EAE3311 Lecture 8

Question 1

What depth are Surface water masses?

Answer 1

Upper 500m

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Question 2

What depth are Intermdeiate water masses?

Answer 2

500-1200m

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Question 3

What depth are deep water masses?

Answer 3

1200-4000m

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Question 4

What depth are bottom water masses?

Answer 4

Below 4000m

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Question 5

What is the the abyssal circulation?

Answer 5

The presence of deep cold water at lower latitudes

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Question 6

What is Ventilation?

Answer 6

Transmission of surface characteristics to deeper layers

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Question 7

What is charactersistion of the Labrador Sea?

Answer 7

Intermediate Water Convection (heat loss, eddy)

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Question 8

Atlantic Ocean Stratification

What is a front?

Answer 8

The boundary between two distinct water masses

I.e. Where the different water masses meet

Strong horizontal gradients of temperature/salinity

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Question 9

Atlantic Ocean Stratification

Where is the coldest water formed?

Answer 9

Off the coast of Antarctica

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Question 10

How does temperature and salinity change?

Answer 10

Both temperature and salinity are conserved properties.

They are modified only by interaction with the atmosphere and mixing with other waters and not by biological or chemical activities.

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Question 11

Compare stratification in Pacific and Atlantic.

Answer 11

Pacific Ocean less complex stratification than Atlantic

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Question 12

What is the Mixed Layer?

Answer 12

At the surface of the ocean, wind stirs the water creating a well mixed layer of uniform denisty

(typically 100 m or less)

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Question 13

What is the Pycnocline?

4 points.

Answer 13

The depth range at which density changes rapidly

• Pycnocline not present in the poles
• The ocean’s pycnocline is very stable thus suppressing mixing between the mixed layer and deep layer
• The pycnocline acts as a barrier to vertical motion within the ocean.
• The pycnocline is a porous barrier, transfer of kinetic energy occurs, and most importantly: settling of particles traverses the boundary

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Question 14

Describe

Light Penetration into the ocean

2 points.

Answer 14

I_Z = I₀ e⁻ᴷᵈ ᶻ

I_Z = Irradiance at depth z

I₀ = Irradiance at the surface

Kd = attenuation coefficient (m⁻¹)

• Exponential decrease with depth
• Kd will be different for each wavelength

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Question 15

What is the Euphotic Zone?

3 points.

Answer 15

The zone above the depth where I_{z = 1% of I₀}

• At 0.1-1% light: Photosynthesis = Respiration (compensation depth)
• Clear waters ~200 m deep
• In turbid waters <1 cm

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Question 16

What gases are primarily disolved in the ocean?

Answer 16

CO₂, O₂, N₂

These three gasses are non-conservative (influenced by biology) Ratios are modified by life
The amount of dissolved gasses in a liquid is proportional to the partial pressure in the gas phase

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Question 17

How does the oxygen level vary at the surface?

Answer 17

Equilibration of surface ocean and atmosphere occurs on a time scale of roughly one year

During the day, photosynthesis>respiration i.e. Net O2 production→ supersaturates the surface water

During the night, respiration only → undersaturation

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Question 18

What is Positive gas flux?

Answer 18

Net transfer of oxygen to the ocean from the atmosphere

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Question 19

How does CO₂ interact with the ocean?

4 points.

Answer 19

• CO₂ gas disolves in water just like other gasses
• CO₂ then reacts with the water (forms Bicarbonate and Carbonate ions)
• Only CO₂ exchanges in the atmosphere
• The direction and strength of the reactions are strongly dependent on pH

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Question 20

Why doesn’t pH continue to decrease with depth (even increases slightly)?

Answer 20

Respiration (reduces pH) is balanced with shell dissolution (which increases pH) = The carbonate Buffering system

CO₃²⁻+Ca ⇔ CaCO₃

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Question 21

Why is the Pacific more acidic than the Atlantic?

2 points.

Answer 21

This is related to the circulation, biology and chemistry in the ocean

• Calcite compensation depth in the North Pacific is dramatically shallower than the North Atlantic
• The Pacific holds older water masses, and they accumulate more CO₂ (from dissolution of shells as they age)

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Question 22

What are the Dissolved Nutrients?

Answer 22

Most Important: Nitrogen, Phosphorous

Also important (sometimes limiting): Silicon, Iron, Zinc

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Question 23

What is the Biological Pump?

3 points.

Answer 23

• Phytoplankton extract dissolved inorganic nutrients out of the surface water
• Combine them in their organic matrix
• Sink and Decay (returned to dissolved state) in the deep ocean

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Question 24

What determines ocean fertility?

3 points.

Answer 24

• The abundance of nutrients determines how fertile the oceans are.
• A measure of this fertility is the primary production, which is the rate of fixation of carbon per unit of water per unit time.
• Primary production is often mapped by satellites using the distribution of chlorophyll.

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Question 25

What are Prochlorococcus?

5 points.

Answer 25

• Phytoplankton
• cyanobacteria
• ~5% of global photosynthesis
• ~ 50% of the chlorophyll in your samples
• Requires nutrients, Utilises DIN

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Question 26

What are the minor nutrient inputs?

3 points.

Answer 26

Pelagic

• Eolian dust
• Nitrogen Fixation
• Aerosols (atmospheric deposition)

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Question 27

What are the major nutrient inputs?

2 points.

Answer 27

Neritic

• Attached to terrigenous sediments (rivers, glaciers…)
• People

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Question 28

What happens to the pycnocline at high latitudes?

Answer 28

No pycnocline at the high latitudes

surface water is cold and therefore the density gradient is weak

→ vertical mixing of water to depths greater than the euphotic zone

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Question 29

What is the Physical Carbon Pump?

Answer 29

Downwelling currents bring DIC into the deep ocean
Upwelling brings cold ocean to the surface (degassing)

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Question 30

What is the Arctic Convergence?

Answer 30

Areas where surface water cools and ice forms.

Question 31

How fast is Thermohaline Circulation?

Answer 31

10-20 km/year