Geological and Physical Factors of the Marine Environment 1. The Sea Floor a. The oceans cover most of the globe (71%) and play a crucial role in regulating our climate and atmosphere b. Average depth of the oceans is 4 km (3800 m). Pacific is the deepest, Arctic is the shallowest. 2. Geography of the Ocean Basins a. Oceans are divided into 4 large basins: Atlantic, Pacific, Indian & Arctic 3. Topography of the ocean Floor a. Continental Margins i. Continental Shelf The part connected to the continent 8% of the ocean floor Most productive portion of the ocean. Has most life (more Fishing) Atlantic side of N. America is wide, Pacific side is narrow Drops off at approximately100-200 meters ii. Continental Slope Steeper gradient to the ocean floor Edge of the continent iii. Continental Rise The boundary between the continental slope and the ocean floor b. Ocean Basin i. Abyssal Plains – flattest part of the Earth ii. Abyssal Hills – small hills on the abyssal plains iii. Seamount – underwater volcanoes iv. Trenches – deepest part of the ocean v. Guyots – flat topped seamounts vi. Ridges – mountain ranges within the ocean vii. Rifts – cracks that are found generally by the ridges c. Mid Ocean Ridges – formed when material rising from below the mantle pushes up on the oceanic crust i. Central Rift Valley – a great gap or depression caused by the plates pulling apart at the center of the ridge ii. Hydrothermal Vents – water seeps down through the rifts, gets heated and forces its way back up thorough the crust 4. Plate Tectonics – the mid-ocean ridge system is a continuous chain of submarine volcanoes that run through the ocean basins. Earthquakes and volcanoes are associated with the mid-ocean ridge. The Earth’s surface is broken up into a number of plates that are separated by the earthquake belts, which are trenches, ridges and faults. a. There are 7 major plates: i. North American ii. African iii. Indian Australian iv. South American v. Eurasian vi. Pacific vii. Antarctic b. Plate Boundaries i. Convergence – 2 plates coming together →} {← The site of mountains ex. Himalayas ii. Divergence – 2 plates separating ←} {→ The site of sea floor spreading New sea floor is formed ex. Mid Atlantic Ridge iii. Subduction – 1 plate goes under the other The site of trenches Where old sea floor is destroyed ex. Hawaii, Marianas Trench iv. Transform Fault – 2 plates going in opposite directions ↑} {↓ Site of earthquakes Fault is a crack in the Earth’s crust ex. San Andreas Fault