1OUR OCEAN PLANET

OUR OCEAN PLANET

SECTION 1 – OUR OCEAN PLANET

2REVISION HISTORY

Date Version Revised By Description

Aug 25, 2010 0.0 VL Original

31. OUR OCEAN PLANET

1. OUR OCEAN PLANET

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1.1 THE OCEAN

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1.1 THE OCEANAlthough we refer to our planet as Earth, the most dominant physical feature of our planet is the ocean which covers more than 70% of the planet’s surface. The total area covered by ocean is about 362 million sq km (140 million sq miles) with an average depth of 3,720 m (12,200 ft). The ocean so dominates the planet and is so important to us that Earth should perhaps be thought of as the “ocean planet”.

Our planet’s ocean is connected by currents and can thus be considered to be one continuous ocean. However, it is customary to divide it into 5 individual oceans, namely, the Pacific, Atlantic, Indian, Antarctic (or Southern) and Arctic Oceans. We can also further divide the Pacific and Atlantic Oceans into the North and South Pacific, and the North and South Atlantic Oceans.

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Ocean Area (million sq km) Area (million sq miles)

Pacific 153 59

Atlantic 82 32

Indian 67 26

Antarctic 21 8

Arctic 9 3

Ocean Literacy Principle 1(a)The ocean is the dominant physical feature on Earth – covering approximately 70% of the planet’s surface. There is one ocean with many ocean basins, such as the North Pacific, South Pacific, North Atlantic, South Atlantic, Indian and Arctic.

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An “ocean” is a very large body of saltwater while a “sea” is a much smaller body of saltwater that is considered part of its closest ocean. Thus, the Coral Sea is considered part of the Pacific Ocean while the Caribbean Sea is considered part of the Atlantic Ocean. The term "sea" is often given to a saltwater area on the margins of an ocean (e.g. the Mediterranean Sea is beside the Atlantic). A sea is also often enclosed or partially enclosed by land while an ocean is on the margin of land. The difference is not entirely precise and there are exceptions to the general definition.

The ocean generally looks blue because seawater does not absorb blue light from sunlight. When sunlight hits the water, the blue light is scattered in all directions making the ocean look blue. In seas or oceans that appear to be green, the colour is generally due to plants in the water. The northern Atlantic and Pacific Oceans, for example, are green near the coast because of a rich abundance of plants in the water. In contrast, the clear blue waters of the Caribbean Sea indicate the absence or reduced number of plants.

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The ocean covers a number of ocean basins including the North Pacific, South Pacific, North Atlantic, South Atlantic, Indian and Arctic basins. An ocean basin at the bottom of the sea is composed of numerous underwater islands, trenches, mid-ocean ridges, rift valleys and sea mounts.

The sea bed may move as a result of lithospheric plate activity. Volcanic activity also occurs underwater which can cause violent land-forming activity. Earth’s highest peaks, deepest valleys, and flattest, largest plains are all in the ocean. We will explore some of the ocean’s features in the rest of this section.

The ocean is not a just a large static volume of water but a highly dynamic system. Each ocean has large surface circulating currents that transport warm surface water from the equator towards the poles, and cool polar water towards the equator. These currents are called “gyres” and they travel clockwise around ocean basins in the northern hemisphere, and anti-clockwise in the southern hemisphere.

Ocean Literacy Principle 1(b)An ocean basin’s size, shape and features (islands, trenches, mid-ocean ridges, rift valleys) vary due to the movement of Earth’s lithospheric plates. Earth’s highest peaks, deepest valleys and flattest vast plains are all in the ocean.

Ocean Literacy Principle 1(c)Throughout the ocean there is one interconnected circulation system powered by wind, tides, the force of the Earth’s rotation (Coriolis effect), the Sun, and water density differences. The shape of ocean basins and adjacent land masses influence the path of circulation.

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Interconnected circulation systems powered by the force of the Earth’s rotation (Coriolis effect) and the Sun’s heat transports water from the surface of the ocean to the bottom of the ocean and back again. The driving force in this vertical mixing process is differences in water density – cooler deep water is denser than warmer surface water resulting in vertical mixing.

The shape of ocean basins and adjacent land masses also influence the path of both surface circulation and deep mixing.

At sea level, a variety of forces, such as the Sun and Moon, act on the ocean to stir and move the water. This movement can be gentle as the lapping of water at the ocean’s edge, or extremely violent with huge waves that can destroy whole swathes of coastline.

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1.1.1 Plate TectonicsThe Earth can be divided into three basic layers, namely, the core, mantle and crust. Plate tectonics explains the movement of the continental crust in the upper layer of the Earth. Heat and magma from the interior of the Earth rises and cools as it reaches the upper mantle. This causes movements of the Earth’s crust and shifting of large sections of the crust known as “tectonic plates”. Plate tectonics cause ocean basins, earthquakes, mountains, volcanoes and faults to form. This dynamic process, driven by the heat deep inside the Earth, is what sets the Earth apart from any other planet.

It is now recognized that the surface of the Earth has at least 7 major plates and a large number of smaller ones, all floating on the partly molten layer of the mantle beneath. Some of these plates carry continents while others are purely oceanic.

The areas where these plates meet are called “plate boundaries”. Different types of powerful natural phenomena occur at these boundaries depending on the type of boundary.

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1. DIVERGENT BOUNDARYAt a divergent boundary, plates are moving apart as hot magma rises and moves upwards to the surface of the earth. When the magma reaches the surface, it cools and solidifies to form a new crust. Imagine two giant conveyor belts, facing each other but slowly moving in opposite directions as they transport newly formed oceanic crust away from the ridge crest. This process continues over many millions of years and eventually results in the formation of an ocean basin. Examples include the Mid-Atlantic Ridge which spread apart to form the Atlantic Ocean and the Red Sea. Divergent boundaries may give rise to volcanoes and earthquakes.

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2. CONVERGENT BOUNDARYAt a convergent boundary, the plates move toward each other. If an oceanic plate and continental plate collide, the denser oceanic plate is forced underneath the continental plate, forming a subduction zone. As the oceanic plate is forced below the continental plate, it melts and becomes magma. The magma collects to form a magma chamber and may rise up through cracks in the continental crust. As pressure builds, a volcanic eruption may occur. When two continental plates push towards one another, the continental crust is squashed together and forced upwards to form mountain belts. This is how the Himalayas were formed. Convergent boundaries may give rise to mountains, volcanoes, faults, and earthquakes.

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3. TRANSFORM BOUNDARYAt a transform boundary plates slide horizontally past each other. Transform boundaries do not create or destroy land and often give rise to earthquakes and major faults but not volcanoes. A well-known example is the San Andreas Fault, which runs through the state of California in the USA.

Volcanic and earthquake activity is frequent at active plate boundaries and can be extremely violent. For example, in the Pacific Ocean, the "ring of fire" is a rough ring or circle stretching from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America. It is where the Pacific Plate interacts with other plates such as the Indo-Australian and North American plates. Over 75% of the world's active and dormant volcanoes are found along the ring of fire.

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In the Caribbean, the island of Monserrat has an active volcano that began erupting in 1995 and it is still continuing to so today. The North American tectonic plate is subducting beneath the Caribbean plate and forming the entire Lesser Antillean Island Arc system. The island arc is a series of volcanic islands that are formed as a result of this convergent tectonic activity.

In the figure below, some of the Earth's major plates are shown with dotted lines indicating the plate boundaries. An arrow indicates the direction in which the plate is moving. The “ring of fire” is also outlined with a solid line. Note that the figure is only an approximation and is not intended to be definitive.

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REFERENCES & FURTHER READINGhttp://www.mvo.ms/http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/Maps/map_plate_tectonics_world.htmlhttp://www.bbc.co.uk/schools/gcsebitesize/geography/platetectonics/index.shtmlhttp://pubs.usgs.gov/gip/dynamic/understanding.html

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1.1.2 Sea LevelSea level is the average height of the ocean relative to the land taking into account the differences caused by tides. The sea level is not constant but changes over time.

1. SHORT TERMSome short-term causes of sea level changes include:

(a) TidesThe tides, which are caused by the gravitational pull of the Moon and the Sun on the Earth, regularly change the sea level so that it oscillates between high tide (the highest sea level) and low tide (the lowest sea level).(b) Storm SurgesStorm surge is caused primarily by high winds pushing water toward the shore causing the sea surface to rise. The wind causes the water to pile up higher than the ordinary sea level.(c) Seawater Expanding/ContractingSea levels also change as sea water expands and contracts when ocean water warms and cools.(d) FloodingRiver runoff levels or flooding due to seasonal differences in the amount of rainfall can also cause changes to sea level.

Ocean Literacy Principle 1(d)Sea level is the average height of the ocean relative to the land, taking into account the differences caused by tides. Sea level changes as plate tectonics cause the volume of ocean basins and the height of the land to change. It changes as ice caps on land melt or grow. It also changes as sea water expands and contracts when ocean water warms and cools.

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(e) Earthquakes/LandslidesUndersea earthquakes can generate huge waves called tsunamis that can temporarily change sea level. Abrupt landslides in the sea can also change sea levels.

2. LONG TERMSome long-term causes of sea level changes include:

(a) Plate MovementSea levels can change as shifting plates cause the volume of ocean basins and the height of the land to change. (b) Glaciers MeltingSea levels can rise as mountain glaciers melt and the water enters the ocean.(c) Icecaps MeltingSea levels can rise as icecaps break off and enter the ocean. Note that the sea level rises when the ice first enters the ocean not when the sea ice melts because the ice is already displacing an equivalent volume of water.

REFERENCES & FURTHER READINGhttp://www.weatherincayman.com/tideprediction.html http://www.tide-forecast.com/locations/GrandCayman-CaymanIslands/tides/latesthttp://tidesandcurrents.noaa.gov/sltrends/sltrends.html

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1.1.3 Sea FloorThe sea floor is divided into a number of geographically distinct areas depending on depth, plate tectonic zone, and distance from the coast:

1. CONTINENTAL SHELF The Continental Shelf lies between the coast and the 200 m (660 ft) depth contour. The Continental Shelf surrounds the continents on earth but occupies only 7.5% of the sea floor. The shelf corresponds to the submerged portion of the continental crust.

2. CONTINENTAL SLOPEThe downward slope of the Continental Shelf increases abruptly at the seaward edge to form the Continental Slope, which occupies 8.5% of the sea floor. At a depth of about 3,000 m (9,842 ft), the slope flattens out to a gradient of 1:100 and the beginning of the Continental Rise.

3. CONTINENTAL RISEThe Continental Rise is typically a thick flattish wedge of sediment that runs from about 3,000 m (9842 ft) to 4,000 m (13,123 ft). At around 4,000m (13,123 ft) the Continental Rise levels out again to an almost imperceptible gradient (1:1000 or less) to meet the Abyssal Plain.

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4. ABYSSAL PLAINThe Abyssal Plain extends from about 4,000 m (13,123 ft) to 6,000 m (19,686 ft). It is a huge flat floor of an ocean basin that is covered with a layer of sediment. It covers over 50% of the ocean area and is the single largest environment on Earth.

5. OCEAN TRENCHThe deepest places on the earth's surface are known as Ocean Trenches. These trenches are like deep wounds in the ocean floor. They form when two tectonic plates collide and one subducts beneath the other, forming a depression. The deepest trench, the Mariana Trench, extends to a depth of 11,033m (36,198 ft).

6. SUBMARINE RIDGESIn some oceans, narrow, elongated ridges, resembling mountain ranges on the land, rise from the sea floor as a result of plate tectonic collisions. These are called “Submarine Ridges”. Peaks of these ridges may rise above sea level to form islands.

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Some of the features of the sea floor are as amazing as those we see on land. For example:

DEEPEST TRENCHThe Mariana Trench, which is located in the western Pacific Ocean southeast of the Mariana Islands, is the deepest point on Earth. At 11,033 m (36,198 ft), the Mariana Trench is farther below sea level than Mount Everest is above it.

The Cayman Trench (also known as the Bartlett Deep or Bartlett Trough) lies on the floor of the Caribbean Sea between Jamaica and the Cayman Islands. This relatively narrow trough has a maximum depth of 7,686 m (25,216 ft) and is the deepest point in the Caribbean Sea.

TALLEST MOUNTAINMountains are generally measured from sea level, in which case Mount Everest (8,848 m; 29,028 ft) is the tallest. However, Mauna Kea on Hawaii’s Big Island rises 10,203 m (33,476 ft) from the depth of the Pacific Ocean floor. Measured from base to peak, Mauna Kea is the tallest mountain on earth.

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GLOBAL MID-OCEAN RIDGEThe ocean ridges form a great mountain range wound around the Earth like the seam on a baseball. The global mid ocean ridge is about 64,000 km (40,000 miles) long and is the single largest topographic feature on Earth. Several smaller mid-ocean ridges make up the global mid-ocean ridge, one of the best-known being the Mid-Atlantic Ridge which runs down the centre of the Atlantic Ocean.

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REFERENCES & FURTHER READINGhttp://hypertextbook.com/facts/2001/BeataUnke.shtmlhttp://www.redcomet.org/Preview/Ces5xPrv.htmlhttp://smithsonianeducation.org/educators/lesson_plans/science_technology.htmlhttp://www.msstate.edu/dept/geosciences/CT/TIG/WEBSITES/RESEARCH/Christine_Oxenford/index.html

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1.1.4 Depth Zones Scientists have divided the ocean into layers or "zones" based on the penetration of light and depths which extend from the surface to the bottom of the ocean as follows:

1. EPIPELAGIC ZONE (PHOTIC ZONE)The Epipelagic zone extends from the surface to a depth of 200 m (656 ft). The water in this zone is fairly well mixed and, under ideal conditions, sunlight can penetrate the entire zone. Temperatures in the Epipelagic zone vary with climate and season but the worldwide average temperature of the surface zone is 22°C.

2. MESOPELAGIC ZONE (TWILIGHT ZONE)The Mesopelagic Zone extends from a depth of 200 m (656 ft) to 1,000m (3281 ft). This zone is also called the twilight zone and the mid-water zone. The sunlight in this zone is extremely faint. It is in this zone that we begin to see the twinkling lights of bioluminescent creatures. A great variety of strange and bizarre fish are also found here.

3. BATHYPELAGIC ZONE (DARK ZONE)The Bathypelagic Zone extends from a depth of 1,000 m (3,281 ft) down to 4,000 m (13,123 ft). The only visible light in this region is the light produced by bioluminescent life forms. The water pressure at this depth is crushing but a surprisingly large number of creatures can be found. Sperm whales can dive down to this level in search of food. Most of the animals that live at these great depths are black or red in colour due to the lack of visible light.

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4. ABYSSOPELAGIC ZONE (“ABYSS”)The Abyssopelagic Zone extends from a depth of 4,000 m (13,123 ft) to 6,000 m (19,686 ft). Its name comes from a Greek word meaning "bottomless". The water temperature of this zone is near freezing and there is no light at all. Very few creatures can be found at these depths because of enormous pressure. Most organisms found at these depths are invertebrates and include basket stars and tiny squids.

5. HADALPELAGIC ZONE (“TRENCHES”)The Hadalpelagic Zone extends from a depth of 6,000 m (19,686 ft) to 10,000 m (32,810 ft). This zone is mostly found in deep water trenches and canyons. In spite of the pressure and cold temperature, life can still be found in this zone, particularly invertebrates, such as sea stars and tubeworms, which thrive at these depths.

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1.1.5 Oceans Past/Oceans PresentThe ocean and continents didn’t always look the same as they do today. In the past, one huge ocean called Panthalassa surrounded the supercontinent of Pangaea because of plate (tectonic) movements.

Pangaea was a C-shaped landmass that was spread across the equator. The body of water that was enclosed within the resulting crescent has been named the Tethys Sea.

The break-up of Pangaea took place about 180 million years ago, first into the two supercontinents Gondwanaland (to the south) and Laurasia (to the north), and thereafter into the continents we have today.

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The sequence of maps to the right (adapted from the USGS) shows how Pangaea continued fragmenting to form today’s ocean basins.

As the plates moved apart along divergent boundaries to create new ocean basins, convergent boundaries resulted in subduction and recycling of crustal material into the mantle.

The Earth's current continental landmasses formed and eventually moved to their current positions.

REFERENCES & FURTHER READINGhttp://pubs.usgs.gov/gip/dynamic/dynamic.htmlhttp://mineralsciences.si.edu/tdpmap/

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1.2 WATER

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1.2 WATER1.2.1 What is Water?Water is the most abundant resource on our planet. One molecule of water is made up of one atom of oxygen and two atoms of hydrogen, which is written as the chemical formula H2O. The two hydrogen atoms lie at 105° to each other. This arrangement results in the hydrogen end having a slightly positive charge and the oxygen end a slightly negative charge. Since opposite charges attract, individual water molecules come together through a weak attraction called a “hydrogen bond”. Hydrogen bonds allow water to exist in different states:

1. Ice (Solid)When water is frozen, the molecules are held by hydrogen bonds in a hexagonal structure.

2. Water (Liquid)As the temperature rises, ice turns into water, the molecules move freely, forming and breaking hydrogen bonds.

3. Water Vapour/Steam (Gas)As the temperatures rises even further and the molecules vibrate faster, the hydrogen bonds break, the molecules are set free, and the liquid becomes water vapour. At high temperatures, water becomes steam.

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Water is able to change between these states by the addition or removal of heat/energy. These transitions occur naturally between the ocean, clouds and land, as we will see later.

1. MeltingMelting is the process by which ice (solid) warms up and becomes water (liquid).2. SublimationSublimation is the process by which water changes from a solid (ice or snow) to a gas bypassing the liquid phase. This happens in places such as the Rocky Mountains as dry and warm Chinook winds blow in from the Pacific in late winter and early spring. When a Chinook arrives, local temperatures rise dramatically. When dry air hits the snow, the snow becomes water vapour bypassing the liquid phase. Sublimation is a common way for snow to disappear quickly in arid climates.3. EvaporationEvaporation is the process by which water changes from a liquid to a gas or vapour when heat is added to water.4. CondensationCondensation is the process by which warm water vapour in the air cools and changes into liquid water as water droplets.5. FreezingAs liquid water cools further, it becomes a solid (ice).

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1.2.2 What is Sea Water?Water is a remarkable substance as it has many unusual properties and can behave in unexpected ways. For example, it is a very good solvent and is able to dissolve many elements.

Seawater is a complex solution and is composed of the following:

• 96% pure water• 3% sodium chloride (common salt or halite)• 1% other elements (e.g. magnesium, calcium, potassium)

Sodium and chlorine are the most abundant elements dissolved in seawater. However, it is the combination of all of the different elements and compounds dissolved in the ocean that make the ocean “salty”.

Seawater has unique properties:

• it is saline• its freezing point is slightly lower than freshwater • its density is slightly higher that freshwater• its electrical conductivity is much higher than fresh• it is slightly basic (or alkaline)

Interesting!Ordinary seawater contains about 35 parts per thousand of salt (3.5%). In other words, 1 kg of sea water contains 35 g of salt. The density of sea water is about 1.025 g/ml at the surface of the ocean.

Ocean Literacy Principle 1(e)Most of Earth’s water (97%) is in the ocean. Seawater has unique properties: it is saline, its freezing point is slightly lower than fresh water, its density is slightly higher, its electrical conductivity is much higher, and it is slightly basic. The salt in seawater comes from eroding land, volcanic emissions, reactions at the seafloor, and atmospheric deposition.

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The salt in seawater comes from eroding land, volcanic emissions, reactions at the sea floor, and atmospheric deposition.

The amount of dissolved salts in the oceans does not vary greatly from place to place or from time to time throughout the ocean. However, slight differences in salinity along with larger differences in water temperature results in water masses with different densities.

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1.2.3 Where Does Earth’s Water Originate?

1. MagmaPrimordial Earth was an incandescent globe made of magma. All magmas contain water. Water set free by magma began to cool down the Earth’s atmosphere until eventually it became cool enough for the water to stay on the surface as a liquid.

2. VolcanoesVolcanic activity kept (and still keeps) introducing water in the atmosphere thus increasing the surface and ground water volume of the Earth.

3. CometsScientists suspect that comets made of ice may have collided with the Earth in the past, releasing their water into the oceans.

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1.2.4 Where Is All The Water?All the water we will ever have is already here on Earth in one form or another (except possibly for ice-laden comets striking the Earth).

Of the total supply of about 1386 million cubic km of water in the world, almost 97% of the total is saline. Of the 3% freshwater, ~69% is locked up in ice and glaciers while ~30% of freshwater is in the ground. Only 1% is readily available for drinking. Fresh surface-water sources, such as rivers and lakes, only constitute about 93,100 cubic kilometers (22,300 cubic miles), which is only 1/700th of 1% of the total water. Yet, rivers and lakes are the sources of water most people use.

In considering how precious fresh water is, it is helpful to remind oneself of the following quote:

"Water, water, everywhere,And all the boards did shrink;Water, water, everywhere,Nor any drop to drink."

The Rime of the Ancient Mariner – Samuel Coleridge

Interesting!Largest freshwater area – Antarctica (frozen) or Lake Baikal in Russia.Antarctica is a continent covered with ice but because the water is frozen it is not easily potable.Antarctica is also the driest continent on Earth with very low rainfall and with all moisture and water locked up in the ice.Saltiest sea is the Dead SeaCertain bacteria and other organisms can tolerate extremely high salinity conditions (over 5 times that of the ocean). These organisms are called “halophiles” (salt-lovers).

Ocean Literacy Principle 1(h)Although the ocean is large, it is finite and resources are limited.

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1.2.5 Water CycleEarth's water is constantly changing states from liquid to vapour to ice to liquid again in a cycle that has operated for billions of years and upon which all life on Earth depends.

The “Water Cycle” is driven by the sun which heats water in the ocean. Some of it evaporates into the air as water vapour. Ice and snow can also sublimate directly into water vapour. Rising air currents take the vapour into the atmosphere along with water from evapotranspiration (water transpired from plants and evaporated from soil). Cooler temperatures here cause the vapour to condense into clouds. As air currents move clouds around the globe, cloud particles collide, grow, and fall from the sky as precipitation. Some precipitation falls as snow and accumulates as ice caps and glaciers which can store frozen water for thousands of years. Snow in warmer climates thaws in spring and it flows overland as snowmelt.

Ocean Literacy Principle 1(f)The ocean is an integral part of the water cycle and is connected to all of the earth’s water reservoirs via evaporation and precipitation processes.

Ocean Literacy Principle 1(g)The ocean is connected to major lakes, watersheds and waterways because all major watersheds on Earth drain to the ocean. Rivers and streams transport nutrients, salts, sediments and pollutants from watersheds to estuaries and to the ocean.

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Most precipitation falls as rain back into the oceans or onto land, where the precipitation flows over the ground as surface runoff. A portion of runoff enters rivers which transports the water towards the oceans. Runoff and ground-water seepage accumulate and are stored as freshwater in lakes. However, not all runoff flows into rivers. Much of it soaks into the ground as infiltration. Some water infiltrates deep into the ground and forms groundwater which can flow or be stored in the rocks for long periods of time. Some infiltration is close to the land surface and can seep back into lakes and the ocean as groundwater discharge, while some groundwater finds openings in the land surface and emerges as freshwater springs. Over time, all water keeps moving, some of which reenters the ocean to start the cycle again.

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REFERENCES & FURTHER READINGhttp://ga.water.usgs.gov/edu/watercyclehi.htmlhttp://www.kidzone.ws/water/

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1.3 ACTIVITIES

1.3.1 Ocean

CORE ACTIVITY

(a) Find and label the world’s oceans:

Pacific Ocean Atlantic Ocean Indian Ocean Arctic Ocean Antarctic (or Southern) Ocean

(b) How many oceans are there?

(c) What is the difference between an ocean and a sea?

(d) Why is the ocean blue?

(e) Why is the ocean sometimes green?

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ANSWERS

(a) Find and label the world’s oceans:

Pacific Ocean Atlantic Ocean Indian Ocean Arctic Ocean Antarctic (or Southern) Ocean

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(b) How many oceans are there?There is just one ocean on Earth but there are many ways to divide it. Many scientists think there are 5 oceans (Pacific, Atlantic, Indian, Arctic and Antarctic (or Southern) Oceans) while others further divide the Pacific and Atlantic Oceans into North and South Pacific and North and South Atlantic. Thus, depending on your view, there may be 1, 5, or 7 oceans!

(c) What is the difference between an ocean and a sea?An “ocean” is a very large body of saltwater while a “sea” is a much smaller body of saltwater that is considered part of its closest ocean. Thus, the Coral Sea is considered part of the Pacific Ocean while the Caribbean Sea is considered part of the Atlantic Ocean. The term "sea" is often given to a saltwater area on the margins of an ocean (e.g. the Mediterranean Sea is beside the Atlantic). A sea is also often enclosed or partially enclosed by land while an ocean is on the margin of land. The difference is not precise and there are exceptions to the general definition.

(d) Why is the ocean blue?The ocean generally looks blue because seawater does not absorb blue light from sunlight. When sunlight hits the water, the blue light is scattered in all directions making it look blue.

(e) Why is the ocean sometimes green?In seas or oceans that appear to be green, the colour is generally due to plants in the water. The northern Atlantic and Pacific Oceans, for example, are green near the coast because of a rich abundance of plants in the water. In contrast, the clear blue waters of the Caribbean Sea indicate the absence or reduced number of plants.

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1.3.2 Plate Tectonics

EXTENDED ACTIVITY

(a) Find and label the following major plates in the figure below:

North American plate South American plate Caribbean plate Indo-Australian plate African plate Antarctic plate

Eurasian plate Arabian plate Iranian plate Pacific plate Nazca plate

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(b) On which plate do the Cayman Islands reside?

(c) What is the “Ring of Fire”?

(d) The spreading rate of the sea floor along the Mid-Atlantic Ridge averages about 2.5 cm per yr (or 25 km in a million years). If the distance between the U.S. and North Africa is currently 4,830 km, how many years ago were they joined assuming a constant rate of movement?

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ANSWERS

(a) Find and label the following major plates in the figure below:

North American plate South American plate Caribbean plate Indo-Australian plate African plate Antarctic plate

Eurasian plate Arabian plate Iranian plate Pacific plate Nazca plate

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(b) On which plate do the Cayman Islands reside?Caribbean plate

(c) What is the “Ring of Fire”?The point where two plates meet is called a “plate boundary”. Earthquakes and volcanoes are most likely to occur either on or near plate boundaries. The "ring of fire" is a rough ring or circle stretching from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America. It is where the Pacific Plate interacts with other plates such as the Indo-Australian and North American plates. Over 75% of the world's active and dormant volcanoes are found along the ring of fire.

(d) The spreading rate of the sea floor along the Mid-Atlantic Ridge averages about 2.5 cm per yr (or 25 km in a million years). If the distance between the U.S. and North Africa is currently 4,830 km, how many years ago were they joined assuming a constant rate of movement?

25 km = 1 million years4,830 km = x million yearsCross-multiplying: (25 * x) = (4,830 * 1)Therefore: x = (4,830 / 25) or 193 million years

Over the past 200 million years the Atlantic Ocean has grown from a tiny inlet of water between the continents of Europe, Africa, and the Americas, into the vast ocean that exists today.

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1.3.3 Sea Level

CORE ACTIVITY

(a) Rising Sea Levels

Materials:• One glass half filled with water• One ice cube• One marker• Plastic cling film (to cover glass)

Method:• Take a glass of water and use a marker to mark off the water level• Place an ice cube in it and mark off the new water level• Cover the glass with plastic cling film• Allow the ice cube to melt and observe the level of the water

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(b) What happens to the water level when you add ice?

(c) What happens to the water level when the ice melts?

(d) What is “sea level”?

(e) If an iceberg is floating in the ocean and it melts as it floats towards the tropics, will the sea

(f) What are some events that can cause sea level changes?

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ANSWERS

(a) Rising Sea Levels

Materials:• One glass half filled with water• One ice cube• One marker• Plastic cling film (to cover glass)

Method:• Take a glass of water and use a marker to mark off the water level• Place an ice cube in it and mark off the new water level• Cover the glass with plastic cling film• Allow the ice cube to melt and observe the level of the water

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(b) What happens to the water level when you add ice?The water level rises

(c) What happens to the water level when the ice melts?There is no change in the water level

(d) What is “sea level”?Sea level is the average height of the ocean relative to the land taking into account the differences caused by tides. (e) If an iceberg is floating in the ocean and it melts as it floats towards the tropics, will the sea level rise? Why or why not?The sea level will not rise as the iceberg melts. The sea level will have already risen slightly when the icecap first broke off from land and crashed into the water (think about the experiment!)

(f) What are some events that can cause sea level changes?• Earthquakes/Landslides• Plate Movement• Glaciers Melting/Freezing

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1.3.4 Sea Floor

EXTENDED ACTIVITY

(a) Find and label the following ocean floor features:

• Continental Shelf• Ocean Trench• Submarine Ridges / Island• Continental Slope• Abyssal Plain• Continental Rise

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(b) Where is the world’s deepest trench?

(c) Where is the world’s highest mountain?

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ANSWERS

(a) Find and label the following ocean floor features:

• Continental Shelf• Ocean Trench• Submarine Ridges / Island• Continental Slope• Abyssal Plain• Continental Rise

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(b) Where is the world’s deepest trench?The Mariana Trench, which is located in the western Pacific Ocean southeast of the Mariana Islands, is the deepest point on Earth. At 11,033 m (36,198 ft), the Mariana Trench is farther below sea level than Mount Everest is above it.

(c) Where is the world’s highest mountain?Mountains are generally measured from sea level, in which case Mount Everest (8,848 m; 29,028 ft) is the tallest. However, Mauna Kea on Hawaii’s Big Island rises 10,203 m (33,476 ft) from the depths of the Pacific Ocean floor. Measuring from base to peak, Mauna Kea is the tallest mountain on earth.

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1.3.5 Ocean Trenches

EXTENDED ACTIVITY

(a) Find and label the following in the figure below:

• Mariana Trench (11,033 m below sea level)• Cayman Trench (7,686 m below sea level)• Mount Everest (8,848 m above sea level)• Mauna Kea (4,200 m above sea level but 10,203 m tall)

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(b) Which is taller – Mount Everest or Mauna Kea? Why?

(c) True or False: If the tallest mountain on land, Mount Everest (8,848 m; 29,028 ft), was sunk in the deepest part of the ocean – the Mariana Trench (11,033 m; 36,198 ft) – its peak would stick out of the water.

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ANSWERS

(a) Find and label the following in the figure below:

• Mariana Trench (11,033 m below sea level)• Cayman Trench (7,686 m below sea level)• Mount Everest (8,848 m above sea level)• Mauna Kea (4,200 m above sea level but 10,203 m tall)

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(b) Which is taller – Mount Everest or Mauna Kea? Why?Mountains are generally measured from sea level, in which case Mount Everest (8,848m; 29,028 ft) is the tallest. However, Mauna Kea on Hawaii’s Big Island rises 10,203m (33,476 ft) from the depths of the Pacific Ocean floor. Measuring from base to peak, Mauna Kea is the tallest mountain on earth.

(c) True or False: If the tallest mountain on land, Mount Everest (8,848 m; 29,028 ft), was sunk in the deepest part of the ocean – the Mariana Trench (11,033 m; 36,198 ft) – its peak would stick out of the water.

False – The peak would be covered by more than 2,000 m (7,000 ft) of water!

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1.3.6 Water State Transitions

CORE ACTIVITY

(a) Water can exist is several 3 forms or states. What are these states?

(b) How does water change from solid state (ice) to liquid state? What is this process called?

(c) What is Sublimation?

(d) What is Evaporation? At what temperature does freshwater boil?

(e) What is Condensation?

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(f) What is Freezing? At what temperature does freshwater freeze?

(g) Label the following figure with the following terms:• Condensation• Melting• Sublimation• Evaporation• Freezing

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ANSWERS

(a) Water can exist is several 3 forms or states. What are these states?• Solid – Ice • Liquid – Water• Gas – Water Vapour or Steam

Water is able to change between these states by the addition or removal of heat/energy.

(b) How does water change from solid state (ice) to liquid state? What is this process called?When ice is warmed up, it changes from solid to liquid state. This process is called “melting”.

(c) What is Sublimation?Sublimation is the process by which water changes from a solid (ice or snow) to a gas, bypassing the liquid phase.

(d) What is Evaporation? At what temperature does freshwater boil?Evaporation is the process by which water changes from a liquid to a gas or vapour. Evaporation occurs when heat is added to water. Freshwater boils at 100°C (212°F)

(e) What is Condensation?As warm water vapour cools, it forms water droplets. Condensation is the process by which water vapour in the air is changed into liquid water.

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(f) What is Freezing? At what temperature does freshwater freeze?As liquid water cools further, it becomes a solid (ice). Freshwater freezes at 0°C (32°F).

(g) Label the following figure with the following terms:• Condensation• Melting• Sublimation• Evaporation• Freezing

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1.3.7 Water Cycle

EXTENDED ACTIVITY

(a) Label the Water Cycle with the following terms:• Evaporation• Condensation• Precipitation• Sublimation

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(b) Find as many water storage areas as you can

(c) What is evaporation?

(d) What is condensation?

(e) What is precipitation?

(f) What is sublimation?

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ANSWERS

(a) Label the Water Cycle with the following terms:• Evaporation• Condensation• Precipitation• Sublimation

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(b) Find as many water storage areas as you can• Atmospheric storage• Ice & snow storage• Groundwater storage• Freshwater storage (in lakes and springs)• Saltwater storage (in oceans)

(c) What is evaporation?Evaporation is the process by which water changes from a liquid to a gas or vapour. Evaporation occurs when heat is added to water. (d) What is condensation?As warm water vapour cools, it forms water droplets. Condensation is the process by which water vapour in the air is changed into liquid water. (e) What is precipitation?Precipitation occurs when so much water has condensed that the air cannot hold it anymore. The clouds get heavy and water falls back to the earth in the form of rain, hail, sleet or snow.

(f) What is sublimation?Sublimation is the process by which water changes from a solid (ice or snow) to a gas, bypassing the liquid phase.