Oceans

Why study the ocean? One of the last frontiers Biological & mineral resources Food & oil shortages on land Influences weather & climate Travel & communication

Oceanography the science of our oceans that mixes biology, geology, chemistry, and physics (among other sciences) to unravel the mysteries of our seas.  

Divisions of Oceanography Chemical Oceanography – study of chemical reactions Biological Oceanography – study of living things in their environment

Divisions of Oceanography (cont.) Physical Oceanography – study of changes in motion of sea water Geological Oceanography – study of sediments & topography

Covers 71% of the Earth’s surface Salt Water 97% of all water on Earth The Global Ocean Covers 71% of the Earth’s surface Salt Water 97% of all water on Earth Where is the “other” water?

The Hemispheres of the Earth Northern Hemisphere 39% land “Land Hemisphere” Southern Hemisphere 19% land “Water Hemisphere”

Divisions of the Global Ocean Pacific Ocean Atlantic Ocean Indian Ocean Arctic Ocean Southern Ocean

Distinguishing Characteristics of Oceans Size Currents Water Masses Submarine Ridges Some definable Land Boundaries

Pacific

Pacific Ocean Largest and Deepest Holds 52% of Earth’s ocean water Covers 33% of Earth’s surface Average depth = 4.3 kilometers (2.7 miles) Mountain building along margins Abundant islands (mostly volcanic) Marianas Trench 6.8 miles deep

Atlantic

Atlantic Ocean 2nd largest ocean 26% of Earth’s ocean water Avg. depth = 3.9 km (2.4 miles) Mid-Atlantic Ridge Few islands Large sediment deposits from rivers (Amazon & Congo – 25% of world’s river discharge)

Indian

Indian Ocean 3rd largest ocean Avg. depth = 3.9 km (2.4 miles) 20% of Earth’s ocean water Mostly in the S.Hemis. Abundant fresh water due to river discharge (Ganges, Brahmaputra, Indus)

Arctic

Arctic Ocean 4.2% of ocean water Smallest & Shallowest Surrounds the North Pole Almost completely surrounded by land Covered with sea ice most of the year Extension of the Atlantic

Southern (Antarctic) “Defined” in 2000 Starts at 60o S latitude Surrounds Antarctica 6.1% of ocean water

Earth’s Oceans and Seas

What is Ocean Water Composed of?

Composition of Seawater Salinity – amount of dissolved salt in water; usually expressed as parts per thousand (ppt) Average salinity = 33 – 38 ppt (3.3-3.8%) Main salts/minerals present in oceans (ppt): 1. NaCl (halite) 23.48 (about 2.35%) 2. MgCl 2 4.98 (about 0.50%) 3. Na2SO4 3.92 4. CaCl2 1.10 5. KCl 0.66 6. NaHCO3 (Sodium bicarbonate) 0.192 7. KBr 0.096 8. H3BO3 (Hydrogen borate) 0.026  

Where do the salts come from?   Where do the salts come from? 1. Weathering of rocks and minerals 2. Outgassing from Earth's interior 3. Hard parts of marine organisms (i.e., shell material)

What affects salinity?

What affects salinity? Increase salinity (remove water) – Evaporation Formation of sea ice Decrease salinity (add water) – Precipitation Sea ice melting

Ocean Temperature Surface water temperature varies with amount of solar radiation received Variation with depth – Low latitudes = rapid decrease in temp. w/depth (thermocline) High latitudes = no rapid change in temp. w/depth

Ocean Density Density = mass/volume Depends on: temperature and salinity Determines water’s vertical position in the ocean Pure water = 1 g/cm3 Remember – densest water is COLD & SALTY

Ocean Layers Determined based on density:   1. Surface mixed zone (Epipelagic): 2%, warmest from solar energy, mixed by waves, 300 m, most saline 2. Transition zone (Mesopelagic): 18%, “Twilight Zone”, 200 – 1000 m, includes thermocline 3. Deep zone (Bathypelagic): 80%, “Midnight Zone”, just slightly above or below freezing, not very saline

Light in the Ocean Photic Zone - Sunlit layer of water Deepest in tropics Typical value: 100 meters Photosynthesis occurs here Most ocean life found here Aphotic Zone – Complete darkness

15 ft. deep Ocean depth 14,500 ft. Midway islands area

Circulation Atmospheric Circulation Surface Ocean Circulation Depends on density Surface Ocean Circulation Depends on the wind Deep Ocean Circulation

Why is Ocean Circulation Important? Transports heat from equator to poles Transport nutrients and organisms Influences weather and climate 4 th century BC ,Pytheas of Massalia, a Greek ship captain, explored eastern Atlantic Okeanos (Greek for “Great River”) because he found the ocean flowing south (Canary Current) and thought it was a river too wide to cross.

Ocean Circulation

Surface Currents   *Coriolis Effect - ocean currents are directed to the right (clockwise) in the northern hemisphere and to the left (counterclockwise) in the southern hemisphere *Upwelling is the force that vertically moves cooler, nutrient rich water from approximately 1000 feet below the surface to the near surface. Where winds blow towards the equator and parallel to the coastline (ex: west coast of California), surface water movement is deflected away from the coast and deeper water is thrust upward to the surface. This creates a vertical component that causes temperatures drops in surface waters to nearly 10-15 degrees. Thus, extensive nutrients like nitrates and phosphates are "upwelled" to the surface and plankton and other fish populations flourish.

Upwelling

Equatorial to polar heat transport and water flow

Thermohaline Circulation North Atlantic Deep Water (NADW 15 million m3 of near surface water descend into the deep ocean each second.

Deep Ocean Currents (Thermohaline) Two factors are important in creating a dense mass of moving water: 1. Temperature 2. Salinity  *Colder and salty water is denser than warmer, less salty water.  

Thermohaline Circulation - The Ocean Conveyor