11.1 Ocean Basins The surface of the ocean floor is as varied as the land. The five major oceans, from largest to smallest, are w the Pacific w the Atlantic w the Indian w the Southern w the Arctic The low points in the oceans are called basins. Oceans are vital to life, as they control temperature, create weather patterns and provide water for water cycles. See page 402
The Origin of Ocean Water Oceans have filled over hundreds of millions of years. Scientists believe the oceans are more than 3 billion years old. Water may have originally been released from volcanic eruptions, or arrived on Earth via icy comets. See page 404
Features of the Ocean Floor Although the word basin makes it sound flat, many features found on land, including mountain ranges, valleys, flat plains, canyons, and volcanoes also exist on the ocean floor. The basin is the large, flat middle part, while the continental margins are the edges rising up to the land. The ocean topography of the Caribbean See pages 404-405
Ocean Basins The largest changes to the ocean basin occur through the movement of tectonic plates, although there is also erosion via storms, earthquakes and icebergs. Mid-ocean ridges occur where new rock is forced up, and ocean floor spreads outward. w The Mid-Atlantic Ridge is the largest example on Earth w The Juan de Fuca plate lies 200 km off Vancouver Island A trench forms when the dense oceanic plates run into, and slide under, the continental plates. See pages 406-407
Ocean Basins (continued) Abyssal plains are the pieces of oceanic crust between a spreading mid-ocean ridge and the trench it disappears into. w These make up 30% of the Atlantic sea floor, and 65% of the Pacific seafloor. w Abyssal plains can be covered in 1 km of sediments Seamounts are old volcanic mountains found on abyssal plains. The Hawaiian Islands are an example. See page 407
Continental Margins Continental margins are part of continental plates. Continental margins are made up of a continental shelf (averaging 80 km wide) and a continental slope down to the oceanic plate. Continental shelves were above water during the last ice age. Turbidity currents are slides on the slopes, and can create large submarine canyons in the shelf. Take the Section 11.1 Quiz See pages 407-409
Continental Drift The continental plates drift over time of the order of a few cm/year. Originally about 300 million years ago, all the continental plates were joined together in a supercontinent called Pangaea. How do we know continental drift is occurring? Earthquakes continue to happen because of plate movement Fossil evidence shows that the plates at one time did fit together and have since moved apart
11.2 Ocean Currents There are more than 20 major currents which move large amounts of water predictably around the oceans. w Currents move large quantities of water, minerals, solar energy, oxygen and carbon dioxide, plankton and fish. w Currents are caused and driven by water density and salt content, the wind, the spin of Earth, coastlines and the moon. w Largest current is the Antarctic Circumpolar Current in the Southern Ocean, at 24 000 km long Ocean currents are either w Surface currents (0-200 m) w Deep water currents (200 m and deeper) See page 414-416
What Makes Surface Currents Move? Wind w As air warms from solar energy, it rises, and cooler air rushes to replace it. This creates wind. w As the wind passes along the surface of the water, it bumps the water molecules and moves them along in the same direction. Spin of the Earth w Earth spins from West to East (counter clockwise) w The Coriolis effect deflects winds and currents to the right/east in the Northern hemisphere (opposite in the Southern hemisphere) Shape of continents w Currents move through the oceans and around the continents like rocks in a stream. See page 416-417
What Makes Deep Currents Move? Water temperature w Like air, warm water rises, and cool water falls w Density current = cool, dense water moving on an ocean floor. w Three layers of water dependent on temperature: Surface: 0-200 m, warmest Thermocline: 200 m - 1 km, rapidly cools Deep water: 1 km and deeper, just above freezing Water salinity w Adding fresh water decreases salinity w Evaporation and freezing increases salinity w Densest ocean waters at the poles w Upwelling occurs when nutrient-rich cold water finally moves up to the surface See page 418-420
Ocean Waves and Their Effect on Shaping Land Most waves are created by wind. In open ocean, waves are called swells. w Swells break in shallow water, show characteristic curl. The largest waves are tsunamis, caused by undersea earthquakes, landslides or volcanic eruptions. Waves erode coastal areas based on the force of the waves, and the composition of the shoreline. w Headlands made up of harder rock, and erode less, but absorb most wave force. w Bays occur between headlands, are generally calm. w Sea stacks are extra-hard rock left behind from eroded headlands. See page 421
Tides Tides are caused by gravities of Earth and the Moon. w High tides occur where the Moon is closest to Earth (and opposite side) w Low tides occur at 90º to the high tides. Tidal range (difference between high and low) averages 3 m in BC. The Sun s gravity, when lined up properly, can produce extreme tides. w These are called spring tides w When the Sun, Moon and Earth are not lined up, the tides are called neap tides. Take the Section 11.2 Quiz See page 423-424
11.3 Oceans and Climate Water has a high heat capacity w Water heats up and cools down slowly, and can absorb large amounts of thermal energy. w Oceans can store and transport huge amounts of energy w Oceans influence weather through the water cycle Weather tracked over many years = climate w Climates vary greatly around the world w Climate measures temperature + precipitation > 30 years See page 428
How Oceans Affect Weather Through convection, heat energy transfers from the ocean s surface to the air, and this warm air rises w The warm bubble of air is called a thermal w The thermal rises until it loses its heat, and then drops back down again. This process of heat transfer is called convection. El Niño is the warming ocean effect that occurs some years in December off the Pacific coast of Ecuador. w El Niño can change the weather around the world, including warmer and wetter in BC, and droughts in Africa and Australia. w Changing ocean temperatures also cause sea life to change behaviours. w La Niña is a cooling of similar waters, and produces almost the opposite effects of El Niño. See page 430
The Moderating Effect of Oceans on Climate Oceans can make cold, northern locations warmer w Locations like BC, Norway and England benefit w Because of water s high heat capacity, heat energy can be carried from south to north by currents like the Gulf Stream (in England and Norway) or the Pacific Drift (in BC). As the warm water evaporates, it carries energy over the mainland of the province. Mountains block the warmth from reaching into the interior. Edmonton and Manchester, England are the same latitude Edmonton, Alberta Manchester, England January average temperature = -7 C January average temperature = +6 C See pages 431-432
The Moderating Effect of Oceans on Climate (continued) For these reasons, we can see considerable differences between locations at the same approximate latitude (distance from the equator) in BC See pages 431-432