Oceanography

The Oceans

Oceanography Oceanography is the scientific study of Earth’s Oceans Oceanographers study: Chemical composition Temperature Movement of ocean water Seafloor sediments Topography Marine Life

Earth’s Water Ocean’s contain 97% of water found on Earth 3% is located in frozen ice caps(Greenland, Antarctica) Sea level has risen and fallen due to warming and cooling of the Earth Tectonic Processes

Earth’s Oceans Earth is known as the “Blue Planet” 71% of the surface is covered by water Average Depth is 3800 meters Most landmasses are in the Northern Hemisphere 81% of the Southern Hemisphere is water

Oceans and Seas Oceans make up around 70% of the Earth’s surface Divided into 4 Oceans: Pacific-Largest Atlantic-Between the Americas and Europe and Africa Indian-3rd largest between Africa, Asia and Australia Arctic-North of the Arctic Circle

Oceans and Seas The Arctic and Antarctic areas are covered by sea ice Ice is less dense than water therefore ice crystals form at the surface Parts break up in the summer

Oceans and Seas Seas are parts of the ocean that are partially landlocked Black Sea Mediterranean Sea Caribbean Sea Bering Sea Seas that are completely landlocked have a different composition(More salt water) Caspian Sea Aral Sea

Studying The Ocean The Challenger-Late 1800’s, British research ship Investigated ocean currents, water temperature, sediments, topography Used nets, dredges and other tools Meteor- German ship in the 1920’s Used sonar, first to map the Mid-Atlantic Ridge

Ocean Origin The Earth is believed to be 4.6 Billion years old The Ocean’s are thought to be about that old Ancient lava flows suggest this

Formation of the oceans One hypothesis suggests that water was released from Earth’s interior by volcanism(out gassing) As the Earth cooled this water vapor condensed and filled the oceans

Formation of the Oceans The second hypothesis says that the water came from comets The impact of comets releases water

Chemical Properties of Seawater

Properties of Seawater Seawater is a solution of salts dissolved in water Salinity is the concentration of all salts in seawater Measured in grams of salt per kilogram of water or ppt The average salinity is about 35 ppt Seawater is a solution of salts dissolved in water Salinity is the concentration of all salts in seawater Measured in grams of salt per kilogram of water or ppt The average salinity is about 35 ppt

Properties of Seawater Most of the salt is NaCl which splits about in solution Other ions: Sulfate, Magnesium, Calcium, Potassium, Bicarbonate

Variations in Salinity The highest salinity is found in subtropical regions(20-30 latitudes) The rate of evaporation exceeds the rate of precipitation Polar regions have lower salinities

Variations in Salinity Higher salinities are found in enclosed seas near deserts such as the Mediterranean Sea, Red Sea The Baltic Sea receives fresh water from rivers, lower salinity Estuaries are partly enclosed bodies of water at the mouths of rivers. Very low salinities(2-10 ppt)

Addition of Salt The salinity of the oceans has remained fairly consistent over time Volcanoes release chlorine and sulfur dioxide which dissolve in water Weathering of continental rocks generates other ions in seawater

Removal of Salt When water evaporates ions stay behind and form minerals When organisms die ions in their shells, bones and death accumulate on the ocean floor

Density Pure water has a density of 1 g/ml Seawater ranges from 1.02-1.03 g/ml This is due to variations in salinity and temperature Density increases with increasing salinity. Density decreases with increasing temperature The salinity can alter the freezing point (-2 C)

Light Absorption Water absorbs light. Intensity decreases with depth The absorption of different wavelengths varies as well Marine animals may appear red near the surface but look black at a depth of 10 meters

Temperature The surface of the ocean waters 15 degrees C(Is warmer near the equator) In the Polar regions the water is cold from the surface to the seafloor After about 100 m of ocean to about 1000 m the temperature drops from about 22 C to about 4 C

Temperature The zone of rapidly decreasing of temperature with depth is called the thermocline After the thermocline the temperature is uniform at roughly 4 degrees Celsius Caused by differences in density

Water Masses Cold, salty water comes from the Earth’s poles Sea ice forms  Salt ions are left behind  Water underneath sea ice is dense Sinks The cold, salty water then migrates towards the equator

Movement of Ocean Water

Movement of Ocean Water Oceans are always in constant movement caused by: Variations in temperature Variations in Density Winds blowing across the water’s surface Gravitational pull of the Moon and the Sun

Density Currents The low temperatures of water at Earth’s poles are responsible for the movement of seawater Salts accumulate beneath the ice which increasing the density of the seawater The dense seawater sinks and moves toward the equator. This is called a density current

Upwelling Upwelling is the process where cold water from the bottom of the ocean moves toward the surface Occurs near continents. Winds push water away from the land which is replaced by deeper water which rises Upwelling water is rich in nutrients which supports marine life

Surface Currents Surface currents are formed by Earth’s global wind systems In the tropics trade winds blow from east to west, water moves in the same direction Mid latitudes-Prevailing westerlies move from west to east Polar Regions-Winds move from east to west

Surface Currents Gyres are large circular current systems that flow from north to south The Coriolis effect influences this 5 major gyres: 2 in the Pacific Ocean 2 in the Atlantic Ocean 1 in the Indian Ocean

Surface Currents When a current encounters a landmass the water is deflected away from the equator As the warm current moves North it cools and turns eastward Gulf Stream-Flows along the east coast of North America

Waves A wave is a rhythmic movement that carries energy through space or matter Waves carry small amounts of water

Waves Crest-Highest point of a wave Trough-Lowest point of a wave Wave Height-Distance between the crest and trough Wavelength-The distance between two crests or troughs Factors influencing wave height: Wind Speed Wind Duration Fetch

Waves Waves lose energy when they reach shallow water due to friction As they slow they become higher and steeper Breakers are collapsing waves

Tides Sea level-Average height of the ocean’s surface Tides-Periodic rise and fall of ocean waters caused by the gravitational attraction of the Moon and Sun

Tides One full tidal cycle takes about 24 Hours 50 Minutes. This is due to the Moon rotating around the Earth Spring Tides-When the Moon is full or new. High tides are higher than usual, low tides are lower than usual Neap Tides-The Earth, Moon and Sun form a right angle. Lower tidal range

Shoreline Features

Shorelines Shorelines are shaped by waves, tides and currents by erosion and deposition Ocean floor is shaped by tectonic processes

Erosion Wave Refraction is the bending of a wave when it reaches shallow water This is caused by wave speed and water depth A wave will reach a headland first and will bend towards the headland

Erosion Most of the energy is concentrated on headlands, therefore they undergo erosion This forms a wave cut platform at the base of a steep cliff

Deposition Coastal landforms are formed by sediment from eroded land that are carried to the oceans by rivers When waves and currents slow down these sediments settle out and build coastal landforms

Beaches Beaches A beach is a sloping band of loose sediment at the edge of an ocean The size of the sediments depends on the energy of the wave that deposited it A beach is a sloping band of loose sediment at the edge of an ocean The size of the sediments depends on the energy of the wave that deposited it

Longshore Current Sediment is deposited in areas where the current slows Sandbars often form and run parallel to most beaches Result from waves breaking and dumping sediment

Longshore Current A longshore current is when a water approaches the shore at an angle Prevailing winds and wave patterns influence which direction it will flow Longshore currents causes and is wash up and down the beach in a zigzag pattern

Longshore Current Gaps in the sandbars allow water to return to the ocean. This forms a rip current Barrier Islands form when sandbars form at low tide and winds pile up sand

Barrier Island Spit-Forms when longshore currents slow due to increased water depth Baymouth-A spit that has grown across the mouth of a bay

Spit, Baymouth Bar

Artificial Protective Structures Jetties-Walls of concrete or boulders that extend into the ocean on either side of the entrance to a harbor Groins-Similar structures to jetties that trap sand on one side and not the other

Artificial Protective Structures Seawall-An embankment built along the shore to protect the land from powerful waves Erosion increases because waves are bounced back with most of their original energy

Changes in Sea Level Sea level has fluctuated over time Rises in sea level after often attributed to melting glaciers If the polar ice sheets melted sea level would rise about 70 meters Tectonic forces can cause a change in sea level

Mapping The Seafloor

Sonar Sonar-Emits sound pulses that the detect the depths of the ocean floor Side Scan Sonar-Sound pulses are directed toward the seafloor at an angle. Topographic features can then be mapped

Continental Margin The continental margin is an area of continental crust that lies below sea level. Continental crust is less dense than oceanic crust

Continental Shelf Continental Shelf is the portion of the continental margin that lies closest to land Average width is about 60 km Most of this was exposed during the last ice age

Continental Shelf The continental slope is where the ocean floor drops steeply below the continental shelf Continental Rise forms when sediments carried down the continental slope settle at its base

Ocean Basins Ocean basins are areas of the seafloor that are above the oceanic crust

Ocean Basins Abyssal Plains are smooth parts of the ocean basins Sohm Abyssal Plain Hatteras Abyssal Plain Abyssal Plains sediment has been deposited over millions of years

Ocean Basins Deep Sea Trenches-Deep depressions in the ocean basins May stretch for thousands of kilometers Mariana Trench These are sites where tectonic plates converge

Ocean Basins Mid Ocean Ridges-Chain of mountains that is broken into segments by numerous cracks(fracture zones) May emerge from the ocean’s surface as volcanic islands Form when magma rises along divergent plate boundaries Mid-Atlantic Ridge

Hydrothermal Vents Hydrothermal Vents are rifts in mid ocean ridges that contain springs of hot water Seawater seeps into cracks and is warmed by the magma from the mantle Black Smokers-Eject thick, smoke like plumes of water that can reach 350 degrees Celsius

Ocean Basins Seamounts are submerged mountains that are most likely extinct volcanoes Tablemounts (guyots) are submerged mountains with flat tops The lack of erosional processes cause these features to last forever