CHAPTER 3 Marine Provinces

Bathymetry – measuring ocean depths

It was once thought that the deepest parts of the ocean were in the middle of the ocean basins

○ But that is now known not to be true

Fathom○ Standard unit of measurement for ocean

depth○ 1.8 meters (~6ft)

Measuring bathymetry Ocean depths and topography of ocean floor ““Sounding”Sounding”

Rope/wire with heavy weight○ Known as lead lining○ When it hit bottom, it would be pulled up and measured

○ That’s where the term “fathom” came from, 1 fathom = outstretched arm

Echo soundingEcho soundingReflection of sound signals1925 German ship Meteor

Measuring bathymetry Precision depth recorder (PDR) 1950s

Focused beamHelped confirm plate tectonics

Multi-beam echo sounders AND Side-scan sonar

More detailed “picture” of sea floor

Measuring bathymetry

Fig. 3.2

Measuring bathymetry Satellite measurements –

measure ocean surface that corresponds with bathymetry Deep areas like trenches exert lower gravitational pull, higher

areas such as seamounts exert more gravitational pullDifferences affect sea level that can be detected by satellite

Seismic reflection profiles looks at ocean structure beneath sea floor

Ocean provinces 3 major provinces

Continental marginsContinental margins○ Shallow-water areas close to shore

Deep-ocean basinsDeep-ocean basins○ Deep-water areas farther from land

Mid-ocean ridgeMid-ocean ridge○ Submarine mountain range

Continental margins Passive or active PassivePassive

Not close to any plate boundaryNo major tectonic activityExample: east coast of United

States

Continental margins Active (2 types)Active (2 types)

Associated with convergent or transform plate boundaries

Much tectonic activity 1 - Convergent active margin1 - Convergent active margin

Oceanic-continental convergenceExample: western South America

2 - Transform active margin2 - Transform active marginAssociated with transform plate

boundariesExample: Coastal California along

the San Andreas fault

Continental margin features Continental shelfContinental shelf Shelf breakShelf break Continental slopeContinental slope Continental riseContinental rise

Continental shelf Extends from shoreline

to shelf breakshelf break Shallow, low relief,

gently sloping Similar topography to

adjacent coast Average width 70 km

(43 m) but can extend to 1500 km (930 m)

Average depth of shelf break 135 m (443 ft)

Continental slope

Change in gradient from shelf Average gradient 4o

Submarine canyonsSubmarine canyons cut into slope by turbidity currentsturbidity currentsMixture of seawater and sedimentsMove under influence of gravityErode canyonsDeposit sediments at base of slope

Continental slope and submarine canyons

Continental rise

Transition between continental crust and oceanic crustSubmarine fansSubmarine fans

Deep ocean basin features

Abyssal plainsAbyssal plains Volcanic peaksVolcanic peaks Ocean trenchesOcean trenches Volcanic arcsVolcanic arcs

Abyssal plains Very flat depositional surfaces from base of

continental rise Suspension settlingSuspension settling of very fine particles Sediments cover ocean crust irregularities Well-developed in Atlantic and Indian oceans

Volcanic peaks

Poke through sediment cover Below sea level:

Seamounts, tablemounts, or guyotsSeamounts, tablemounts, or guyots at least 1 km (0.6 m) above sea floor

AbyssalAbyssal hills hills or seaknollsseaknolls are less than 1 km

Above sea level:Volcanic islandsVolcanic islands

Ocean trenches Linear, narrow, steep-sided Associated with subduction

zones Deepest parts of ocean

Mariana Trench, 11,022 m (36,161 ft)

Majority in Pacific Ocean

Ocean trenches

Volcanic arcs

Landward side of ocean trench Island arcIsland arc

Chain of islands, e.g., Japan Continental arcContinental arc

Volcanic mountain range, e.g., Andes Mountains

Mid-ocean ridge

Longest mountain chain On average, 2.5 km (1.5 miles) above

surrounding sea floor Wholly volcanic Divergent plate boundary

Mid-ocean ridge features Central rift valley, faults, and Central rift valley, faults, and

fissuresfissures SeamountsSeamounts Pillow basaltsPillow basalts Hydrothermal ventsHydrothermal vents

Deposits of metal sulfidesUnusual life forms

Fracture zones Fracture zones and transform faults transform faults

Mid-ocean ridge features Oceanic ridgeOceanic ridge

Prominent rift valleySteep, rugged slopesExample: Mid-Atlantic Ridge

Oceanic riseOceanic riseGentler, less rugged slopesExample: East Pacific Rise

Volcanic features of mid-ocean ridge Pillow lava or pillow basaltsPillow lava or pillow basalts

Hot lava chilled by cold seawaterSmooth, rounded lobes of rock

Volcanic features of mid-ocean ridge

Hydrothermal ventsHydrothermal ventsHeated subsurface seawater migrates

through cracks in ocean crust○ Warm-water vents <30oC or 86oF○ White smokers >30oC <350oC or 662oF○ Black smokers > 350oC

Unusual biological communities Able to survive without sunlight

Chemosynthesize instead of photosynthesize Archaeon bacteria and bacteria oxidize hydrogen sulfide gas to provide

food

Fracture zones and transform faults

Long linear zones of weakness offset axes of mid-ocean ridge

Transform faultsTransform faults: movement in opposite directions

○ Still seismically active

Fracture zonesFracture zones: extensions of transform faults (aseismic)

○ Beyond offset segments of oceanic ridge

Ocean Literacy Standards 1b - An ocean basin’s size, shape and features (islands, trenches, mid-ocean ridges, rift

valleys) vary due to the movement of Earth’s lithospheric plates. Earth’s highest peaks, deepest valleys and flattest vast plains are all in the ocean.

5g - There are deep ocean ecosystems that are independent of energy from sunlight and photosynthetic organisms. Hydrothermal vents, submarine hot springs, methane cold seeps, and whale falls rely only on chemical energy and chemosynthetic organisms to support life.

Sunshine State Standards SC.7.E.6.1 Describe the layers of the solid Earth, including the lithosphere, the hot convecting

mantle, and the dense metallic liquid and solid cores. SC.7.E.6.3 Identify current methods for measuring the age of Earth and its parts, including the law

of superposition and radioactive dating. SC.7.E.6.4 Explain and give examples of how physical evidence supports scientific theories that

Earth has evolved over geologic time due to natural processes. SC.7.E.6.5 Explore the scientific theory of plate tectonics by describing how the movement of

Earth's crustal plates causes both slow and rapid changes in Earth's surface, including volcanic eruptions, earthquakes, and mountain building.

SC.7.E.6.7 Recognize that heat flow and movement of material within Earth causes earthquakes and volcanic eruptions, and creates mountains and ocean basins.

SC.912.E.6.1 Describe and differentiate the layers of Earth and the interactions among them.

SC.912.E.6.3 Analyze the scientific theory of plate tectonics and identify related major processes and features as a result of moving plates.

SC.912.E.6.5 Describe the geologic development of the present day oceans and identify commonly found features.