Labs Next Week Don’t forget your lab book!!!

1. Labs Next WeekDon’t forget your lab book!!! • Read pages iii-v, xv-xx in your lab book • Exploring the Ocean Environment by Hall-Wallace et al. • Lab assignments now posted on web • dusk.geo.orst.edu/oceans/103labs.html

2. Shape of the SeafloorChapter 2

3. Techniques of Bathymetry - 1 • Challenger expedition (1872-1876) -1st systematic bathymetric survey • ocean floor not flat - significant topographic relief • German ship Meteor (1920’s) - 1st echosounding survey • sounds travels through water much better • velocity = distance/time • SONAR (Sound Navigation and Ranging)

4. Bathymetry - 2 • WWII - U.S. Navy further developed SONAR technology • knowledge of the enemy • knowledge of the ocean • 1950’s - 1960’s - single, focused high-frequency, short wavelength sound beam • “wide-beam” bathymetry • sound beam spreads out as it reaches bottom • range of depths - fuzzy estimate

5. single, focused high-frequency, short wavelength sound beam

6. Bathymetry - 3 • 1970’s - revolution in bathymetric mapping with multibeam bathymetry • multiple, focused, high-frequency, short wavelength sound beams • “narrow-beam” or “multibeam” bathymetry • sound beam stays narrow and focused all the way to the bottom • depths much more precise • e.g., Sea Beam has 16 beams, Sea Beam 2000 has 121, Simrad EM120 has 191

7. multiple, focused, high-frequency, short wavelength sound beams A Gigabyte of data an hour A Gigabyte of data a day

8. Bottom Coverage & Data Density by Survey Method Leadline Single Beam Multibeam 1-2 K soundings per survey 500 - 750 K soundings per survey 400,000 – 1,000,000 K soundings per survey Image courtesy of NOAA & UNH

12. N

13. N

17. Shallow Water Multibeam

18. Shallow Water Multibeam (cont.)

19. Tutuila Surveys

22. Tutuila Surveys

23. Fagatele Bay National Marine Sanctuary

24. FBNMS Benthic Habitat

25. 2005 HURL Sub & ROV surveys Ka‘imikai-o-Kanaloa Pisces IV or V HURL = Hawaii Undersea Research Lab ROV= remotely-operated vehicle RCV-150

26. Sonar Also Used as... • a “catscan” of oceans to see water structure ABOVE seafloor • an “x-ray” of seafloor to see structure BENEATH seafloor • seismic reflection & seismic refraction • low frequency, long-wavelength sound • sidescan sonar to get pictures of seafloor in addition to depth • backscatter strength as opposed to traveltime

27. Sidescan Sonar Image courtesy of USGS Woods Hole

28. DSL-120 Vehicle Image courtesy of WHOI Deep Submergence Lab and Dr.Dan Fornari Image courtesy of USGS Woods Hole

33. Resolution • with multibeam bathymetry can see things on seafloor the size of this room • swath width of 6 km or 3.7 miles • good, high-resolution maps possible only since 1980’s • other instruments needed to see things smaller than size of room • remotely-operated vehicles (ROVs) • submersibles

34. “Fine Scale” Mapping • on the order of tens of meters to meters • features the size of a can of beer!

36. Seafloor Features: Continental Margins • continental shelf - extends from shore to a point marked by great increase in slope • continental slope - steep slope beyond the continental shelf break • slopes often cut by submarine canyons • turbidity currents - dense flows of sediment-laden water • deepsea fans • continental rise • abyssal plain - extensive, flat

38. Seafloor Features: Deep Ocean • seamounts - underwater volcanoes 500 m to 1000 m high • flat-topped ones are called guyots • volcanic features (buoyed up by hot rock, lava) • abyssal hills - features around 200 m high • pervasive on seafloor • volcanic AND tectonic in origin - still debated

40. Seafloor Features: Deep Ocean • Plate Boundaries • Ridges (Rises), Trenches, Transform Faults, Fracture Zones