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Y1,S1-Natural Hazards > Y1,S2 - Oceanography > Flashcards

Y1,S2 - Oceanography Flashcards

1
Q

Who and when was the gulf stream investigated and discovered?

A

Benjamin Franklin, 1773

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2
Q

Who aided in the birth of modern oceanography and when?

A

Sir Charles Wyville Thomson (1830-1882)

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3
Q

What did Sir Charles Wyville Thomas observe?

A

Systematic observations of animal and plant life, bathymetry, bottom samples, water chemistry and physic and marine meteorology

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4
Q

What did Sir Charles Wyville Thomas demonstrate?

A

-Abundant sea life with genera only previously known from the fossil record
-Demonstration of deep aea currents and temperature differences

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5
Q

What were John Murrays contribution to oceanography?

A

-Study of ocean depth and noted existence of ocean trenches
-Attempted to construct temperature and salinity profiles in order to understand movements in the ocean
-Investigated carbonate dissolution in seawater
-Produced the first map of sediment distribution in the ocean

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6
Q

What did Fridtjof Nansen achieve?

A

-Polar oceanography and the interaction of ice and water
-Charting current flow in the Greenland and Norwegian seas
-Voyage of the Fram (1893-1896) to test the theory of wind generated currents)
-Water temperature sampling (Nansen bottle)
-Discovery of the first polar basin in the Arctic

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7
Q

Name 3 types of Remote sensing?

A

-Ship-borne sonar and seismic surveys
-Passive satellite imagery
-Active satellite microwave altimetry and scattrerometry

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8
Q

What is ship-borne sonar and seismic surveys?

A

-‘Radar’ images using sound waves
-3 dimensonal picture of water density and ocean bottom rock structure

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9
Q

What is passive satellite imagery?

A

-Pictures formed from microwave and different coloured optical emissions
-Intensity of infra-red (heat) gives surface water temperature green colour of chlorophyll gives phytoplankton concentration

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10
Q

What is active satellite microwave altimetry and scatterometry?

A

-Satellite transmits microwaves pulse and recieves it reflected from the sea
-Pulse shape defines surface roughness so can deduce wave height and hence wind speed
-Detailed sea surface shape determines both ocean current speed and sea bottom topography

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11
Q

What are bathymetric profiles?

A

Depth profiles

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12
Q

What is a hypsographic curve?

A

A cumulative frequency curve showing the percentages of the Earth surfcae that le above, below or between any given levels

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13
Q

What is Ocean bathometry classifed by?

A

The slope and depth of the sea floor

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14
Q

What is the depth of the Abyssal plane?

A

~4.5km deep

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15
Q

What is the water depth of the MOR?

A

1.5-2.5km deep

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16
Q

How deep is the trench?

A

6-11Km deep

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17
Q

What is the height of the MOR?

A

2.5Km

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18
Q

What can be used as a proxy for ocean bathymetry?

A

Satellite altimetry

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19
Q

submarine canyons may appear on…

A

Continental shelves

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20
Q

What is Isostasy?

A

The proposition that at some depth under the ocean, the combined weight of overlying mantle, ocean crust and water is the same as the combines weight of mantle and continetla crust the sme depth under the continental crust the same depth under the continents.

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21
Q

What does an isostaic balance between oceanic and cotinental crust produce?

A

A 5km step at the Ocean basin edge

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22
Q

What would happen if the heat generated bynatural radioactivity in the Earths deep interior was not brought to the surface?

A

The mantle would melt

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23
Q

How is heat generated by natural radioactivity in the Earth transported?

A

By convection, which involves the flow of the transport of the underlying. mobile asthenosphere as well as transport of the overlying lithosphere

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24
Q

What forms at the axial ridge of a mid-ocean spreading centre when the asthenosphere cools?

A

The lithospheric plate

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25
Q

What continuosly replaces existing lithospheric plates?

A

New asthenosphere rising and cooling at the ridge axis; i then thickens as it moves away and cools.

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26
Q

How does the lithosphere change as it approaches he MOR axis?

A

The lithosphere is progressively younger, warmer and less dense. Its lower density makes it more elevated

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27
Q

What is Ocean crust generated by?

A

Partial melting of the upper mantle

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28
Q

What is the thickness of the ocean crust determined by?

A

The amount of melt, which in turn is determined by the temperature of the upper mantle

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29
Q

What is the normal upper mantle temperature?

A

1385C

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30
Q

What oceanic crust thickness does the normal upper mantle temperature produce?

A

Crustal thickness of 7km

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31
Q

What is necessary to allow convection to carry away heat generated by the decay of natural radioactivity within the Earth?

A

Internal mobility i.e. the asthenosphere

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32
Q

What is the purpose of a breach in the lithosphere?

A

Necessary to allow this heat to escape because the lithosphere acts as an insulating blanket. Conduction is much less efficient and convection is impossible within the lithosphere, so heat would build up at its base and general melting of the mantle would still take place.

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33
Q

Where is the lithospheric breach?

A

The breach is at the centre of mid-ocean ridges. It is the central point of symmetry for sea-floor spreading which creates new lithosphere by the cooling of rising asthenosphere. The two lithospheric plates seperate and recede at a few cm/y, keeping open the breach.

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34
Q

What happens as the lithospheric plates recede?

A

The lithospheric plates cool by conduction of heat to sea water. As it cools, the lithosphere contracts and so becomes of higher density. Also as it cools, the lithosphere contracts and so becomes of higher density. Also as it cools, the depth of the critical ~800C isotherm and so the lithosphere thickens

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35
Q

Is asthenospheric mantle warmer than lithospheric mantle?

A

Asthenospheric mantle is warmer than lithospheric mantle and so is more expanded and less dense

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36
Q

What is also an important mechansim of heat loss?

A

Hydrothermal circulation

37
Q

What is hydrothermal circulation?

A

Near ridges-precolation of sea-water through cracks

38
Q

Where does a plate lose heat from when it cools?

A

By loosing heat from its top surface ONLY

39
Q

How does a plate cooling affect the depth to the critical isotherm?

A

When a plate cools, the depth to the critical isotherm increases like the square root of time. When a pplied to the ocean lit5hosphere, this simple formula explains the observed shape of mid-ocean ridges up to about 80 million years old.

40
Q

What is the formula that explains the observed shape of mid-ocean ridges?

A

d=200 + 350t^1/2

where t= age in million years,
and d=water depth in metres

41
Q

What mineral are sea-floor basalts rich in?

A

Iron

42
Q

Sea-floor basalts can be…

A

Magnetised

43
Q

How does temperature affect the ability for sea-floor basalt to magnetise?

A

When heated above a characteristic temperature (called the Curie Temperature and typically about 300-500C), they, like all magnetic materials, lose their ability to be magnetised but gain again on coolingn

44
Q

What remnant magnetisation do volcanic rocks cooling through their curie temperature aquire?

A

A remnant magnetisation in the direction of the Earths magnetic field at that time.

45
Q

Describe the timescale of the Earths cycle of a reversing magnetic field?

A

The legnth of these normal and revered periods averages about 1 million years but is characteristically irregular, making a unique pattern which can be used for dating.

46
Q

Why is there a characteristically irregular pattern in tree rings?

A

Due to the irregular pattern of severe winters or dry summers

47
Q

What acts as a magnetic tape recorder of the reversal sequence of the Earths magnetic field?

A

Spreading sea floor, formed of cooling basaltic lavas

48
Q

What confirms the model of sea floor spreading?

A

Measuring the pattern of stronger magnetisation (recorded when the field was normal) and weaker magnetisation (the recorded feild is opposite to the present one). The pattern is symmetrical about the mid-ocean ridge axis

49
Q

How do we know the crustal ages?

A

1.Magnetic anomoly stripes
2.Simulated hot-spot plume

50
Q

Describe the formation of ocean crust…

A

1.At shallower depths, the pressure is less. A decrease i pressure lowers the melting point of mantle rocks
2.The thinner lithosphere at a mid-ocean ridges causes the asthenospheric isotherms to be shallower and domed up there
3.Under normal temperature conditions (a temp at the top of the freely convecting zones of about 1280C), about 13% of partial meltial melting occurs becasue of uplifted isotherms. The mineral components of the mantle which melt first rise to the surface where they cool to form the basaltic ocean crust
4. 13% of melt results in an ocean crust which is 7km thick.

51
Q

What happens if the temperature of the undisturbed mantle happens to be higher andd name an example?

A

There is a grerater proportion of partial melting, producing a thicker oceanic crust. Iceland is a place where the spreading centre straddles a ‘hot spot’ and crust up to 25km thick has been produced here

52
Q

Why do older plates sink?

A

-Because the mantle component of oceanic lithosphere is cooler (and hence more contracted and more dense) than the underlying asthenospheric mantle
-A more dense material DOESN’T FLOAT on a less dense material
-The higher density mantle component inreases in thickness with age and eventually offsets the buoyancy of the crust welded to it after about 150-200 mn years of cooling:it is then unstable and sinks

53
Q

What does the mantle component of the oceanic lithosphere thicken with?

A

Age- after about 100mys, it’s about 80km thick. But there is always a fixed thickness of ocean crust welded on it.

54
Q

Where does oceanic lithosphere subduct (sink)?

A

At ocean trenches, causing a characteristic dipping zones of EQs ( a Benioff Zone)

55
Q

Describe the nature of EQs found in Benioff zones?

A

-Can ONLY occure in the lithosphere
-Tend to normally be found in the to 20km where the lithosphere is particularly brittle

56
Q

What creates an island arc volcano?

A

Any water combined with basalt during hydrothermal circulationnear ridges, together with any sediment accumulated on the volanic floor of the ocean which is not physically scraped off as the pate descends, boils off or melts at the higher temperatures found at a depth- a subduction zone generates a characteristic type of island arc volcano

56
Q

Describe the depth of EQs found near trenches?

A

Found at depths up to 700km

57
Q

What temperature would the Earths surface be without greenhouse gases?

A

~-18 degrees C

58
Q

Where does the Earth itersect less solar radiation?

A

Earth intersects less solar radiation at high latitudes.
Incoming flux is proportional to cosine(latitude)

59
Q

True or False:
All attitudes on the Earth radiate similar heat back into space…

A

True

60
Q

What is thermal radiation?

A

A function of the temperature of the object (absolute temperature)

61
Q

What is absolute temperature?

A

C + 273

62
Q

Does incoming heat create net surplus/ loss of radiation at the equator?

A

Net surplus

63
Q

Does incoming heat create net surplus/ loss of radiation at higher lattitudes ?

A

Net loss

64
Q

What should heat input from the sun be balanced with?

A

Heat loss by the atmosphere, ocean and land

65
Q

In what mediums is heat transferred between the equator and the poles?

A

In the atmosphere and ocean

66
Q

Is the Earths surface or atmosphere hotter?

A

The Earths surface is hotter than atmosphere above, thus heat moves form hot to cold and so is transferred upwards.

66
Q

At what rate does the troposphere temperature typically decrease?

A

typically decreases upwards at a rate of 6.5/km

66
Q

Adding or taking ways heat from water can…

A
  1. Increase or decrease the temperature of liquid water
    2.Keep the temperature of the water the same but make it evaporate or freeze
66
Q

What is the heat capacity of water?

A

4.2 kilo-Joules raise 1kg of water by 1degC

66
Q

True or false:
Evaporation and ice melting (changes of state) require more heat energy than just raising the temperature of liquid water?

A

True

67
Q

What is the latent heat of fusion of water?

A

355 kilo-Joules melt 1kg of ice

67
Q

What is the latent heat of evaporation of water?

A

2257 kilo-Joules evaporate 1kg of water

68
Q

Water stores about ___ times as much heat as rock?

A

8 times

69
Q

What is adiabatic expansion?

A

Expansion when things cool

70
Q

What is the drop in temperature due to adiabatic expansion of dry air?

A

~10/km

70
Q

What is temperature?

A

A measure of the amount of internal energy per unit volume

71
Q

What is the effect of adiabatic expansion of dry air when rising in the atmosphere?

A

Becomes coolwe than the surrounding air and so contracts more, becomes more dense and sink. Thus dry air will not rise far in the atmosphere.

72
Q

Why might adiabatic decrease in temperature with height for air containing a lot of water apour may be much less than 10/km?

A

Because as it cools some water condenses as rain drops and the latent heat of vapourisation is released. Hense when moist air rises, it becomes less dense than the surrounding air and can accelerate upwards till the adiabatic temp. gradient becomes more than 6.5/km

73
Q

When does air in the atmosphere lose heat?

A

When it stops rising, it will lose heat slowly by radiation out into space and it will gradually sink.

74
Q

What direction are the winds in the Northern Hemisphere deflected?

A

Right

75
Q

What direction are the winds in the Southern Hemisphere deflected?

A

Left

76
Q

What are the Hadley cells driven by?

A

Driven by thermal convection of air that must be both warm and moist; precipitation within thunder clouds is a necessary part of the system. Thus they control the geographic distrubution of both evaporation and precipitation.

77
Q

What is Aphelion?

A

Distant path position to the sun

78
Q

What is Perihelion?

A

Close path position to the sun

79
Q

What causes seasonality?

A

Land as rocks heat up and cool down at a much faster speed than water

80
Q

Why is there a larger evaporation rate in the sub-tropics than the tropics?

A

Because drier trade winds blow towards the equator and smaller evaporation i the tropical belt as the air becomes moister.

81
Q

What are the asssossications woth sea surface salinity?

A

Higher salinity - sub tropical evaporation
Lower salinity - Due to equatorial rainfall

82
Q
A

Y1,S1-Natural Hazards (2 decks)

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