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ES2003 > Oceanography > Flashcards

Oceanography Flashcards

1
Q

What does ocean circulation do?

A

Key regulator of climate by storing and transporting heat, carbon and nutrients around the globe
Key player in driving glacial-interglacial cycles

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2
Q

What does vertical ocean circulation do?

A

Ventilates oxygen into deep waters

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3
Q

What drives vertical ocean circulation?

A

Vertical ocean circulation occurs when the density of water changes, allowing waters to sink or rise

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4
Q

Where do high surface seawater densities occur?

A

North Atlantic Ocean
The southern ocean (Antarctica)

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5
Q

What drives the circulations of oceans?

A

Temperature and salinity (thermohaline)

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6
Q

What are the characteristics of Antarctic bottom water (aabw)

A

Forms at multiple sites (polynyas) and migrates out of the Antarctic region
Very cold and quite saline
Cooling by cold wind reduces surface water temp and promotes ice formation, increasing salinity so it sinks

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7
Q

What are polynyas?

A

Ice free areas of sea in the ice cover
Ie maud rise polynyas, September 2017

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8
Q

What is the formation of North Atlantic deep water (nadw)?

A

Forms in Labrador Sea (upper NADW) and seas between Iceland, Greenland and Norway (lower NADW).
North Atlantic drift current carries warm salty Gulf Stream water into they Nordic sea and then to the arctic
Cold fresh polar surface water flows south through the Fram Strait and mixes with the warmer salty Atlantic water in the Nordic seas.
Heat from the Atlantic water is released to the atmosphere and the mixed water is dense enough to sink.

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9
Q

How can NADW and AABW be detected?

A

Based on temperature and salinity depth profiles

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10
Q

What eventually happens to deep water?

A

Mixes to become less dense ie in the pacific

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11
Q

What are the conservative properties of seawater?

A

Potential temperature and salinity

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12
Q

What speed does the ocean move at?

A

Surface currents up to 1m/s
Deep water up to 1cm/s

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13
Q

How old is the ocean deep waters?

A

Oldest deep water >2000 yrs old before upwelling in the pacific.

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14
Q

Where are intermediate water masses formed?

A

North Pacific
Mediterranean
Antarctic

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15
Q

What is simple evidence for ocean circulation?

A

More heat is emitted by the poles than received
Less heat is emitted by the equator than received

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16
Q

Why are the Antarctic and North Atlantic waters so dense?

A

Antarctic = high density from cold
North Atlantic = high density from salinity, less dense than Antarctic

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17
Q

What is the depth of the ocean?

A

Typical = 4km
Up to 11km

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18
Q

What is OCW?

A

Ocean common water
Mixture of different water bodies
Can’t tell where it formed

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19
Q

What causes the mixing of deep water?”

A

Turbulence

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20
Q

What are ocean currents principally driven by?

A

Wind

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21
Q

How fast does the earth rotate?

A

Equator 1000mph
60 degree latitude 500mph

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22
Q

Why does the earth spin at different speeds?

A

Because the earth is a sphere and thus at higher latitudes there is a smaller radius of curvature

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23
Q

Where is the coriolis effect at its minimum and maximum?

A

Minimum at equator ~0
Maximum at poles

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24
Q

In what direction do ocean gyres rotate?

A

Clockwise in the northern hemisphere
Anticlockwise in the southern hemisphere

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25
Q

What causes ocean gyres to rotate?

A

Coriolis effect which deflects water/air masses

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26
Q

At what angle did Fridtjof Nansen observe that ice moved to wind direction?

A

20-40 degrees to the right of wind direction

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27
Q

What is modelled Ekman transport?

A

Ocean transport is at 90 degrees to the right (in N hemisphere, left in S hemisphere) of wind direction

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28
Q

How deep is the Ekman layer?

A

<100m

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29
Q

Give examples of gyres that rotate in the opposite direction than expected?

A

Alaskan and Norwegian currents rotate anticlockwise

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30
Q

What is the result of Ekman transport?

A

Pile up of water in the centre of ocean gyres
Variations in sea surface height

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31
Q

What do variations in sea surface height generate?

A

Horizontal pressure gradients
Low pressure/pressure gradient force/ high pressure

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32
Q

What is geostrophic current?

A

The flow when coriolis force balances the pressure gradient

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33
Q

Where is the apex of the sea slope found in ocean gyres?

A

In the west

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34
Q

What is westward intensification?

A

When the apex of the sea slope is in the west of the gyre
Part of the coriolis effect

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35
Q

What are ocean gyres a result of?

A

Wind currents
Geostrophic currents
Westward intensification

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36
Q

What does oceanic convergences and divergences led to?

A

Vertical circulation

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37
Q

What do diverging after currents look like?

A

A sea surface valley \/ with water coming from the depths and spreading outwards. Anticlockwise rotation.
Upwelling

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38
Q

What do convergence currents look like?

A

Sea surface hill /\ with water coming in from surrounding and being forced downwards
Clockwise rotation

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39
Q

What divergence cause?

A

Upwelling of nutrient rich deep waters

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40
Q

Where do we find divergence currents?

A

Alaskan and Norwegian currents
North and south equatorial currents
Antarctic currents

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41
Q

What causes the coriolis effect?

A

Occurs due to something moving across a surface but isn’t frictionally bound to it ie wind

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42
Q

What can affect Ekman transport?

A

Shallow water friction with sea bead

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43
Q

What does the pressure gradients force do?

A

Forces water from the inside of a gyre to the outside

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44
Q

Why does the deep ocean have more nutrients than the surface ocean?

A

Phytoplankton eat nutrients in the photic zone
Dead phytoplankton sinks and acculmalates

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45
Q

Why must there be mixing in the ocean?

A

Allows deep waters to gradually decrease in density and upwelling back to the pacific and Indian oceans rather than filling ocean basins

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46
Q

How are counter surface ocean currents created?

A

By the upwelling of deep waters to the surface in the North Pacific and Indian oceans

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47
Q

What is the scale of molecular diffusion and turbulent diffusion?

A

Molecular diffusion: cm scale process
Turbulent diffusion: M to 100’s km process

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48
Q

What is turbulent diffusion?

A

Chaotic flow with irregular fluctuations in speed and direction

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49
Q

What causes turbulent diffusion?

A

Wind driven waves
Current shear
Movement over an irregular seabed
Movement along an irregular sea coast
Tidal currents

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50
Q

What is current shear?

A

Interfaces between different water bodies flowing in different directions or at different speeds

51
Q

How much faster is horizontal diffusion than vertical diffusion?

A

~10^5 - 10^8 times faster

52
Q

Why is vertical ocean mixing so much slower than horizontal mixing?

A

Because of density

53
Q

What is the effect of stratification on vertical mixing?

A

Stratified waters mix vertically much more slowly than unstratified waters

54
Q

What inhibits turbulent mixing?

A

Stratification

55
Q

What is meant by stratification?

A

Two or more distinct layers within the ocean of different densities which prevents turbulent mixing

56
Q

What drives vertical changes in seawater density?

A

Temperature (inversely)
Salinity (likewise)

57
Q

How are sea surface temperatures measured and what does it reflect?

A

By satellite
Reflect balance of heat gain (solar) and loss (albedo, conduction, evaporation)
Net heat gain below 30 degrees lat
Net heat loss above 30 degrees lat

58
Q

What is sea surface salinity defined as?

A

Practical salinity units (psu)

59
Q

What does sea surface salinity reflect?

A

Reflect balance of freshwater inputs (precipitation, runoff, ice melt ) and outputs (evaporation, freezing)

60
Q

Where is sea surface salinity highest?

A

Atlantic, Mediterranean Sea
In subtropics where evaporation>precipitatiom

61
Q

What is an isotherm?

A

Lines joining points of equal temperature

62
Q

What is a isohaline?

A

Lines joining points of equal salinity

63
Q

What is a thermocline?

A

Section below which temperature changes very rapidly with depth

64
Q

What and where is the mixed surface layer?

A

Surface section where temperature has little variation
~10-300m

65
Q

How far can solar energy penetrate the ocean?

A

<100mk, mostly first few metres

66
Q

How can heat be transmitted deep into the water column?

A

Turbulent mixing
Conduction
Downwelling

67
Q

Are thermoclines permanent or temporary?

A

Most oceans have a permanent thermohaline
Seasonal thermoclines can form in mid latitudes

68
Q

Does salinity increase or decrease with depth?

A

Typically decreases at low and mid latitudes
Can increase

69
Q

What is a halocline?

A

The section of a profile where salinity changes very rapidly

70
Q

What is a isopycnal?

A

Lines joining points of equal density

71
Q

What is a pynocline?

A

Section of a profile where density changes very rapidly

72
Q

How does the pynocline change with latitude?

A

Equator: very horizontal
Sub tropics: 45 degrees angle
High latitude: vertical

73
Q

How does stratification of the water column affect primary production?

A

Tropical Atlantic has permanent stratification therefore no nutrient recycling from depth

North Atlantic has seasonal stratification that breaks down in winter, allowing upwelling of nutrient rich deep waters annually

74
Q

What is the rate of molecular diffusion dependent on?

A

Temperature

75
Q

How fast does molecular diffusion travel in seawater?

A

10^-5 cm2 s-1

76
Q

Why is heat diffusion faster than salt diffusion?

A

X100 faster
Warm molecules move faster and bounce off each other, transmitting heat

77
Q

What is the affect of temperature diffusing faster than salt?

A

Warm salty water overlies cool, fresh water

78
Q

What is the impact of double diffusion?

A

The temperature gradient will diffuse away in 1% of the ice it takes for the salt gradient to diffuse.
Remaining salinity gradient becomes unstable, and overturning occurs

79
Q

What is salt fingering?

A

When sinking cells of salty water (that are losing heat) alternate with rising cells of fresher water that are gaining heat.

80
Q

What is the scale of salt fingering?

A

1-5 cm wide
10s cm long

81
Q

What is the result of salt fingering?

A

Thermohaline staircase in oceanographic profiles

82
Q

Where does salt fingering occur?

A

Where warm saline waters overlie cool fresh waters
Subtropics

83
Q

How does climate change affect the Meridional ocean circulation pattern?

A

Influx of freshwater from the melting of high latitude ice
Increased evaporation by higher temperatures and increased wind speed

84
Q

What is the importance of the meridional ocean circulation pattern?

A

Transports heat from tropics to high latitudes
Ventilates the deep ocean
Redistributes nutrients, oxygen, carbon and pH

85
Q

What trend was observed in the thickness of AABW over the past twenty years?

A

Reductions in thickness from 64m/decade (Weddell sea) to 132m/decade (Mawson sea)

86
Q

What is a possible reason for a slight recovery of Antarctic bottom water formation?

A

Positive El Niño+Sam -> weakened easterly winds -> reduced sea ice transport -> more space in Ross sea -> increased sea ice formation on the shelf -> saltier water ->increased AABW

87
Q

How is NADW formation tracked?

A

Using two arrays (RAPID sub tropics, OSNAP sub polar) measuring temperature, salinity, current velocity

88
Q

What is the trend of change in the upper and lower sections of AMOC?

A

Reduced northward flow of surface waters
Reduced southward flow of deep waters

89
Q

What is the decrease of NADW circulation annually?

A

~0.5 Sv/year

90
Q

What is Sv?

A

Sverdrup
Measure of current volume
1 x10^6 m^3

91
Q

What is MOC?

A

Meridional overturning circulation

92
Q

What is EKM?

A

Wind driven Ekman component

93
Q

What is UDW?

A

Upper deep water
1100-3000m

94
Q

What is LDW?

A

Lower deep water
3000-5000m

95
Q

What happens if NADW formation is reduced?

A

Velocity of entire thermohaline circulation is reduced

96
Q

Why is the MOC closing
?

A

Decrease in high latitude surface water density
High latitude surface waters becoming warmer and more buoyant
Input of freshwater from melting ice sheets = less saline

97
Q

What is the biological pump?

A

Phytoplankton creates sugar and takes up nutrients and carbon (co2)
Phytoplankton is consumed and released as fecal matter, or dies and decays.
Aggregate forms from matter and sinks into deep water
Remineralisation, carbon export, digestion

98
Q

What is the vertical profile of nutrients in the ocean?

A

Depleted in surface waters
Concentrated at depth

99
Q

What is the slope where nutrient concentrations increase the most rapidly called?

A

Nutricline

100
Q

What is the biolimiting factor?

A

Where concentrations are zero at the surface

101
Q

Where are nutrient concentrations the highest and lowest in the surface?

A

Lowest in open ocean waters
Highest in upwelling regions or in areas of coastal runoff

102
Q

Where are there high concentrations of nutrients in the deep ocean?

A

In areas of deep water with great age

103
Q

What is he impact of climate change on ocean stratification and primary production?

A

Surface warming leads to:
Increased water stratification
Decreased vertical mixing
Decreased primary production

104
Q

What is stratification principally controlled by?

A

Temperature

105
Q

What has caused the strengthing of stratification around Antarctica?

A

Salinity changes

106
Q

What is the effect of off shore wind farm structure on stratification?

A

Mixing effect
Laminar flow to strong vertical mixing

107
Q

what is the chemical composition of seawater?

A

in 1kg. 965.6g water, 35.4g salinity including sodium, chloride, calcium, bicarbonate, magnesium, potassium and sulphate

108
Q

what is the relationship between seawater and rain?

A

rainwater is dilute seawater that is derived from sea aerosols
has far lower concentrations of na and cl

109
Q

what is the chemical difference between seawater and river water?

A

Seawater NaCl rich, rover water depleted but high in Ca2+ and HCO-3 due to weathering of carbonate r0cks

110
Q

what is the length of the hydrological cycle?

A

~4000 years

111
Q

what does seawater chemistry reflect?

A

inputs: evaporated river water, oceanic volcanism, aeolian dust, atmospheric gases
outputs: inorganic precipitation, biological processes, export to sediments

112
Q

what are biological processes?

A

production of organic matter
biogenic precipitation

113
Q

how can we classify the elements/ions in seawater?

A

based on their vertical profiles
conservative, nutrient behaviour, scavenged elements

114
Q

what are the characteristics of conservative elements?

A

constant normalised salinity with depth
includes most major seawater ions (Na, Cl), and non-major elements with weak biological reactions that are relatively soluble and not particle reactive
long residence time x10^6 -10^8 years

115
Q

What elements are minor non-conservative and why?

A

calcium - small variations due to formation and dissolution of CaCO3 and hydrothermal vent input
magnesium - removed at high temp hydrothermal vents
dissolved inorganic carbon - formation and dissolution of CaCO£ and organic matter
SO2-4 - conservative in oxic basins, not in anoxic basins or sediments

116
Q

what are the characteristics of nutrient behaviour elements?

A

concentrations controlled by biological cycling
depleted in surface waters and increase with depth
biologically essential elements macronutrients (P, N, Si) or micronutrients (Fe, Zn)
elements with no or limited biological function (Ba, Cd)
residence time = x10^3 - 10^5 years

117
Q

what are the characteristics of scavenged elements?

A

concentration decrease with depth
adsorption of ions onto particles (dust, minerals, biological, bacteria)
overcomes friction and drops through water column as accumulations
very particle reactive
high conc in Atlantic deep waters compared to pacific
ie aluminium supplied by aelion dust
residence time = x10^2 - 10^3 years

118
Q

what is residence time?

A

the average time an element spends in the ocean before being removed
=total mass dissolved in ocean/rate of supply or removal

119
Q

why do scavenged elements have a low residence time?

A

rapidly exported to sediments

120
Q

What is a possible application of understanding ocean chemistry?

A

palaeoceanography

121
Q

how does palaeoceanography use seawater chemistry?

A

chemistry of biogenic CaCO3 records seawater chemistry
chemistry of CaCO3 is affected by environment i.e. strontium substitutes for calcium in aragonite and low temperatures
Cadmium substitutes for calcium in aragonite cooler waters in areas of upwelling

122
Q

what is the ITCZ?

A

intertropical convergence zone
area where northern and southern trade winds meet
moves seasonally and is divergent causing upwellings

123
Q
A

ES2003 (5 decks)

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