The Dynamic Ocean

1. The Dynamic Ocean Earth Science Ch. 16

2. 16.1 Ocean CirculationOcean Surface Circulation • Surface currents develop from friction between the ocean and the wind. • Surface currents are related to the patterns of the atmosphere. • Large circular moving surface currents are called gyres.

4. Wind generates surface currents but the most significant factor is the Coriolis effect. • The Coriolis effect is a deflection of currents as a result of earth’s rotation. • Currents are deflected to the right in the northern hemisphere and to the left in the southern hemisphere

6. Ocean currents have an important effect on climate. • Warm currents • Travel from low latitude to high latitudes • Transfers heat from warm to cool areas • Moderates the cold of winter • Gulf stream moderates our weather • Cold currents • Travel from high latitude to low latitude • Moderates the heat of summer.

8. Winds can also cause vertical water movements. • A common vertical movement is called upwelling. • Upwelling occurs when cold deep water rises to the surface and replaces warm surface water that has been blown by wind. • Upwelling is a very important process because it brings nutrients from the ocean floor to the surface.

10. Deep Ocean Circulation • Vertical currents are caused by changes in density. • The density of sea water is affected by temperature and salinity. • Salinity is increased by evaporation or formation of sea ice. • Salinity is decreased by precipitation, runoff, melting of icebergs and sea ice.

12. Ocean circulation is similar to a conveyor belt that travels throughout the world. • In this conveyer belt warm water in the oceans upper layers flows toward the poles. • When the water reaches the poles the temperature drops and salinity increases making it more dense. • This more dense water sinks and moves toward the equator. • This cold water remains in the deep ocean until upwelling forces it to the surface.

15. 16.2 Waves and TidesWaves • Waves are caused by a transfer of energy through water. • Most ocean waves obtain energy and motion from the wind.

16. Parts of a Wave • The tops of waves are called crests. • Crests of waves are separated by troughs. • The distance between the crest and trough is called the wave height. • The distance between 2 crests or troughs is the wavelength. • The time it takes for one full wave to pass a fixed point is the wave period. • Wave speed = wavelength / wave period

18. Height, length, and period of a wave depends on 3 factors: • Wind speed • Length of time the wind has blown • Fetch: distance the wind travels across open water • As the amount of energy from the wind increases the height and steepness of the wave increases. • Eventually the wave grows so tall that it topples over forming ocean breakers called whitecaps.

20. As a wave travels, water particles pass energy along by moving in a circle. This movement is called circular orbital motion. • As you move deeper in the ocean, circular motion decreases.

22. The turbulent water caused by the breaking wave is called the surf. • The water that moves up the beach from the collapsing breaker is called the swash. • The water that flows back down the beach is called the backwash.

24. Tides • Tides are regular changes in the elevation of the ocean surface. • Ocean tides result from differences in the gravitational attraction exerted upon the earth by the moon and, to a lesser extent, the sun. • The primary body that influences tides is the moon.

25. Gravity causes water to be pulled toward the moon causing a tidal bulge on the earth’s surface. • There are 2 tidal bulges at any given time on the Earth’s surface. • Tidal bulges remain in place while the earth rotates through them. • High tide occurs when a location on the Earth moves through the tidal bulge. • The east coast of the U.S. experiences 2 high tides and 2 low tides each day. (semidiurnal)

27. The sun does play a role in producing tides. • This is most noticeable when there is a new and full moon. • During these times the sun and moon are aligned and their gravitational forces are combined. • This produces a larger than normal tidal range • The name given to these types of tides is spring tides. • Each month there are 2 spring tides.

28. During a 1st and 3rd quarter moon, the gravitational forces of the moon and sun act on the earth at a right angle. • This causes the tidal range to decrease. • These tides are called neap tides. • Each month there are 2 neap tides.

31. 16.3 Shoreline Processes and FeaturesForces Acting on the Shoreline • A beach is the accumulation of sediment found along the shore of an ocean • Beaches are composed of whatever sediment is locally available • Beaches are formed by deposition of weathered and eroded material. • Material for the coastal plain comes from the Appalachian mountains

32. Wave impact • Waves are constantly eroding, transporting, and depositing sediment • Water is a very strong agent of weathering and erosion

33. Abrasion • Abrasion is a type of mechanical weathering that commonly occurs along coast lines. • The water and sediment smooth the land surfaces.

34. Wave Refraction • The bending of waves • Affects the distribution of energy along a shoreline • It affects where erosion and deposition will take place.

35. Because of wave refraction, the energy from the wave is more concentrated on any headlands the protrude into the water. • Erosion occurs along the headlands. • Wave action is weaker in bays • Because that wave energy is less in the bays, deposition occurs

37. Longshore Currents • Water tends to move toward the shore at an angle. • The movement of water away from the shore is straight down. • These angled waves produce a current called a longshore current. • Longshore currents move parallel to the shore and move large amounts of sediment.

39. Erosional Features • Wave cut cliffs • Wave cut platform • Sea arches • Erosion of a cave through an entire headland • Sea stacks • Form when the land that forms the arch collapses.

42. Depositional Features • Spits • Extensions of a coastline into a bay • Baymouth bars • Sediment that extends over the mouth of a bay • Tombolos • Sediment that attaches the mainland to an island • Barrier islands • Large accumulations of sediment parallel to the shore. • Not permanent due to water erosion.

45. Stabilizing the shoreProtective Structures • Groins • Barriers built at right angles to the beach to trap sand that is moving parallel to the shore.

46. Breakwaters • Built parallel to the shore to protect shorelines from wave erosion.

47. Seawall • Built parallel to the shore to shield the coast from breaking waves.

48. The Chesapeake Bay • Drainage Basins of Virginia • Gulf of Mexico • North Carolina Sounds • Chesapeake Bay • The Chesapeake Bay is the largest estuary in the US • An estuary is any body of water where fresh and salt water mix • Water in the estuary is brackish which means it has a lot of salts and minerals • The Chesapeake Bay contains thousands of species and many important resources.

49. Nutrients contributed to the bay • Wastewater treatment plants • Runoff from farms • Air pollution • While nutrients are needed by organisms, excessive amounts of phosphorus and nitrogen threaten life in the bay. • The threat comes from the growth of dense algal blooms which block sunlight and consume oxygen.

50. Too much sediment is also entering the bay due to erosion caused by humans. • The excess sediment clouds the water, causes the spread of nutrients, and suffocates bottom dwelling organisms. • Chemicals enter the bay through waste water, runoff, and air pollution. • These chemical contaminants threaten the food chains of the bay and food sources.