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

The Oceans 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

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

Where the Ocean Meets Land 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 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 the 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 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 Estuary

Where Ocean Meets Land 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

Coastal Processes & Problems Lab 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