower spreading ridges.

Question 23

what causes the major high strands?

Answer 23

• What causes the major high strands? Spreading rates also important. So increase in spreading rates would lead to sea level rise- transgression.

Question 24

what are the changes in total volume of ocean water? (6)

Answer 24

1. Volume of hydrosphere: is negligible.
   
   2. Changes in the volume of land ice: big effects,
   3. Desiccation of ocean basins and marginal seas: rare and small
   4. Change in mean oceanic temperature: negligible
   5. Variation in atmospheric moisture content : negligible
   6. Increased water storage on land: small

Question 25

what are the changes in the volume of the ocean basins? (3)

Answer 25

7. Flooding of shelves and formation of trenches: negligible
   
   8. Deposition of land-derived sediments: negligible
   9. Variation in volume of ocean spreading ridges : very long lasting and depends on the length of axes and spreading rate