1. Unit 2: Surface Processes and the Hydrosphere Lesson 7: Physical Oceanography ( Heath Earth Science – Pg. 308-352)

2. Today’s Objectives  Describe features and processes associated with physical oceanography, including:  Identify techniques used to study the ocean and ocean floor  Diagram a typical ocean floor including continental margins, mid-ocean ridge, rift, trench, abyssal plain, and seamounts  Relate the formation of turbidity currents to submarine canyons  Identify the physical properties of sea water (temperature, density, etc)  Explain the general pattern of major currents in oceans

3. How do we study the ocean floor?  During the last century, we have learned a lot about the ocean floor:  Deep sea mountain ranges  Underwater volcanoes and faults  Trenches  Type/age/composition of rock/sediment  But……the ocean floor is very deep, and is under enormous pressure…how do we learn all of this?  Three methods:  1) Remote Sensing  2) Sediment Sampling  3) Direct Observations

4. 1) Remote Sensing  Early days, depth was measured using a weight on a line  This took a very long time  Today, ships have a device called a precision depth recorder to find the distance to the ocean floor  Sends a sound signal through the water to the seafloor  Length of time needed for signal to reach the bottom and echo back to ship measures the depth of the water  Traces a continuous profile of area which ship is sailing over  This method can make accurate maps of the seafloor  Variations of this method can even detect different layers of sediment on the seafloor  Satellites in space use same technology to map at much higher speeds than boats

5. 1) Remote Sensing

6. 2) Sediment Sampling  Echo sounding provides data about the shape of the seafloor, but not much about what materials are present  Sampling is a method used to collect sediment from the seafloor for observations  A) A scoop called a dredge is dragged along the seafloor to collect rock samples on seafloor without sediment  B) When sediment samples are needed, a corer is used  Corers are devices used to collect long, cylindrical samples of sediment from the seafloor  They are shaped like a hollow tube with an open end, and are lowered from a ship into the water  Several types of corers are used which can take samples up to 1500 meters long! (pg. 324)

7. 2) Sediment Sampling Dredge Gravity Corer

8. 3) Direct Observations  Sometimes, we can make direct observations from inside mini-submarines  Alvin is an example of such a submarine  One drawback is much time required to descend/ascend too/from surface  Another option is deep-towed vehicles  Argo is an example of a deep-towed vehicle  “fly” above the seafloor as they are towed along by a research ship at the surface  Cameras onboard Argo send photographs back to the research ship through cables

9. 3) Direct Observations Deep-tow vehicle Mini-submarine

10. Practice  Topic Questions  Pg. 325, #1-3

11. The Ocean Floor  The ocean floor is divided into two major regions:  1) the continental margins  2) the ocean basins  The continental margins themselves are further divided up into three more sub-regions:  1a) continental shelf  1b) continental slope  1c) continental rise  In addition to these regions are several other prominent features of the ocean floor, such as the: seamount, abyssal fan, trench, rift, abyssal plain, abyssal hills, guyots, coral atolls and mid-ocean ridge

12. 1) Continental Margins

13. 1a) Continental Shelf  Underwater extension of the continent  Extremely flat  Extend from shoreline of the continent to the shelf edge, (boundary between the shelf and continental slope)  Shelf edge marks location where sea depth increases rapidly  On average, the shelf edge is 130 meters deep  Characteristics depend on type of continental margin:  Active margin: narrow shelf, bordered by ocean trench, shoreline is rugged with coastal mountains  Passive margin: broad shelf, up to 300 km wide, no trench or mountains, bordered by coastal plain

14. 1b) Continental Slope  Begin at the shelf edge, where water depth starts to increase rapidly  Boundary is clear and abrupt  Seafloor is no longer level, but begins to slope toward the deep ocean at an average angle of 4 degrees  Generally about 200 km wide, and descend to 3 km deep  Change from continental to oceanic crust often occurs beneath the continental slope  Active margin: slope ends in a deep-sea trench  Passive margin: slope ends in a wide band of sediment, the continental rise

15. Submarine Canyons  Sometimes, gigantic canyons, called submarine canyons cut into the continental shelf and slope  These canyons can be larger than the grand canyon!  Two possible causes for these canyons:  1) Continuation of a continental river valley that has been drowned by rising sea level  2) Cut by powerful currents called turbidity currents  A turbidity current is a massive underwater landslide caused by either an earthquake or gravity  “turbid” means muddy

16. Turbidity Currents Turbidity currents build up great fan- shaped deposits at the mouths of many submarine canyons These features are called submarine fans, or abyssal fans

17. 1) Continental Margin  1c) Continental Rise:  The gently sloping region between the continental slope and the ocean basin  Formed by deposition of masses of sediment several km’s thick  Sediment originates from the land, brought to the region by turbidity currents and gravity flows  Not found at active margins – deep-sea trenches that occur there trap sediments  Found only at passive margins – may reach 1000 km wide

18. Practice  Topic Questions  Pg. 329, #4-7

19. 2) Ocean Basin  The ocean basin is the second major region of the ocean floor  There are several features that are found in the ocean basin, the most expansive of which are the abyssal plains  Abyssal plains range in depth from 3000-6000 meters, and are extremely flat (flattest areas of Earth’s surface)  Composed of sediments over 1 km thick in some areas  Most of this material came from the continents via turbidity currents

20. Abyssal Plain

21. Ocean Basin Features  Abyssal hills are another part of the ocean basin  They are small, rolling hills that occur in groups next to continental margins and oceanic ridge systems  In the Atlantic ocean, abyssal hills follow the mid-Atlantic ridge on either side  Seamounts are cone-shaped mountain peaks that rise high above the deep ocean floor  May occur alone but more commonly found in clusters, or rows, often near plate boundaries  Volcanic in origin  The Hawaiian Islands are actually a group of seamounts that are tall enough to rise above the surface

22. Ocean Basin Features

23.  Some seamounts have a flat top, and these are called guyots (gee-oh)  Guyots started as seamounts, but their tops reached sea-level and were worn down by wave action  Sinking oceanic crust lowered the guyots below the surface  Coral atolls are also results of crustal sinking  Imagine a seamount rises above sea-level, and a coral reef grows around the island  The crust begins to sink, causing the island to sink  The coral continues to grow in a ring around the sinking island forming a ring of coral called a coral atoll

24. Ocean Basin Features

25.  Trenches are long, deep, steep sided depressions formed along active continental margins at subduction zones (when one plate is forced beneath another plate)  Usually occur along coasts where a dense, oceanic plate is subducting below a less dense, continental plate

26. Ocean Basin Features  Mid-ocean ridges are long mountain ranges that form along divergent (two plates moving apart) plate boundaries on the ocean floor  Formed by magma pouring out of the rift between the two plates  The rift is located down the center of the ridge  Mid-Atlantic ridge runs the entire length of the Atlantic ocean

27. Ocean Basin Features

28. Practice  Topic Questions  Pg. 335, #8-11