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GEOL200 > Week 7: Ocean circulation > Flashcards

Week 7: Ocean circulation Flashcards

1
Q

What is going on?

A

Two currents meet at Cape Hatteras (Northwest Atlantic Shelf) creating rough and treacherous water

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2
Q

Why should we care?

A

Fastest warming regions in global ocean
Ecologically and economically valuable species

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3
Q

What happened in summer 2008?

A

Gulf stream migrated closer to tail of the grand banks (TGB) in a shift toward higher sea surface temp
- impinges flow of cold, O2 rich water

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4
Q

Ocean currents

A

Continuous directed movement of water from one place to another

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5
Q

Wind driven- surface currents

A

Horizontal movements in upper 10% of water

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6
Q

Density-driven (thermohaline)- deep currents

A

Vertical movement, mixing; 90% of all ocean water
- slow moving 10-12km/year

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7
Q

Where do currents go?

A

Direct or indirect observation and measurement
Diff methods for surface and deep currents
(ex. current buoys, flow meter, drift carts)

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8
Q

Tracking currents- flotsam

A

Flotsam= floating wreckage of a ship or cargo

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9
Q

How much water is being transported?

A

Measured in sverdrups (SV) (massive amounts of water)
One sverdup= 1,000,000m3 per sec

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10
Q

Surface currents

A

Occur above and within pycnocline
Primary force behind movement– wind

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11
Q

Which way does the northern hemisphere create flow?

A

To the right of wind direction

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12
Q

Ekman spiral

A

Ocean circulation model
Surface layer in contact w wind- 45 degrees to the right of the wind direction in northern hemisphere due to coriolis effect

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13
Q

Ekman spiral- what is happening?

A

Visualize many water layers
Moves at an angle to the right of the overlying layer
Energy passed from layer to layer
Slows down due to friction

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14
Q

Ekman transport

A

Net motion of water down to 100 m
Why- eventually water flows in direction opp of surface current
Theoretically 90 degrees to right northern hemisphere and 90 degrees to left southern hemisphere

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15
Q

Coastal upwelling

A

Upwards movement of cold, nutrient rich water, high biological productivity and essential for coastal fisheries
caused by…
Ekman transport= movement away from shore, deeper water moves in to replace missing surface water

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16
Q

Coastal downwelling

A

Downward movement of surface water to deeper parts of ocean
- Low productivity, nutrient poor
- Ekman transport= water stacks up against shore, moves downwards

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17
Q

Coastal upwelling and weather

A

Strong control on regional weather
- Cooler temps, fog and precipitation
ex. coast of Peru

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18
Q

Open ocean- coastal upwelling

A

Divergence and convergence- ekman transport

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19
Q

Surface currents and gyres

A

Ekman transport moves surface water to centre of subtropical gyre

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20
Q

Gyre

A

Large scale circular patterns of surface circulation

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21
Q

Surface currents- geostrophic currents

A

In northern hemisphere ekman transport results in movement towards centre of gyre and water piles up in centre but gravity pulls water downhill creating a pressure gradient (hi to lo pressure)
- water deflected by Coriolis effect resulting in clockwise current

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22
Q

Subtropical gyres

A

Collection of currents w diff properties
Centered around 30 degrees north or south

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23
Q

Direction of subtropical gyres in northern hemisphere

A

Clockwise

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24
Q

Direction of subtropical gyre in southern hemisphere

A

Counter clockwise

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25
Q

How many major current circuits in the world?

A

6
5 are subtropical gyres
1 is the eastward-flowing Antarctica Cicumpolar current driven by westerlies

26
Q

5 subtropical gyres

A
  1. North Pacific
  2. South Pacific
  3. North Atlantic
  4. South Atlantic
  5. Indian Ocean
27
Q

Western boundary currents - Gulf stream (North Atlantic)

A

Fast moving- average 6.4 km/hr to a depth of 450m
Narrow and deep (<100km)
Transports warm water northwards (swift speed in large amounts- 50 Sv)
Nutrient poor
Sharp boundaries
Little or no upwelling

28
Q

Eddies

A

Cold and warm core rings

29
Q

Creation of meanders from eddies

A

Over time warm water eddy rotates and rotates and eventually breaks off creating a patch of warm water within cold water

30
Q

Western boundary currents - Kuroshio current

A

Temp diff support distinct populations
Warm, nutrient poor
Eddies aren’t persistent features

31
Q

Eastern boundary currents

A

Shallow and broad (1000km across, <500 m deep)
Moves cold water towards equator (slow)
Poorly defined boundaries, rare eddy formation
Low volume of water transported (10-15 Sv)
Nutrient rich (coastal upwelling common)

32
Q

Eastern boundary currents- Coastal desert in Namibia

A

Caused by Benguela current
Low water vapour content, air cooled by current

33
Q

Types of eastern boundary currents

A
  1. Canary current (North Atlantic)
  2. Benguela current (South Atlantic)
34
Q

Westward intensification

A

Currents on western side of a gyre are faster, deeper and narrower than currents on Eastern side bc Coriolis effect isn’t equal everywhere on earth

35
Q

Diff in speed at high latitudes

A

Greater difference
(earlier deflection to right)
ex. Gulf stream

36
Q

Diff in speed at lower latitudes

A

Lesser differences
(later deflection to right)
ex. Canary current

37
Q

Transverse currents

A

Currents that flow east to west= equatorial currents
Currents that flow west to east= northern/southern boundary currents

38
Q

Thermohaline circulation (global ocean conveyer belt)

A

Driven by diff in water density
Vertical movement, horizontal flow
Links major surface and deep water currents in the Atlantic, Indian, pacific and southern oceans
Transports heat, delivers O2 to deep water

39
Q

Surface water

A

To depth of 200 m
Less dense, warmer, less saline

40
Q

Central water

A

Bottom of main thermocline- latitude dependent

41
Q

Intermediate water

A

to 1500m

42
Q

Deep water

A

Water not in contact bottom (4000m)

43
Q

Bottom water

A

In contact w sea floor
Denser, colder, more saline

44
Q

Temp of intermediate water masses

A

-1.5- 14 degrees celcius

45
Q

Temp of deep and bottom water masses

A

-10.5- 4 degrees celcius

46
Q

Conservative water masses

A

Consistent temp, salinity; no sinks or sources in ocean interior

47
Q

Non-conservative water masses

A

Changed in course of time by chemical, physical or biological processes

48
Q

Deep water masses

A

North Atlantic Deep water (NADW)
Antarctic bottom water (AABW)

49
Q

Caballing

A

Mixing of two water masses
ex. AABW

50
Q

AABW

A

Salinity= 3.47%
Temp= -0.5
Density= highest of all water masses
Most oxygenated deep water

51
Q

How is AABW created?

A

Strong wind blowing off Antarctica creates ice-free areas of water- polynyas
Water is now exposed to cold wind- sea ice formation and brine expulsion
Salt is forced out and concentrates in remaining water
Cold, saline water sinks

52
Q

North Atlantic deep water (NADW)

A

Layer of high salinity, high O2 and low nutrients btwn 1500-3500 m depth
Forms in Labrador and Greenland seas
Lower density than AABW

53
Q

How is NADW created?

A

As warm water flows north salinity increases
- Wind blows over the water and cools it
- Evaporation (causes increased salinity) and downwelling occur

54
Q

Upper vs Lower NADW

A

Upper
- warmer, less dense
- convection in winter
- production depends on NAO(north atlantic oscillation)
Lower
- cooler
- overflow water- Greenland- Iceland - Scotland ridge

55
Q

Formation of Lower NADW

A

Wind blows across water, causes freezing and brine expulsion
Sea ice forms and it sinks

56
Q

Henry Stommel

A

Westward intensification
Global circulation (surface water sinks in polar regions)
Feeds deep boundary currents on Western sides

57
Q

What will happen to water masses in about 1500 years?

A

NADW- most nutrients depleted, Co2 depleted and well O2 water
Pacific ocean water masses- most nutrient rich, CO2 rich and oxygen depleted water

58
Q

AMOC- Atlantic Meridional Overturning circulation

A

Southern to north Atlantic ocean
Major tipping point in climate change
Currently observing slowing down

59
Q

AMOC

A

Series of surface and deep-water currents
- Northward flowing warm water in upper layer of Atlantic (GULF stream)
- Deep convection in nordic and labrador seas
- Southward flowing of colder water at depth (NADW)

60
Q

Why is AMOC slowing down?

A

Climate change
-Warm water= less prodcution of deep, cold, saline water
Freshening
- Fresh water in sea water= less salinity

61
Q

Thermohaline circulation and climate change

A
  • Gulf stream is slowing; cooler NW europe and more water piles up on east coast of north america(sea level rise)
  • Southward shift in rain belt

GEOL200 (10 decks)

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