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Oceanography > Jan - Oceanography > Flashcards

Jan - Oceanography Flashcards

1
Q

Who were the 2 people to first successfully circumnavigate around the globe ?

A

El Cano and Magellan

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2
Q

When did El cano and Magellan travel around world?

A

1519 - 1522

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3
Q

When were el cano and Magellan able to systematically map the ocean?

A

Late 1700s

Because they couldn’t determine the longitudinal position accurately

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4
Q

What is the longitudinal position ?

A

Longitude is a measurement of locations east to west

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5
Q

What was the first scientific research ship called?

A

The challenger expedition

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6
Q

What years did the challenger expedition explore the oceans ?

A

1872-1876

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7
Q

What did the challenger expedition discover ?

A
  • sea depths - Mariana Trench
  • trawling -4700 new species found
  • current measurements
  • water composition
  • dredging - sediment samples
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8
Q

How deep is Mariana Trench ?

A

8184m

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9
Q

Name 2 Ways to measure ocean depth?

A

Sounding

Sonar

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10
Q

What is sounding

A

Weighted rope lowered over ship into water.

When weight hits ocean bed the rope becomes slack.

Water marks the line on the rope to show how deep the ocean is.

Used in past and very time consuming

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11
Q

What is sonar?

A

Transmitter and receiver called a transducer sends a sound impulse down to ocean bed.

The pulse bounces off the floor and the transducer picks up the reflected sound.

Computer precisely measures how long it takes for noise to travel.

Quick - shallower water

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12
Q

What is bathymetric province?

A

Study of underwater ocean or lakes floors

  • topography
  • terrain
  • shape
  • depth
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13
Q

What is passive continental plate ?

Give examples

A

Technically stable
Few earthquakes
No volcanoes

Sedimentary deposits cover older rock

Low relief

Eg India and Antarctica

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14
Q

What is active continental margin ?

Example

A

Tectonically active

Narrow and steep

Eg west coast of USA

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15
Q

What is the Archimedes principle ?

A

A body totally or partially submerged in water or fluid is subject to an upward force equal in magnitude of weight of fluid it displaces

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16
Q

Where do oceanic and continental crust float on ?

A

Asthenosphere

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17
Q

What density floats on top?

A

Lighter density floats on top of object with higher density

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18
Q

Continental crust

A

Less dense - 2800kg/m3

Thicker - 30-70km

Elevation - 840m

Surface area - 29%

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19
Q

Oceanic crust

A

Denser - 3000 kg/m3

Thinner - 5-10km

Elevation - -3800m

Surface area - 71%

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20
Q

What is the continental shelf ?

A

Portion of continent relatively submerged under an area of shallow water

Some exposed during glacial periods and interglacial periods

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21
Q

What is the continental slope?

A

The slope seaward from the shelf to the upper edge of rise

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22
Q

What is the continental rise ?

A

Sediment underwater feature found between the smile and the abyssal plain

Represents final stage in boundary between continents and deepest part of ocean

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23
Q

What is the rough surface temp of ocean ?

A

-2 - 30 degrees

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24
Q

Where is the warmest waters found?

A

Equator

They drop as you go towards latitudes

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25
Q

How are the meridional variations explained?

A

By differences in heat fluxes

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26
Q

What does it mean by regional variations in water temp ?

A

West Coast of north and South America is colder

So is west Africa

Colder than usual

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27
Q

What does meridional mean ?

A

In or at the south.

Meridional flow is a general flow from north to south or south or north along the earths longitude lines

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28
Q

What does seasonal variations in temp mean ?

A

Warmer in summer months
Colder in winter months

This varies across the globe

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29
Q

What does inter annual mean ?

A

Over 2 or more years

History

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30
Q

Key points relating to inter annual variations in sea surface temp

A
  • sea temps increased since 20th century and continue to rise still
  • highest temp records over past 3 decades, since 1880
  • inter annual variability eg El Niño and La Niña cycles but uncertainties in measurements eg ww2
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31
Q

What is El Niño

A

Irregularly occurring and complex set of climate changes affecting equatorial pacific region.

Unusually warm, nutrient poor waters off northern Peru and Ecuador - late December.

Wind reversal across pacific
Drought in Australasia
Heavy rain in South America

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32
Q

What is La Niña

A

Sea surface temps across equatorial eastern central Pacific Ocean is lower than normal by 3-5 degrees.

5 months

Affects Atlantic and pacific hurricane seasons, more tropical cyclones due to low wind and warmer sea surface temps in Atlantic basin

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33
Q

What does salinity mean

A

Saltiness of water

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34
Q

What is the main salts in ocean

A

Sodium

Chloride

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35
Q

Where is the origin of salts in water ?

A

Weathering and erosion of rocks

Our gassing of chloride from earths interior

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36
Q

What is the Average concentration of salt in water

A

34.5 g/kg

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37
Q

How is salt left behind ??

A

Heat forces ocean surface water to evaporate, putting water into atmosphere and leaving behind salts and minerals, constantly keeps water salty.

If 1 metric ton of water evaporates it leave behind 34.5kg of salt

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38
Q

What impacts salinity of ocean

A

Evaporation rates - more evaporation more salt left behind.

Atmospheric temps.

Wind.

Addition of freshwater from rivers / rain / melting of glaciers

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39
Q

Where is salinity higher in the ocean, the Atlantic or pacific

A

The Atlantic

Pacific has more rainfall so less salt

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40
Q

What has greater salinity in ocean, tropics or polar regions

A

Tropics

More evaporation

More icemelt in polar regions

41
Q

Is there a higher or lower salinity at river mouths

A

Lower

42
Q

Why is ocean water still a liquid at 0 degrees

A

The salt means a lower temp is needed to feeeze
water

That’s why ocean is liquid at polar regions - up until -1.8 degrees

43
Q

As temp increases,

What happens to density

A

It decreases

44
Q

As salinity increases,

What happens to density

A

It increases

45
Q

Where is ocean very saline / salty?

A

Med sea
Red Sea
N/s Atlantic

46
Q

Where is ocean not very saline / salty

A 
Kara sea 
Laptev sea (n russia)

N Canada

Polar regions

47
Q

Where is ocean very dense ?

A

Med sea
Red Sea
North Atlantic around Iceland and uk

48
Q

Where is not very dense ?

A

Equatorial regions

Mouth of Amazon at crazy

Black Sea

49
Q

What happens when salt water and fresh water collide

A

This may happen when fresh water flows out of river and meets salty ocean mouth

This is called gravity current.

The heavier dense water which is salty will sink flow fresh lights water

50
Q

Name the 3 layers on density profile of ocean

A

Surface mixed layer

Pycnocline

Uniform deep layers

51
Q

What is the state of surface mixed layer like ?

A

Wind and waves mix water well

52
Q

What is the state of the pycnoline like ?

A

Sharp transition in density due to changes in temp and salinity

53
Q

What is the state of uniform deep layers like ?

A

Slowly evolving and shielded from external forces like precipitation/ cooling / warming / evaporation

54
Q

Name different layers of water

A

Surface water

Intermediate water

North Atlantic deep water

Antarctic bottom water

55
Q

Surface water properties

A

Warm

Saline

56
Q

Intermediate water properties

A

Cold 3-7 degrees

Less saline 33-34

57
Q

North Atlantic deep water properties

A

Cold 2-4 degrees

Saline 34-35

58
Q

Antarctic bottom water properties

A

Very cold -0-4 degrees

Saline 34

59
Q

Why is Antarctic bottom water saline

A

Because cold salty water doesn’t freeze as easily so this leaves behind lots of salt and the fresh water is locked up as ice

60
Q

What is the global conveyor belt

A

Constantly moving system of deep ocean circulation

Driven by temp and salinity - thermohaline currents

Warmer lighter water floats on top and dense colder water sinks

Cool flow next to Antarctica and warmer flow adjacent next to India and Australia

61
Q

Name the 2 components of ocean circulation that redistribute solar energy

A

Quasi- horizontal

Meridional overturning

62
Q

What is the quasi Horus atlas circulation driven by

A

Wind

63
Q

What is the MOC driven by

A

Cold water sinking next to poles before moving to equator and rising in low latitudes or opposite hemisphere

64
Q

Describe the circulation occurring 15 - 45 degrees

A

Subtropical gyres
5 gyres - N/S Atlantic, N/S pacific and Indian Ocean.

Flows eastward at mid latitudes.

Flows westward at equator

Circulation happens in upper 100m of ocean and gets weaker at depth

65
Q

Describe the currents northward of 45 degrees

A

Subpolar gyres which arent as pronounced as subtropic gyres due to complexity in ocean basic geometry and topography.

2 gyres - N pacific and N Atlantic

Eastward flows at horse latitudes

Westward flow at piles and intense westward currents flow equatorwArd

66
Q

Describe the Antarctic circumpolar currents

A

Largest current in world - transporting 100-175Sv of water.

No topographic constraint so flows all way around globe.

Measuring flow due to seabed steering and instabilities in flow.

ACC fronts create steep temp and salinity gradients meaning warmer water from equator never reaches Anterctixa

Water can be measured at passages such as Drake passage S.US

Important as connects Indian/pacific / Atlantic oceans helps earths climate

67
Q

Define horse latitudes

A

Belt of calm air and sea occurring in both northern and Southern Hemisphere between trade winds and westerlies

68
Q

Define trade wind

A

Wind blowing equatorwArd from north east in northern hemisphere or south east in Southern Hemisphere Especially at sea.

2 belts of trade winds - tropical high pressure belts and low pressure zone at equator

69
Q

Define westerlies

A

Wind blowing from the west to east in mid latitudes

70
Q

Define sub Antarctic front

A

Northern boundary of the ACC

71
Q

Define polar front

A

The boundary separating air masses of polar origin from those of tropical or subtropical origin.

Position of polar front changes during seasons

72
Q

Describe what happens in meridional overturning circulation

A

Dense water sinks at poles and moves equator ward and rises

Stronger overturning in Atlantic than pacific

Water lighter surface water circulating in gyres

73
Q

What is the Navier-Stokes principle ?

A

Describes the movement of fluid parcel through time in atmosphere and ocean.

Exact solutions to equation doesn’t exist but computer models help obtain approx solution

74
Q

Define hydrostatic balance

A

Vertical balance between the pressure force and gravity

Pressure increases with ocean depth

75
Q

Name the 2 dominant forces in horizontal direction

A

Pressure gradient - high to low pressure

Coriolis force - water gets deflected due to earths spinning right/ left in n/s hemisphere

76
Q

Define geostrophic balance

A

Horizontal direction between pressure grad and CF

77
Q

Who noticed that ships and icebergs get blow across ocean surface at 45 degrees with the direction of wind

A

Nansen

Ekman

78
Q

Describe the process if ekman spiral

A

Wind exerts drag on surface

Water moves in direction of wind

Motion gets deflected by CF

Stress transmitted to fluid below surface layer

Flow shifts - left in s.hemisphere / right in n.hemisphere

Flow weakens with depth - at 100m flow falls to 0

79
Q

Define ekman spiral

A

Under the influence of the wind the top 100m of water column moves at 90 degree angle to direct of wind

80
Q

What is the ekman layer

A

Layer of water from surface to the point of dissipation of this spiral

Net transport of water is 90 degree - right in n.hemis and and s.hemis

81
Q

What causes the western boundary currents ?

A

Cf stronger away from equator.

Eastward flowing water at midlatitudes experiences stronger coriolis deflection.

As a result, centre of geostrophic hill moves westward and the pressure Grad increased on western boundary causing strong circulation - western boundary current and

82
Q

What is the western boundary current AS A RESULT OF?

A

Meridonial variations in cf and boundary steering

83
Q

What causes the over turning circulation

A

It’s density enabled so cold dense water sinks at the poles

It’s maintain by diffusion and the wind

84
Q

How is the entire ocean bashing not filled with cold dense water ?

A

Heat diffusion at low latitudes - at equator warmer surface water diffuses deeper.

Ekman pumping of deep water to surface in Antarctica

85
Q

How does ekman pumping in Antarctica help stop the entire ocean basin filling with cold dense water ?

A

The westerly winds coming into Antarctica plus the ekman transport of surface waters towards north

Create counter currents of deep water towards south and upwelling towards surface

86
Q

What causes upwelling of cold surface waters at Eastern boundaries?

A

Wind driven ekman transport causes upwelling of cold nutrient rich water

Similar to Antarctica

87
Q

How does ocean respond to El Niño ?

A

Weaker trade winds

So weaker equatorial currents

Meaning less upwelling of cold water

So warmer water flowing eastward

88
Q

How does the ocean respond to La Niña?

A

Opposite to El Niño

Colder surface at eastern pacific (cooling)

Stronger trade winds

89
Q

What place as the highest tides in the world ,

A

Bay of fundy, Nova Scotia

2 High 2 low tides in 24 hours

90
Q

Give example of tidal island

A

Mont Saint Michel , france

91
Q

Define tidal range

A

Sea surface height difference between high and low tide

92
Q

What 2 things does the tidal range depend on

A

Geographical location

Time

93
Q

Whats the phrase called where locations don’t have a tide?

A

Amphidromic points

94
Q

Name 3 events that aren’t associated with astronomical tides

A

Rip currents

Storm surge

Tsunami

95
Q

Define astronomical tide?

A

Tidal levels which result from gravitation effects

Eg Earth / sun / moon without atmospheric influences

96
Q

What causes the tides ?

A

Gravitation attraction between sun/ moon and earth

They align to Create extreme tides such as spring

Went they arent alighed they are weaker and create neap tides

97
Q

Why are there 2 high and 2 low tides?

A

Moon takes 24 hours to orbit earth.

Only stands at same point once per day, which will experience a high tide.

Due to centrifugal forces on ocean by the earths orbit the same Area will experience a second high tide once positioned directly opposite to moon

98
Q

Define centrifugal force

A

A force arising from the body’s inertia which appears to act on a body moving in circular path and is directed away from centre around which body is moving

Oceanography (2 decks)

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