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Chapter 12 – THE OCEANS
The Oceans• Ocean basins
– No geologic record of time before water
– Origin of water on Earth is debated• 1st proposal = water
originated inside Earth• 2nd proposal = water arrived
from outer space via meteorite impacts
• Ocean basins– Earth has 4 huge water basins
• Pacific Ocean• Atlantic Ocean• Indian Ocean• Southern Ocean• *Arctic Ocean
– Cover 71% of Earth’s surface
The Oceans
• Composition of seawater– Salinity
• Measure of salt content of solution
• Seawater salinity ranges 3.3 - 3.7%
– Elements in seawater come from:• Chemical weathering of rock• Volcanic eruptions & black smokers• Evaporation of surface water (increases salinity)• Freezing of seawater (increases salinity)
The Oceans
• Layers in the ocean– 3 major layers in oceans in which density differs:
• Surface layer ( 2%; warmest)• Thermocline (18%; just above freezing point)• Deep Zone (80%; temperature low & constant)
The Oceans
• Ocean currents– Surface currents
• Christopher Columbus
The Oceans
• Ocean currents– Deep currents: “Great Ocean
Conveyor Belt” (thermohaline circulation)• North Atlantic
Deep Water• Antarctic
Bottom Water• Gulf Stream
The Oceans
• How oceans regulate climate– Oceans moderate
coastal climates• Continental
interiors = more extreme
– Conveyor belt re-distributes heat from tropics to poles• Elimination of
conveyer belt (e.g., Gulf Stream) could cause ice age
The Oceans
Where the Ocean Meets Land• Changes in sea level
– Global volume change• Barely noticeable in human
lifetime • Account for great change in
position of shore line over geologic time
• Global warming = sea level rise
– Current global warming = 2.4 mm/year rise
• Global cooling = sea level drop
• Changes in sea level– Tides
• Regular daily cycle of rise & fall of sea level resulting from gravitational action of Moon, Sun, & Earth
Where the Ocean Meets Land
• Changes in sea level– Tides
• Run-up height• Tidal range
– Spring tide– Neap tide
• Tidal bore
Where the Ocean Meets Land
• Changes in sea level (continued)– Waves
• Ocean waves receive energy from wind
• Surf– “Broken”,
turbulent water found between line of breakers &shore
– Rip currents• Wave refraction
Where Ocean Meets Land
• Changes in sea level continued– Erosion & transport of sediment by
waves• Longshore current
– Current in surf zone; flows parallel to coast
• Beach drift– Particles driven up/down beach
slope by wave action
Where Ocean Meets Land
• 3 kinds of shorelines & coastal landforms– Rocky coasts
• Wave-cut cliff– Coastal cliff cut by wave action at base of rocky coast– Wave-cut
bench– Marine terrace
Where the Ocean Meets Land
• 3 kinds of shorelines & coastal landforms– Beach
• Wave washed sediment along coast
Where the Ocean Meets Land
• Kinds of shorelines & coastal landforms– Barrier Island
• Long, narrow, sandy island offshore & parallel to low land coast
– Spit– Lagoon
Where Ocean Meets Land
• Kinds of shorelines & coastal landforms– Tombolo– Bay barrier– Estuary
Where Ocean Meets Land
Estuary
• Kinds of shorelines & coastal landforms– Reefs
• Hard structure on shallow ocean floor, built by coral
• Polyps- tiny coral animals that deposit calcium carbonate
• Fringing reef• Barrier reef• Atoll• Highly productive ecosystems
Where Ocean Meets Land
• Active continental margin– Located near plate
boundaries– Narrow continental shelf &
coastal plain• I.e. Pacific coast
• Passive continental margin– Not located near plate
boundaries– Wider continental shelf &
coastal plain• I.e. Gulf
coast; Atlantic coast
Coastal Processes & Problems Lab
• Waves– Crest– Trough– Wave height (crest –
trough)– Wavelength (crest to crest)– Wave period (time it takes
2 crests to pass fixed point)• Factors that affect waves
– Wind speed– Wind duration– Fetch
Coastal Processes & Problems Lab
• Coastal erosion & deposition– Headlands = erosion (energy
concentrated)– Bays = deposition (energy
dispersed)• Wetland erosion
– Wetlands = barriers for storm surge & large waves
– Mississippi River delta wetlands being eroded due to human actions
• River modifications
Coastal Processes & Problems Lab
• Human modification of coastlines– Groins– Jetties– Breakwaters– Seawalls– Problems
Coastal Processes & Problems Lab
• Hurricane ingredients– Atmospheric disturbance– Warm ocean water– Light upper atmospheric
winds• Hurricane damage
– Storm surge– High winds– Rainfall &
flooding– Tornadoes
Coastal Processes & Problems Lab
