The Ocean Floor Ch. 23

Studying the ocean floor Submersibles, satellites, and other technology allow scientists to study the structure and composition of the ocean floor.

1. Echo sounding a system that uses transmitted and reflected sound waves to measure distances to the ocean floor; SONAR. measure how long it takes for signal to be emitted and come back multi-beam echo sounding measures area twice as wide as ship use info to make seafloor maps intensity of sound beams determine seafloor composition rock & gravel reflect more strongly than mud

Echo sounding

2. Sediment Sampling Core sampling: hollow cylinder removes long cores of material from seafloor layers are preserved 1-1500m of sediment are gathered can analyze past climate, life, and ocean events

3. Satellite observations greater range & speed for mapping doesn’t reach floor, bounces off surface Ocean surface varies based on what’s below higher over mountains, lower over trenches determines differences down to cm’s makes high-resolution seafloor image

HIGH RESOLU-TION SEAFLOOR IMAGE Pacific and Western Atlantic Oceans

The CONTINENTAL MARGIN In order to understand the continental margin, we must first understand the crust of the Earth. The continental margin is part of the crust.

two types of crust Continental Crust Oceanic Crust lighter, less dense rock Makes up all continents, but not necessarily all islands Oceanic Crust darker, dense rock any ocean floor or ocean basin

THE MOVING CRUST all of the crust is divided into ‘pieces’ or plates (Called lithospheric plates or tectonic plates) the plates move around on the semi-solid mantle Plates meet= called plate boundaries at plate boundaries, the crust can be moving side by side, apart, or together different topographic features are created, depending on the type of boundary topography: the shape of the land

World plate boundaries

The CONTINENTAL MARGIN The underwater portion of the continental crust. There are two types of continental margins.

1. Active CONTINENTAL margins continental margins that occur along plate boundaries plates are moving side by side or together when one plate sinks under another, a trench is formed when plates move past each other, a fault is formed continental rise is small or nonexistent rocky, short beach w/ cliffs rugged, coastal mountains on land EX: West coasts of North America and South America

2. Passive continental margins continental margins that don’t occur along plate boundaries broad continental shelf long, sandy beach no trenches, mountains, or faults EX: East coast of North America

Parts of the continental margin In order from land  Sea: continental shelf: part of the continent that extends from the shoreline to the continental slope flat, lengths vary depending on location continental slope: begins at the shelf edge where depth decreases rapidly to the rise. 20km long; descends 3.6km sediment builds up temporarily, then falls continental rise: descends gradually from the slope to the ocean floor considered part of ocean basin very long & gradual

Submarine canyon an undersea gully that cuts across the continental shelf and slope rivers erode the continental shelf and deposit sediment on continental slope gravity and powerful turbidity currents carry sediment down to the continental rise Very powerful agents of erosion coarse particles settle first, then fine such as clay

The Ocean Basin Abyssal Plain – flattest of all Earth’s surfaces, composed of sediment from continents Occur in all oceans More in Atlantic Ocean where there are fewer trenches Abyssal hills – small hills, occur in groups next to oceanic ridge systems

Deep-sea trenches Deep-sea trenches – long, narrow, steep-sided troughs that run parallel to continental margins occur when one plate slides beneath each other Exist at subduction zones Earthquakes & volcanoes common

Two scenarios for trenches to form: 1. Continental-oceanic collision (O-C collision): Deep sea trench forms Volcanic islands form on continent bordering trench 2. Oceanic-Oceanic collision (C-C collision): Deep sea trench Volcanic islands form on overriding plate

Deep-sea trenches

Vents and ridges Deep ocean vents – geyser that erupts underwater, mixing hot and cold water and bringing up minerals from beneath the surface; hydrogen sulfide Mid-ocean ridges- are undersea mountain ranges, where 2 plates are moving apart & magma rises

Sea mounts & guyots Seamounts- cone-shaped volcanic mountain peaks, rising high above the ocean floor All oceans, but mainly Pacific Ocean Volcanic in origin (ex. Hawaiian islands) Guyots are flat-topped seamounts- extinct volcanoes; older, eroded by wind & waves

Coral &coral Atolls Corals= tiny animals that live in warm shallow seas Atolls: reefs form around volcanic islands b/c of nutrients volcanic island goes extinct- cools, contracts, sinks coral atoll is left- reef surrounding shallow lagoon

Complete the Quick-Write on how coral atolls form. PAGE 10 INB Complete the Quick-Write on how coral atolls form.

Ocean Floor Sediments Sediment reaches the ocean floor in several ways: turbidity currents, fall from above, settle from glaciers, remains of microscopic shells Terrigenous sediments – come from continental rocks an minerals broken down from weathering an erosion wash into rivers and out to sea may come from glaciers breaking and dropping into sea

Ocean Floor Sediments Biogenous sediments come from living sources; they are oozes made mostly of shells and skeletons from tiny marine animals Calcareous ooze=calcium carbonate Most common from shells and skeletons Dissolve as they sink below 4500 meters Siliceous ooze=silicon dioxide More common around Equator and Antartica

Ocean Floor Sediments Hydrogenous sediments form when chemical reactions cause minerals to crystallized from seawater. Manganese nodules are most common – has manganese, iron oxide, nickel, cobalt, copper… They form on the sea floor from sediment that falls on them and mixes with the sea water, a few mm every million years Important to humans but hard to get

Ocean Floor Sediments Cosmogenous- meteorites from space; rarest sediment type

Importance of sediments studying sediments: past climates ancient water temperatures prevailing winds Climate Once-living organisms The sediments, unique organisms, magnetic records, industrial resources on the ocean floor represent a past look at Earth’s hydrosphere, biosphere, and geosphere.

What type of sediments are each of these? PAGE 12 inb What type of sediments are each of these?

Ocean floor Know these features for your quiz!!!