chapter 16 the dynamic ocean. 16.1 ocean circulation
TRANSCRIPT
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