1. AICE Marine Unit 6 – The ocean floor and coasts
The Coast
AICE Marine Unit 6 – The ocean floor and coasts

2. Isostasy “weighing the same”
Buoyant properties of layers of rocks that float on other layers (due to density and thickness)
Crust ‘floats’ on denser, underlying layer
(d) Explain how isostasy may produce shallow seas within or at the edge of continents.

3. Continental shelf
Continental shelf – gently sloping region surrounding continents (sea is relatively shallow)
Covered in sediments (erosion of continents)
Part of continent was above sea level during ice age (sea level was lower then)
Water depth over continental shelf depends on 2 factors:
Isostatic changes in land height
Changes in sea level

4. Principle of Isostasy Layer Density = g per cm3 Continental Crust
Crust is higher where it is thicker and less dense
Lower = thinner and denser
Layer
Density = g per cm3
Continental Crust
2.7 – 3.0
Sediments on continental shelf
2.4
Oceanic crust
3.0 – 3.3
Mantle
3.3 – 5.7
Highest density

5. Continental crust – mostly made of granite (less dense rock)
Granite: igneous rock made with ~20% quartz
Oceanic crust – basalt (more dense rock)
Basalt: igneous rock less than 20% quartz, mostly volcanic
So, continental plates ride on the denser oceanic plates

7. Littoral Zone Land meets sea Nature of shore factors:
Geology of adjacent land
Exposure to erosion by sea
Area of coast between high water mark and lowest part of submerged shore
(e) Demonstrate an understanding of the processes of erosion and sedimentation that give rise to the morphology of the littoral zone, including rocky shores, sandy shores, muddy shores, estuaries and deltas

8. Rocky Shore Rock exposed to sea erosion
Variety sized boulders, stones and pebbles
Granite = resistant to weathering
Sandstone = easily broken down

9. Rocky Shore Most exposed type of shore Most resistant to erosion
Largest boulders left at the top of the shore due to pounding waves
Very steep cliffs to horizontal flat rocks with a wave-cut platform

10. Rocky Shore Limiting Factors Support wide range of organisms
Stable substrate
Large rocks and stones – firm surface
Algae
Mollusks and cnidarians (and sea anemones)
Rock pools retain water when tide recedes

11. Rocky Shore Environmental Factors that influence communities:
Desiccation (extreme drying)
Species near top of shore exposed to air for longer periods
Temperature
Wave action
Light intensity
Aspect
Slope
Nature of substrate

12. Sandy Shores Erosion of sandstone Deposition of sand by the sea
Silica and other minerals
Slope gradually toward sea

13. Sandy Shores Unstable Not a suitable substrate
Fine particles are easily moved by winds and tides
Not a suitable substrate
Sea weeds
No shelter for organisms at surface
Under: burrowing organisms
Ghost crabs, bivalve mollusks, annelid worms (ragworms and lugworms)
If sand mixed with muddy deposits, more stable and supportive

14. Muddy Shores Least exposed to erosion silt particles can settle
Very fine mineral sediments
Organic remains
Little slope
Can form mud flats

15. Estuary Semi-enclosed body of water
Freshwater meets sea water
Muddy substrate – slow flow of water allows suspended particles to settle

16. Delta (∆)
Get their name from the Greek letter
River carrying suspended sediments reaches large body of water (lake or ocean)
River increase in width = flow rate decreases
Suspended sediments settle
Accumulate into a fan-shaped structure over time
River divides to form distributary channels
2 examples (next page)

17. Nile River Delta ∆

18. Mississippi River Delta ∆

19. Diameters of Mineral Particles
Particle Type
Diameter (mm)
Silt
0.002 to 0.02
Fine Sand
0.02 to 0.2
Coarse Sand
0.2 to 2.0
Gravel (small stones)
> 2.0

20. Mangroves (Swamp, Forest)
Trees and shrubs in tropical/subtropical saline coastal habitats
Between 25⁰N and 25 ⁰S
Form woodland or shrub land habitat (coastal/estuarine conditions where sedimentation of silts occur)
Specifically adapted to:
Wide range of salinity
Low oxygen concentrations
in sediments

21. Mangroves
Pneumatophores - specifically adapted root-like structures that obtain oxygen directly from air
Extensive root systems:
Trap particles suspended in water
Reduce water flow
Increases deposition of sediments
Dissipates wave energy
Protects coastal area from erosion
Habitats for:
Algae, oysters, crabs, barnacles and other crustaceans, sponges, fish