3/5/2018

1

Oceans I NotesOutlines on the front table

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

The Hemispheres of the Earth

Northern Hemisphere

39% land

“Land Hemisphere”

Southern Hemisphere

19% land

“Water Hemisphere”

3/5/2018

2

Hydrosphere

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

Composition of SeawaterMain salts/minerals present in oceans (ppt):

1. NaCl (halite) 3.5%

2. MgCl 2

3. Na2SO4

4. CaCl25. KCl and others…

Salinity – amount of dissolved salt in water; usually expressed as parts per thousand (ppt)

Average salinity = 33 – 38 ppt (3.3-3.8%)

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?

3/5/2018

3

What affects salinity?

• Increase salinity (remove water) –

–Evaporation

–Formation of sea ice

• Decrease salinity (add water) –

–Precipitation

–Sea ice melting• Regions of heavy precipitation at the Equator

shows lower surface salinity than regions of excess evaporation at the mid-latitudes that shows increased surface salinity.

What is Ocean Water Composed of? Divisions of the Global Ocean

•5 characteristics

1. Salinity

2. Currents

3. Seafloor depth

4. Submarine ridges

5. Some definable continental boundaries.

Divisions of the Global Ocean

•Pacific Ocean

•Atlantic Ocean

•Indian Ocean

•Southern Ocean

•Arctic Ocean

Pacific

3/5/2018

4

Pacific Ocean

• Largest and Deepest

• Holds 50% of Earth’s ocean water

• Covers 31% 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

• 23% 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)

Southern (Antarctic)

• “Defined” in 2000

• Starts at 60o S latitude

• Surrounds Antarctica

• 5.5% of ocean water

3/5/2018

5

Arctic Arctic Ocean• 1.5% 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

Determined based on density:

Determined based on light: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

3/5/2018

6

Ocean LayersDetermined based on density:

1. Surface mixed zone(Epipelagic): 2%, “sunlit zone” 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 at freezing, not very saline

Ocean Layers

• Determined based on Light

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

The color red is the first color absorbed by water so therefore most water we see is blue.

Circulation

• Atmospheric Circulation

– Depends on density

• Surface Ocean Circulation

– Depends on the wind

• Deep Ocean Circulation

– Depends on density

Why is Ocean Circulation Important?

• Transports heat from equator to poles

• Transport nutrients and organisms

• Influences weather and climate

Ocean Circulation

3/5/2018

7

Upwelling is the force that vertically moves cooler, nutrient rich water from approximately 1000 feet below the surface to the near surface.

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

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.

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 (tides)

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

3/5/2018

8

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

Earth’s Oceans