Oceanography Flashcards
1
Q
Why is ocean circulation and chemistry important?
A
Balances the global heat budget
Key regulator of climate via storing & transporting, heat, carbon and nutrients globally
vertical ocean circulation ventilates oxygen into deep ocean
key player in driving glacial and interglacial cycles
2
Q
What is the driver of vertical ocean circulation?
A
Density
3
Q
What are the two locations with sufficient density for surface seawater to sink?
A
North Atlantic and Southern Ocean
4
Q
What drives the thermohaline circulation?
A
Temperature and salinity
5
Q
What does surface seawater does require to facilitate sinking?
A
Sufficient density
6
Q
What is AABW?
A
Antarctic Bottom Water formation
7
Q
How does AABW form?
A
At multiple sites, mainly polynyas, and migrates out into antarctic region
8
Q
What are polynyas?
A
Ice free areas of sea in the ice cover, can be very large
9
Q
How does polynyas produce deep water?
A
cooling by antarctic winds at the sea surface promotes ice formation and increases salinity causing sinkage
10
Q
Where is a majority of deep water trapped in Antarctica?
A
Basin on the continental shelf
11
Q
What can the AABW and NADW be detected by on depth profiles?
A
temperature and salinity
12
Q
What is the NADW?
A
North Atlantic Deep Water formation
13
Q
Where does NADW form?
A
The Labrador sea [upper] and seas between iceland, greenland and norway [lower]
14
Q
How does lower NADW form?
A
fresh polar water from Fram strait mixing with N Atlantic water in nordic seas, and with heat loss causing sinkage of mixed waters
15
Q
What do chimneys have in relation to NADW?
A
NADW forms intermittently in chimneys, can be <100km in diameter
16
Q
What must sinking NADW deep water overflow?
A
the shallow ridge running from greenland to scotland
17
Q
What area has lower surface densities than North Atlantic and Southern Ocean?
A
North Pacific
18
Q
Where is there no deep water formation?
A
North Pacific Ocean
19
Q
What is Ocean Common Water (OCW)?
A
Water where sufficient mixing causes the loss of ocean bodies fingerprint
20
Q
What happens to deep water as its transported for site of formation?
A
Topography causes turbulence between layers resulting of mixing of water leadings and degradation of deep water
21
Q
Give and example of where deep water degradation occur?
A
The pacific
22
Q
What are conservative properties of seawater?
A
Potential temperature and salinity
23
Q
How old is North Atlantic deep water compared to south?
A
North is 400yrs and South is +1000yrs
24
Q
Why is deep water much older than surface water?
A
surface currents can move up to 1m.s but deep water currents move at ~1cm/s, so low recycling rate of deep water
25
How old can the deep waters be before upwelling occurs?
>2000yrs
26
What are surface ocean currents driven by?
wind, coriolis effect
27
What direction do Northern Hemisphere gyres rotate?
Clockwise
28
What does the coriolis force affect?
Items moving across the ground which aren't frictionally bound to it
29
How fast dos the equator rotate compared to the poles
~1000mph vs ~500mph
30
Why if there a difference in equator and poles rotation speed?
The curvature of the earth
31
What is the coriolis effect like at the poles and equator?
Maximum at poles and zero at equator
32
What causes the difference between northern and southern gyre rotation?
Coriolis effect
33
How does the Coriolis affect work?
It deflects water and air mass via rotation of the earth
34
Which explorer show cased the coriolis effect in 1893 - 1986?
Fridtjof Nansen, Fram expedition
35
Which physicist developed a model to explain change in water direction with increasing depth?
Walfrid Ekman
36
How deep is the Ekman layer?
<100m
37
What is difference between modelled ekman transport and reality?
The deflection is less
38
Why does water ten to move in direction of wind in shallow water?
bottom friction dominates over ekman
39
Which currents rotate in opposite direction than predicted by coriolis effect?
Norwegian and Alaskan currents
40
What does ekman cause in centre of gyres?
Water to pile up, 1.4m above average
41
What does variation in sea surface height generate?
Horizontal pressure gradient forces
42
What happens when pressure gradient is balanced by coriolis force?
geostrophic equilibrium
43
What is the flow around the water pile up in gyres?
Geostrophic current
44
What are ocean gyres a combination of?
wind currents, geostrophic currents and westward intensification
45
TRUE or FALSE: ocean gyres apex is in the centre of the gyre
FALSE
46
What is the westward apex of gyres?
Westward intensification
47
What causes westward intensification?
coriolis force effect difference on equator and pole water flow
48
What can lead to vertical circulation not driven by density?
oceanic convergences and divergences created by wind action
49
TRUE or FALSE: Divergence creates downwelling
FALSE
50
What Northern Hemisphere currents are divergences?
Alaskan, norwegian and scandinavian currents
51
What does upwelling cause?
nutrient rich deep water being brought to the surface
52
What is upwelling important for?
phytoplankton and fish populations
53
What are the currents on respective sides of equators?
divergences
54
TRUE or FALSE: Chlorophyll concentrations along the equator are higher than surrounding open ocean
TRUE
55
What does antarctic divergence promote?
upwelling of relatively deep waters i.e. NADW
56
Why is thermohaline a rarely used term now?
It implies that temperature controls the circulation of water despite up/downwelling of cold water
57
What happens to deep water as it moves to the equator?
Degrades, losing density and upwelling to the surface in N Pacific/indian ocean
58
What does upwelling of degraded deep water form?
counter surface ocean currents
59
What is OCW in the Pacific?
Ocean common water created by a mixture of differnet water bodies
60
What created ocean mixing?
Molecular diffusion and turbulent diffusion
61
To what scale is molecular diffusion?
~cm's
62
To what scale is turbulent diffusion?
~mm to ~100s km
63
What is turbulent diffusion?
chaotic flow with irregular fluctuations in speed and direction
64
Give examples of turbulent diffusion
wind driven waves
current shear
movement over/along irregular seabed and coast
tidal currents etc.
65
Define current shear
Interfaces between different water bodies flowing in different directions of at different speeds
66
Ocean movement can be tracked by ....
fluorescent dyes injected at depth over a wide area and observed arially
67
What can the tracked spreading of fluorescent dye be used for?
estimate turbulent diffusivity
68
What is evidence by fluorescent dye tracking?
Horizontal mixing is faster than vertical
69
How much faster is horizontal mixing than vertical?
~10^5 - 10^8
70
TRUE or FALSE: the difference in vertical and horizontal mixing is due stratification of ocean layers i.e. density
TRUE
71
TRUE or FALSE: Unstratified waters mix vertically slower than stratified waters
FALSE
72
Strification ... turbulent mixing
inhibits
73
Where are water columns highly stratified?
Tropics
74
Define straification
there are two or more distinct layers within the ocean of different densities which prevent turbulent mixing
75
... and ... drives vertical changes in seawater
temperature, salinity
76
What can be sea surface temperature be measured by?
Satellites
77
Balance of heat gain/loss reflects what?
Sea surface temperature
78
What is creates heat loss?
albedo, conduction, evaporation
79
What range latitude is heat gain and loss?
gain ~<30o lat
loss >30o lat
80
What are salinity units?
dimonsionless
81
what does sea surface salinity reflect?
balance of freshwater inputs (precipitation, runoff, ice melt) and outputs (evaporation, ice freezing)
82
What is the difference between the Pacific and Atlantic Oceans?
Atlantic has higher salinity than Pacific
83
Why does tropics have greater salinity?
evaporation > precipitation
84
Where in the tropics is the area of higher salinity?
centre of gyres has increased evaporation and low precipitation
85
what is constant away from the sea surface?
temperature and salinity
86
Define Isotherms
Lines joining points of equal temperature
87
Define Isohalines
Line joining points of equal salinity
88
Define thermocline
The section below where temperature changes very rapidly with depth
89
Define mixed surface layer
the surface section where temperature shows little variation with depth
90
What is the typical depth of the mixed surface layer?
20s - ~300m
91
Where is most solar energy absorbed in the ocean?
first few m's
92
What depth do small and large wavelengths penetrate the ocean surface?
small: 100m
large: ~1m
93
How is heat transmitted deeper in the water column?
turbulent mixing, conduction, downwelling
94
What do most oceans have?
Permanent thermoclines
95
What do some mid latitude oceans have?
Seasonal thermoclines
96
TRUE or FALSE: Salinity depth profiles are more variable e.g. salinity can increase with depth
TRUE
97
Define halocline
The section of the profile where salinity changes very rapidly
98
TRUE or FALSE: The mixed surface salinity later isn't similar in depth to the mixed surface temperature layer
FALSE
99
What is used to calculate density?
temperature and salinity
100
Define Isopyncals
Lines joining points of equal density
101
Define pynocline
the section of where density changes very rapidly
102
What does the permenant starification in the tropical atlantic prevent?
Nutrient recycling from the depth
103
What is the consequence of seaonsal breakdown of straification in the north atlantic?
Upwelling of nutrient rich deep waters annually which supports high productive of primary production
104
What are molcular diffusion rates dependent on?
temperature
105
What is the molecular diffusion rate in seawater?
~10^-5 cm^2 s^-1
106
What is the differnce bewteen salinity and heat diffusion?
Salinity requires movement of ions from high to low which is much slower than heat diffusion
107
Why is salinity diffusion slower than heat?
Heat has two modes of transfer; physical molecule movement and conduction
108
Define molecular diffusion
the motion of individual molecules
109
How much faster is heat diffusion than salinity?
~100 x
110
What is the result of greater tempertaure diffsion than salinity in the water column?
The temperature gradient will becomre constant causing the ermaining salinity gradient to become unstable resulting in overturning (cm scale process)
111
Define double diffusion
The difference in heat and salinity diffusion rates
112
Define salt fingering
sinking cells of high salinity water alternated with rising cells of fresher water
113
How wide and long are the fingers?
1-5 cm wide and 10s cm long
114
What does salt fingering create?
thermohaline straircases in oceanographic profiles
115
Where does salt fingering occur?
thermocline (200 - 300m) and at depth (however limited)
116
Where is salt fingers more frequent?
atlantic, but at depth its the subtropic atlantic
117
What is the most important mechanism in nutrient transport?
mechanical turbulence
118
Where is salt fingering the most important mechanism for nutrient transport?
sub tropics atlantics, Australian coast and sub indian ocean
119
What is the MOC?
Meridional Ocean Circulation
120
Why is the MOC important?
Balances heat budget, ventilate deep ocean and redistributes nutreinets, oxygen, carbon and pH
121
How deep is the AABW in the anatrtaic?
2500m
122
How has the AABW been affected by climate change?
reduction in thickness in somes place by 20% over 20yr period
123
Where is a site of potentail AABW recovery?
Ross Sea
124
What has supported Ross sea AABW recovery?
+SAM and El Nino
125
How has the Ross sea recovered?
Weakened easterly winds ->reduced sea ice import -> increased sea ice formation on shelf -> saltier DSW -> increased AABW formation
126
What is something about the Ross sea which impliatces its recoevry?
its a rare combination of climatic events and is very small recovery overall
127
What two arrays moniter the NADW?
RAPID and OSNAP
128
What do the arrays moniter of the NADW?
Temperature, salinity and current velocity
129
What is a Sverdrup?
million metre cubed per second of seawater
130
What produced the winter of 2010?
reduced northward flow of surface waters and reduced southward flow of deep waters
131
What was the overall finding of the RAPID array?
Decreased northward transport of MOC is balanced by decrease in southward transport of dee NADW
132
What was the decrease finding of the RAPID array?
~0.5 Sv year-1
133
What is the preditcted decrease from anthropogenic climate change?
~0.5 Sv decade-1
134
Whate does the ASNAP array overserve?
compenents of the AMOC (since 2014)
135
What did the updated RAPID record for 2018 show?
There is a regime shift, not a steady decrease, unsure if this will change back
136
What is a consequence of decreased NADW formation?
reduced velocity of entire thermohaline circularion
137
Why is MOC slowing?
1) decrease in high lat surface water density
2) high lat surface waters become warmer and more bouyant
3) high lats become less saline with increased freshwater input (contintal ice sheets)
138
What is the biological pump?
the export of biological materials to the deep ocean
139
When organic material interact to form an aggregate formation, what happens?
sinks to deep ocean
140
What are the vertical profiles of nutrients in ocean?
Depleted in surface and increase in concentration at depth
141
define biolimiting
low/zero concentrations at surface where phytoplankton utilise inorganic nutrients which limits biological activity
142
define nutricline
slope where nutrient concentrations increase most rapidly
143
Where are surface nutrient concentrations highest and lowest?
L; open ocean
H; upwelling region & coastal runoff areas
144
TRUE or FALSE: Nutrients concentrations decrease in deep waters with age
FALSE
145
TRUE or FALSE: Atlantic has less nutrients as its younger
TRUE
146
define inter-ocean fractionation
difference between ocean nutrients
147
What is effects of climate change on ocean with surface warming?
increased stratification + decreased overturning and primary production
148
What has happened to antartic waters?
increased in freshwater volume
149
What has happened to the surface mixing layer?
gotten deeper
150
What is straification principally controlled by?
temperature
151
Whats strengthens stratification?
World; temp
Antartica; salinity
152
How is deepening of the surface mixed layer suggested to function?
increase in salinty associated with surface warming and high latitude surafce freshening + wind driven intensification of upper-ocean turbulence
153
What does poor stratification promote?
seasonal cholorphyll activity
154
What conclusion was draw between stratification and primary production?
no significant correlation on a decadel scale
155
What has happened to the north sea primary production?
reduced, less carbon fixation
156
What could wind turbines do to north sea?
promote primary production by decreasing predation and straification with circular vertical movement
157
158
What is the proportion of dissolved constituents in ocean?
Major > 1ppm
Minor > 1ppb
Trace < 1ppb
159
In 1L of seawater what is the main elements?
sodium, sulphate, magnesium, bicarbonate, calcium, potassium, chloride
160
What does TDS stand for?
Total dissolved solute
161
What minerals is seawater high in?
sodium and chloride
162
What is rain?
dilute sea water
163
explain why rain is dulite seawater?
aerosols carry marine salts into atmopshere
164
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