ch 18 oceans

How much of the Earth's surface is covered by oceans? What proportion of the world's population lives near a coast?

70.8% and 60%

How do the shelf and slope of an active continental margin differ from those of a passive margin?

active margin-narrow shelf and slope corresponds to the face of the accretionary prism(narrow shelf forms where apron of sediment spreads out over the top of an accretionary prism-the pile of material scraped off the downing subducting plate passive-bigger shelf

Describe the components of a beach profile.

beach profile: cross section drawn perpendicular to the shore, illustrates the shape of a beach beginning from the sea and moving landward, a beach consists of a foreshore zone, or intertidal zone, across which the tide rises and falls. then the beach face, steeper, concave-up par of foreshore zone, forms where smash of waves scours the sand. the back shore zone extends from a small step to the front of the dunes or cliffs that lie farther inshore. the back shore zone includes one or more berms, horizontal to landward-sloping terraces that received sediment during a storm

What is an estuary? Why is it such a delicate ecosystem? What is the difference between an estuary and a fjord?

estuary: seawater and river water meet they are delicate because oceanic and fluvial water combine to make nutrient rick brackish water with salinity between oceans and rivers. they inhabit unique species of shrimp, clams, oysters, worms and fish that can tolerate large changes in salinity fjord: flooded glacial valleys

Discuss the different types of coastal wetlands. Describe the different kinds of reefs, and how a reef surrounding an oceanic island changes with time.

in temperate climates- swamps(wetlands dominated by trees), marshes(wetlands dominated by grasses) and bogs(wetlands dominated by moss and shrubs) tropical or semitropical-mangrove swamps reefs fringing reef: forms directly along coast barrier reef: develops offshore(separated from coast by lagoon) atoll: makes circular ring surrounding a lagoon eventually reef itself sinks too far below sea level to remain alive and it becomes the cap of a guyot

Where does the salt in the ocean come from? How does the salinity in the ocean vary? How does the T of the oceans vary?

most cations in sea salt come from general chemical weathering of rocks and the anions come from volcanic gases. rivers deliver over 2.5 billion tons of salt to the sea every year. salinity varies with location. it reflects the balance between the addition of freshwater by rivers or rain and the removal of freshwater by evaporation. it may also depend on water T bc warmer water can hold more salt general correlation of average T with latitude exists bc the intensity of solar radiation varies with latitude

How does beach sand migrate as a result of longshore currents? Explain the sediment budget of a coast.

sediment follows a sawtooth pattern of movement that results in gradual net transport of beach sediment parallel to the beach(longshore drift) Sediment budget refers to the balance between sediment added to and removed from the coastal system

What factors control the direction of surface currents in the ocean? What is the Coriolis effect, and how does it affect oceanic circulation? Explain thermohaline circulation.

surface currents result from interaction between the sea surface and the wind and the rotation of the Earth. Coriolis effect: causes surface currents in the northern hemisphere to veer toward the R and surface currents in the southern hemisphere to veer toward the left of the average wind direction. it's caused by earth's rotation thermohaline circulation: rising and sinking of water driven by density contrasts caused by differences in T and salinity

How do plate tectonics, sea-level changes, sediment supply, and climate change affect the shape of a coastline? Explain the difference between emergent and submerging coasts.

tectonic setting of a coast plays a role in determining whether the coast has steep sided mtn slopes or a broad plain that borders the sea(active margin creates mtns and passive margin leads to broad coastal plain) emergent coast: land is rising and terraces form along some coasts submergent: land sinks relative to sea level causes estuaries and fjords erosional vs accretionary coasts warmer climate means weathering happens less quickly

Describe how waves affect a rocky coast, and how such coasts evolve.

they don't have a beach so a breaker can pick up boulders and smash them together until they shatter and it can squeeze air into cracks making enough force to widen them. the shattering, wedging, and abrading(wave erosion) gradually undercut a cliff face and the cliff retreats if it becomes unstable enough and breaks away

What causes the tides? Why does the range and reach of tides vary with location?

tides are caused by the tide-generating force-due partly to the gravitational attraction of the Sun and Moon and partly to centrifugal force caused by the revolution of the Earth-Moon system around its center of mass. forces causing tides: gravitational pull, centrifugal force, earth-moon system, center of mass range and tide reach varies bc of tilt of Earth's axis, the moon's orbit, the sun's gravity, and the focusing effect of bays, basin shape, and air pressure

Describe the typical topography of a passive continental margin, from the shoreline to the abyssal plain. How does the lithosphere beneath a passive margin differ from that beneath an abyssal plain?

when rifting stops and sea-floor spreading begins, the stretched lithosphere at the boundary gradually cools and sinks. sand and mud that washed of the continent, along with the shells of marine creatures that grow on the sea floor or settle bury the sinking crust, making a pile of sediment up to 20 km thick. the flat surface of the pile it the continental shelf.

Describe the motion of water molecules in a wave. How does wave refraction cause longshore currents?

within a deep ocean wave, water molecules follow a circular path and the radius of the circle decreases with depth. beneath the wave base, water modules are not affected by the wave. wave refraction occurs when waves approach the shore at an angle. if the wave reaches the beach at an angle, it causes a longshore current and beach drift of sand