Chapter 3Marine Provinces

Essentials of Oceanography

7th Edition

Bathymetry

Bathymetry is the measurement of ocean depths and the charting of the shape or topography of the ocean floor The ocean floor is a highly varied terrain that contains many interesting features Early methods of determining ocean depths involved using a long weighted line (called a sounding line)

Bathymetric techniques

Echosounders send sound through water to determine water depth and sea floor features Figure 3-1

Bathymetric techniques

Side-scan sonar uses a “fish” towed behind a ship to give a more detailed picture of the sea floor

Figure 3-2

Bathymetric techniques

Low frequency sound is used to determine structure beneath the sea floor

Figure 3-3

Bathymetric techniques

Satellites measure sea surface elevation, which mimics sea floor bathymetry

Figure 3D

The hypsographic curve

The hypsographic curve shows the relationship between the height of the land and the depth of the oceans Figure 3-4

Major regions of the North Atlantic Ocean floor

Continental margin

Ocean basin floor

Mid-ocean ridge

Figure 3-5

Passive versus active continental margins

Passive marginNo plate boundary

Shelf

Slope

Rise

Figure 3-6

Passive versus active continental margins

Active marginPlate boundary

ConvergentShelfSlope (steep)Trench

TransformContinental

borderland

Figure 3-6

Submarine canyons and deep-sea fans

Turbidity currents carve submarine canyons into the slope and shelf

Debris from turbidity currents creates graded bedding deposits and deep-sea fans

Figure 3-8a

Diver in the La Jolla Submarine Canyon

Figure 3-8b

Abyssal plains

Deep flat areas formed by suspension settlingVolcanic peaks poke through the sediment

Abyssal hills (seaknolls)SeamountsTablemounts (guyots)

Figure 3-9

Ocean trenchesDeepest parts of the oceanFormed by plate convergenceMost trenches are in the Pacific OceanAssociated with volcanic arcs

Island arcContinental arc

Figure 3-10

The mid-ocean ridge

Circles the globe like the seam of a baseballMostly traverses the middle of ocean basins A topographically high mountain rangeEntirely volcanic in originAssociated with plate divergenceIn the Pacific Ocean, called the East Pacific RiseIn the Atlantic Ocean, called the Mid-Atlantic RidgeInternet flybys of portions of the mid-ocean ridge

The Mid-Atlantic Ridge

Traverses the center of the Atlantic OceanContains a central down-dropped rift valleyComes above sea level in Iceland

Figure 3-12

Features of the mid-ocean ridge

Rift valleysForm when plates split apartDown-dropped areas associated with faults and earthquakes

Figure 3-13

Features of the mid-ocean ridge

Pillow lavaForms when hot lava comes into contact with cold seawater and quickly cools

Basalt composition

Figure 3-14

Features of the mid-ocean ridge

Hydrothermal ventsForm when seawater is heated by magmaBlack smokers emit hot water through chimneysAssociated with metal sulfide deposits and unusual lifeforms

Figure 3-15

Transform faults and fracture zones

Transform FaultsOccur between segments of the mid-ocean ridge

Transform plate boundaries

Movement in opposite directions

Figure 3-16

Transform faults and fracture zones

Fracture ZonesOccur beyond segments of the mid-ocean ridge

Not plate boundaries

Movement in the same direction

Figure 3-16

End of Chapter 3

Essentials of Oceanography

7th Edition