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Oceans study guide – test Friday, March 30

Know the parts of the ocean floor

Know what causes the different levels of salinity in the ocean

Know the 3 types of ocean motions and what causes them

Be able to draw in the Gulf Stream movement and be able to tell how this movement affects different

places in the world

Know the different levels of the ocean and how this affects life in the ocean

Be able to describe the ocean’s food web

5.6 Oceans

If you look down at our planet from outer space, most of what you see is water; 71% of the planet's surface is covered by ocean and it is because of this that the Earth is sometimes called "the water planet". Only about three-tenths of our globe is covered with land.

The ocean wraps the globe and is divided into four major regions: the Atlantic Ocean, the Pacific Ocean, the Indian Ocean and the Arctic Ocean. Some scientists consider the waters around Antarctica to be a separate, fifth ocean as well. These oceans, although distinct in some ways, are all interconnected; the same water is circulated throughout them all.

If all the continents were crammed into one corner of the Earth, the vast extent of the world ocean could easily be seen. In reality, of course, the continents are not bunched together as shown in the figure to the right, but instead are spread out over the entire Earth's surface. Most oceanographers, however, believe that a long time ago in the Earth's geologic history all of the continents were once grouped closely together in much the same manner.

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Seventy-one percent of the Earth's surface is ocean.

Ocean FloorBeneath the world's oceans lie rugged mountains, active volcanoes, vast plateaus and almost bottomless trenches. The deepest ocean trenches could easily swallow up the tallest mountains on land.

Around most continents are shallow seas that cover gently sloping areas called continental shelves. These reach depths of about 650 feet (200 m). The continental shelves end at the steeper continental slopes, which lead down to the deepest parts of the ocean.

Beyond the continental slope is the abyss. The abyss contains plains, long mountains ranges called ocean ridges, isolated mountains called seamounts, and ocean trenches which are the deepest parts of the oceans. In the centers of some ocean ridges are long rift valleys, where Earthquakes and volcanic eruptions are common. Some volcanoes that rise from the ridges appear above the surface as islands.

Other mountain ranges are made up of extinct volcanoes. Some seamounts, called guyots, are extinct volcanoes with flat tops. Scientists think that these underwater mountains were once islands but their tops were worn away by waves. The diagram below shows the main features found on the ocean floor.

Oceanographers know these features exist because much effort has been spent on mapping the ocean bottom. In order to make maps of the ocean floor, the depth of the ocean must be known in many places. In the early days of ocean exploration, sailors made depth determinations called soundings by means of a lead line. This was simply a long piece of rope, marked off in fathoms (six-foot intervals) and having a lead weight at one end. The depth was measured by dropping the weight into the water and noting how much line went out when the lead weight reached the bottom.

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Measuring Water Depth

Today's

oceanographers use sonar instruments to generate a sound signal that is bounced or "echoed" off the sea floor and then recorded on board the ship. The speed of sound in water is 1,500 m per second, four times faster than the speed of sound in air. By carefully measuring the round-trip time of the sound waves and taking into account the variables of temperature and salinity, the depth of the water and the distance to another object can be measured accurately.

Taking soundings this way is time-consuming, especially in deep water. Today most depth measurements are made using an echo sounder. Instead of dropping a weight, a pulse of sound energy is transmitted electronically toward the bottom. The time it takes the pulse to travel to the bottom and be reflected back up to the surface is measured. From this time interval, the depth of the water can be calculated. When pulses are sent out and received in quick succession, an almost continuous recording of the ocean depth called a bottom profile may be obtained.

The sedimentary rocks that exist on the ocean bottom are much younger than any similar rocks found on the continents. The cores of mud and rock brought back by deep-sea drilling ships vary greatly in age, but no deposits from the ocean floor seem to be more than about 200 million years old. This makes oceanic crust very young compared with the continents, which contain rocks up to about 4 billion years old.

Continental DriftThe face of the Earth is always changing and throughout geologic history oceans have been created and destroyed. Modern geologic evidence indicates that the ocean bottom is moving at a rate from about one-half to six inches a year through a process called plate tectonics.

Roughly 200 million years ago the Earth's surface was very different from the familiar pattern of land we know today. All of the

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CONTINENTAL DRIFTPangaea broke up with part of the continent drifting north and part south. 1) The northern part split to form the North Atlantic Ocean 208-146 million years ago (mya). 2) The South Atlantic and Indian oceans began to form 146-65 mya. 3) The continents continue to drift. Today the oceans are still changing shape; the Atlantic Ocean gets wider by a few inches each year.

land masses were grouped together into one vast supercontinent called Pangaea. The rest of the globe was covered by a single great ocean known as Panthalassa.

Slowly, over millions of years, the great land mass split apart. The pieces began to move over the Earth's surface driven by slowly churning currents in the molten rocks beneath the Earth's hard outer layers. The gigantic plates on the Earth's crust move like a conveyor belt. As new areas of ocean floor form at mid-ocean ridges, old areas are dragged down, or subducted, into the Earth's mantle, which explains why the older rocks cannot be found.

By about 35 million years ago the pattern of land and sea was very much like it is today. But the continents are still moving and as the Atlantic and Indian oceans continue to get wider by a few inches every year, the Pacific is slowly shrinking. At the northeast corner of Africa we can see the start of a new ocean. For

the last 25 million years, the Red Sea has been widening. If it continues at the same rate, in 200 million years it will be as wide as the Atlantic is today.

Water CycleMillions of years ago there were no oceans on the planet. The surface of the Earth was so hot that water simply boiled away. But volcanoes poured huge amounts of steam into the atmosphere and as the Earth cooled down the steam turned to water vapor that condensed as droplets and began to fall as rain. This downpour lasted for many thousands of years filling great hollows in the land and thus forming the world's first seas.

Today, the oceans are always losing and gaining water in a never-ending process called the water, or hydrologic, cycle. They lose water when the sun and wind lift tiny particles of moisture from the ocean surface. These invisible particles of water vapor mix with air. If the air cools, vapor particles join up as water droplets that form clouds. Clouds shed rain or snow and most of it, in fact 77 percent of all

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precipitation, falls directly back over the sea. Rain water and melted snow that fall on land run into rivers flowing back into the sea. Thus, the oceans never dry up.

Within the last few decades, scientists have developed a fairly clear understanding of the role the ocean and the hydrologic cycle play in weather formation. One interesting result has been the explanation of the effects of El Niño. The warm surface water temperatures associated with El Niño lead to alterations in the movement of air masses and the development of irregular ocean currents. Changes in the normal formation of weather conditions are the result, and the entire world is eventually affected.

HOW SALTY IS THE OCEAN? How salty the ocean is, however, defies ordinary comprehension. Some scientists estimate that the oceans contain as much as 50 quadrillion tons (50 million billion tons) of dissolved solids.

If the salt in the sea could be removed and spread evenly over the Earth's land surface it would form a layer more than 500 feet thick, about the height of a 40-story office building. The saltiness of the ocean is more understandable when compared with the salt content of a fresh-water lake. For example, when 1 cubic foot of sea water evaporates it yields about 2.2 pounds of salt, but 1 cubic foot of fresh water from Lake Michigan contains only one one-hundredth (0.01) of a pound of salt, or about one sixth of an ounce. Thus, sea water is 220 times saltier than the fresh lake water. What arouses the scientist's curiosity is not so much why the ocean is salty, but why it isn't fresh like the rivers and streams that empty into it. Further, what is the origin of the sea and of its "salts"? And how does one explain ocean water's remarkably uniform chemical composition? To these and related questions, scientists seek answers with full awareness that little about the oceans is understood.

SALINITY AND ITS VARIABILITY... Oceanographers report salinity (total salt content) and the concentrations of individual chemical constituents in sea water -- chloride, sodium, or magnesium for example -- in parts per thousand, for which the symbol o/oo is used. That is, a salinity of 35 o/oo means 35 pounds of salt per 1,000 pounds of sea water. Similarly, a sodium concentration of 10 o/oo means 10 pounds of sodium per 1,000 pounds of water.

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The salinity of ocean water varies. It is affected by such factors as melting of ice, inflow of river water, evaporation, rain, snowfall, wind, wave motion, and ocean currents that cause horizontal and vertical mixing of the saltwater.

THE SALTIEST WATER... The saltiest water (40 o/oo ) occurs in the Red Sea and the Persian Gulf, where rates of evaporation are very high. Of the major oceans, the North Atlantic is the saltiest; its salinity averages about 37.9 o/oo. The saltiness of this sea is due in part to the high water temperature (up to 83º F) causing a high rate of evaporation and in part to its remoteness from land; because it is so far from land, it receives no fresh-water inflow.

Low salinities occur in polar seas where the salt water is diluted by melting ice. The salty water sinks down low where the colder water is.

Water Movement – waves, tides, currentsOcean Currents – Know what causes currents to flowThe world's oceans travel in well-defined circular patterns called currents which flow like rivers. When wind pushes over the surface of the ocean some of the energy goes to forming waves while the rest goes to pushing the water in the direction of the wind. North of the equator currents bend to the right; south of the equator, they bend to the left. This is called the Coriolis effect. Winds, continents and the Coriolis effect make currents flow around the oceans in huge loops called gyres.

Energy from the sun also causes currents to flow. Water near the equator is heated more than water at middle latitudes causing a surface flow toward the poles. Where two currents meet, the colder water sinks pushing warmer water up to the surface, and this causes currents to flow.

Currents are also caused by differences in temperature and salinity in different parts of the ocean. Each current has its own characteristic salinity, density and temperature. The Gulf Stream, which was first mapped by Benjamin Franklin, runs along the east coast of the United States and is one of the strongest currents known. It is a warm, salty current up to 37 miles wide, 2600 feet deep and in some places it may travel more than 60 miles in a day.

Gravity plays a role in the movement of surface currents because the top of the ocean is uneven. Mounds in the water form in areas where the water meets land, where water is warmer, or where two currents converge. Gravity then pushes this water down and creates currents.

Can you name three things that cause oceans’ currents? ________________________________

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Historical map of the Gulf Stream.

GULF STREAM

The majority of the Gulf Stream is classified as a western boundary current. This means that it is a current with behavior determined by the presence of a coastline - in this case the eastern United States and Canada - and is found on the western edge of an oceanic basin. Western boundary currents are normally very warm, deep, and narrow currents that carry water from the tropics to the poles.

The Gulf Stream was first discovered in 1513 by the Spanish explorer Juan Ponce de Leon and was then used extensively by Spanish ships as they travelled from the Caribbean to Spain. In 1786, Benjamin Franklin mapped the current, further increasing its usage.

Path of the Gulf StreamToday, it is understood that the waters feeding into the Gulf Stream begin flowing off the west coast of Northern Africa (map). There, the Atlantic North Equatorial Current flows from that continent across the Atlantic Ocean. Once the current reaches eastern South America, it splits into two currents, one of which is the Antilles Current. These currents are then funneled through the islands of the Caribbean and through the Yucatan Channel between Mexico and Cuba.

Because these areas are often very narrow, the current is able to compress and gather strength. As it does so, it begins circulating in the Gulf of Mexico’s warm waters. It is here that the Gulf Stream becomes officially visible on satellite images so it is said that the current originates in this area.

Once it gains enough strength after circulating in the Gulf of Mexico, the Gulf Stream then moves east, rejoins the Antilles Current, and exits the area through the Straits of Florida. Here, the Gulf Stream is a powerful underwater river that transports water at a rate of 30 million cubic meters per second. It then flows parallel to the east coast of the United States and later flows into the open ocean near Cape Hatteras but continues moving north. While flowing in this deeper ocean water, the Gulf Stream is its most powerful, forms large meanders, and splits into several currents, the largest of which is the North Atlantic Current.

The North Atlantic Current then flows further north and feeds the Norwegian Current and moves the relatively warm water along the west coast of Europe. The rest of the Gulf Stream flows into the Canary Current which moves along the eastern side of the Atlantic Ocean and back south to the equator.

Can you draw the path of the Gulf Stream?

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Causes of the Gulf StreamThe Gulf Stream, like all other ocean currents is mainly caused by wind as it creates friction when moving over the water. This friction then forces the water to move in the same direction. Because it is a western boundary current, the presence of land along the Gulf Stream’s edges also aids in its movement.

The northern branch of the Gulf Stream, the North Atlantic Current, is deeper and is caused by temperature/salt circulation resulting from density differences in the water.

Impacts of the Gulf StreamBecause ocean currents circulate water of different temperatures all over the globe, they often have a significant impact on the world’s climate and weather patterns. The Gulf Stream is one of the most important currents in this regard since it gathers all of its water from the warm tropical waters of the Caribbean and the Gulf of Mexico. As such, it keeps sea surface temperatures warm, causing the areas around it to be warm and more hospitable. Florida and much of the Southeastern United States for instance is mild all year round.

The greatest impact the Gulf Stream has on climate is found in Europe. Since it flows into the North Atlantic Current, it too is warmed (though at this latitude the sea surface temperatures are cooled considerably), and it is believed that it helps keep places like Ireland and England much warmer than they would otherwise be at such a high latitude. For example, the average low in London in December is 42°F (5°C) while in St. John’s, Newfoundland, the average is 27°F (-3°C). The Gulf Stream and its warm winds are also responsible for keeping northern Norway’s coast free of ice and snow.

As well as keeping many places mild, the Gulf Stream’s warm sea surface temperatures also aid in the formation and strengthening of many of the hurricanes that move through the Gulf of Mexico. Additionally, the Gulf Stream is important to the distribution of wildlife in the Atlantic. The waters off of Nantucket, Massachusetts for example are incredibly biodiverse because the presence of the Gulf Stream makes it the northern limit for southern species varieties and the southern limit for northern species.

Waves

A wave is a way in which energy travels from one place to another. There are many kinds of waves, such as water waves, sound waves, light waves, radio waves, microwaves and earthquake waves. All waves have some things in common.

The highest point the wave reaches is called the crest. The lowest point is called the trough. The distance from one crest to the next is the wave length. The number of waves that pass a given point in one second is the wave's frequency.

When wind blows over the ocean's surface, it creates waves. Their size depends on how far, how fast and how long the wind blows. A brief, gentle breeze forms patches of tiny ripples on the surface called

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catspaws; strong, steady winds over long distances create large waves. But even when you feel no wind at all, you may encounter large swells created by distant storms.

In the open sea, waves make floating boats bob up and down instead of pushing them along. This is because the waves travel through water; they do not take the water with them. As a wave arrives it lifts water particles. These travel forward, then down and back so that each particle completes a circle. Circling movements of particles near the surface set off smaller circling movements below them

TidesTide-generating forces are a result of the gravitational attraction between the Earth, sun, and moon. It was not until Sir Isaac Newton (who lived from 1642-1727) discovered the law of gravity that the effect of the sun and the moon on the tides was fully understood. All surfaces of the Earth are pulled toward the moon and sun. This force has little effect on land masses, but it does have a very great and obvious effect on the water of the Earth's oceans. Twice each month the tidal range reaches a maximum and these large tides are called the spring tides. Halfway through the monthly cycle the range is much smaller, and these weak tides are called neap tides.

As the moon rotates around the Earth, it pulls the water on the nearest side of the Earth outward into a bulge. A similar bulge on the opposite side of the Earth is caused by the water being thrown outward by the planet's spin. These two bulges travel around the globe, producing two high tides each day.

During time of the new moon and full moon, when the sun and moon are in a straight line, their gravitational pulls combine and produce spring tides; at this time the high tides are very high and the low tides are very low. When sun and moon are at right angles from the Earth, during the quarter phases of the moon, the gravitational pull on the oceans is less producing a smaller difference between high and low tide known as a neap tide.

Life in OceansThe sea is home to billions of plants and animals. Many live only near the sunlit surface. Here you'll find everything from microscopic plankton to the giant blue whale. Oceanographers classify marine organisms by separating them into two primary groups: plants and animals.

Plants

There are two general types of plants found in the ocean, those having roots that are attached to the ocean bottom and those not having roots which simply drift about with the water. The rooted plants in the ocean are only found in shallow water because there is not enough sunlight to sustain photosynthesis in deeper waters. Since sunlight does not penetrate more than a few hundred feet into the ocean, most of the ocean is not capable of supporting rooted plants. Nevertheless, plants are found throughout most of the oceanic surface waters.

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The most abundant plants in the ocean are known as phytoplankton. These are usually single-celled, minute floating plants that drift throughout the surface waters of the ocean. A bucket of sea water might hold a million microscopic diatoms which are relatives of seaweed encased in glassy boxes. To grow, phytoplankton need nutrients from the sea water and lots of sunlight. The most light occurs in the tropics but nutrients there, especially nitrogen and phosphorus, are often in short supply. When large quantities of diatoms and other phytoplankton are present they give a color to the sea. Spectacular phytoplankton blooms are found in cooler waters where nutrients are brought up from the sea floor during storms.

Animals of the SeaMarine animals are divided into three groups: zooplankton, nekton, and benthos. Zooplankton are drifting animals and are usually small, however, they can grow to fairly large size. For example, the jellyfish and the Portuguese man-of-war are examples of larger types of zooplankton which are unable to propel themselves effectively and are therefore at the mercy of either wind or current. The zooplankton population also includes some temporary members such as fish eggs or larval forms of organisms which may grow up and leave the planktonic community to join the nekton or benthos.

Nekton are the free swimmers and probably the largest portion of familiar animals found in the ocean belong to this class. Common fishes, the octopus, whales, eels and squid are all examples of nekton. The nekton category includes a number of very diverse creatures. The whale, dolphin and porpoise are certainly very different from codfish or trout because whales represent sea mammals whereas cod are true fishes.

The third type of sea animal spends its entire life on or in the ocean bottom. This group of marine animals is called the benthos. It includes lobsters, starfish, various worms, snails, oysters and many more. Some of these creatures, such as lobsters and snails, may be able to move about on the bottom but their lifestyle is so bound up with the ocean floor that they are unable to survive away from this environment.

Who eats what?All living organisms need food. The basic difference between plants and animals is that plants make their own food, while animals obtain food from their environment. Through photosynthesis, plants manufacture organic materials (food) from inorganic materials (water, carbon dioxide, and nutrients) using sunlight as their source of energy. Because plants make their own food, they are called producers. Animals are known as consumers. They gather and consume organic material rather than making it themselves. Herbivores are animals that eat plants; carnivores are animals that eat meat. Omnivores are animals that eat both plants and other animals. Scavengers eat all the leftovers

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Marine animals are divided into three groups: zooplankton (those that float), nekton (those that actively swim) and benthos (those that live on or in the ocean bottom).

and other dead organisms. No matter what an animal eats, all of its food can be traced back to the ability of plants to produce organic materials from the sun.

As far as we know, nearly all life in the ocean is dependent on plants. Only plants have the ability to manufacture food out of inorganic substances, such as energy from the sun. Thus all animals are dependent on plants, since animals cannot derive nutrition from inorganic substances. Plants produce; animals consume. Being producers, plants form the first link in the food chain.

A food chain is a sequence of organisms in which each is food for the next member in the sequence. The surface of the sea swarms with billions of microscopic plants, called diatoms. With other plants such as seaweed, diatoms form the first link in most marine food chains. All subsequent links in the food chain are consumers, or the animals.

Orcas (killer whales) often eat cod and cod eat bivalves, especially mussels and cockles. In turn, the bivalves feed on tiny zooplankton that they filter out of the water. These zooplankton eat even tinier plants: the diatoms and other phytoplankton. Thus the diatoms are the producers and the zooplankton, bivalves, cod and orca are all consumers.

In the ocean there are innumerable individual food chains overlapping and intersecting to form complex food webs. Most marine creatures eat a variety of foods. If one link in a chain is depleted, the other consumers in the chain have alternate food sources. Organisms generally belong to several different food chains that are linked to form a food web.

The rich diversity of life in the sea forms a delicately balanced network of predators and prey and all organisms are dependent on one another for survival.

What are Phytoplankton?Derived from the Greek words phyto (plant) and plankton (made to wander or drift), phytoplankton are microscopic organisms that live in watery environments, both salty and fresh.

Some phytoplankton are bacteria, some are protists, and most are single-celled plants.

Phytoplankton are extremely diverse, varying from photosynthesizing bacteria), to plant-like diatoms, to armor-plated coccolithophores.

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Like land plants, phytoplankton have chlorophyll to capture sunlight, and they use photosynthesis to turn it into chemical energy. They consume carbon dioxide, and release oxygen. All phytoplankton photosynthesize, but some get additional energy by consuming other organisms.

Phytoplankton are the bottom (or the beginning) of the ocean’s food chain.

Study guide questions:

1. How much of the earth’s surface is covered by water? __________________________

2. List the five parts of the ocean floor and draw a diagram in the box below.

3. Explain the water cycle and draw a diagram.

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4. Name the three types of water movement in the oceans and describe each.

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5. What factors affect the salinity of the oceans? _____________________________________

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6. Name the most famous current, tell why it is important, and draw a diagram.

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7. Tell what you know about life in the oceans and describe the food chain.

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Draw a diagram showing the ocean’s food chain.

8. What characteristics of the oceans affect the number of organisms that live there?

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