Chapter 3

Chapter 3 - Intro to Oceanography Chapter 3 I What...

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Intro to Oceanography : Chapter 3 I. What Techniques Are Used to Determine Ocean Bathymetry? a. Bathymetry (bathos = depth, metry = measurement) is the measurement of ocean depths and the charting of the shape or topography o the ocean floor b. Soundings i. First recording to measure ocean depth was attempted by Greek named Posidonius (dropping a line down to the floor) ii. Fathom = 1.8 meters (6 feet) iii. First bathymetric measurements of the oceans made by HMS Challenger 1. every so often, they stopped and measured the depth (found reliefs – variations in the elevation) c. Echo Soundings i. Early 1900s, echo sounders – sends a sounds signal, a ping, and echoes when it bounces off any density differences ii. often inaccurate iii. most of our knowledge of ocean bathymetry iv. precision depth recorder (PDR) (1950s) uses a focused high-frequency sound beam to measure depths to a resolution of about 1 meter v. multibeam echo sounders (uses multiple frequencies of sound simultaneously) and side-scan sonar is used today vi. Seabeam – first multibeam echo sounder – made it possible to map features up to 60 km wide 1. Sea MARC and GLORIA were towed behind a ship 2. ship travels back and forth (“mowing the lawn”) vii. Satellites are increasingly used d. Seismic Reflection Profiles i. Ocean structure beneath sea floor can be maaped through low- frequency sounds produced by explosions or air guns 1. sounds penetrate beneath sea floor and reflect off boundaries between difference rock or sediment layers, producting seismic reflection profiles (used in mineral and petroleum exploration) II. What Does Earth’s Hypsographic Curve Reveal? a. Shows the relationship between the height of the land and the depth of the oceans b. Five difference slopes i. Tall mountains (steep segment) ii. Low coastal plains (gentle slope) iii. Shallow Parts of the continental margin (including mountainous mid- ocean ridge) iv. Deep-ocean basins (longest, flattest) v. Ocean trenches (last steep part) c. Used to support the existence of plate tectonics d. Hypsographic curves have been used to determine plate tectonics in other planets and moons
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III. What Features Exist on Continental Margins? a.
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Chapter 3 - Intro to Oceanography Chapter 3 I What...

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