THE DYNAMIC OCEAN

Earth Science11/9/10

16.1- Ocean Circulation

• #1- Surface Circulation-– Surface currents- movements of water that flow

horizontally in the upper part of the ocean’s surface• Develop from friction between the ocean and wind that

blows across its surface– Gyres- huge circular-moving current systems • Coriolis effect- deflection of currents away from their

original course as a result of Earth’s rotation• Currents are deflected to the left in the Southern

hemisphere and the right in the Northern hemisphere.

Gyres

16.1 (cont.)

– Ocean Currents and Climate- • When currents from low-latitude regions move into

higher latitudes, they transfer heat from warmer to cooler areas on Earth.• As cold water currents travel toward the equator, they

help moderate the warm temperatures of adjacent land areas.

– Upwelling- rising of cold water from deeper layers to replace warmer surface water.• Brings greater concentrations of dissolved nutrients,

such as nitrates and phosphates, to the ocean surface.

16.1 (cont.)

• #2- Deep Ocean Circulation-– Density Currents- vertical currents of ocean water

that result from density differences among water masses• An increase in seawater density can be caused by a

decrease in temperature or an increase in salinity– High Latitudes- • Surface waters salinity increases as sea ice forms. When

it becomes dense enough, it sinks. Deep waters will not reappear at the surface for about 500-2000 years.

16.1 (cont.)

– Evaporation- • Conditions, such as dry winds and sunny days lead to

ocean evaporation. Water that has a higher salinity (due to evaporation) can then sink and form density columns.

– Conveyor Belt• Warm water flows to the poles where its temperature

drops and its salinity increases. This makes it more dense, so it sinks and then moves back towards the equator.

16.2- Waves and Tides

• #1- Waves– Wave Characteristics- most waves obtain their

energy and motion from the wind• Wave height- vertical distance between trough (bottom

of a wave) and crest (top of a wave)• Wavelength- horizontal distance between 2 successive

crests or two successive troughs• The height, length and period of a wave depend on 1)

wind speed, 2) length of time of wind, & 3) fetch (distance wind has traveled on open water)

16.2 (cont.)

– Wave motion- • Circular orbital motion allows energy to move forward

through the water while the individual water particles that transmit the wave move around in a circle.

– Breaking Waves- • As a wave advances toward the shore, the speed and

length of the wave decrease. This causes the wave to grow higher. When the wave is too steep to support itself, it breaks, or collapses, and water move onto the shore.

• This turbulent water is called surf, and the sheet of water made from collapsing breakers is called swash.

16.2 (cont.)

• #2- Tides- daily changes in the elevation of the ocean surface. Caused by the gravitational attraction exerted upon Earth by the moon, and, to a lesser extent, the sun.– Tide-Causing Force

• Force that produces tides is gravity.– Tidal Cycle

• Tidal range- difference in height between successive high and low tides

• Spring tides- tides that have the greatest tidal range due to the alignment of the Earth-moon-sun system

16.3 (cont.)

– Tidal patterns• 3 main tidal patterns-– Diurnal tide- one high tide and one low tide each

day– Semidiurnal tide- 2 high tides and 2 low tides each

day–Mixed tide- large inequality in high water heights,

low water heights or both

16.3- Shoreline Processes & Features

• Beach- accumulation of sediment found along the shore of a lake or ocean

• #1- Forces Acting on the Shoreline– Wave Impact• Waves are constantly eroding, transporting, and

depositing sediment.– Abrasion- sawing and grinding of rock fragments in

the water

16.3 (cont.)

– Wave Refraction- bending of waves• Wave energy is concentrated against the sides and ends

of headlands that project into the water– Longshore Transport• Longshore current- currents that flow parallel to the

shore and move large amounts of sediment• Turbulence allows longshore currents to easily move

the fine suspended snad and to roll larger sand and gravel particles along the bottom.

16.3 (cont.)

• #2- Erosional Features– Wave-Cut Cliffs and Platforms• Wave-cut cliffs result from the cutting action of the surf

against the base of coastal land. Eventually, only a flat, bench-like surface is left.

– Sea Arches and Sea Stacks• When the arch of a sea arch caves in, only an isolated

sea stack is left.

16.3 (cont.)

• #3- Depositional Features– Spits, Bars, and Tombolos• Spit- elongated ridge of sand that projects from the

land into the mouth of an adjacent bay• Baymouth bar- sandbar that completely crosses a bay

and seals it off from the open ocean• Tombolo- ridge of sand that connects an island to the

mainland or to another island

Barrier Islands• Formed from the general rise in sea level

following the last glacial period• former sand dunes• Narrow sand bars parallel to the shore

Stabilizing the Shore

1. Protective structures such as groins, breakwaters, and seawalls

2. Beach nourishment is the addition of large quantities of sand to the beachThis increases the water’s turbidity and kills offshore reefs