Chapter 15 Physical Oceanography Importance of Oceans Oceans

Chapter 15: Physical Oceanography

Importance of Oceans �Oceans are important sources of food, energy, and minerals. �Energy sources such as oil and natural gas are found beneath the ocean floor.

Importance of Oceans �Approximately one-third of the world’s table salt is extracted from seawater through the process of evaporation. �Oceans also allow for the efficient transportation of goods. For example, millions of tons of oil, coal, and grains are shipped over the oceans each year.

�Oceanography – study of Earth’s oceans

�SONa. R – sound navigation and ranging �Uses return time of an echo and the known velocity of sound in water to determine water depth �Side-scan Sonar – sound waves hit floor at an angle so features are mapped �Has mapped large portions of the seafloor

Origins of Water �Scientists hypothesize that Earth’s water could have originated from two sources �Comets and meteorites colliding with the planet � Impacts release water, possibly enough to fill the ocean basins over geologic time �Volcanoes – emit significant quantities of gas, mostly water vapor and carbon dioxide � Earth cooled and water vapor condensed into oceans

Distribution of Earth’s Water � 97% of water in oceans, 3% of water is fresh �The percentage of ice on Earth has varied over geologic time from near zero to as much as 10% of the hydrosphere �Global sea level has risen and fallen by hundreds of meters in response to melting and freezing ice �Tectonic forces that lift or lower portions of the seafloor

The Blue Planet � 71% of Earth’s surface is covered by oceans �Average depth of an ocean is 3800 meters �All the oceans are really one vast, interconnected body of water �Divided into specific oceans and seas because of historic and geographic considerations

Major Oceans �Pacific Ocean �Largest – contains roughly half of Earth’s seawater �Atlantic � 2 nd largest – extends from Antarctica to the arctic circle �Arctic �Atlantic Ocean north of the arctic circle �Indian �Located mainly in the southern hemisphere

Minor Oceans �Antarctic �Storm-lashed region surrounding Antarctica �South of 50 degrees south latitude �Sometimes referred to as the Southern Ocean

Seas �Seas are smaller than oceans and are partly or mostly landlocked � 3 major seas are �Mediterranean �Caribbean �Bering

15. 2 Seawater

Seawater �Seawater is a solution of about 96. 5% water and 3. 5% dissolved salts. �Most abundant salt in seawater is sodium chloride (Na. Cl) �Other salts present are chlorides and sulfates of magnesium, potassium, and calcium �Salinity is the measure of the amount of dissolved salts in seawater

Variations in Salinity �Average salinity of the oceans is 35 ppt (parts per thousand) �Salinities higher in subtropics due to higher rates of evaporation �In equatorial regions salinities are lower due to abundant precipitation �Polar regions low due to melting sea ice �Lowest salinities occur where large rivers empty into the ocean

Sources of Sea Salt �Ancient seas salinity not much different from today �Volcanic gases contain chlorine and sulfur dioxide �Gases dissolve in water and form the chlorine and sulfate ions of seawater �Weathering of crustal rocks generates most of the other abundant ions in seawater �Sodium, calcium, potassium, iron, magnesium

Removal of Sea Salts �Salinity in ocean never really increases �Removal involves several processes �Some precipitate from seawater near arid, coastal regions �Small salty spray droplets from breaking waves are picked up by winds and deposited inland �Marine organisms also remove ions from seawater to build their shells, bones, and teeth

Physical Properties of Seawater �Physical properties of seawater are quite different than freshwater �Salt ions are heavier than water molecules and increase the density �The freezing point of seawater -2 degrees C �Determining factors for temperature are �Depth �Latitude �Salinity

Temperature �Average Sea-Surface Temperature (SST) = 26 C �Ocean water temperatures decrease significantly with depth �Zones �Surface � 0 -100 meters � Little to no temperature change

�Thermocline (intermediate) � 100 -1000 m �Rapid decrease in temperature �Bottom �Below 1000 m �Temperature levels out and becomes stable because of pressure

Absorption of Light �Light intensity decreases with depth �Water absorbs light �Penetrates only the upper 100 m of seawater �Photosynthesis will only occur in this first 100 m �Some blue light reaches below that, but is not used for photosynthesis

Light Zones �Sunlit Zone – Euphotic Zone � 100 -200 ft �>90% of marine animals live here �Twilight Zone – Disphotic Zone �About 900 ft �Midnight Zone – Aphotic Zone �Below 900 ft

Other Zones �Littoral Zone �Between tide lines �Neritic �Low tide line to the edge of the continental shelf �Pelagic �Open ocean �Benthic �Bottom of open ocean

15. 3 Ocean Movements

�Oceans are never completely motionless �Most obvious movement is the constant motion of the waves �Rhythmic movement that carries energy through space or matter �Water moves up and down in a circular pattern and returns to its original position

Waves �Typical wave characteristics �Crest – highest point of a wave �Trough – lowest point of a wave �Wave height – distance between crest & trough �Wave length – distance from crest to crest

Wave Height �Depends on 3 things �Wind speed �Wind duration(how long) �Fetch (how much distance wind blows across)

Breaking Waves �As ocean waves reach the shallow water near shorelines, they lose energy because of friction with the ocean bottom �Waves slow down �Incoming waves become higher, steeper, and unstable, and their crests collapse forward �Breakers – waves where the crest collapse