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Oceanography > Sea level > Flashcards

Sea level Flashcards

1
Q

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

A

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

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2
Q

Factors controlling sea level change

A
  • Tectonic movements ( local scale)
  • Temperature cycles
  • Global warming
  • Glacial melt
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3
Q

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

A

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

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4
Q

What processes impact global sea level?

A
  • 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
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5
Q

Impact of sea level on climate

A

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)

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6
Q

Sea floor spreading rate

A

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

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7
Q

Slower sea floor spreading=

A

Less elevated crust and a lower sea level

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8
Q

Continental margins

A

Have a lot of volume and displace large amounts of seawater

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9
Q

Most promising result for reconstructing sea level changes

A

Corals

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10
Q

Why can we use corals to reconstruct sea level change?

A

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

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11
Q

Acropora Palmata

A

Only survived within top 5m of ocean

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12
Q

Isostatic Pressure

A

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

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13
Q

Hudson Bay- isostatic rebound

A

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

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14
Q

Weight applied to the crust:

A

Dispersed throughout the lithosphere

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15
Q

Consequence of the lithosphere being ridgid

A

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

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16
Q

Extent of depression beyond ice margin 150-180km

A

Can record relative sea level change

17
Q

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

A

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

18
Q

Isostatic rebound in Scotland

A
  • Emergence at a modest rate
  • Outpaced by sea level rise
19
Q

Processes impacting global sea level:

A
  • 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
20
Q

Estimates of sea level further back in time

A

Suffer from a growing uncertainty

21
Q

Sea water albedo

A

0.06

22
Q

Soil Albedo

A

0.25

23
Q

Sand albedo

A

0.40

24
Q

Less continental shelf exposed=

A

MORE sunlight absorbed- by the surface of the earth

25
Q

Faster sea floor spreading

A

Produces a hotter crust and a more elevates mid ocean ridge

26
Q

Slower sea floor spreading

A

Produces less elevates crust and a lower sea level

27
Q

Continental margins …

A

have a large volume and displace large amounts of seawater

28
Q

Lots of continental fragments

A

= lots of margins therefore sea level=high

29
Q

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

A

High sea level flooded MOST continental interiors

30
Q

Oceanic plateaus (large igneous provinces)

A

Can be very big and displace large volumes of water

31
Q

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

A
  • Decrease in ocean ridge volume
  • Collision of India and Asia
  • Decrease in volcanic plateau volume
  • Water stored in ice sheets
    -Thermal contraction of seawater
32
Q

The Messinian Event

A

The Mediterranean Sea dried up due to continental movement

33
Q

Why did the Messinian event occur?

A

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

34
Q

Evidence for the Messinian event

A

Evaporite minerals, soils and fossil plants

35
Q

2 scenarios used to explain the salinity crisis

A
  • Uplift Model
  • Drying- out model
36
Q

Uplift Model

A
  1. Large-scale regional uplift
  2. Draining of the basin into the Atlantic Ocean
  3. Large-scale regional sinking of crust
37
Q

Drying Out Model

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

Oceanography (23 decks)

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