The Dynamic Ocean
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Transcript of The Dynamic Ocean
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The Dynamic Ocean
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The Dynamic Ocean
• Surface Circulation• Deep-Ocean Circulation• Shorelines & Shoreline Features• Waves & Wave Erosion• U.S. Coastal Problems• Tides
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Terms• Gyre
– A circular pattern of connected surface currents
• Tides– Daily rise and fall of shorelines around the
world ocean
• Tidal range– Difference in height between high and low tide
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Surface Circulation
PSCI 131: The Dynamic Ocean
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Surface CirculationPSCI 131: The Dynamic Ocean
• Surface ocean currents are “rivers” with very different temperature and density than surrounding water
• Driven by wind blowing across ocean surface
• Ultimate energy source: Sun
• Carry warm water from tropics to poles and vice versa
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Surface Current PatternsPSCI 131: The Dynamic Ocean: Surface Circulation
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Influence on Climate: The Gulf StreamPSCI 131: The Dynamic Ocean: Surface Circulation
• Moves warm water north from tropics
• Gives British Isles a temperate climate
North America
Water movement
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UpwellingPSCI 131: The Dynamic Ocean: Surface Circulation
• Vertical movement of water
• Deeper water moves up to replace surface water moved away by winds
• Depths: 150-1,000 feet
• Replenishes nutrients
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UpwellingPSCI 131: The Dynamic Ocean: Surface Circulation
• Upwelling along African coast
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Deep-Ocean Circulation
PSCI 131: The Dynamic Ocean
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Deep-Ocean CirculationPSCI 131: The Dynamic Ocean
• Much deeper than surface circulation or upwelling – can affect ocean floor
• Vertical motion driven by density differences– If upper layers become denser, they sink
• Density controlled by temperature and salinity– aka “thermohaline” circulation
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Deep-Ocean CirculationPSCI 131: The Dynamic Ocean
Cold, dense surface water in polar regions sinks, driving deep-ocean circulation
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Shorelines & Shoreline Features
PSCI 131: The Dynamic Ocean
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Shoreline: TerminologyPSCI 131: The Dynamic Ocean: Shorelines
• Shoreline: contact between water and land• Coast: area from shoreline inland as far as
ocean-related features are found• Coastline
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Shoreline: TerminologyPSCI 131: The Dynamic Ocean: Shorelines
• Coastline: Highest line affected by storm waves
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PSCI 131: The Dynamic Ocean: Shorelines: Terminology
• Shore: low tide line to coastline– Foreshore: low tide line to high tide line– Backshore: high tide line to coastline
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PSCI 131: The Dynamic Ocean: Shorelines: Terminology
• Nearshore: surf line to low tide line
• Offshore: beyond surf line
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Shoreline Features: BeachesPSCI 131: The Dynamic Ocean: Shorelines
• Accumulations of sediment along margin of ocean or lake
• Berm: level area, usually dry• Beach face: sloping area, usually wet• Berm:
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Shoreline Features: BeachesPSCI 131: The Dynamic Ocean: Shorelines
• Composition: any locally available sediment type– Quartz sand– Shells– Volcanic material– Etc.
Black volcanic sand
Shells
Rocky Great Lakes beach
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Shoreline Features: Barrier islands
PSCI 131: The Dynamic Ocean: Shorelines
Wave-cut cliff
(uplifted wave-cut platform)
• Wide beaches – Separated from mainland by
marshes or narrow seaways
• Shaped by wave erosion and storms
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Shoreline Features: Cliffs, Platforms, Terraces
PSCI 131: The Dynamic Ocean: Shorelines
Wave-cut cliff
(uplifted wave-cut platform)
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Shoreline Features: Sea Arches and Sea Stacks
PSCI 131: The Dynamic Ocean: Shorelines
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Shoreline Features: Spits, Bars, Tombolos
PSCI 131: The Dynamic Ocean: Shorelines
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Changing Shoreline Features Along Irregular Coastlines
PSCI 131: The Dynamic Ocean: Shorelines
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Changing Shoreline Features Along Irregular Coastlines
PSCI 131: The Dynamic Ocean: Shorelines
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Evolving Shoreline Features Along Irregular Coastlines
PSCI 131: The Dynamic Ocean: Shorelines
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Waves and Wave Erosion
PSCI 131: The Dynamic Ocean
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Ocean WavesPSCI 131: The Dynamic Ocean: Waves & Wave Erosion
• Created by wind
• Energy propagating along water-air boundary
• Waves move differently in deep and shallow ocean– Deep: no net movement of water, circular motion– Shallow: water is displaced, linear motion
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Ocean WavesPSCI 131: The Dynamic Ocean: Waves & Wave Erosion
Wave base
Wave base: depth below which water does not “feel” waveWave base = ½ wavelength
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Deep ocean wave motion is circularPSCI 131: The Dynamic Ocean: Waves & Wave Erosion
Boat returns to starting position
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Shallow ocean wave movementPSCI 131: The Dynamic Ocean: Waves & Wave Erosion
Wave base
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Wave ErosionPSCI 131: The Dynamic Ocean: Waves & Wave Erosion
• Direct impact of water• Abrasion by sediment in the water
Cliff undercut by wave impactsRocks polished by abrasion
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Shoreline Sediment MovementPSCI 131: The Dynamic Ocean: Waves & Wave Erosion
• Longshore transport
– Beach drift
– Longshore currents
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U.S. Coastal Problems
PSCI 131: The Dynamic Ocean
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Pacific CoastPSCI 131: The Dynamic Ocean: U.S. Coastal Problems
• Emergent: Steep, geologically active, rugged– Cliffs with narrow beaches
• Beaches are getting narrower– Natural sand supplies from rivers
have been restricted by damming
• Since beaches absorb wave energy, narrower beaches means faster wave erosion of cliffs
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Atlantic and Gulf CoastsPSCI 131: The Dynamic Ocean: U.S. Coastal Problems
• Submergent: Flat, geologically quiet– Wide beaches, barrier islands
• Rising sea level is causing more frequent flooding– Gentle slope of coastline
amplifies effect of sea level rise
• Wetlands and barrier islands– Natural protection for
mainland from storms– Draining and development is
diminishing this protectionGulf Coast wetlands
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Tides
PSCI 131: The Dynamic Ocean
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PSCI 131: The Dynamic Ocean: Tides
Moon’s gravity pulls harder on side closer to Moon, creating bulges of ocean water on opposite sides of Earth
Tidal bulge animation
Bulges are always aligned with Moon, and Earth rotates through them
Tides are caused by Moon’s gravity (and Sun’s to a lesser extent)
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PSCI 131: The Dynamic Ocean: Tides
Monthly Tidal Cycle
Spring tide: Lunar and solar gravity work together to produce largest tidal range twice per month
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PSCI 131: The Dynamic Ocean: Tides
Monthly Tidal Cycle
Neap tide: Lunar and solar gravity work against each other to produce smallest tidal ranges twice per month
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