Ocean Systems

Earth’s Ocean Systems
If you have ever observed a photograph of Earth taken from space, you know that Earth
appears mostly blue. Earth appears blue because water covers 70 percent of its surface.
Most of Earth’s water—97 percent—is salt water in the oceans. An ocean system includes
one or more oceans and other interconnected bodies of water and their interactions
with the rest of the hydrosphere, the atmosphere, the geosphere, and the biosphere.

Human Dependence on Ocean Systems
Every human life is affected by the ocean. Humans depend on ocean systems for water,
oxygen, weather and climate regulation, food, medicine, and other resources. 

Water
Humans depend on water in many ways, such as transportation, cleaning, drinking, and
growing crops. When water evaporates from the surfaces of oceans, the salt in the salt
water stays in the oceans. The water that condenses into clouds and then falls back to
Earth’s surface is freshwater. Scientists estimate that approximately 90 percent of
evaporated water in the water cycle comes from oceans. If water from oceans did not
naturally recycle through the water cycle, converting salt water to freshwater, humans
would not have the freshwater on which we depend.

Oxygen
Humans need oxygen to survive. Our cells need oxygen in order to perform cellular respiration. Oxygen is also part of many substances that are important to life, such as carbon dioxide (CO2) and water (H20). During photosynthesis, plants and some other organisms take in carbon dioxide and release oxygen. Approximately 70 percent of the world’s oxygen is released from
ocean organisms. Most photosynthesis in the oceans is performed by single-celled organisms called phytoplankton.

Weather and Climate Regulation

Humans depend on ocean currents to regulate our weather and climate. An ocean

current is a large volume of water flowing in a certain direction. Rotation of the Earth,

wind, and the dense, salty water produced by the formation of sea ice drives convection

in the oceans causing warm- and cold-water currents in the major gyres on Earth. A gyre

is a large circular system of ocean currents. Gyres occur at the water's surface. Warm

and cold currents affect weather and climate in different ways. Regions near warm-water

currents are often warmer and wetter than regions near cold-water currents.

Several warm-water currents affect coastal areas of the United States. For example, the

Gulf Stream transfers a lot of thermal energy and moisture to the surrounding air from the

equator. As a result, summer evenings in the southeastern United States are often warm and humid. Evening rain is common in these areas.

The Great Ocean Conveyor Belt
Aside from gyres, there is another large system of ocean currents that affects weather
and climate. This current system is called the Great Ocean Conveyor Belt. Scientists use
this model to explain how ocean currents circulate thermal energy around Earth.

In this model, density currents in the North Atlantic Ocean and the Southern Ocean “run”
the conveyor belt. A density current is the vertical movement of water caused by
differences in density. Water in those regions is so cold and dense due to the freezing of
sea ice that it sinks to the ocean bottom and travels along the seafloor. Upwellings in the
Pacific Ocean and Indian Ocean eventually bring this deep, cold water to the surface
where it is warmed by the Sun. Upwelling is the vertical movement of water toward the
ocean’s surface.

As warm surface water travels from the equator toward the poles, it releases thermal
energy to the atmosphere, which warms the surrounding region. Then, the cold water
sinks until it is upwelled at a different location and the cycle repeats. This regulates
global climate, helping to counteract the uneven distribution of solar radiation reaching
Earth's surface.

 
Carbon Storage
The ocean regulates Earth's climate by absorbing and storing carbon. When there is less
carbon in the atmosphere, Earth tends to be cooler. The ocean stores 50 times more
carbon than the atmosphere. Oxygen (Oz) and carbon dioxide (CO,) gases move freely
between the atmosphere and seawater. As the amount of CO; increases in the
atmosphere, the amount of CO dissolved in seawater also increases. This is because of
gas exchange at the ocean’s surface. These gases dissolve in seawater, and wave action
helps mix them deeper below the water surface. Carbon is also absorbed and stored
when ocean plants and phytoplankton perform photosynthesis and when shelled
organisms and phytoplankton make their shells.

Food and Medicine
Humans depend on ocean systems as a source for food and medicine. Oceans provide
the primary source of food for more than 3.5 billion people on Earth. The oceans also
provide ingredients used in many food products. When you think of food that comes
from the ocean, you might think of seafood. While this is true, the ocean provides
ingredients found in surprising foods such as ice cream and soymilk.

Some medicines are derived from ocean organisms. For example, a chemical derived from sea squirts is used in an antitumor medication, and one type of painkiller uses chemicals
derived from cone snails. There are medications with ingredients from the ocean currently being tested, and scientists expect they will find even more medical uses from ocean organisms that have not yet been discovered.

The Economy
Ocean systems are a major contributor to the global economy. Each year, billions of
dollars are generated from industries that depend on ocean systems. Millions of people
have jobs in commercial fishing and aquaculture, which is the farming of aquatic
organisms for food. Ocean systems provide jobs in other areas as well, such as tourism
and recreation, biotechnology, shipping, oil and gas, and transportation.

People around the world travel to coastal areas to enjoy the beauty and participate in
activities such as scuba diving, boating, fishing, and water skiing. Americans spend
billions of dollars every year on ocean recreation. The largest segment of global tourism
is marine and coastal tourism

Human Impacts on Ocean Systems
Whether or not it is intentional, humans influence the ocean in many ways. The ways in
which humans can influence ocean systems have both positive and negative impacts.
Humans have negative impacts by creating pollution and contributing to climate change.
However, we can also positively impact ocean systems through conservation efforts. 

Ocean Pollution
Have you ever seen a photograph of a pelican or sea otter covered with oil? Spills from
oil tankers harm wildlife. They also harm the ocean. Any harm to the physical, chemical,
or biological health of the ocean ecosystem is ocean pollution. Ocean pollution has both
immediate effects and long-term effects on ocean systems. 

Solid Waste
Trash, including plastic bottles and bags, glass, and foam containers, causes problems for marine organisms. Many birds, fish, and other animals become entangled in plastic or mistake it
for food. Plastic breaks up into small pieces, but it does not degrade easily. Some of it becomes trapped in circular currents, or gyres. Gyres can collect large amounts of trash in a whirlpool-
like state, forming garbage patches in the ocean. The North Pacific Gyre has collected so much plastic and other debris that some people have named a portion of it “the Great Pacific Garbage Patch” 

Excess Sediments
Large amounts of land-based sediment wash into oceans. Erosion often occurs on steep
coastal slopes after heavy rains. Some of this erosion is natural. However, some is
caused by humans, who cut down trees near rivers and ocean shorelines. Without the
roots of trees and other vegetation to hold sediments in place, the sediments more
readily erode. Excess sediments can clog the filtering structures of filter feeders, such as
clams and sponges. Excess sediments can also block light from reaching its normal
depth. Organisms that use light for photosynthesis may not survive, 

Dead Zones
Algae need nutrients, such as nitrogen and phosphorus, to survive and grow. However,
100 many nutrients can cause an explosion in algal populations. An algal bloom occurs
when algae grow and reproduce in large numbers. Many scientists suspect that a major
source of excess nitrates and phosphates is from land-based fertilizers that wash into
Oceans.

Many algal blooms are harmless, but others can disrupt marine ecosystems and harm organisms. Some algae produce poisonous substances that can kill organisms that eat them.
Other algal blooms are so large that the bacteria that break down the algae when they die use up oxygen in the water, creating dead zones. A dead zone is an area of an ocean or large lake
where there is not enough oxygen to support marine life.

Dead zones can occur where large numbers of algae die and decompose in one area.
Decomposition requires oxygen. When the algae decompose, oxygen levels in the water
decrease. Fish and other marine organisms cannot get enough oxygen to survive.

Global Climate Change
Solid waste, excess sediments, and algal blooms can cause immediate harm to ocean
ecosystems. Other threats to oceans are related to long-term changes in Earth's climate.
Climate data indicate that Earth’s average temperature has increased over the past
century and continues to increase. The amount of carbon dioxide (CO2) in Earth's atmosphere has also increased. Increased CO2; in the atmosphere causes Earth to become warmer. Some of the increased CO2 is due to human activities, such as the burning of fossil fuels. 

Increased CO2 in Seawater
When CO2 mixes with seawater, a new substance called carbonic acid forms. Many
marine organisms build shells and skeletons from calcium carbonate absorbed from
seawater. As more carbonic acid forms in seawater, it is harder for organisms to absorb
calcium. Increased carbonic acid can cause shells and skeletons to weaken or dissolve
Over time, this could affect food webs.

Sea Level Rise
Scientific studies indicate that Earth's glaciers are melting. Sea ice that covers the Arctic
Ocean is also melting. Why? Earth is getting warmer. Data collected by scientists who
study Earth's climate show that Earth's average surface temperature has risen
approximately 11°C; since 1880.

Rising sea levels erode beaches and coastal wetlands and can flood low-lying areas,
Coastal flooding is a serious concern for the 600 million people living in low-lying areas
on Earth. Wildlife habitats will be disrupted, forcing animals to change their ways of lfe.
The intrusion of salty seawater could also contaminate freshwater sources used for
drinking and crop irrigation.

Coral Bleaching
Some marine organisms, such as coral, are very sensitive to temperature changes. A
Temperature increases as small as 1°C can cause corals to expel their algae. Algae gives
corals their color and provide nutrients. Coral bleaching is the loss of color in corals
that occurs when stressed corals expel the colorful algae that live in them. Near-shore
corals can experience bleaching due to runoff from storms that carry pollutants. In
addition, overexposure to sunlight and overexposure to air during low tides can bleach
corals in shallow waters. Corals do not die when they bleach, but they become stressed
and more susceptible to death as they lose their algae.

Dissolved Oxygen
The temperature of seawater affects the amount of oxygen dissolved in it. The warmer
the water, the less oxygen it contains. The solubility of oxygen decreases as temperature
increases, meaning that itis less prone to dissolving into water. Marine organisms need
oxygen to survive. As water warms, less oxygen is available, and organisms can die. The
process of removing dissolved oxygen from a liquid, such as water, is called
Deoxygenation.

Conservation
Not all human modifications to ocean systems are negative. There are also ways in which
humans protect ocean systems. Due to the loss of natural coral reefs as a result of coral
bleaching, humans have engineered artificial reefs to replace lost habitats. Artificial reefs
are human-made structures created in underwater areas to enhance the habitat for reef
organisms, including corals, fish, and other marine life that live among coral reefs.
Artificial reefs enhance this marine environment by providing additional habitats needed
by marine life.

Rebuilding Barriers

Coastal construction workers rebuild natural barriers, such as dunes and beaches to

restore coastlines. To accomplish this, large volumes of sediment must be moved to the

coast. Coastal construction workers create systems of pipelines through which the

sediment moves. Heavy machinery, such as cranes, excavators, and trucks, are used to

create the pipelines and move the sediment.