Ocean Dissolved Gases
Seawater has many different gases dissolved in it,
especially nitrogen, oxygen and carbon dioxide. It
exchanges these gases with the atmosphere to keep a
balance between the ocean and the atmosphere. This
exchange is helped by the mixing of the surface by
wind and waves. Temperature and Pressure also play a
role in the amount of gases found in different parts of
the ocean.
Gases and life
Dissolved oxygen and carbon dioxide are vital for marine life. Marine plants use dissolved carbon dioxide,
sunlight and water to make carbohydrates through the process of photosynthesis. This process releases
oxygen into the water. All marine organisms use oxygen for respiration, which releases energy from
carbohydrates and has carbon dioxide and water as byproducts. Marine animals with gills, such as fish, use
these organs to extract oxygen from the seawater.
Variation in dissolved gases
Some of the properties of seawater affect how much gas can be dissolved in it:



Cold water holds more gas than warm water. You will have seen this with bottles of sodas, which are
basically carbon dioxide in water. Warm sodas cannot hold its gas, so as soon as you open a bottle of it,
the carbon dioxide leaves the water in a big spray of bubbles. It is less messy to open a cold bottle of
soda.
Seawater with low salinity holds more gas than high salinity water.
Deep water, which has a high pressure, holds more gas than shallow water.
The use and creation of dissolved gases by living things can over-ride the effect of these properties. For
example, warm water with lots of plankton in it can hold more carbon dioxide than cold water with few living
things in it.
Carbon dioxide
Carbon dioxide is one of the most
important gases that dissolve in the
ocean. Some of it stays as dissolved
gas, but most reacts with the water
to form carbonic acid or reacts with
carbonates already in the water to
form bicarbonates. This removes
dissolved carbon dioxide from the
water.
Many plants and animals use the
bicarbonate to form calcium
carbonate shells. When these organisms die, some of
the bicarbonate is returned to the water, but a lot of
it settles down to the sea bed. This process locks up,
for long periods of time, carbon that originated in
carbon dioxide in the atmosphere.
If the ocean and atmosphere stayed the same, there
would be a balance between the concentrations of
carbon dioxide in each, but carbon dioxide levels in
the atmosphere are rising, so more of the gas is
dissolving in the ocean.
Published 22 June 2010
Photosynthesis and
Chemosysnthesis
Photosynthesis and chemosynthesis are both
processes by which organisms produce food;
photosynthesis is powered by sunlight while
chemosynthesis runs on chemical energy.
Ecosystems depend upon the ability of some
organisms to convert inorganic compounds
into food that other organisms can then
exploit (or eat!). In most cases, primary food production occurs in a process called photosynthesis, which is
powered by sunlight. In a few environments, primary production happens though a process called
chemosynthesis, which runs on chemical energy. Together, photosynthesis and chemosynthesis fuel all life on
Earth.
Close up of a tubeworm “bush,” which mines for
sulfide in the carbonate substrate with their roots.
The sulfide is metabolized by bacteria living in the
tubeworms and the chemosynthetic energy
produced sustains both organisms. It is a classic
symbiotic relationship. Lophelia II 2010 Expedition,
NOAA-OER/BOEMRE
Photosynthesis occurs in plants and some
bacteria, wherever there is sufficient sunlight – on land, in shallow water, even inside and below clear ice. All
photosynthetic organisms use solar energy to turn carbon dioxide and water into sugar and oxygen. There is
only one photosynthetic formula: CO2 + 6H2O -> C6H12O6 + 6O2.
Chemosynthesis is the use of energy released by inorganic chemical reactions to produce food.
Chemosynthesis is at the heart of deep-sea communities, sustaining life in absolute darkness, where sunlight
does not penetrate. All chemosynthetic organisms use the energy released by chemical reactions to make a
sugar, but different species use different pathways. For example, the most extensive ecosystem based on
chemosynthesis lives around undersea hot springs. At these hydrothermal vents, vent bacteria oxidize
hydrogen sulfide, add carbon dioxide and oxygen, and produce sugar, sulfur, and water: CO2 + 4H2S + O2 ->
CH20 + 4S + 3H2O.
Other bacteria make organic matter by reducing sulfide or oxidizing methane. Chemosynthetic bacterial
communities have been found in hot springs on land and on the seafloor around hydrothermal vents, cold
seeps, whale carcasses, and sunken ships.
Did You Know?
Our knowledge of chemosynthetic communities is relatively new, brought to light by ocean exploration. The
thriving communities associated with hydrothermal vents shocked the scientific world when humans first
observed a vent on the deep ocean floor in 1977.
The discovery of hydrothermal vents and cold-water methane seeps gave us a new vision of primary
production in the deep sea. The irony is that once scientists knew what to look for, they went to other wellknown ecosystems that were rich in hydrogen sulfides, such as salt marshes, and found the same mutualistic
association of chemosynthetic bacteria and animals that had stunned them in the deep vents.
No one had ever thought to look for them, but these communities were there all along.
http://oceanexplorer.noaa.gov/facts/photochemo.html
1. What are three gases that become dissolved in the ocean waters?
2. What factors help mix the gases into the ocean waters – name at least two:
3. What life form relies on carbon dioxide and what do these life forms make using the carbon dioxide?
4. What gas must be present for all life forms to do respiration, thus getting energy for life activities?
5. What three properties impact the quantity of a dissolved gas mixing into the water?
6. Once carbon dioxide combines with water to make bicarbonate – what do the ocean life forms use the
bicarbonate for?
7. What is the difference between Photosynthesis and Chemosynthesis?