16. Thermohaline Circulation

Question 1

Which drives winds- Horizontal or vertical pressure gradients?

Answer 1

horizontal

Question 2

____ , light air rises near the equator and ____ , dense air sinks near the poles

Answer 2

warm
cold

Question 3

Pressure gradients in the ocean are created by differences in:

Answer 3

sea level (eg. convergence due to sfc winds) AND DENSITY

Question 4

Below the surface layer, what drives ocean currents?

Answer 4

density gradients

Question 5

Ocean density is determined by ___ __ _____

Answer 5

Equation of State
(temp, salinity, pressure)

Question 6

In the ocean, where do heat losses/ gains mainly occur?

Answer 6

at ocean sfc (air-water interface)

Question 7

In the ocean, where do freshwater/ salt gains/ losses mainly occur?

Answer 7

at ocean sfc (air-water interface)

Question 8

Density-driven flow in the ocean is called _____ ______

Answer 8

thermohaline circulation

Question 9

Give 2 ways that the densest water can be formed

Answer 9

1. cooling of salty water by low air temp (occurs only at high lats in spots where sfc water is salty)
2. intense evaporation in high temp basins (eg Mediterranean sea)

Question 10

Dense water will sink to level of neutral _____ and spread out laterally due to:

Answer 10

buoyancy

horizontal pressure gradients

Question 11

molecular diffusion=

Answer 11

spreading of a component due to random motion of particles

Question 12

Below the ocean surface, water properties can only change by mixing with other water masses through 2 processes:

Answer 12

1. Molecular diffusion: extremely slow process. Allows temp & salinity to be used as tracers at depth
2. Turbulent mixing: via breakdown of internal waves, shear along boundaries, interaction w topography, convection etc. Huge range in time scales

Question 13

In a simplified model, circulation of the water in the world’s ocean can be compared to a giant ____ ____

Answer 13

conveyor belt

Question 14

Describe the “conveyor belt” of the world’s oceans

Answer 14

water is cooled near the poles where it sinks –> it’s transported in the deep ocean where it mixes with other waters –> it returns to the surface far from where it sank –> it’s then transported back on the surface to the high lats (where it cooled/ sank) to start the cycle again

Question 15

Why is global ocean circulation so difficult to study?

Answer 15

b/c of being in the deep ocean + large spatial and temporal scales
- also very slow velocities

Question 16

Give 3 reasons why global ocean circulation is so important

Answer 16

• carries heat and dissolved chemicals around the planet
• transports properties b/w the sfc and deep ocean
• by transporting heat, it’s important in regulating climate and can cause climate variability

Question 17

Give 4 regions of deep water formation (cold/ salty/ dense water)

Answer 17

• Labrador sea
• Iceland/ Nordic Sea
• Weddell Sea
• Ross Sea

Question 18

The complete ocean circulation circuit is estimated to take how long?

Answer 18

100s to 1000 years

Question 19

Global Ocean Circulation is often called the following. Describe the emphasis of THC and MOC
- Ocean conveyor belt
- THC (thermohaline circulation)
- MOC (Meridional circulation)
- AMOC (Atlantic meridional circulation)

Answer 19

THC: conceptual picture of the circulation; emphasis in circulation driven by density differences

MOC: something that’s theoretically observable: takes into consideration not only the movement generated by density diffs but also the essential participation of energy brought by winds and tides into mixing processes

Question 20

The Atlantic Ocean has 2 cells:

Answer 20

1. NADW (North Atlantic Deep Water) cell
2. AABW (Antarctic bottom water) cell

Question 21

Explain the meridional circulation (MOC) travel path from the north

Answer 21

In N. Atlantic, warm salty water is cooled in the winter by cold Arctic winds
- density of sfc water increases, so it sinks & forms NADW
- sinks to depth of same density and flows through the deep Atlantic in the deep western boundary current

Question 22

Explain the meridional circulation (MOC) travel path from the south

Answer 22

water formed in the S ocean travels north in the Atlantic’s deep water boundary current, below NADW & more offshore

• it ‘upwells’ in the NADW layer and disappears in the N. Atlantic subtropical region

Question 23

Does water formed in the Southern Ocean (AABW) make it all the way to the North Atlantic?

Answer 23

No
It ‘upwells’ in the NADW layer and disappears in N Atlantic subtropical region

Question 24

T/F
Once water reaches the ACC, it flows around Antarctica 1+ times as part of the Circumpolar deep water

Answer 24

true

Question 25

Which can dissolve more oxygen- cold or warm water?

Answer 25

cold= more oxygen

Question 26

T/F
life in surface waters would be significantly reduced without circulation of deep water that brings nutrients to the sfc

Answer 26

true

Question 27

T/F
Without thermohaline circulation, there would be more macroscopic life in the deep ocean because more oxygen would be present

Answer 27

False
the opposite is true
thermohaline circulation bring O2 to the deep waters

Question 28

Are nutrients higher in the deep ocean or sfc waters?

Answer 28

deep ocean: due to decomposition and reduced use

Question 29

Give 4 disadvantages of the thermohaline circulation model

Answer 29

• very simplified version of a complicated process
• probably no water parcel flows the complete circuit in reality
• missed high latitude processes
• implies we know how the ocean (esp deep ocean) works- we don’t

Question 30

Give a key advantage of the thermohaline circulation model

Answer 30

• gives a simplified picture that most people can understand
  ie. boils down the complicated large-scale ocean circulation to a few key ideas

Question 31

T/F
Some upwelling occurs around Antarctica

Explain why/ why not

Answer 31

True

This is a big question: best answer= rough topography due to tides and waves breaking

Question 32

The lack of a thermocline and pycnocline in high latitude regions allows what to occur?

Answer 32

vertical mixing

Question 33

T/F

Antarctic bottom water is so dense that it spreads out along the sea floor into ALL ocean basins of the world

Answer 33

true!

Question 34

Some of the water in meridional circulation upwells around Antarctica. What is this called

Answer 34

Antarctic divergence

Question 35

What happens to water that upwells around Antarctica from MOC?

Answer 35

either goes south and sinks again with AABW or goes north and forms AAIW
–> AAIW will progress northward as sfc water and sink again as part of NADW

Question 36

draw out MOC path & know it