16. Thermohaline Circulation Flashcards
Which drives winds- Horizontal or vertical pressure gradients?
horizontal
____ , light air rises near the equator and ____ , dense air sinks near the poles
warm
cold
Pressure gradients in the ocean are created by differences in:
sea level (eg. convergence due to sfc winds) AND DENSITY
Below the surface layer, what drives ocean currents?
density gradients
Ocean density is determined by ___ __ _____
Equation of State
(temp, salinity, pressure)
In the ocean, where do heat losses/ gains mainly occur?
at ocean sfc (air-water interface)
In the ocean, where do freshwater/ salt gains/ losses mainly occur?
at ocean sfc (air-water interface)
Density-driven flow in the ocean is called _____ ______
thermohaline circulation
Give 2 ways that the densest water can be formed
- cooling of salty water by low air temp (occurs only at high lats in spots where sfc water is salty)
- intense evaporation in high temp basins (eg Mediterranean sea)
Dense water will sink to level of neutral _____ and spread out laterally due to:
buoyancy
horizontal pressure gradients
molecular diffusion=
spreading of a component due to random motion of particles
Below the ocean surface, water properties can only change by mixing with other water masses through 2 processes:
- Molecular diffusion: extremely slow process. Allows temp & salinity to be used as tracers at depth
- Turbulent mixing: via breakdown of internal waves, shear along boundaries, interaction w topography, convection etc. Huge range in time scales
In a simplified model, circulation of the water in the world’s ocean can be compared to a giant ____ ____
conveyor belt
Describe the “conveyor belt” of the world’s oceans
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
Why is global ocean circulation so difficult to study?
b/c of being in the deep ocean + large spatial and temporal scales
- also very slow velocities
Give 3 reasons why global ocean circulation is so important
- 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
Give 4 regions of deep water formation (cold/ salty/ dense water)
- Labrador sea
- Iceland/ Nordic Sea
- Weddell Sea
- Ross Sea
The complete ocean circulation circuit is estimated to take how long?
100s to 1000 years
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)
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
The Atlantic Ocean has 2 cells:
- NADW (North Atlantic Deep Water) cell
- AABW (Antarctic bottom water) cell
Explain the meridional circulation (MOC) travel path from the north
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
Explain the meridional circulation (MOC) travel path from the south
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
Does water formed in the Southern Ocean (AABW) make it all the way to the North Atlantic?
No
It ‘upwells’ in the NADW layer and disappears in N Atlantic subtropical region
T/F
Once water reaches the ACC, it flows around Antarctica 1+ times as part of the Circumpolar deep water
true
Which can dissolve more oxygen- cold or warm water?
cold= more oxygen
T/F
life in surface waters would be significantly reduced without circulation of deep water that brings nutrients to the sfc
true
T/F
Without thermohaline circulation, there would be more macroscopic life in the deep ocean because more oxygen would be present
False
the opposite is true
thermohaline circulation bring O2 to the deep waters
Are nutrients higher in the deep ocean or sfc waters?
deep ocean: due to decomposition and reduced use
Give 4 disadvantages of the thermohaline circulation model
- 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
Give a key advantage of the thermohaline circulation model
- gives a simplified picture that most people can understand
ie. boils down the complicated large-scale ocean circulation to a few key ideas
T/F
Some upwelling occurs around Antarctica
Explain why/ why not
True
This is a big question: best answer= rough topography due to tides and waves breaking
The lack of a thermocline and pycnocline in high latitude regions allows what to occur?
vertical mixing
T/F
Antarctic bottom water is so dense that it spreads out along the sea floor into ALL ocean basins of the world
true!
Some of the water in meridional circulation upwells around Antarctica. What is this called
Antarctic divergence
What happens to water that upwells around Antarctica from MOC?
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
draw out MOC path & know it
