Deep Currents

Question 1

Thermohaline circulation

Answer 1

Driven by changes in temp or salinity
* t and s control desnity, which controls buoyancy
* describes the buoyancy-driven part of global cirulation

Processes at ocean surface that change t & s:
* heating/cooling
* freshwater/salt fluxes:
* evaporation and precipitation (adds more removes freshwater)
* river and freshwater runoff (adds freshwater)
* brine rejection during sea ice formation (increases salinity)
* ice melt (adds freshwater)

Almost synonymouse with Meridional Overturning Circulation (MOC)
* the transport in n/s direction

Question 2

Very basic structure if the global circulation

Question 3

Dense water sinks at high latitudes

Question 4

Meridional Overturning Circulation (MOC)

Question 5

MOC in 3 ocean basins

Question 6

Implications of the overturning circulation for climate?

Answer 6

Transport of heat, carbon, nutrients, freshwater
1. warm water flows from north at surface
2. cooling at surface in high lats –> water becomes denser & sinks
3. colder water flowers south at depth
(net transport of heat towards arctic)

Question 7

TRacing the pathways of water masses in the overturning circulation

Question 8

Water mass

Answer 8

A body of water with a common formation history, having origin in particular region of the ocean
- water masses are identified by their temp and salinity

Question 9

Identiifying water masses from t/s properties

Question 10

Tracers

Answer 10

• use tracers to determine pathways of circulation, age of waters, idenitfy a water mass
• conservative vs non-conservative
• natural vs anthropogenic
• ex:
• temp and salinity = conservative tracers below ocean surface
• dissolved oxygen & nutrients = biologically active & non-conservative
• CFCs = anthropogenic tracer, conservative below surface

Question 11

Anthropogenic tracers

Answer 11

• atmospheric record of compounds used as anthrogenic tracers of ocean circulation
• many of these tracers are gases, enter the ocean by air-sea exchange
• cfc-11 = refridgerants

Question 12

How long does it take seawater to return to the surface once it sinks?

Answer 12

up to 1000s of years
overturning circulation is slow - only a few cm per second, it is much easier to measure properties of the water that change with time, than it is to measure such slow currents