Ocean Circulation Flashcards
(175 cards)
1
Q
(L1)
What is meridional ocean (thermohaline) circulation?
A
A global ocean circulation system which connects the worlds oceans.
2
Q
What is meridional ocean circulation driven by?
A
Wind and variations in water density.
3
Q
What does the term Thermohaline not encompass?
A
The importance of wind in driving the circulation system.
4
Q
Why is meridional ocean circulation important?
A
- It caries heat from tropical Atlantic to higher latitudes
- Ventilates the deep ocean
- Redistributes nutrients, oxygen, carbon, pH
5
Q
What is sea density a function of?
A
Temperature and salinity
6
Q
Which part of the globe has the highest sea-surface density?
A
The poles
7
Q
What are isopycnals?
A
Contours of equal density (sigma)
8
Q
Why do we use potential temperature (theta)?
A
It is in situ temperature corrected for the effects of compression at depth
9
Q
What density is seawater?
A
1.025-1028g cm⁻³
10
Q
What are the conditions of Antartic bottom water?
A
Very cold, high salinity
11
Q
Where does AABW form?
A
On the shelves of the Weddell Sea, Prydz Bay, Adelie Land and Ross Sea Polynyas
12
Q
How does deep water form from coastal/latent polynyas?
A
Coastal polynyas occur where the wind drives newly formed ice off shore creating areas of open ocean. The continual freezing cools the surrounding waters and increases it’s salinity. The sinking water circulates over the continental shelf and then forms deep waters/
13
Q
How does deep water form from open ocean/sensible polynynas?
A
Heat is lost from the water by convection/conduction (sensible heat loss) and the cooled water sinks.
14
Q
How are open ocean polynyas kept open?
A
By the upwelling of warm waters
15
Q
Where does deep water go after it is formed?
A
Most remains trapped in the deep basins around the Antarctic but some escapes and contributes towards the world oceans.
16
Q
Where does Antarctic bottom mix with less dense water?
A
Antarctic Circumpolar Current to form Antarctic Circumpolar Current bottom water.
17
Q
What causes AABW formation reduction?
A
Freshening of surface Antarctic Waters due to increased glacial melt and possibly increased precipitation.
18
Q
Where is North Atlantic Deep Water (NADW) formed?
A
In the Labrador sea (upper) and the seas between Iceland, Greenland and Norway (lower).
19
Q
Where is NADW formed in the Labrador sea?
A
Cold, polar surface water flows through the Fram straight in the East Greenland Current. This mixes with warmer water Atlantic water, rounds the southern tip of Greenland and flows into the Labrador sea as the west Greenland Current.
20
Q
How is NADW formed in the Nordic Seas?
A
Fresh polar water in the Nordic sea and the warm salty Atlantic water mix. Heat from the Atlantic is released to the Air above, the mixing and cooling increases the density of the surface water so it becomes dense enough to sink.
21
Q
What are the three routes taken by NADW to cross across the shallow ridge between Greenland and Scotland?
A
a) The Denmark Strait
b) The Shetland Faroe ridge
c) Scotland Faroe channel
22
Q
What doe the Atlantic Intermediate water mic with to become NADW?
A
Nordic overflow
23
Q
What two methods are used to track NADW?
A
RAPID and OSNA
24
Q
What do the moorings monitors measure in order to analyse Atlantic meridional overturning circulation?
A
Conductivity(salinity), temperature, depth, current direction and intensity.
25
What has been the decadal change in north flowing NADW current?
Significant decrease in volume.
26
What has been the decadal change in the south flowing current?
Significant increase in volume.
27
What is the reason for this anomaly?
Reflects the decadal variability in the AMOC.
28
At what rate doe the thermohaline current move?
1cm/s
29
Why is there currently no deep water formation in the North Pacific
The surface water is too fresh for deep water formation.
30
What is the fingerprint for AAIW, AABW and NADW?
Temp-4 Salinity - 34.4, Temp - 0 Salinity - 34.7, Temp-2 Salinity- 34.9.
31
(L2)
| What does the Coriolis Affect?
Items moving across the ground that are not frictionally bound to it.
32
What direction does the Coriolis force senf objects from the Equator?
To the right in the north and to the left in the south.
33
What direction do the main ocean gyres rotate?
Clockwise in the northern hemisphere and anticlockwise in the southern hemisphere (caused by the Coriolis effect).
34
Why is the sea surface higher in the centre of the gyre than at the edges?
Ekman transport (using coriolis) forms a dome which sinks compressing the layers beneath and forcing the layers to spread.
35
When do we reach geostrophic balance?
When the coriolis force equals the pressure gradient causing flow perpendicular.
36
Where is the Coriolis effect at its greatest?
At the poles
37
What impact does this phenomenon (known as western intensification) have on water water flowing in the gyre at the equator?
It is deflected much less than water flowing at higher latitudes.
38
What type of currents does westward intensification create?
Fast deep narrow western boundary currents (i.e. gulf stream) and shallow slow wide eastern boundary currents (i.e. Canary current)
39
What are currents that travel in different directions to the wind called?
Counter currents
40
Where are the divergences on a world map?
At the equator, beside Antarctica and above Norway and west of Canada.
41
What happens to NADW as it moves north?
It gains heat from the atmosphere and is freshened by excess precipiatation -> now called AASW
42
What water body does Antarctic surface water converge with?
The sub antarctic water (which is much warmer).
43
What then happens to the antartic surface water?
It sinks to form the Antarctic intermediate water
44
(L3)
| What does ocean mixing reflect?
Molecular diffusion and turbulence diffusion (chaotic flow with irregular fluctuations in speed and direction)
45
Which is quicker-horrizontal or vertical turbulent diffusion?
Horizontal by about 10^5
46
What can the spreading of fluorescent dyes be used to estimate?
Turbulent diffusivity
47
What inhibits vertical ocean mixing?
Density
48
Which mix more-unstratified or stratified waters?
Unstratified
49
What drives vertical changes in seawater?
Temperature
50
What does sea surface temperature reflect?
Balance of heat gain (solar) and heat loss (albedo, conduction, evaporation)
51
What drives vertical changes in seawater density?
Seawater salinity
52
What are isotherms?
Lines joining points of equal temperature are called isotherms.
53
Where do salinity and temperature become more constant?
Further from the surface.
54
What do we call the surface section where temperature shows little variation with depth?
Mixed surface layer.
55
What is the name given to the section of the profile where temperature changes very rapidly?
Thermocline
56
Most solar energy is absorbed within a few meters of the surface of the ocean. How can heat be transmitted deeper?
By turbulent mixing, conduction and downwelling.
57
At which time of year would we expect to see less efficient mixing of the surface warming with the waters at depth and stratified layers?
Summer months.
58
What is the name given to the section of the profile where salinity changes very rapidly?
Halocline.
59
What can we use to work out density?
Temperature and Salinity.
60
What are the lines joining points of equal density called?
Isopycnals
61
What is the name of the section of the profile where density changes very rapidly?
Pynocline
62
Which water would have the greatest pynocline (the greatest variation in density) - equator, tropics or high latitude?
Equator, it has a very low density at the surface (warm water)
63
Why does the tropical Atlantic not show a boom in nutrients over summer?
It has a permanent Thermocline so nutrients at depth are not recycled to the surface.
64
Why does the northern Atlantic show a boom in nutrients over summer?
It has a seasonal Thermocline which breaks down over the winter allowing nutrients in deeper waters to be recycled to the surface.
65
What is the impact of climate change on ocean stratification and primary production?
Surface warming-increased water stratification, decreased vertical mixing/overturning of surface waters and decreased primary productivity.
66
Which is faster- the diffusion of heat or salt?
Heat (100x)
67
What happens if warm salty water overlies cold fresh water?
The water column will overturn/mix
68
What is salt fingering?
When sinking cells of salty water alternate with rising cells of fresher water.
69
Where does salt fingering occur?
When warm, saline waters overlie cool, fresh waters.
70
Does Salt fingering mic water faster than local turbulence?
Yes- forms a Thermohaline staircase.
71
What happens if cool fresh water overlies warm salty water?
Temperature will diffuse faster than salt so temperature will become constant throughout the column. At some point temperature will be constant but salinity will be lower at the surface. the column will be stable.
72
give a situation where fresh water overlies warm salty water.
At high latitudes where ice melts.
73
(L4)
| What are the main elements in seawater?
Chloride, sodium, sulphur, magnesium, calcium and potassium.
74
What are the main elements in rainwater?
Chloride, sodium, sulphur, magnesium, calcium and potassium (same as seawater).
75
What re the major ions in river water?
Bicarbonate and calcium.
76
Why doe rainwater and seawater have the same composition?
Aerosols carry marine salts into the atmosphere.
77
What doe river water composition reflect?
Rock weathering
78
Where does chloride in water come from?
Volcanic gasses- large quantities were emitted early in Earth's history.
79
Why is there less Ca²⁺, HCO₃₋ and SiO₂ in seawater?
They get remover quicker than Na and Cl
80
Where do Mn and Ca come from?
Hydrothermal vents
81
Where does Fe and Al come from?
Aeolian dust.
82
What does a conservative element/ion profile in seawater look like?
The concentration of ions to salinity (Na, Cl, most non-major elements which are non reactive and relatively soluable) is constant with depth in different oceans.
83
Describe a nutrient (recycled) profile.
The concentration of these elements/ions is controlled by biological cycling. Profiles are depleted in surfaced waters and concentrations increase at depth.
84
Why are nutrient levels low at shallow depths?
Because Phytoplankton utilise inorganic nutrients in the photic zone.
85
What is the slope where nutrient concentrations increase most rapidly?
Nutrucline
86
Which ocean has a greater concentration of nutrients?
The Pacific- it is older
87
Which nutrient is the biggest ocean primary productivity limiter?
Nitrate
88
Which elements undergo nutrient behaviour?
Biologically essential elements (P, N, Si, Fe, Zn)
89
Why are calcium and carbon called bio-intermediate nutrients?
They show some depletion in surface waters but are never limiting.
90
What do scavenged element profiles look like?
They show some concentration decrease with depth.
91
Describe the process of scavenging.
Ions are absorbed onto particles such as bacteria/fecal pellets and are dropped through the water column.
92
What type of elements are scavenged?
Elements which are very particle reactive- such as aluminium- so have short ocean residence times.
93
Is there a higher percentage of scavenged elements in Atlantic or Pacific ocean?
Atlantic
94
Why? (Is there a higher percentage of scavenged elements in Atlantic or Pacific ocean?)
Pacific deep waters are very old so there has been plenty of time for these particle reactive elements to be scavenged onto particles and out of dissolved phase.
95
How are scavenged elements delivered?
By rivers or as dust to surface waters
96
What is the equation used to calculate residence time?
Total mass dissolved in ocean/rate of supply (or removal)
97
Which elements (conservative/nutrient/scavenged) have the shortest and longest residence time?
Scavenged has the lowest and conservative has the longest.
98
Fe has a nutrient type profile yet does not exhibit its properties fully- which properties of the nutrient type profile does iron not exhibit?
The inter-ocean fractionation and long residence time.
99
What minerals record seawater chemistry?
Biogenic calcium carbonates.
100
Which elements are not well preserved in ocean sediments and calcareous structures?
Nitrogen and Phosphorus.
101
How can we measure the Cd concentration in seawater?
Look at the Cd/Ca in carbonates as Cd substitutes in place of Ca.
102
Is Cd/Ca higher in Atlantic or Pacific?
Pacific
103
Is Cd/Ca higher in glacials or interglacials?
Glacials
104
What might the analysis of Ba and Cd in carbonate minerals/corals reflect?
Presence of seawater upwelling
105
Where does ocean divergence/ upwelling occur?
Along the equator.
106
What are the three wind currents associated with this upwelling?
South equatorial current, equatorial counter current, north equatorial current.
107
Coral records may potentially reflect movement of the intertropical convergence zone. What is this?
The area where the northern and southern winds meet.
108
(L5)
| Describe oxygen concentrations at different depths.
-High at surface waters, minima at 300-800m at OMZ, increases at depth.
109
What happens to the solubility of oxygen with temperature?
Solubility decreases as temperature increases.
110
Why is oxygen concentration high at ocean surfaces?
Gas diffusion and photosynthesis - CO2+H2O -> (CH2O)n + O2
111
What happens at the compensation depth?
Light declines and photosynthesis and respiration balance, below this respiration dominates and CO2 is produced and O2 consumes.
112
What dies the oxygen minima zone represent?
High respiration associated with the decay of sinking particulate matter.
113
Why does oxygen increase again at depth?
Input of cold, oxygen rich deep waters which formed at the poles.
114
Which ocean contains more dissolved oxygen at the surface?
Atlantic
115
Why? (Which ocean contains more dissolved oxygen at the surface?
Pacific deepwater are NADW which have migrated all the way through the Atlantic and Indian Ocean basins. On this journey particles have dropped from the surface water into the deep water and have decomposed using up oxygen.
116
Which ocean contains more dissolved oxygen at the surface?
Much of a muchness.
117
What happens to NADW as it moves across the surface of the ocean floor?
It decreases in oxygen as it is gradually consumed during respiration particularly as sinking organic particles are decayed by bacteria.
118
What impact has climate change had on oceanic dissolved oxygen?
The oxygen minimum zone has expanded and intensified during the last 50 years. The decline in oxygen content has been most intense in the tropical Atlantic, where present hypoxic regions are small compared with the Pacific and Indian Oceans.
119
What is Hypoxic?
The region of stress threshold for mobile macroorganisms (60-120umolkg-1)
120
What is suboxic?
Less than 10umolkg-1
121
What is anoxic?
No dissolved oxygen
122
What is causing OMZ expansion?
Reduction in convective mixing from surface (due to increased stratification)
Reduction in deep water subduction due to increased seawater density at deep water formation sites.
Reduction in O2 solubility in warmer surface waters.
Increased O2 consumption from organic decay at depth.
123
Describe the solubility of CO2 with regards to temperature, salinity and pressure.
Like oxygen, CO2 solubility increases as temperature and salinity decrease and increases with increasing pressure.
124
What happens to dissolved carbon dioxide in water?
It partitions between carbon species-bicarbonate and carbonate to produce protons.
125
Does increasing atmospheric carbon dioxide increase or decrease the concentrations of aqueous carbon dioxide, H⁺ bicarbonate and carbonate?
Increases aqueous CO₂, bicarbonate and H⁺ but decreases carbonate.
126
What is the equilibrium constant dependent on?
Temperature, Salinity and Pressure.
127
If we double atmospheric CO₂ what will happen to HCO3?
We will drive the reaction to the right a little.
128
Why only a little?
The concentration of hydrogen ion pH 8.1 is very small (by a factor of 10^6) compared to carbon species.
129
Why doesn't the concentration of carbonate increase too?
Because protons are generated in the formation of bicarbonate, this affects the concentration for protons in the second stage i.e. the (CO₃²⁻)(H⁺) increases. In order for an equilibrium to be met, the concentration of bicarbonate must also increase driving the reaction to the left.
130
What two factors are ocean pH controlled by?
Total dissolved inorganic carbon and total alkalinity.
131
What is the total alkalinity?
The abundance of bases which can accept protons.
132
Where does total dissolved carbon reach a maximum due to the release of CO2 by respiration?
At around 500m.
133
(L6)
| What are the 4 types of particle source?
Terrigenous/Lithogenous, biogenous, hydrogenous and cosmogenous.
134
Give an example of a terrigenous particle source.
Particles from weathering or erosion of land and volcanic activity transported by rivers, wind and glaciers.
135
Give an example of biogenous particle sources.
Organic materials such as CaCO3
136
Give an example of hydrogenous particle sources.
Reaction of dissolved chemicals in seawater (evaporites, hydrothermal vent deposits)
137
Give an example of cosmogenous particle sources.
Particles originating in outer space.
138
List some ocean sediments.
Terrigenous red clays and biogenic carbonate ooze.
139
What is the lifespan of most biogenic organisms?
A few weeks.
140
What is the name given to the calcareous organism that is a protiste, contains algae, are calcitic and have tiny spiny forms?
Foraminifera
141
What is the name given to the calcareous organism that are aragonitic, to 1cm and are planktonic gastropods.
Pteropods
142
Give the name of the calcitic phytoplankton that shed its plates, is calcitic and abundant in central ocean gyres.
Coccolithophores
143
What is the name given to the silicaceous organism that is made of hydrated silica or opal, is a uniclellular algae abundant in highly productive areas?
Diatoms
144
What is the name given to the hydrated silicaceous organism abundant at low latitudes?
Radiolarians
145
What is the particle settling velocity dependent on?
Size, shape and density.
146
Which law looks at the relationship between the settling velocity of round particles increasing with particle size?
Stoke's law.
147
How do small particles settle through the water column to reach the seabed before they decompose?
They must be packaged into larger particles (i.e. fecal pellets) before they sink 'biopackaging'
148
What is the 30% rule?
If the deep ocean sediments contain over 30% biogenic material, then it is a calcareous or siliceous ooze. If the ocean sediment contains under 30% then it's a red clay.
149
Which dominates at shallower depths: Carbonates or red clays?
Carbonates
150
What conditions is CaCO₃ most soluble?
Low temperatures, higher salinity and pressure.
151
What is Kₛₚ?
The solubility product constant- the equilibrium constant for a solid in equilibrium with a solution.
152
Which is more soluble- calcite or aragonite?
Aragonite
153
How do we work out the saturation of seawater? (omega)
(Ca²⁺)(CO₃²⁻)/Kₛₚ
154
When omega is higher than 1, what state is the mineral in seawater?
The seawater is supersaturated and the mineral should precipitate.
155
When omega is less than 1, what state is the mineral in seawater?
Undersaturated and the mineral should disolve,
156
When omega is equal to 1, what state is the mineral in seawater?
Saturation depth.
157
Why is omega controlled by CO₃²⁻?
Because Ca varies only a little.
158
What does presevation reflect?
Saturation state of seawater, temperature, salinity, pressure of seawater, sedimentation rate.
159
Is CaCO3- preserved best on the surface or at depth?
On the surface, pH is higher at the surface so a higher proportion of the dissolved inorganic carbon will be present as carbonate and solid calcium carbonate will be less likely to dissolve.
160
Is CaCo3- preserved best in the pacific or atlantic?
In the atlantic- pH is higher in the Atlantic than Pacific so again solid calcium carbonate will be better preserved in the Atlantic.
161
Is the saturation depth of calcite and aragonite shallower in the Pacific or Atlantic?
Pacfic- it is more acidic and has a lower CO₃²⁻ concentration compared to the Atlantic.
162
At what depth does aragonite dissolve in the Pacific ocean?
Around 1km
163
At what depth does aragonite dissolve in the Atlantic ocean?
Around 2.5km
164
At what depth does calcite dissolve in the Pacific ocean?
Around 3km
165
At what depth does calcite dissolve in the Atlantic ocean?
Around 4km
166
(L7)
| What is the impact of ocean acidification on calcium carbonate production and preservation?
It is harder for CaCO3 to form and easier for it to dissolve.
167
Is calcite or aragonite more susceptible toocean acidification?
Aragonite
168
Why is aragonite saturation state lower at high latitudes?
Because CO2 dissolution increases at low temperature.
169
What are the effects of ocean acidification on coral reefs?
losses in diversity, biomass and tropic complexity og benthic marine communities.
170
How can some corals gain under ocean acidification?
Corals increase the pH of their calcification fluids above that of seawater. Calcification occurs at the base of the tissue in the space betweem the tissue and the underlying skeleton. Corals increase the pH of the fluid in this space. The increase in pH drives the carbonate equilibria to increase the concentration of CO₃²⁻ and facilitates calcium carbonate precipitation.
171
Which boron isotope is incorporated in aragonite?
Borate B(OH)₄₋
172
What does the isotope fractionation of boron tell us?
The pH of the Seawater.
173
Do corals upregulate the calcification fluid pH more at low or high temperartures?
Low pH
174
What does this require?
ATP (Energy)
175
What is ocean acidification doing to coral reefs?
Causing them to dissolute.
