Lecture 10: Stratification in the coastal ocean

Question 1

How can we change stratification (what to do to the layers)?

Answer 1

Only change 1 layer to change stratification, if both then it will stay the same (proportional)

Question 2

Is the nearby coastal ocean typically stratified?

Answer 2

No,

• In the vertical, water is uniform
  (shallow and lots of mixing)

Question 3

What are Implications of strong stratification: disconnect between layers?

Answer 3

• Stratification inhibits transfer of properties between water layers
• Impacts biology, sediment, geochemistry

Question 4

How does the sun affect stratification?

Answer 4

• Increases stratification by warming
  the surface layer via shortwave solar
  radiation -> decreasing density in the
  surface layer.

Question 5

How do rivers affect stratification?

Answer 5

• Increases stratification by decreasing
  density (salinity) in the surface layer.

Question 6

Are river plumes affected by the coriolis force?

Answer 6

Yes…

• Plume has local and remote impact on stratification

The plume Stops spreading and turns to left (Southern Hemisphere) because of the Coriolis force

But water keeps on coming, needs to go somewhere

• Plume turns to the left
• Reattaches to coast
• Continues down coast

Question 7

How are internal waves generated and what are they similar to?

Answer 7

• Consider a two-layer fluid - with deep second layer
• Disturbances at interface can propagate - waves!
• Propagation speed is related to the density difference between layers and thickness
• Similar to shallow water “surface” ocean wave:
• Internal waves are generated by
  winds and tides.

Question 8

Solve example on slide 14

Answer 8

Yippee

Question 9

How can tides affect internal waves?

Answer 9

• Flow of the ebb tide drag the pycnocline down at the shelf edge.
• As tidal flow relaxes, the pycnocline depression propagates on-shelf
• As it moves into shallower water, the depression slows down, steepens and then scatters into a ‘train’ of nonlinear internal waves (NLIWs)

Internal waves can shoal on the shallower shelf

Question 10

Can internal waves be expressed on the surface?

Answer 10

Yes

• Convergent and divergent zones of flow are produced at the sea surface by the
  horizontal flow field associated with internal waves

Convergent zones cause floating organic matter to accumulate in bands (“slicks”). These alternate with the bands of water that is smoother over divergent zones

Question 11

What is an internal tidal bore?

Answer 11

The breaking of internal waves on the continental slope can produce internal bores:

• Internal bores can rapidly change the
  nearshore environment – as they enter
  the nearshore, they bring deeper
  offshore waters that have different
  properties (e.g. colder, higher in
  nutrients, lower in oxygen, lower in pH)