Properties of the Oceans

how the atmosphere and the oceans are connected

They exchange gases and are both affected by the composition and quality of the other.

As we begin to research ways of mitigating the effects of global warming, the oceans are especially important

They have the capacity to store large amounts of carbon dioxide, but only up to a certain point

Ocean water is 96% pure water and about 4% dissolved solids

This gives ocean water very high salinity, which is a measure of the dissolved solids in water.

The oceans and the atmosphere are intricately connected

connected in a great cycle that moves water from the surface to the atmosphere and back to the surface again.

sloped part of the continental edge that descends downward from the continental shelf

continental slope

Several consequences arise

from this melting of the polar ice

One way they are connected is through the relationship between

global warming and melting of sea ice and the polar ice sheets

the extent of global sea ice is shrinking due to the

global warming you learned about in the previous section. It also varies by season—with the winter time obviously having more ice cover than the summer.

These studies also show that the oceans' ability to store carbon may be reaching its maximum capacity

that the oceans are releasing carbon back to the atmosphere. This disrupts Earth's natural carbon balance and worsens global warming.

Once hidden from scientific view

the majority of the ocean floor has now been widely studied though the use of sonar technology that allows us to image the ocean floor by bouncing sound signals off of it

In the oceans, the major dissolved solid which contributes to salinity is sodium chloride

the same chemical compound known as table salt

In the polar regions

the surface water is almost as cold as the deep water, and sometimes the temperature is so low that solid ice forms

polar regions

the temperature of the ocean water varies less with depth than it does in other areas.

The oceans are connected to life on Earth as well;

they were the first places on Earth to support complex life forms and are currently home to millions of species.

piece of land that is formed by under sea volcanic activity

volcanic island

bottom of the ocean floor

you would find a diverse environment filled with numerous landforms. You would find both mountains and plains, rugged topography and broad areas of flat ground.

True or False: The ocean contains only dissolved solids and not any dissolved gases.

False Feedback: The ocean contains the same prin ciple gases that the atmosphere contains.

The opposite happens

when the sea ice melts in the spring

We can also study seafloor sediments

which are much like the rings in a tree in that they record annual changes in the ocean composition

True or False: The deep ocean water is less dense than the surface water

False Feedback: The deep ocean water is colder and denser than the surface water

Seamount

A seamount is a submerged underwater volcano.

Currents

Because of temperature differences, the ocean has two distinct layers: the surface and the deep water, as you have already learned. Just like the atmosphere, the ocean waters are in constant motion. The surface water is driven mostly by the wind. The deep water is driven by differences in density, which are in turn caused by differences in temperature and salinity. This kind of movement is called thermohaline circulation (THC). You will learn more about thermohaline circulation of ocean water in the next section of this unit.

True or False: Ocean water is coldest at the surface

False Feedback: Ocean water is warmest at the surface.

connects the continents to the abyssal plains

continental rise

Ocean Trench

The ocean trenches are deep valleys that cut into the ocean floor.

shallow seabed just adjacent to the continents

continental shelf

The Properties of Ocean Water

While ocean floor topography is not easily seen by just a visit to the beach, another important property of the oceans is very easily detected.

sea ice covers

about 15 percent of Earth's surface

deepest, flattest part of the ocean floor

abyssal plain

Oceans cover nearly 70 percent of Earth's surface

and affect nearly every phase of Earth's dynamics.

They hold 97 percent of Earth's water

and are the major source of water vapor that eventually becomes precipitation such as rain or snow.

deep valley that cuts into the ocean floor

ocean trench

Because seawater contains salt

, it does not freeze at the same temperature as regular water

The oceans also store vast amounts of heat

and thus moderate seasonal temperature changes and slow long-term climate change.

There are many types of sea ice ranging from

small ice floes to pieces of glacier fallen into the sea called icebergs.

Shrinkage of Polar Bear Habitat

A direct consequence of polar ice melting is the loss of wildlife habitat. Many large mammals, like polar bears, walruses, and seals, rely on the polar ice as habitat and for hunting their food. As the polar ice retreats, these animals lose their vital habitat. They also must shift their feeding and migration routes. This map shows how polar bear habitat is expected to diminish over the next few decades if global warming continues. The darker red areas are those areas where habitat loss is the greatest. The native peoples who hunt these animals will also be affected. Native people of some Arctic cultures depend on hunting seals and walruses for food and other needs. As these animals' migration paths and habitats are disrupted by melting ice, the lives of the people that hunt them will also be disrupted.

Guyot

A guyot is an extinct undersea volcano. They have distinctive flat tops because they have been eroded by ocean waves

Volcanic Island

A volcanic island is a piece of land that forms by volcanic activity at the ocean floor and the resulting build up of lava

Density

Density is the mass of a substance per unit of volume. Pure water has a density value of 1.0 grams per milliliter (g/ml). Ocean water contains dissolved salts, which add to its mass, so it has a higher density than pure water. However, the temperature of ocean water actually affects its density even more than the amount of dissolved solids in it. Cold ocean water is considerably denser than warm ocean water, and both are denser than pure water. Overall, colder saltier water is denser than warmer, less salty water.

Dissolved Solids

Every year, 400 billion kilograms of dissolved solids are dumped into oceans by rivers and streams that empty into them. Most of these solids are salts and minerals. Overall, the ocean is about 96 percent pure water and about 4 percent dissolved solids. That 4 percent may seem like a small number but it equals about 40 grams of dissolved salt in every 1 kilogram of water. That would be like adding, stirring and dissolving about seven teaspoons of salt into just one quart of water. Salinity is highest in surface ocean water near the tropics because intense evaporation leaves the salt behind. On the other hand, away from the tropics, it is cooler and evaporation rates are slower. This makes the ocean water in those areas have a lower salinity value

What evidences indicates that the oceans may already be releasing carbon to the atmosphere?

Evidence from carbon isotopes in the bodies of microscopic marine organisms, and evidence from seafloor sediments, reveals that the oceans are already releasing carbon to the atmosphere.

True or False: Ocean water has the same density as pure water because water always has the same properties.

False Feedback: Ocean water is denser than pure water because it contains dissolved solids.

True or False: Ocean water salinity is highest at the poles.

False Feedback: Ocean water salinity is highest in the tropics and subtropics w here evaporation is high.

True or False: The salinity of ocean water is about 35 percent.

False Feedback: The salinity of ocean water is about 3.5 percent.

Methane Release

Melting of sea ice and the polar ice caps will also result in greater release of methane gas to the atmosphere. Arctic soils and ice hold large quantities of this gas. As the ice melts, the gas is released to the atmosphere. Methane, like carbon dioxide, is a greenhouse gas, and so release of it to the atmosphere would just accelerate global warming. This scientist is measuring methane release from an Arctic soil.

Summarize the effects of melting sea ice on people and wildlife.

Melting sea ice takes away habitat from animals and disrupts their feeding and migration paths. It also harms the people who depend on these animals for hunting. Melting ice can also contribute to rising sea levels and shifted shorelines, which can displace cities and lead to more flooding of coastal towns.

Trend in Global Sea Level Rises

One of the most obvious consequences of global warming is shifted shorelines. As the oceans warm, the water undergoes thermal expansion and takes up more space, thus causing a rise in sea level. Sea level rises are being noted all over the globe. Rises in sea level will mean that coastal areas that are now dry land will gradually be placed under water. This further leads to more flooding, changes in ecosystems, and the displacement of human-populated cities.

What is the relationship between sea ice and atmospheric motion?

Sea ice reflects large amounts of sunlight away from Earth's poles. This contributes to the imbalance in net solar radiation between the poles and the equatorial region. This imbalance of solar radiation is what drives atmospheric motion.

Abyssal Plain

The abyssal plain is a relatively flat area that covers most of the ocean floor and is the deepest part of the ocean floor.

Continental Rise

The continental rise is the gently sloping sect ion of the continental margin. It connects the continent to the abyssal plain.

Continental Shelf

The continental shelf is the shallow seabed just adjacent to the continents.

Continental Slope

The continental slope is the part of the ocean floor that extends downward from the continental shelf.

What role do the oceans play in mitigating global warming? How is that role being disrupted?

The oceans can store large amounts of carbon, but that role may be diminished if the oceans become too warm and start sending carbon back to the atmosphere. That carbon (in the form of carbon dioxide gas) is a greenhouse gas that traps heat and contributes to global warming.

This cycle is called the water cycle

and it is the process whereby water evaporates from the oceans, rises into the atmosphere, cools, and comes back down as precipitation.

Temperature

This graph is called a thermocline. It shows you how ocean water temperature varies with depth. Note the sharp decline in temperature from 200 to 1000 meters of depth. In most cases, the ocean is stratified (layered) into warm surface water and cooler and denser deep water. With the exception of water in the polar regions, ocean water becomes markedly cooler with depth. The upper 100 meters is well mixed because it is stirred by winds and waves. It is relatively warm and oxygen-rich. The deep ocean is relatively calm and slow-moving. It undergoes very little mixing. Because water in the deep ocean is so cool, it is also relatively dense. Therefore, it cannot rise up to the surface and interact with the atmosphere like the surface water does. It contains less oxygen than the surface water.

Gases

Three principle gases in the atmosphere are also present in seawater. These are dissolved nitrogen, oxygen, and carbon dioxide. Of these, carbon dioxide is most easily dissolved in seawater. All of these gases can enter seawater from the atmosphere and go back to the atmosphere from the ocean. Their movement between the ocean and atmosphere depends a lot on water temperature. The warmer the ocean is, the less gas it will hold, and the more gas it will send back to the atmosphere. The colder the ocean, the more gas it will hold. It will send back less into the atmosphere. The map shows the levels of human-caused carbon dioxide in the ocean waters of the world. As human activity puts more carbon dioxide into the air, the oceans absorb more of it. This makes ocean water more acidic than normal and harms marine life. The oceans store huge amounts of carbon dioxide, thus helping to moderate global warming, but as the levels of this gas get higher and higher in the atmosphere, the oceans will not be able to hold any more. This will be especially true if the ocean water becomes warmer; as it gets warmer it will release carbon dioxide to the atmosphere.

True or False: As the ocean gets warmer, it sends more gas back to the atmosphere.

True Feedback: As the ocean gets warmer, it sends more gas back to the atmosphere.

true or False: Human-caused input of more carbon dioxide in the atmosphere leads to more carbon dioxide in the oceans

True Feedback: Human-caused input of more carbon dioxide in the atmosphere leads to more carbon dioxide in the oceans.

True or False: Ocean water is layered based on its temperature with depth.

True Feedback: Ocean water is layered based on its temperature with depth

True or False: The most common dissolved solid in seawater is sodium chloride.

True Feedback: The most common dissolved solid in seawater is sodium chloride.

The oceans also hold clues about Earth's past climate

Understanding how climate has responded to environmental changes in the past helps us predict how the climate might change in response to the large scale change that humans are inducing on the atmosphere.

an extinct undersea volcano with a flat top

guyot

For example, we can study the nature of carbon isotopes in the bodies of microscopic sea organisms to gain

information about how the oceans are absorbing carbon and how that capacity has changed through time

Because seawater contains salt,

it freezes at negative two degrees Celsius instead of zero degrees like pure water.

As the oceans get warmer and sea ice melts

more greenhouse gases may be released to the atmosphere—only advancing the problem of global warming.

The diagram below shows some features of the ocean floor. Roll over the yellow terms in the image with your mouse to learn about each one.

pg 4

This map shows how sea ice is shrinking in the Arctic region of the globe. The yellow line shows the outline of where the ice was prior to the year 2000. You can see that it has shrunken considerably just between 2000 and 2007.

pg. 11

Sea ice is common in the polar regions

plays an important role in Earth's solar radiation balance because it reflects large amounts of sunlight back to space

. As the water freezes and leaves the salt behind,

really dense salty water forms right under the ice

One of the consequences of global warming may be

rising sea levels as the oceans undergo thermal expansion and as continental ice sheets melt and contribute water to the oceans.

Global trends show that

sea ice is shrinking and that the polar ice caps are melting as Earth becomes gradually warmer due to the enhanced greenhouse effect and global warming

a volcano completely submerged underwater

seamount