Exploring Oceans, Currents, Waves & Coasts

1. The Oceans & Waves Steve Terrill/Stock Market

2. I. SEAWATER • Covers 71% of Earth’s surface • Nature of seawater • 35o/oo dissolved salts (30-38) • Varies from place to place • Origin of seawater • Volcanoes? • Comets? • Excess H+ & O-?

3. CURRENTS • Ocean water moves constantly - sideways, up, down because it is: • Heated unevenly • Evaporated unevenly • Blown by wind • Affected by Earth’s rotation • Pulled by sun & moon • Currents are the flow of water between areas of different surface levels or different densities

4. Surface ocean currents arerun by climate & rotation

5. Density Currents • Function of • Temperature (polar regions) • Salinity (Mediterranean Sea) • Suspended materials (turbidities- flow of muddy water down a slope) • Deep ocean currents move by • density & thermal differences • the Coriolis effect • NADW, AABW

6. Average surface salinity of the oceans

7. August sea-surface temperatures

8. Circulation of the Atlantic Ocean

9. CONVEYOR BELT

10. Turbidity Currents

12. III. Tides Twice daily rise and fall of the sea caused by the gravitational attraction between • earth and moon (lunar tides) • earth and sun (solar tides) Function of distance between and mass of the Earth, Moon and Sun

14. Interaction between lunar and solar tides during the lunar month causes: • Neap tides: when two tidal components are out-of-phase, hence lower than usual, and • Spring tides: when two tidal components are in-phase, hence higher than usual.

15. The highest and lowest tides occur due to the interaction of earth, moon, and sun

16. The effect of tides on a tidal inlet.

17. Mont-Saint-Michel France Exposed tidal flats Thierry Prat/Sygma

18. Terrace Exposed at Low Tide James Valentine

19. IV. WAVES • Waves are described by • Wave length(L): distance between crests • Wave height (H) : vertical distance between crest and trough • Wave period (T): time for successive waves to pass a fixed point • Wave velocity (V) of waves (V = L/T) • 2 kinds of waves • Deep water waves • Shallow water waves

20. Wind-generated Orbital Waves

21. Most waves are generated in the open ocean & • height depends on: • Wind velocity • Wind duration • Distance over which wind blows called the FETCH, usually a big storm.

22. Shallow water waves • At water depth of L/2, wave feels bottom. Then: • Wave height Increases as • Wave length decreases. • Velocity decreases because wave is dragging on bottom. • Period doesn’t change • When wave reaches 1.3H -> BREAKER

24. Wave refraction • Bending of wave crests as they approach the beach at an angle • Caused by the change in velocity of waves as a function of water depth • Only a small part of each wave feels bottom at a time so only a small part of wave slows.

25. Wave Refraction

26. Waves Bending as they Approach the Beach John S. Shelton

27. Sediment transport near shore, parallel to the beach • Longshore drift: sediment carried by swash and backwash along the beach • Longshore currents: currents parallel to the beach within the surf zone

28. Longshore Drift

29. V. COASTS • BEACHES • EROSIONAL COASTS -uplift • DEPOSITIONAL COASTS - sinking • CHANGES IN SEA LEVEL-relative

30. Refraction at Headlands and Bays

31. Carving a coast • Waves & currents act the same as streams except work in both directions • Erode - in high energy areas by • Abrasion • Solution • Wave pressure • Deposit -in low energy areas

32. Sandy Beach, North Carolina Barrier Island Peter Kresan

33. Boulder Beach, Massachusetts Raymond Siever

34. Major parts of beaches • Offshore: from where the waves begin to feel bottom to the surf zone • Foreshore: includes the surf zone, tidal flats, and swash zone • Backshore: from beyond the swash zone to the highest level of the beach

35. Major Parts of a Beach

36. Sand Budget of a Beach

37. Factors determining rates of erosion or deposition • Uplift • Subsidence • Rock type • Sea-level changes • Storm wave heights • Tidal range

38. Erosional Coasts • Region of up-lift - JOB IS TO STRAIGHTEN SHORELINE • Prominent cliffs & headlands • Narrow inlets, irregular bays & beaches • Undercut cliffs • Sea stacks • Wave-cut terraces • Falling sea level

39. Sea Stacks Kevin Schafer

40. Wave-cut Terrace Exposed at Low Tide John S. Shelton

41. Uplifted Coastal Terrace John S. Shelton

42. Depositional Coasts • Sinking coasts • Long, wide beaches • Bars • Spits • Barrier islands • Tidal flats & shallow lagoons • Low-lying, sedimentary coastal plains • Rising sea level - estuary

44. Southern Tip of Cape Cod Steve Durwell/The Image Bank

45. Partially Developed Barrier Island Mainland Florida Lagoon BarrierIsland Gulf of Mexico Richard A. Davis, Jr

46. Effects of rising sea level:Eastern North America and Europe

47. VI. Preventing beach erosion • Structural approaches (e.g., groins): typically cause increased erosion down current of structure • Non-structural approaches (e.g., beach nourishment, land use planning): expensive, but don’t cause erosion in new areas

48. Groin: Built to Prevent Updrift Erosion Causes Downdrift Erosion Erosion Deposition Phillip Plissin/Explorer

49. Interrupting longshore currents

50. Beach Nourishment, New Jersey U.S. Corps of Engineers, New York District