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EAS 212: The Oceans > 15. Arctic and Southern Oceans > Flashcards

15. Arctic and Southern Oceans Flashcards

1
Q

The southern ocean is ___ surrounded by ___, while the arctic ocean is ___ surrounded by ____

A

southern: land surrounded by ocean

arctic: ocean surrounded by land

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2
Q

The contribution of arctic water masses for the world ocean differs substantially from the southern ocean water masses. Why is this?

A

topography!
Arctic is separated from the major ocean basins by sills, which limit the exchange of deeper waters

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3
Q

The Arctic ocean is divided into 2 basins:

What are these basins separated by?

A

Canadian basin
Eurasian basin

Lomonosov ridge

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4
Q

How does the arctic ocean ‘communicate’ with the atlantic ocean?

A

through the canadian archipelago and nordic seas

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5
Q

How does the arctic ocean communicate with the pacific ocean?

A

through the Bering straight

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6
Q

There is ___ pressure near the north pole, and the arctic ocean is under the influence of which winds?

A

high
polar easterlies

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7
Q

What’s the effect of the polar easterlies in the arctic ocean? What about in the southern ocean?

A

Arctic: force anticyclonic sfc circulation

Southern: only noticeable in a weak westward current along the Antarctic continent

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8
Q

In the summertime, the winds are much _____(stronger/weaker) and the atmospheric low is centered over:

A

weaker

the north pole

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9
Q

The arctic surface circulation is divided roughly into 2:

A
  1. cyclonic circulation in the north sea & eurasian basin
    - around center of atmospheric low, not a defined/ closed gyre
  2. anticyclonic circulation in the canadian basin (Beaufort gyre)
    - around center of atmospheric high
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10
Q

T/F

The anticyclonic circulation of the beaufort gyre is not just on the surface, but also at depth

A

false

it’s superficially anticyclonic, but intermediate and deep circulations are cyclonic

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11
Q

What divides the 2 parts of the arctic circulation system?

A

Transpolar drift (TPD)/ transpolar current= major cross-polar circulation b/w the 2 systems

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12
Q

What inhibits the generation of strong currents in the artic?

A

permanent ice coverage

avg speeds are ~0.02m/s

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13
Q

T/F

The Arctic is a Mediterranean sea

Why/why not?

A

true
B/c it has only limited circulation with the major ocean basins and its circulation greatly influenced by thermohaline forcing

Mediterranean= enclosed with land (or mostly)

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14
Q

What happens when evaporation exceeds precipitation in the arctic?

A

increases the density of the sfc waters, resulting in deep vertical convection

  • inflow of oceanic water in the upper layer and outflow of Mediterranean waters at depth
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15
Q

What does Mediterranean water outflowing into ocean water do if evap > precip?

A

it sinks until it reaches isopycnal that matches its own
so it can be traced through the ocean basin by its high salinity

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16
Q

Why are mediterranean seas “concentration basins”?

A

b/c the salinity of the oceanic water is increased as it passes through the mediterranean sea= concentration basin
- this happens if evap > precip

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17
Q

What happens if precipitation exceeds evaporation in the arctic?

A

freshwater gain drives an outflow into the ocean basin through the upper layer
- strong pycnocline develops, so renewal of the deeper waters is inhibited
- sfc density decreases, & the resulting density diff at the sill causes inflow of oceanic water in deep layers

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18
Q

If precip > evap, in a mediterranean sea, it becomes a ___ basin

A

dilution

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19
Q

Does the Arctic act as a dilution basin or a concentration basin for the atlantic ocean?

A

dilution
b/c precip over the arctic > evap

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20
Q

The reality of thermohaline forcing is more complex than the basic model.
- In the sfc layer, the outflow into the Atlantic Ocean is restricted to the ____ side of the sill
- The water below sill depth is what temp/ density?
- Is outflow of water from the arctic seas really restricted to the sfc layer?

A
  • western
  • colder than the oceanic water, so more dense. This means the inflowing water doesn’t sink but spreads out through an intermediate layer
  • no
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21
Q

Anywhere in the Arctic (except Norwegian Sea) has 3 layers of water masses:

A
  1. Arctic surface water
  2. Atlantic water
  3. Arctic deep/ bottom water
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22
Q

Describe the Arctic surface water:
- depth range
- temp
- salinity

A
  • surface to ~200m
  • temp is close to freezing point
  • salinity varies strongly:

Top sfc layer= ~50m thick
- low salinity due to runoff/ ice melt

Subsurface layer:
~50-200m
- strong salinity gradient but uniform temp (cold halocline)

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23
Q

What is the source of subsurface water?

A

the cold and saline shelf water produced during winter (sea ice freezing)

The seasonal sfc mixed layer is due to brine rejection during sea ice formation –> convective mixing

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24
Q

The means by which the arctic ocean halocline is maintained are very similar to those responsible for the formation of Antarctic bottom water. What’s the one big difference?

A

The Arctic halocline water is insufficiently dense to reach the bottom

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25
Q

T/F
The subsurface layer of sunken shelf water acts as a heat shield for the surface layer

A

true!
With its very low temp, this layer prevents the atlantic water from melting the ice layer above

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26
Q

What’s the source of subsurface water in the arctic?

A

relatively fresh inflow from the pacific ocean and the cold + relatively saline shelf water produced during winter sea ice freezing

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27
Q

Which layer is below the arctic surface water?

A

Atlantic water

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28
Q

Describe the atlantic water layer of the arctic
- depth range
- how does it enter the arctic?
- salinity/ temp compared to other layers

A
  • 150-900m
  • enters from the north atlantic
  • same salinity as bottom water, but is warmer
  • warmer than sfc water, but high salinity makes it denser
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29
Q

T/F

Arctic bottom water is a mix of different dense waters

A

true

  • dense waters produced through deep convection
  • dense water from arctic shelf
30
Q

Arctic bottom water is the ____ water of the world ocean. Is it found anywhere other than the Arctic region?

A

densest
no

31
Q

Explain how dense waters of arctic bottom water are produced through deep convection

A

sinking of water to the bottom occurs in events (usually storms- less than 1 week in a small area). Ice formation= concentration of salt= initiates sinking
- dense water sinks, warmer water upwells, which melts the ice and ends the cycle

32
Q

Explain how dense water from the arctic shelf becomes arctic bottom water

A

shelf water has low salinity–> initiates ice formation. Brine rejection= salinity in water below the ice increases (& is very cold)

33
Q

Give some freshwater inputs to the arctic

A
  • numerous large rivers empty into the arctic shelf
  • pacific water through bering straight –> also relatively fresh
34
Q

Give some freshwater exports from the Arctic

A
  • net freshwater transport when sea ice forms in the arctic and melts somewhere else

Mainly in the form of sea ice: goes to atlantic/ Beaufort Gyre. Can go into North Atlantic via Fram Straight and Canadian Arctic Archipelago

35
Q

Freshwater=

A

the amount of zero-salinity water contained in a volume of water with a given salinity relative to a reference salinity

36
Q

T/F

Beaufort Gyre has been getting more saline

A

false
the opposite; it’s been getting fresher

37
Q

Why has the Beaufort Gyre been getting fresher?

A

changes due to shift in pathway of Eurasian runoff forced by strengthening of low pressure on the pole

38
Q

What are the implications of freshening of the Beaufort Gyre?
- on arctic surface water
- on halocline
- on atlantic water layer
- sea ice

A

saltier arctic surface waters –> halocline weakens –> Atlantic water gets in contact with sea ice –> sea ice melts more

39
Q

T/F

The southern ocean communicates with all other oceans

A

true

40
Q

Where is the only region where the flow of water can continue all around the globe?

A

The southern ocean

ocean circulation comes closest to the situation observed in the atmosphere

41
Q

Describe the temp differences observed b/w surface vs bottom of southern ocean

A

Temp diff doesn’t exceed ~5C

This is 20% of the diff seen in the tropics

42
Q

The currents in the southern ocean are not restricted to the upper few hundred meters of the ocean, but can extend to great depths. Why is this?

A

Density variations with depth are small and the pressure gradient force is more evenly distributed over the water column

43
Q

Which current has the largest mass transport of all ocean currents?

A

Antarctic circumpolar current (ACC)

  • Moves a slab of water more than 2000m thick!
44
Q

What are the geographical limits of the southern ocean (in each direction)?

A
  • No east- west boundary
  • southern limit= antarctic coastline
  • definition of the northern limit is controversial
45
Q

What is the northern boundary of the southern ocean, defined by:
1. International hydrographic organization
2. Oceanographic point of view

A
  1. Defined is at 60 degrees S (in year 2000)
  2. Subtropical Front is the northern boundary: this is the line where the tropical/ temperate dynamics break down (permanent thermocline reaches the surface)
46
Q

Why does the topography of the ocean floor have a large impact on southern ocean circulation?

A

because the Antarctic circumpolar current reaches great depths

47
Q

The Drake Passage and the Scotia Ridge have a dramatic combined effect on the circumpolar current. What happens?

A

The current accelerates to squeeze through the gap and hits the obstacle at increases speed. It emerges highly turbulent and shifts sharply northward

48
Q

The coastline of Antarctica includes 2 major indentations:
1
2

A
  1. The Weddel Sea
  2. The Ross Sea
49
Q

Do the Weddel and Ross Seas have western boundaries? What circulation is observed in them?

A

No

Wind-driven gyres with western boundary currents

50
Q

Which winds drive the Antarctic circumpolar current?

A

westerlies (from west)
- drive the ACC –> Called the West Wind Drift

51
Q

Which winds drive the Antarctic Coastal current?

A

easterlies
- called the East Wind Drift

52
Q

Which 2 currents are the southern hemisphere equivalent of the subpolar gyres?

A

Antarctic circumpolar current (ACC) and Antarctic Coastal Current (ACoC)

53
Q

Are the gyres in the Weddell and Ross Seas cyclonic or anticyclonic? Clockwise/ anti?

A

Cyclonic gyres
- clockwise (SH)

54
Q

Are the following currents driven clockwise or counterclockwise?
- Antarctic circumpolar current
- Antarctic Coastal current

A

ACC= clockwise

ACoC= counterclockwise

55
Q

Why are there such high waves in the southern ocean?

A

infinite fetch + large wind speeds + little variation of wind direction

56
Q

Isopleths of all properties in the southern ocean are nearly _____(east-west) to great depths

A

zonal

57
Q

The isopleths in the ACC are organized into __ major fronts separating __ broad zones in which isopleths are more widely spaced.

Within the fronts, the currents are strong and __ward

A

3
4

eastward

58
Q

Describe the flow patterns in the zones between fronts in the southern ocean

A

the flow is dominated by eddies and can be in any direction

59
Q

Subtropical Front (SFT)=

A

a narrow band around Antarctica where the salinity changes rapidly from N to S and temps drop rapidly as well

60
Q

Subantarctic Front is found where?

A

the northern edge of the Antarctic circumpolar current

61
Q

The Polar Front is identified by:

A

the northernmost location of the 2 deg C isotherm (shallow temp min)

62
Q

Antarctic circumpolar current transport is concentrated in:

A

narrow bands (jets) which are focused along fronts

63
Q

T/F

In regions of the ACC, countercurrents exist

A

true

64
Q

Where does Antarctic convergence happen?

This results in the subduction of :

A

between subantarctic front and polar front (water coming from N meet waters coming from S)

= subduction of Antarctic intermediate water

65
Q

Where does Antarctic divergence occur?

The results in the upwelling of”

A

b/w westerlies and easterlies (Ekman transport in opposite directions)
= upwelling of north atlantic deep water

66
Q

Where does Antarctic Bottom Water begin its formation? Driven by what?

  • Why are polynyas important?
A

through deep convection at the continental shelf driven by the freezing of sea ice

  • Polynyas are important b/c give constant supply of dense water
67
Q

How is Antarctic bottom water formation finalized?

A

intense mixing with the water of the ACC while sinking to the bottom

68
Q

T/F

The formation process for Antarctic bottom water is a combination of deep convection and subsurface mixing

A

true

69
Q

Explain how localized formation of Antarctic bottom waters occurs in the Weddell/ Ross Seas

A

brine rejection during sea ice formation creates very cold, saline, dense water
- sinks along shelf and spreads out along the bottom of ocean basins

70
Q

Antarctic bottom water is exported to the bottom of all ocean basins. The pathway is dependent on what?

A

deep ocean bathymetry

71
Q
A

EAS 212: The Oceans (14 decks)

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