Chapter 16 The Dynamic Ocean

16.1 OCEAN CIRCULATION

Surface Circulation

• Ocean currents are masses of ocean water that flow from one place to another

• Surface currents – movements of water that flow horizontally in the upper part of the ocean’s surface– Develop from friction btw the ocean and the wind

that blows across its surface

Gyres

• Huge circular moving current systems dominate the surfaces of the oceans

• 5 Main ocean Gyres– N. Pacific Gyre– S. Pacific Gyre– N. Atlantic Gyre– S. Atlantic Gyre– Indian Ocean Gyre

• Coriolis effect – deflection of currents away from their original course as a result of Earth’s rotation

• Due to Earth’s rotation, currents are deflected to the right in the N. Hemisphere & to the left in the S. Hemisphere

• 4 main currents within each gyre

Ocean Currents & Climate

• When currents from LL regions move into HL 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

• Play a big role in maintaining Earth’s heat balance

Upwelling

• Rising of cold water from deeper layers to replace warmer surface water

• Wind-induced vertical movement• Brings greater concentrations of dissolved

nutrients to the ocean surfaces

Deep – Ocean Circulation

• Density currents – vertical currents of ocean H2O that results from density differences in the H20 masses

• Increase in seawater density can be caused by a decrease in temperature or an increase in salinity

A Conveyor Belt

Warm H20 flows toward

poles

Temperature drops & salinity

increases

Density increases

Dense H20 moves toward equator

Cold, deep water

upwells

Upwelled H20 warms

The cycle repeats

16.2 WAVES & TIDES

Waves

• Energy traveling along the boundary btw ocean and atmosphere

• Most ocean waves obtain their energy & motion from wind

• Top of wave = crest• Trough = separate crests• Wave Height = vertical distance btw trough &

crest

• Wavelength = horizontal distance btw 2 successive crests (or 2 successive troughs)

• Wave period = the time it takes one full wave (one wavelength) to pass a particular spot

• The height, length, & period depend on 3 factors:– Wind speed– Length of time the wind has blown– Fetch (distance that the wind has traveled across

open H20)

• Circular orbital motion allows energy to move forward through the H20 while the individual water particles that transmit the wave move around in a circle

• When waves approach shore, H20 becomes shallower & influences wave behavior (“feels the bottom” at depth = to half of its wavelength)

TidesTide-Causing Forces

• Results from the gravitational attraction exerted upon Earth by the moon (and the sun)

• Gravity & Inertia produce tides

• Gravity attracts the Earth & moon

• Inertia = tendency of moving objects to continue in a straight line (keeps Earth & moon from crashing into each other

Tidal Cycle

• Tidal range – difference in height btw successive high & low tides

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

• Neap tides – lowest tidal range

• Each month = 2 spring tides & 2 neap tides

Tidal Patterns

• 3 main tidal patterns – Diurnal Tides• 1 high tide & 1 low tide each tidal day

– Semidiurnal Tides• 2 high tides & 2 low tides each tidal day

– Mixed Tides• Large inequality in high water heights, low water

heights, or both

16.3 SHORELINE PROCESSES & FEATURES

Forces Acting on the Shoreline

• Waves along the shoreline are constantly eroding, transporting, & depositing sediment

• Wave Impact• Abrasion• Wave Refraction– Bending of waves – Wave energy is concentrated against the sides &

ends of headlands that project into the H20, whereas wave action is weakened by bays

– https://www.youtube.com/watch?v=G1FIBuybN78

• Longshore current – near shore current that flows parallel to the shore

• Turbulence allos longshore currents to easily move the fine suspended sand & to roll larger sand & gravel particles along the bottom

Erosional Features

• Shoreline features that originate primarily from the work of erosion

• Sediment that is transported along the shore & deposited in areas where energy is low produce depositional features

• Wave-Cut Cliffs & Platforms• Sea Arches & Sea Stacks

Depositional Features

• Spits• Bars• Tombolos• Barrier Islands – narrow sandbars parallel to

the coast (separate from coast) (3-30 km offshore)

Stabilizing the Shore

• Groins, breakwaters, & seawalls are some structures built to protect a coast from erosion or to prevent the movement of sand along a beach

• Can be built parallel to shoreline• Beach nourishment is the addition of large

quantities of sand to the beach system