4.6 OCEANOGRAPHY

71% of Earth’s surface is covered with water.

The global ocean is divided by the continents into 5 distinct, or sub-divisional, oceans:

Pacific largest, flows between Asia and the Americas.

Atlantic second largest, ½ the volume of Pacific.

Indian third largest.

Arctic smallest, unique because surface is mainly ice.

Southern extends from the coast of Antarctica to 60° south latitude.

Ocean Background

All People Scream At Insects

◦ Atlantic◦ Pacific◦ Southern◦ Arctic◦ Indian

Ocean Background

300 MYA ◦ During Pangaea oceans formed

one giant body of water called Panthalassa.

200 MYA◦ When Pangaea began to split, the

North Atlantic Ocean and the Indian Ocean formed.

Present Day ◦ Continents continue to move at a

rate of 1-10 cm/yr. The Pacific Ocean is actually getting

smaller while all others are growing.

History of Earth’s Oceans

Panthalassa

4.5 BYA during Earth’s formation, there were no oceans to be found.◦ Volcanoes spewed lava, ash, and

gases all over the place.

◦ Earth was cooling however, and about 4 BYA, it cooled enough for water vapor to condense. Water began falling as rain.

Rain filled the depressions in Earth’s surface and the first oceans began formation.

History of Earth’s Oceans

The two main gases in the atmosphere are Nitrogen, N2, and Oxygen, 02.

◦ These two gases are also the main gases dissolved in ocean water.

◦ While carbon dioxide, CO2, is not a major component of the atmosphere, a large amount of this gas is dissolved in ocean water.

Characteristics of Ocean Water

Ocean water is 96.5% pure water, H20.

◦ Dissolved solids make up only about 3.5% of the mass of ocean water. These dissolved solids, commonly called sea salts, give ocean water its salty taste.

◦ Most salt in the oceans is the same salt we sprinkle on food, sodium chloride (NaCl).

As rivers and streams flow towards the oceans, they carry dissolved minerals from the land.

At the same time, water is evaporating from the ocean and leaving dissolved solids behind like salt! Dissolved solids in ocean include:

Sodium (Na)

Chlorine (Cl)

Potassium (K)

Calcium (Ca)

Magnesium (Mg)

Sulfur (S)

Others

Characteristics of Ocean Water

A measure of the amount of dissolved salts and other solids in a given amount of liquid is known as salinity.◦ Usually measured as grams of

dissolved solids PER gram (g) of water (or parts per thousand - ppt). Example: If 1000 g. of ocean water

contained 35 g. of solids, the salinity of the sample would be 35 parts salt per 1000 parts ocean water (35 ppt). Therefore, if you evaporated 1000 g.

of ocean water, 965 g. of freshwater would be removed and 35 g. of solids would remain.

Salinity of Ocean Water

Increased precipitation Decreased salinityIncreased evaporation Increased salinity

Increased winds Increased salinity

The temperature of ocean water decreases as depth increases, but does not happen gradually.

◦ Divided into 3 layers (zones) based on temperature:

Surface Zone – the warm top layer of ocean water distributing heat down-ward to a depth of 100 to 300 m. Surface currents mix the heated water with cooler waters below, therefore the temperature is relatively constant.

Thermocline – the layer in a body of water in which water temperatures drop with increased depth faster than it does in other layers. This layer exists because water near the surface becomes less dense as energy from the sun warms the water.

Deep Zone – The bottom layer extending from the base of the thermocline to the bottom of the ocean. The temperature in this zone is usually about 2°C.

Temperature of Ocean Water

Surface Zone

Thermocline

Deep Zone

300 m.

Surface

700 m.

Bottom

Surface temperatures of the ocean change dependent on location and season.

Along equator warmer b/c they receive more direct sunlight per year than areas close to poles.

However, both hemispheres receive more direct sunlight per year than areas close to the poles.

Average surface temps: (image below)

Temperature of Ocean Water

The mass of a substance per unit volume is called the density.◦ Equation for density is:

Density = mass volume

For example, 1 cm3 of pure water has a mass of 1 g. So the density of pure water is 1.0 g/cm3.◦ The large amount of dissolved solids in ocean

water makes it denser than pure fresh water. Ocean water has a density between 1.020

g/cm3 and 1.029 g/cm3.

Density of Ocean Water

D = m/v

Why is the ocean blue?◦ The color of ocean water is

determined by the way it absorbs or reflects light.

◦ White light from the Sun contains light from all the visible wavelengths of the electromagnetic spectrum.

Water absorbs most of the wavelengths, or colors, of visible light.

Only the blue wavelengths tend to be reflected.

Color of Ocean Water

Sending people to severe depths of the ocean can be dangerous so how can we study the ocean without doing this?

◦ Study from the surface of the ocean (ships).

◦ Study from high above in space. 2 main ways include:

Sonar

Satellites

The Ocean Floor

SOund Navigation And Ranging◦ Scientists send sound waves, or pulses,

down from a ship.

◦ Sound waves moves through water, bounce off ocean floor, and return to the ship. Deeper water = longer trips Depth calculated by multiplying half the

travel time by the speed of sound in water (1500 m/s). The device used to measure this depth is

called a fathometer. This creates a bathymetric profile: a map

of the ocean floor showing depth.

Sonar

In the 1970’s, scientists began studying the ocean floor via satellite images (radar generated).◦ 1978 – the satellite Seasat was launched.

Focused on the ocean, sending images back to Earth allowing scientists to measure the direction and speed of ocean currents.

Satellites

Geosat, once a top-secret military satellite, has been used to measure changes in the height of the ocean surface.◦ Mountains, trenches affect height

of the water above them. Use measurements to make a

detailed map of the ocean floor. Maps made from satellite

measurements can cover more territory than maps made using ship-based sonar readings.

Satellites

Home to the world’s longest mountain chain, which is about 64,000 km. (40,000 miles).◦ Canyons deeper than the Grand Canyon!

◦ Made of 2 major regions: Continental Margin – made of continental crust. Deep Ocean Basin – made of oceanic crust.

Revealing the Ocean Floor

Imagine the ocean as a giant swimming pool.

Continental margin would be the shallow end.

Deep ocean basin would be the deep end.

Continental Shelf: begins at shoreline and slopes gently down toward the open ocean.

Continues until the ocean floor begins to slope more steeply downward. Continental Slope: begins at the edge of the continental

shelf. Continues down to the flattest part of the ocean floor.

Continental Rise: the base of the continental slope, made of large piles of sediment.

Marks the boundary between the continental margin and the deep ocean basin.

Abyssal Plain: the broad, flat part of the deep-ocean basin. Covered by mud and the remains of tiny organisms.

Revealing the Ocean Floor

Mid-Ocean Ridges: mountain chains forming at divergent plate boundaries (tensional force).

Creates cracks, or rifts, in the ocean floor, where magma rises to fill the spaces.

Rift Valley: a valley forming on the ocean floor in between mountains (mid-ocean ridges).

Normally consist of magma being produced within. Trenches: huge cracks in the deep-ocean basin.

Form where one oceanic plate is pushed beneath a continental plate or another oceanic plate.

Seamounts: individual mountains of volcanic material. Form where magma pushes its way through or between tectonic plates.

If a seamount builds above sea level, it becomes a volcanic island.

Revealing the Ocean Floor

3 main groups of marine life:◦ Plankton

Free-floating microscopic organisms drifting in the waters of aquatic environments.

Phytoplankton – plant like.

Zooplankton – animal like.

◦ Nekton Organisms swimming actively in the open

ocean.

Whales, dolphins, sea lions, sharks, and other fish species.

◦ Benthos Organisms living on or in the bottom of the

ocean.

Crabs, starfish, worms, coral, sponges, seaweed, clams, oysters.

Life in the Ocean

The ocean floor is divided into ecological zones based on where different organisms exist.

Ocean Environments

The benthic zone is the bottom region of

oceans and bodies of fresh water.

The pelagic zone is the

region of an ocean or body of fresh water

above the benthic zone.

Intertidal

SublittoralBathyl

HadalAbyssal

NeriticOceanic

Sublittoral zone

Bathyl zone

Hadal zone(in trenches)

The shallowest benthic zone, the intertidal zone, is located between the low-tide limits and high-tide limits.◦ Twice a day this zone changes.

As tide flows in, the zone is covered with ocean water. As tide flows out, the zone is exposed to air and sun.

Intertidal organisms must be able to live both underwater and on exposed land (ex: crabs, oysters, clams)

The Benthic Environment

The sublittoral zone is located on the continental shelf and is continuously submerged.◦ Ends at the edge of the continental shelf, about 200 m. below sea level.

More stable than the intertidal zone.

Organisms always covered by ocean water (ex: coral, sea stars, and sea lillies).

Temperature, water pressure, and amount of sunlight remain fairly constant.

The Benthic Environment

The bathyl zone extends from the edge of the continental shelf to the abyssal plain.◦ Depth range: 200 m. to 4000 m. below sea level.

Lack of sunlight results in minimal plant life.

Organisms include sponges, brachiopods, and octopuses.

The Benthic Environment

No plants and few animals live in the abyssal zone, which is on the abyssal plain.◦ Largest ecological zone of the ocean and can reach 6000 m. in depth.

Common examples of species: sponges and tube worms. Organisms mentioned in previous zones can live in the abyssal zone such as

crabs and sponges. Organisms live around hot-water vents called black smokers.

The Benthic Environment

The deepest benthic zone is the hadal zone. ◦ This zone consists of the floor of ocean trenches and any organisms

found there. Can reach from between 6000 m. to 7000 m. in depth. Scientists know very little about this zone and believe life there is sparse. However, a few types of sponges, clams, and other organisms have been

identified within this zone.

The Benthic Environment

The neritic zone is the ocean water covering the continental shelf.◦ Warm, shallow zone with the largest concentration of marine

life mainly because of abundant sunlight. Fish, nekton, mammals (ex. dolphins), etc. Receives more sunlight than the other zones in the ocean.

The Pelagic Environment

The oceanic zone includes the volume of water covering the entire sea floor beyond the continental shelf.◦ Water temperature is colder and the pressure is greater.

Divided into 4 zones: epipelagic, mesopelagic, bathypelagic, and abyssopelagic.

The amount of marine life in the pelagic zone decreases as depth increases. Many of the same from neritic zone, but stranger ones at deeper depths (ex.

angler fish, giant squid, whale species).

The Pelagic Environment

Ocean water contains horizontal, stream-like movements of water called ocean currents.◦ Affected by weather,

Earth’s rotation, and the position of the continents. 2 main types of

currents include: Surface currents

Deep currents

Currents

Horizontal movements of ocean water caused by wind and occurring at or near the ocean’s surface are called surface currents.◦ Can reach depths of several hundred meters and lengths of

several thousand kilometers. The Gulf Stream is one of the longest surface currents, transporting

25 times more water than all the rivers in the world combined. Surface currents are

controlled by 3 factors: Global winds

Continental barriers

Coriolis Effect

Surface Currents

Different winds cause currents to flow in different directions.◦ The trade winds are

located just north and south of the equator. In both hemispheres, they

push currents westward across the tropical latitudes.

◦ The westerlies are located in the middle latitudes.

Global Winds

The continents are another major influence on surface currents.◦ They act as barriers to these currents.

◦ When a surface current flows against a continent, the current is deflected and divided.

Continental Barriers

As Earth rotates, ocean currents and wind belts curve.◦ The curving of the paths of

ocean currents and winds due to Earth’s rotation is called the Coriolis Effect.

◦ The wind belts and the Coriolis Effect create huge circles of moving water, called gyres.

Coriolis Effect

Stream-like movements of ocean water located far below the surface are called deep currents.◦ Move much slower than surface currents.

◦ Form as cold, dense water of the polar regions sinks and flows beneath warmer ocean water. The density of ocean water if affected by temperature and

salinity. Decreasing temperature and increasing salinity will increase the

water’s density. Cold water is more dense than warm water!

Deep Currents

Currents can greatly affect the climate in many parts of the world.◦ Warm-water currents:

The Gulf Stream carries warm water from the Tropics to the North Atlantic Ocean.

◦ Cold-water currents: The California current carries cold

water from the North Pacific Ocean toward Mexico along the western coast of the USA therefore, cooler climate year-round than inland states.

Currents and Climate

Every 2 to 12 years, the South Pacific trade winds move less warm water to the western Pacific than they usually do.◦ Therefore, surface water temperatures along the coast

of South America rise and the warming spreads westward. This periodic change in the location of warm and cool

surface waters in the Pacific Ocean bringing warmer conditions to the eastern Pacific is called El Niño.

Sometimes, it can be followed by La Niña, which is a periodic change in the eastern Pacific Ocean in which the surface water temperature becomes unusually cool.

Currents and Climate

Normal Conditions

El Niño Conditions

La Niña Conditions