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ESCI 111 > Ocean circulation and structure > Flashcards

Ocean circulation and structure Flashcards

1
Q

What are three components to water?

A

Temperature, salinity (salty) and pressure.

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2
Q

What is the water at the surface of the ocean like?

A

The surface water is (relatively) warm, and salty.

Nothing much changes going down 100m, except that light begins to go DIM. This s the MIXED LAYER.

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3
Q

What is the mixed layer?

A

The mixed layer is around the first 100m when the light begins to go DIM.

Other than this, it it similar tot he surface water.

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4
Q

How deep is there a rapid change and what is this change?

A

Somewhere before 200m, there is a rapid change where temperature and salinity DROP QUICKLY.

This is called the THERMOCLINE

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5
Q

As depth increases (from 200m) what happens?

A

This trend of temperature and salinity decreasing continues but happens more SLOWLY. They continue to drops until the cold but relatively fresh water is reached.

But the density is steadily increasing (we cross the lines of equal density - isopycnals).

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6
Q

What are isopycnals?

A

This the lines of equal density.

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7
Q

What is the new mass water?

A

The new mass water met when the decrease in Temperature and salinity has reached cold but relatively fresh water.

In this case the new mass water is called Antarctic Intermediate Water (AAIW).

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8
Q

When is there a change in trajectory?

A

The change in trajectory means we’re beginning to mix with a different water mass.

Salinity increases. As it does density increases rapidly, even though temperature remains the same (e.g cold). The new water mass is the North Atlantic Deepwater (NADW).

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9
Q

What are the different layers and the three water masses?

Hint: In the North Atlantic

A
  1. Surface ocean
  2. Mixed layer
  3. Thermocline
  4. Antarctic Intermediate Water (AAIW)
  5. North Atlantic Deepwater (NADW)
  6. Antarctic Bottom Water (AABW)
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10
Q

What is the new trend seen after there has been an increase in salinity and density but no change in temperature?

A

As we go deeper still, the new trend is that salinity STOPS increasing, but temperature DROPS. As we reach ABYSSAL depths, we experience the final water mass, which is very cold, moderately saline. This is called the Antarctic Bottom Water (AABW).

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11
Q

What do the changes in the line (includes salinity, temperature, density) tell us?

A

That the changes in the line are NOT homogenous. There are different layers with DISTINCT physical identity (separated by temperature, salinity, and density).

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12
Q

What allows the different layers to be distinct from each other?

A

They are separated by temperature, salinity, and density.

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13
Q

What does temperature in the oceans say?

A

The temperature in the oceans reflects the amount of energy stored in molecular movement (heat).

Water has a remarkable ability to absorb heat.

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14
Q

What does compression do to molecules?

A

Compression (present with depth) drives molecules together increasing their temperature, for no overall change in heat energy.

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15
Q

What is the ocean surface temperature controlled by?

A

Controlled by sunlight.

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16
Q

Where is the sun’s energy more concentrated at?

A

The sun’s energy is more concentrated at the equator, so more diffuse at poles. So, temperature follows the same pattern.

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17
Q

What does the concept of salinity tell us?

HInt: How much salt does ocean water have?

A

Ocean water contains about 35g of salt (NaCl) per Kg of water (35 part per thousand or 35%).

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18
Q

What do variations in salinity reflect?

A

Salt is generally NOT lost from the oceans, so variations in salinity reflect the loss or gain of WATER.

Water is lost via evaporation
Water is gained via precipitation and river input

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19
Q

How do oceans gain and lose water?

A

Water is lost via evaporation

Water is gained via precipitation and river input

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20
Q

What does ice formation do to salinity?

A

Water freezes eject salts as a brine. Get cold saline water.

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21
Q

Does salinity vary from place to place?

A

Yes, as these processes are not uniform over the ocean, so the surface ocean salinity varies from place to place.

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22
Q

What does evaporation > rain + runoff result in?

A

High salinity
(more water is lost than gained)

E.g. Atlantic, Mediterranean, Arabian Sea.

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23
Q

What does evaporation < rain +runoff result in?

A

Low salinity
(less water lost and more water gained)

E.g Equatorial rainfall belts, polar regions.

24
Q

What does the concept of density mean?

Hint: How and when is the ocean stable?

A

The ocean is stable when density increases systematically (monotonically) downwards.

Where this is violated, one water mass will begin to SINK below the underlying water masses.
Think ‘ocean subduction.’

25
Q

What do temperature and salinity both contribute to?

A

They both contribute to the density of water.

Warm fresh water = least dense
Cold saline water = most dense

26
Q

Is warm freshwater more or less dense?

A

Least dense

27
Q

Is cold saline water more or less dense?

A

Most dense

E.g North Atlantic has a high density (evaporation = salty, strong cooling) as well as Weddell Sea (Katabatic winds + brine (ice) formation.

28
Q

What are the surface waters affected by?

A
  • Affected by winds, waves, freshwater input
  • Affected by sunlight
    Averages about 80m
    About 8% of the total ocean
    Contains 30x the heat of the atmosphere
29
Q

What are the characteristics of the thermocline, pycnocline (halocline)?

A
  • Permanent in tropics (heating)

- Weak or non-existent at the poles (cooling).

30
Q

What are the characteristics of the deep waters?

A
  • Relatively static
  • Only really affected by mixing
  • Affected by density and topography
31
Q

What is the temperature pattern in the thermocline?

A

Sharp graduation in temperature.

low density

32
Q

What is the temperature and density trend in the pycnocline?

A

Sharp graduation in density (largely due to temperature).

Temperature decreasing

33
Q

What is the trend in salinity in the Halocline?

A

Sharp graduation in salinity (not always coincident with others).

34
Q

What is the Coriolis effect?

A

It is NOT a force.

Currents or winds on Earth’s surface follow a STRAIGHT path while the Earth rotates beneath it.

Coriolis ‘Force’ is strongest at poles and weakest at the equator.

35
Q

Where is the Coriolis force strongest at?

A

At the poles.

36
Q

Where does air tend to flow?

A

The air tends to flow from the poles to the tropics

37
Q

Is cold or warm air dense?

A

Cold air = More dense

Warm air = Less dense

38
Q

What direction does the Coriolis force tend to bend the air?

A

The Coriolis force bends the air WESTWARDS.

39
Q

Do winds ‘drag’ the surface ocean along with them?

A

Yes. Westwards near the equator, Eastward near 50o latitude.

The moving water then experiences the Coriolis Force, diverting it at about 45 degrees angle. (right in NH and left in SH). These loops become connected to form OCEAN GYRES.

40
Q

What is the Coriolis Force deflection due to?

A

It is due to the spin/rotation of the planet.

41
Q

What direction is the Coriolis Force in the Northern and Southern Hemisphere?

A

Northern Hemisphere = deflection to the right
Southern Hemisphere = Deflection to the left
Equator = NO deflection

42
Q

What do gyres result from?

A

Gyres result from a BALANCING OF FORCES:

  • The Coriolis Force, which causes water to ‘dome up’ in the center of the gyres.
  • Gravity (pressure gradient) which wants to push water downhill away from the center of the dome.
43
Q

What happens when the forces balance?

A

A current is produced that circulates AROUND the dome (hence the gyres).

This is called a GEOSTROPHIC CURRENT.

44
Q

What is Echkam Transport?

A

When winds drag surface water along, the net movement of water is at 90o to the wind movement.

To the LEFT of the wind = Southern Hemisphere
To the RIGHT of the wind = Northern Hemisphere.

This is due to the Coriolis Effect.
Wind causes the very top surface of the ocean to move, but Coriolis Force deflects this layer.
Tops surface ocean drags on the layer just beneath it, which is then also deflected by the Coriolis Force.

45
Q

What does it mean that ocean gyres are asymmetric?

A

Broader and slower to the eat, tighter and faster to the west.

This is caused by the different strengths of the Coriolis Force at the poles vs the equator.

46
Q

Why do currents along the equator experience LITTLE Coriolis deflection?

A

Water travels all the way to the western ocean before diverting. Therefore, the water stays ‘bunched up.’

47
Q

Why do currents in the mid-latitudes experience STRONG Coriolis deflection?

A

Water starts to deviate EARLIER:

- Before it has travelled the full ocean width. Therefore, return flow is more ‘DIFFUSED.’

48
Q

What does wind-driven divergence produce?

A

Upwelling.

Along the equator = water moves away from the equator.
Around Antarctica = Water is moved away from circumpolar current.

49
Q

How is deepwater formed in the North Atlantic?

Hint 6 steps

A
  1. A DEFICIT of rainfall over evaporation leaves water up to 2psu MORE SALINE than the Pacific.
  2. Strong cold Arctic winds blow over the water.
  3. This cools the water, while evaporation cools it even more and increases salinity still further.
  4. Eventually, around Greenland and Iceland, the water crosses a density threshold where it is dense than the underlying water.
  5. The water beings to sink (‘subduct’).
  6. This becomes the water mass known as North Atlantic Deep Water (NADW).
50
Q

How is deepwater formed around Antarctica?

Hint 3 steps

A
  1. In the Weddell Sea, strong Katabatic Winds (dense air flowing downhill) break up sea ice forming polynyas (patches of ice-free water).
  2. These intensely cold winds strongly chill water.
    Sea-ice is continually reforming. However, ice is fresh, and the residual salt trickles out of the ice as a cold dense brine, increasing the salinity of the water.
  3. Again, here the density becomes enough for the water to sing below the underlying water, forming two water masses (slightly warmer, fresher Antarctic Intermediate Water (AAIW) and a hyper-cold saline Antarctic Bottom Water (AABW)).
51
Q

What deep water is the coldest and therefore, most dense?

A

Antarctic Bottom Water.

Flows along the seafloor, to mid-Northern latitudes following bathymetry.

North Atlantic Deep Water is the most saline, but somewhat warmer, Flows over the top of AABW, eventually upwelling around Antarctica.

52
Q

How do the different water masses/layers differ?

Hint: salinity, temperature

A 
CASW = warm, saline
AAIW = cold, fresher
NADIW = cold, saline
AABW = very cold, intermediate salinity
53
Q

What is mass balance?

A

If water is sinking into depths of the ocean somewhere water must be rising back up to the surface.

Downwelling is matched with upwelling.

54
Q

Where is upwelling known to occur?

A
  • Along the equator
  • Along the eastern ocean margins
  • Around Antarctica

Suspected to occur: In the northern Pacific

55
Q

Where does upwelled water flow to?

A

Upwelled water flows to sites of downwelling via a huge planet-spanning current system. GLOBAL CONVEYER BELT (takes > 1000 years).

ESCI 111 (18 decks)

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