Chapter 16 Deserts - Kean University

Chapter 16 Deserts - Kean University

Oceans and Coastal Processes Four Major Oceans plus Arctic Ocean and nine or so Seas Flashlight Globe Recall Ocean Depths depend on the

Plate Tectonic Province: (0-150 meters) (less than 3 km) ~4 km 7 to 11 km

(4-7 miles) Sea Level Changes Rapid seafloor spreading expands the mid-ocean ridge displacing water and raising sea level. Sea level slowly drops during Ice Ages when substantial volumes of ocean water

are locked up in ice sheets. Sea Level rises "suddenly" when glaciers melt Ocean Salinity Dissolved Salts are ions from weathering Salinity in surface water averages ~35

parts per thousand. Salinity variation more extreme in coastal waters. River input, evaporation in lagoons Salinity and temperature change with depth - rapid change salinity (saltiness) at the halocline. Salt water is more dense than fresh water Ice is less dense than liquid water (so it floats) Ice is freshwater, recall most fw in ice caps

Ocean Temperatures Ocean temperatures of 27oC are typical of tropical surface Waters and temperatures of 2oC are typical for deep ocean waters. Cold water is more dense than warm water. It will move under less dense

water. Salinity varies w/ temperature and ocean lowcurrent mixing salinity of arctic isolated low evap cold, freshwater rivers and snow 40 ppt Red Sea

ocean: 33-37 ppt high 36-37 at +/- 30o, high evap, low eq 34 trop rain Salinity shown in cross-section of ocean in ppt Southern Hemisphere Summer Saltiest at 23.5S South Latitude Sun overhead, more evaporation

Solar Heating The equator receives 2.5 times more sunlight (insolation [photons / m2 ]), incoming solar radiation, than the poles. Highest average annual ocean surface temperatures (~27oC) at equator Lowest 0oC at

high latitudes 23.5 Demo, Flashlight Globe Heat versus Temperature When heat something, its temperature rises. Heat is the total energy of molecular motion in a

substance. Heat energy depends on the speed of the particles, the number of particles (the size or mass), and the type of particles in an object. Temperature is a measure of the average energy of molecular motion in a substance. Temperature does not depend on the size or type of object. For example, the temperature of a small cup of water might be the same as the temperature of a large

bathtub of water, but the tub of water has more heat because it has more water and thus more total thermal energy. Water thermal properties 1 1. Heat capacity Cp water very high. Water can store huge amounts of heat without raising temperature. The bonds vibrate faster, but the water molecules H2O need not speed up.

Cp water = 4.2 x Cp air Heat Capacity: heat to raise 1 cm3 substance 1oC Ocean heat storage plays a crucial role in controlling global climate patterns.

http://hendrix.uoregon.edu/~stanm/phys162s2003/PHYS162/Heat_Capacity.html Water thermal properties 2 Density is mass/unit volume Salt water is denser than fresh water Cold water denser than warm water. Freshwater Ice forms at -2oC from

saltwater. Less dense than Saltwater, floats Remaining Seawater is saltier, denser Average Annual Sea-Surface Temperature ~30C Equator, 0C Poles, average temp for a latitude maintained by currents

Poles should be much colder, but currents carry warm equatorial water poleward Temperature and Currents Surface waters (<300 m) warmed by Sun Currents cause thermal mixing: results in relatively uniform surface temperature by latitude.

The impact of current activity on climate diminishes with depth Temperature and Depth Temperatures exceed 20oC over tropical ocean's surface, 2oC below 2,000 m. The depth zone in which temperature decreases rapidly is called

the thermocline 1000 m 2000 m Continents and Climate Over two-thirds of Earths surface is ocean. Currents started by prevailing winds

Currents deflected by continent positions and Earths rotation Climates caused by current and wind circulation Ocean Currents Again, ocean currents started by winds. Winds are ultimately caused by equator to poles insolation (heat from Sun)

differences Winds drag surface waters as surface currents Winds and currents are influenced by Earth's rotation (Coriolis effect). Currents influenced by distribution of continents Coriolis Effect

Air masses at rest above the equator are moving much faster than air masses at rest over us in NJ. Both must rotate once per day, but the equatorial air goes much further.

Equatorial Air has faster spin it still has it , so it is Coriolis Effect Air in Northern Hemisphere deflects to the right, reverse in Southern H. as it moves toward poles faster than land below

DEMO: Coriolis Clip Winds Start Currents Air molecules in wind push water molecules 3-4% of wind speed. Wind moving nearly parallel to latitude as a result of Coriolis deflection. West-pushed ocean currents form near

equator, east-pushed ocean currents form about 50o Latitude Continents deflect or prevent current flow Results in circular current called a gyre. Example: Generation of North Pacific Gyre The major wind cells

Convection Maximum heat from Sun Define Insolation = radiation from sunlight DEMO: globe,

flashlight if not done previously Surface Currents (Influence Climate) Winds push currents East pushed flow near 50 degrees Gyre CW

West pushed flow near equator West pushed flow near equator Gyre CCW East pushed flow near 50 degrees Note Warm Currents not past S 60o Latitudes

Western Boundary Currents Winds cause water to pile up along the western subtropical sides of major oceans. Generate fast-flowing currents that redistribute warm tropical waters toward the poles. Gulf Stream, Kuroshio, Brazil currents are West Side marine rivers, relatively narrow (less than

100 km across) but deep water masses. Flow at speeds of 100 to 200 km/day for thousands of kilometers, from equator to high latitudes Eastern Boundary Current Eastern boundary currents (Canary, California, Peru) complete the eastern leg of

each gyre Wider, carry less water, and move more slowly. The Canary current, nearly 1,000 km (625 miles) wide but very shallow 1/3 water of Gulf Stream and travels at 30 km/day 2/3 continues as cold deep salty current

WIND North Atlantic Deep Water (NADW) down here Evaporation and Ice formation increases saltiness and density. Arc shallowing lifts Dense water

cold deep water sinks forms NADW Winds blow surface waters west, forcing deep water up to

surface where it warms ThermoHaline Wallace Broecker Conveyer Belt AKA Global Ocean Columbia University Conveyer Belt

Shores and Coastal Processes Shorelines are places where bodies of water meet dry land Coasts are landward of ocean shorelines Beach: a narrow strip of land, washed by waves or tides .

Ordinary Waves are caused by WIND Waves are produced when wind drag causes the surface water of oceans/lakes to rise and fall Waves get refracted on approaching shoreline Typical Coast Waves are caused by _____________?

Parts of A Wave Fetch length of unobstructed wind Southern Ocean inc. Straits of Magellan Dana Two Years Before the Mast Oscillatory and Translatory Motion Wave Refraction

Still a small longshore component Longshore Currents (Swash and Backwash) Longshore current is produced as waves reflect from coastline. Swash and backwash

Rip Currents Cut in Bar Sand Bar Rip Currents are produced when storms cut holes in sandbars just offshore. Tides Daily rise/fall of surfaces of oceans/lakes due

to gravitational pull of the Moon/Sun on the Earth also due to force created as Earth spins on its axis Flood tides- elevate sea surface that cause shoreline to move inland Ebb Tides- low sea surface that cause shoreline to move seaward Tidal Bulges

A mass in circular motion accelerates toward the axis of rotation. This centripetal acceleration is exerted on the mass by some other object,say a string held in my hand. The mass exerts an equal and opposite force on the object, the centrifugal

force. Tides mostly caused by the Moon Affect of the Sun Much less Why? The Effect of Tides On Shorelines River Hebert in Nova Scotia

Tidal Bore flows upstream Source: Clyde H. Smith/Peter Arnold, Inc. Large Tidal Extremes Bay of Fundy tides reach16 m (about 53 ft) at the head of the bay. The 12.4 hour period of the twice daily lunar tides is close to the natural back and forth

sloshing period of the bay. Source: William E. Ferguson Rising Tide at Bay of Fundy Maximum Source: William E. Ferguson

Coastal Erosion (Crashing Surf) Wave erosion occurs when deep water waves hit the shore with full force. Air and water are forced into cracks at high pressure Crashing Surf, Oregon Coast

Fast Erosion Source: Criag Tuttle/The Stock Market Erosional Coastal Landforms Submerged Shallow Area Bends Waves

Erosional Coastal Landforms Sea Caves on Cape Kildare, Prince Edward Island, Canada) Source: John Elk/Bruce Coleman Deposition of A Tombolo A Tombolo Landward of A Sea Stack Big Sur,

California Source: Cliff Wassmann Coastal Protection Riprap/Seawall- protects shore lines Breakwaters Stabilize beaches Jettys Keep inlets clear

Beach-Protection Structures - Riprap Source: Jack Dermid /Photo Researchers, Inc. Beach-Protection Structures Seawall Along the Gulf Coast of Louisiana Source: Martin Miller

Breakwaters Breakwaters off Cape May, New Jersey Source: John S. Shelton Jetties

Jetty in Miami Beach, Florida Source: Townsend P. Dickinson Components of A Typical Beach A beach is a dynamic narrow segment of coast washed by waves/tides and covered with

sediments Foreshore is the area between low tide and high tide Backshore is the area between high tide and sea cliff or inland vegetation line Beach face is the

steepest part of Foreshore Berm is a horizontal Transport and Depositional Features Recall Longshore Drift sand moved by LSC Spit is a finger-like ridge of sand deposited where Longshore drift encounters deeper

water Hook is a curved spit Baymouth is a spit that covers the access to a bay fills with sediment Deposition Spits, Hooks, and Baymouth Bars Organic Coasts

Fringing Reef- initially surround land, grow seaward Barrier Reef- separated from coast by a lagoon Atoll- circular structure from great depth that encloses shallow lagoon Mangroves

Evolution of Coral Atolls Remember Guyots? Charles Darwin coral larvae are planktonic Wake Island, a Coral Atoll

Source: William E. Ferguson Typical Mangrove Coast, Florida Make your own island Source: S. J. Krasemann/Peter Arnold, Inc. Steep Shore

Steep Cliffs may occur at new Divergence (Red Sea) or near a Trench (Oregon Coast) Headlands, benches, sea arches, stacks, tombolos All other things being the same, steep cliffs easier to erode than gentle

slope Source: William Boyce/Corbis Define Active Margin Thailand Island Arcs protect coastline

Cambodia allow deltas to form Laos (Chao Phraya River) Delta Protected from Typhoons and Tsunamis December 26, 04

Tsunami Sumatra, Indonesia Source: Tom Van Sant / Geoshere Project Santa Monica/Science Photo Library Passive Margin coast far from plate margins

Define Passive Margin Active Margins coasts close to plate boundaries

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