Chapter 10 Lecture Outline The Restless Oceans
Focus Question 10.1 How does the Coriolis effect influence ocean currents?
The Ocean s Surface Circulation Ocean currents Masses of water that flow from one place to another Surface currents develop from friction between wind and the ocean surface Huge, slowly moving gyres
The Ocean s Surface Circulation Coriolis effect Deflects surface currents To the right in the Northern Hemisphere To the left in the Southern Hemisphere Four main currents generally exist within each gyre
The Ocean s Surface Circulation Five main gyres 1. North Pacific gyre 2. South Pacific gyre 3. North Atlantic gyre 4. South Atlantic gyre 5. Indian Ocean gyre Related to atmospheric circulation
The Ocean s Surface Circulation
Ocean Circulation
The Ocean s Surface Circulation Importance of surface currents on climate Warm currents transfer heat from low latitudes into higher latitudes (moderating effect) Influence of cold currents is most pronounced in the tropics or during summer months in the middle latitudes Chill the air Increase aridity
Focus Question 10.2 Why is deep-ocean circulation referred to as thermohaline circulation?
Upwelling and Deep-Ocean Circulation Coastal upwelling The rising of cold deep water to replace warm surface water Wind-induced vertical movement Most characteristic along west coasts Coastal winds combined with Coriolis effect cause water to move away from shore
Upwelling and Deep-Ocean Circulation
Ekman Spiral and Coastal Upwelling/Downwelling
Upwelling and Deep-Ocean Circulation Deep-ocean circulation A response to density differences Factors creating a dense mass of water Temperature (cold water is dense) Salinity (density increases with increasing salinity) Called thermohaline circulation
Upwelling and Deep-Ocean Circulation Most water in deep-ocean currents begins in high latitudes at the surface A simple model of ocean circulation is a conveyor belt traveling from the Atlantic Ocean, through the Indian and Pacific Oceans, and back again
Upwelling and Deep-Ocean Circulation
Focus Question 10.3 Describe what interfaces at a shoreline?
The Shoreline: A Dynamic Interface Continental and oceanic processes converge along coastlines Landscapes undergoing rapid change Interface between continent, ocean, and atmosphere Transition zones between marine and continental depositional environments
The Shoreline: A Dynamic Interface Shorelines are constantly being modified by: Waves and storms Sea level change Stream erosion and deposition Glaciation Volcanic activity Tectonic forces Human activity
The Shoreline: A Dynamic Interface
Focus Question 10.4 Describe the motion of a floating object as a wave passes.
Ocean Waves Waves Energy traveling along the interface between ocean and atmosphere Derive energy and motion from wind
Ocean Waves Wave height Distance between a trough and a crest Wavelength Horizontal distance between successive crests (or troughs) Wave period Time interval for one full wave to pass a fixed position
Ocean Waves Wave height, length, and period depend on: Wind speed Length of time the wind blows Fetch (distance the wind travels) As the wave travels, the water passes energy in a circular orbital motion.
Ocean Waves
Ocean Waves Waves are unaffected by depth until they approach shore Waves begin to feel bottom at water depth equal to wave base Slightly faster waves farther out to sea catch up and decrease the wavelength, which causes the wave to grow steadily higher When the wave is too steep to support itself, the wave front collapses, or breaks Surf is turbulent water created by breaking waves
Ocean Waves
Focus Question 10.5 Why do waves approaching the shoreline often bend?
Beaches and Shoreline Processes Beaches are composed of whatever material is available Some have a significant biological component Material does not stay in one place Wave erosion Caused by wave impact and pressure Breaks down rock, supplying sand to beaches
Beaches and Shoreline Processes
Beaches and Shoreline Processes Rivers of sand Sand in the surf zone moves roughly parallel to the shoreline Wave energy causes sand to move perpendicular to the shoreline Wave refraction Bending of waves As waves first touch bottom in the shallows they are slowed, causing them to bend Wave arrives parallel to shore
Beaches and Shoreline Processes Wave refraction Wave energy is concentrated against the sides and ends of the headland Wave erosion straightens an irregular shoreline
Wave Motion and Wave Refraction When Approaching Shore
Beaches and Shoreline Processes Longshore transport Beach drift Sediment moves in a zigzag pattern along the beach face Longshore current Current in surf zone Parallel to shore Moves substantially more sediment than beach drift
Beaches and Shoreline Processes
Beach Drifting and Longshore Currents
Focus Question 10.6 Describe erosional and depositional shoreline features.
Shoreline Features Erosional features Wave-cut cliff Wave-cut platform Marine terraces Associated with headlands Sea arch Sea stack
Shoreline Features
Shoreline Features
Shoreline Features Depositional features Spit A ridge of sand extending from the land into a bay with a hooked end Baymouth bar A sand bar that completely crosses a bay Tombolo A ridge of sand that connects an island to the mainland or another island
Shoreline Features
Shoreline Features Barrier islands Mainly along the Atlantic and Gulf Coasts Parallel the coast Originate in several ways: As spits severed from the mainland Created when turbulent waters heaped up sand scoured from the bottom Former sand-dune ridges that originated along the shore during the last glacial period
Shoreline Features
Shoreline Features
Focus Question 10.7 How permanent are hard stabilization efforts along shorelines?
Stabilizing the Shore Shoreline erosion influenced by local factors: Proximity to sediment-laden rivers Degree of tectonic activity Topography and composition of the land Prevailing wind and weather patterns Configuration of the coastline
Stabilizing the Shore Responses to erosion problems Hard stabilization Building structures Groins Barriers built at a right angle to the beach Designed to trap sand Breakwaters Barriers built offshore and parallel Protect boats from breaking waves
Stabilizing the Shore
Stabilizing the Shore Seawalls Armors the coast against breaking waves Often not effective
Stabilizing the Shore Alternatives to hard stabilization Beach nourishment by adding sand to the beach system Relocating buildings away from beach
Focus Question 10.8 How might building a dam on a river that flows to the sea affect a beach?
Contrasting America s Coasts Erosion problems along U.S. Coasts Shoreline erosion problems are different along the opposite coasts Atlantic and Gulf Coasts Development occurs mainly on barrier islands Face open ocean Receive full force of storms Development taken place more rapidly than understanding barrier island dynamics
Contrasting America s Coasts
Contrasting America s Coasts Erosion problems along U.S. Coasts Pacific Coast Characterized by relatively narrow beaches backed by steep cliffs and mountain ranges Major problem is the narrowing of the beaches Sediment for beaches is interrupted by dams and reservoirs Rapid erosion occurs along the beaches
Contrasting America s Coasts Shoreline classification is based on changes with respect to sea level Emergent coast Uplift of the land, or A drop in sea level
Contrasting America s Coasts Submergent coast Land adjacent to sea subsides, or Sea level rises Features of a submergent coast Highly irregular shoreline Estuaries - Drowned river mouths
Contrasting America s Coasts
Focus Question 10.9 Explain why an observer can experience two unequal high tides during one day.
Tides Changes in elevation of ocean surface Caused by the gravitational forces exerted upon Earth by the Moon, and to a lesser extent by the Sun
Tides
Tides Spring tide During new and full moons Gravitational forces added together Especially high and low tides Large daily tidal range
Tides Neap tide First and third quarters of the Moon Gravitational forces are offset Daily tidal range is least
Tides Tidal patterns Many factors influence the tides: Shape of the coastline Configuration of the ocean basin Water depth Diurnal pattern Semidiurnal pattern Mixed pattern
Tides Diurnal tidal pattern A single high and low tide each tidal day Occurs along northern shore of Gulf of Mexico Semidiurnal tidal pattern Two high and low tides each tidal day Little difference in high and low water heights Mixed tidal pattern Two high and two low waters each day Large inequality in high water heights, low water heights, or both Prevalent along the Pacific Coast of the United States
Tides
Tidal Cycle
Tides Tidal currents Horizontal flow accompanying the rise and fall of tides Flood current Advances into the coastal zone Ebb current Seaward moving water Sometimes tidal deltas are created
Tides