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

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”

Hydrosphere

•Describes the combined mass of water found on, under, and over the surface of the a planet.

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

What is Ocean Water Composed of?

Where do the salts come from?

1. Weathering of rocks and minerals (source of majority of the salt in the ocean)

2. Outgassing from Earth's interior

3. Hard parts of marine organisms (i.e., shell material)

What affects salinity?

• Increase salinity (remove water) –

– Evaporation

– Formation of sea ice

• Decrease salinity (add water) –

– Precipitation

– Sea ice melting

Distinguishing Characteristics of Oceans

•Size

•Currents

•Water Masses

•Submarine Ridges

•Some definable Land Boundaries

Divisions of the Global Ocean

•Pacific Ocean

•Atlantic Ocean

•Indian Ocean

•Arctic Ocean

•Southern Ocean

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 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 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 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

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

Thermocline

• The thermocline is the transition layer between the mixed layer at the surface and the deep water layer. The definitions of these layers are based on temperature.

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 LayersDetermined 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

Determined based on density:

Determined based on light:

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

Circulation

• Atmospheric Circulation

– Depends on density

• Surface Ocean Circulation

– Depends on the wind

• Deep Ocean Circulation

– Depends on density

Current - A steady horizontal movement of water in a definite direction

Why is Ocean Circulation Important?

• Transports heat from equator to poles

• Transport nutrients and organisms

• Influences weather and climate

Upwelling

Surface Currents

*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.

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

ThermohalineDeep Ocean Currents

Two factors are important in creating a dense mass of moving water:

1. Temperature (thermo) 2. Salinity(haline)

Driving by the rising of warmer waters and the sinking of dense salty water.

*Colder and salty water is denser than warmer, less salty water.

Thermohaline Circulation - The Ocean Conveyor

Waves

• A Wave is a rhythmic movement that carries energy through matter or space.

• In oceans, waves move through seawater

Caused by:

• Wind

• Earthquakes

• Gravitational force of the Moon and Sun.

Parts of a Wave

• Crest – highest point of a wave

• Trough – lowest point of a wave

• Wave Height – vertical distance between the crest and the trough

• Wavelength – horizontal distance between two crests or two troughs

Wavelength

Wave Height

Crest

Trough

Still Water

Wave Parts

Wave Movement

•When a wave passes through the ocean, individual water molecules move up and down but they do not move forward or backward.

Wave Movement

•When a wave breaks against the shore, the crest outruns the trough and the crest collapses.

•Called a breaker.

• In this case, water does move forward and backward.

Waves Caused by Wind

•When wind blows across a body of water, friction causes the water to move along with the wind.

•Wave Height depends on ––Wind speed

–Distance over which the wind blows

–Length of time the wind blows