Ocean Water Chemistry
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On average how many grams of salt are in a pot of ocean water?
What is the chemical name for salt, include the periodic symbols?
What happens to salt in water?
What other ions are mixed in with saltwater?
How can the salinity lower in the ocean?
Where is salinity lowest?
How can the salinity of water increase?
Where is salinity higher?
What does salt do to water in freezing temperatures?
How does salt affect water density?
What two gases are in ocean water that are necessary for living things?
How does oxygen get into water?
What is Carbon Dioxide used for in the ocean?
Why is water warm on the surface of the water?
What is water surface temperatures near the equator? What happens to
it as you move north or south?
16. What are the three temperature zones in order with temperatures from
warmest to coldest?
17. Explain how water pressure works.
18. Explain how a submersible works.
If you boiled a kilogram of seawater in a pot
until the water was all gone, there would be
about 35 grams of salts left in the bottom of the
pot. On average, one kilogram of ocean water
contains about 35 grams of salts-that is, 35 parts
per thousand. The total amount of dissolved
salts in water is called salinity.
The substance you know as table salt – sodium chloride- is the
salt present in the greatest amount in ocean water.
When sodium chloride dissolves in water, it separates
into sodium chloride particles called ions. Other salts, such as
magnesium chloride, form ions in water in the same way.
Together, chloride and sodium make up almost 86 percent of
the ions dissolved in ocean water.
Ocean water also contains smaller amounts of about a
dozen other ions, including magnesium and calcium, and
other substances that organism need, such as nitrogen and
phosphorus.
In most parts of the ocean, the salinity is between 34 and 37 parts
per thousand. But near the surface, rain, snow and melting ice add fresh
water to the ocean lowering the salinity there. Salinity is also lower near the
mouths of large rivers such as the Amazon and Mississippi. These rivers
empty great amounts of fresh water into the ocean.
Evaporation, on the other hand increases salinity, since the salt is left behind
as the water evaporates. For example, in the Red Sea, where the climate is
hot and dry, the salinity can be as high as 41 parts per thousand. Salinity can
also be higher near the poles. As the surface water freezes into ice, the salt is
left behind in the remaining water.
Salinity affects several properties of ocean water. For instance,
ocean water does not freeze until the temperature drops about
-1.9 C. the salt acts as a kind of antifreeze by interfering with the
formation of ice crystals. Salt water also has a higher density
than fresh water. That means that the mass of one liter of salt
water is greater than the mass of one liter of fresh water.
Because its density is greater, seawater has greater buoyancy. It
lifts, or buoys up, less dense objects floating in it. This is why an
egg floats higher in salt water than in fresh water.
Just as land organisms use oxygen and other gases in the air,
marine organisms use gases dissolved in ocean water. Two
gases found in ocean water that are necessary for living things
are oxygen and carbon dioxide.
oxygen in seawater comes from the atmosphere and
from algae in the ocean. Algae use sunlight to carry out
photosynthesis, releasing oxygen into the water in the process.
Oxygen is scarcer in seawater than in air and is most plentiful
near the surface. Carbon Dioxide, on the other hand, is about
60 times as plentiful in the oceans as in the atmosphere. Algae
need carbon dioxide for photosynthesis. Animals such as corals
also use carbon dioxide, which provides the carbon to build
their hard skeletons.
in New England, the news reports on New Year’s Day often feature the shivering members of a
“polar Bear Club” taking a dip in the icy Atlantic Ocean. Yet on the same day, people enjoy the
warm waters of the Puerto Rico beach. Like temperature on land, temperatures at the surface
of the ocean vary with location and the seasons.
the broad surface of the ocean absorbs energy from the sun. because warm water is
less dense than cold water, this warm water stays as a layer on the surface. Near the equator,
surface temperatures often reach 25 C, about room temperature. The temperature drops as
you travel away from the equator.
the temperature of water affects the amount of dissolved oxygen it can hold. The
cold waters in the polar regions contain more dissolved oxygen than warm, tropical waters.
But there is still enough oxygen in tropical seas to support a variety of organisms.
Gazing down into the blue-green water from the deck of
a ship, you might think that the vast volume of water
beneath you is all the same. But in fact, conditions
change dramatically from the surface to the depths. If
you could descend from the surface to the ocean floor,
you would pass through a vertical section of the ocean
referred to as the water column.
you would observe a pattern. Temperature decreases as
you descend through the water column. The first zone,
the surface zone typically extends from the surface to
between 100 and 500 meters. Next is the transition
zone, which extends from the bottom of the surface
zone to about one kilometer. The temperature drops
very quickly in the transition zone, to about 4 C. below
the transition zone is the deep zone. The temperature in
the deep zone is a constant 3.5 C or colder in most of the
ocean.
Pressure is the force exerted by the weight of water above pressing down. Pressure
increases continuously from the surface to the deepest part of the ocean. The
average depth of the ocean floor is 3.8 kilometers. There the pressure is about 400
times greater than the air pressure at the Earth’s surface.
Pressure is one obstacle facing scientist who want to study the ocean. A
diver can descend safely only to about 40 meters. To survive in deeper water,
scientists must use a submersible. A submersible is an underwater vehicle built of
strong materials to resist pressure. In a submersible, scientist can directly observe
the ocean floor, collect samples, and study deep ocean water chemistry.