CHAPTER 3 Marine Provinces Bathymetry measuring ocean depths

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 (~6 ft)

Measuring bathymetry Ocean depths and topography of ocean floor “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 sounding Reflection of sound signals 1925 German ship Meteor

Measuring bathymetry Precision depth recorder (PDR) 1950 s Focused beam Helped 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 pull Differences 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 margins ○ Shallow-water areas close to shore Deep-ocean basins ○ Deep-water areas farther from land Mid-ocean ridge ○ Submarine mountain range

Continental margins Passive or active Passive Not close to any plate boundary No major tectonic activity Example: east coast of United States

Continental margins Active (2 types) Associated with convergent or transform plate boundaries Much tectonic activity 1 - Convergent active margin 2 - Transform active margin Associated with transform plate Oceanic-continental convergence Example: western South America boundaries Example: Coastal California along the San Andreas fault

Continental margin features Continental shelf Shelf break Continental slope Continental rise

Continental shelf Extends from shoreline to shelf 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 4 o Submarine canyons cut into slope by turbidity currents Mixture of seawater and sediments Move under influence of gravity Erode canyons Deposit sediments at base of slope

Continental slope and submarine canyons

Continental rise Transition between continental crust and oceanic crust Submarine fans

Deep ocean basin features Abyssal plains Volcanic peaks Ocean trenches Volcanic arcs

Abyssal plains Very flat depositional surfaces from base of continental rise Suspension 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 guyots at least 1 km (0. 6 m) above sea floor Abyssal hills or seaknolls are less than 1 km Above sea level: Volcanic 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 arc Chain of islands, e. g. , Japan Continental 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 fissures Seamounts Pillow basalts Hydrothermal vents Deposits of metal sulfides Unusual life forms Fracture zones and transform faults

Mid-ocean ridge features Oceanic ridge Prominent rift valley Steep, rugged slopes Example: Mid-Atlantic Ridge Oceanic rise Gentler, less rugged slopes Example: East Pacific Rise

Volcanic features of mid-ocean ridge Pillow lava or pillow basalts Hot lava chilled by cold seawater Smooth, rounded lobes of rock

Volcanic features of mid-ocean ridge Hydrothermal vents Heated subsurface seawater migrates through cracks in ocean crust ○ Warm-water vents <30 o. C or 86 o. F ○ White smokers >30 o. C <350 o. C or 662 o. F ○ Black smokers > 350 o. C

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 faults: faults movement in opposite directions ○ Still seismically active Fracture zones: zones extensions of transform faults (aseismic) ○ Beyond offset segments of oceanic ridge

Ocean Literacy Standards 1 b - 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. 5 g - 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 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.