Topic #4 The Oceans

Agenda  Check in  Review last days  Topic 4-The Oceans!

Check In! 1.What do we call the upstream areas of a watershed? 2.Where is the outflow of a watershed? 3.What is one way a watershed’s pattern can be changed? 4.What is the difference between water quantity and water quality?

Topic #4 – The Oceans  No matter where you live, you cannot escape the influence of the ocean.  70% of the Earth’s surface is covered by oceans!! (2/3)  Oceans affect the weather, provide us with food and natural resources (oil, gas, minerals) and allow goods to be easily transported from other continents.

Would you like Salt on that?  Ocean water is salty!!  The most common salt is sodium chloride (NaCl-table salt ) Measuring the amount of salt in a substance is called salinity.

Fraser River dumping into the Pacific

 The oceans form the largest ecosystem on Earth. Visible light does not penetrate beyond a depth of about 100m.  On the ocean floor there are mountain ranges, steep valleys and vast plains – everything larger than on land.

Really? Under water?  Volcanoes are another source of chemicals in ocean water. The lava and gases that erupt add chemicals directly into the water.

 Most features on the ocean floor are attributed to plate tectonics.  Long undersea mountain chains called ocean ridges run along the centre of the oceans.  These ridges are the youngest areas of sea floor and are still being formed by volcanic eruptions.  Molten lava flows out, hardens quickly and pushed the tectonic plates apart

Plate Tectonics  The theory of the lithosphere being in pieces (plates)  There is movement because of convection currents in the magma  Plates are moving toward, and away from each other

 Along some margins of the sea floor, narrow, steep-sided canyons called trenches are formed when an oceanic plate pushed against the edge of a continental plate.  The deepest trench, called the Marianas Trench, extends 11km below sea level.  This is deep enough to submerge an object as tall as Mount Everest

 Between the high mountain ranges at their centre and the deep trenches at their edges, you will find wide, open features called abyssal plains.

 Ocean basins do not begin at the coastline, but may begin kms out to sea  The area between the coast and the edge of the basin is called the continental shelf.  From the edge of the shelf, the continental slope plunges to the sea floor.

Ocean Waves  Ocean waves are just large ripples, set in motion by steady winds.  Waves begin out in open sea and their height depends on how fast, how long and how far the winds blow over the water.  Normal winds produce waves of 2-5m in height.  Hurricane winds can create 30m waves.  Even on a calm day there are smooth waves hitting the shore – called swells

Continental Shelf & Slope  Ocean basins begin many kilometres out at sea  The continental shelf is the submerged part of a continent which stretches out beyond the coast  From the edge of the shelf, the continental slope plunges at a steep angle to the ocean floor (abyssal plain)

Ocean Waves  Waves are changes in patterns that move along the water’s surface  Swells are smooth, steady waves caused by winds and storms at sea  When a wave reaches shore, it changes shape.  As the trough touches the beach, it is slowed by friction, but the crest continues to move at the same speed.  The wavelength shortens and the wave height increases causing the crest to outrun the trough and topple forward  The ensuing tumble of water onshore is called a breaker.

Waves & Shorelines  Waves crashing against a shoreline can cause changes to the shape of the shoreline  Erosion & deposition reshape the shoreline dramatically  As waves collide with the shoreline at slight angles, they create a longshore current which carries sediment to be redeposited

Tsunamis  Large waves caused by undersea earthquakes, seabed slides or large volcanic eruptions  These occur ~5-15 years, but have no patterns and cannot be predicted

Tides  Ocean beaches are sometimes covered with water and sometimes not.  They are uncovered and covered in regular daily cycles by the slow rise and fall of the ocean, called tides.  The largest tidal movements are called spring tides, and the smallest are called neap ties. The difference between the two is called tidal range  Centuries ago, people realized that the cycle of tidal movement is caused by the Moon.

Tides (cont.)  The largest tidal movements are called spring tides and occur when the Earth, Moon and Sun are in a line.

Tides (cont.)  The smallest tidal movements are called neap tides and occur when the Sun and Moon are at right angles to each other.  The difference between these two is called the tidal range.

Tides (cont.)  The movement of water causes a low tide along the opposite coastline.  As the Earth turns on its axis, different location on Earth’s surface face the moon and are affected by its gravitational pull.

Surface Currents  Currents of water at the ocean surface are driven by winds.  Most surface currents flow in the top m of water.

Surface Currents (cont.)  Three factors influence the direction of winds and surface currents: uneven heating of the atmosphere, rotation of the Earth, and the continents.  Warm air expands and moves upward  Cool air moves into the area created when the warm air moves upward.  The moving masses of warm and cool air produce winds.

Surface Currents (cont.)  The rotation of the Earth produces a bending of moving currents.  As the wind and water currents flow over the Earth’s surface, the planet turns beneath them from west to east.  The overall result is that winds along the equator blow from the east, called trade winds.  They push the ocean currents towards the west

Surface Currents (cont.)  Toward the polar regions, westerly winds drive currents the opposite way, from west to east.