Ocean Water

Chapter 24, Section 1 - Properties of Ocean Water                                                                                                                             

Atmospheric Gases

• Nitrogen (N2)
• Oxygen (O2)
• Argon (Ar)
• Carbon Dioxide (CO2)
• Water Vapor (H2O)
• Trace amounts of others.

Gases Dissolved in the Ocean

• Nitrogen (N2)
• Oxygen (O2)
• Carbon Dioxide (CO2)
• Small amounts of other gases.

Gases Enter the Ocean By…

• Direct absorption from the atmosphere.
• From streams and rivers.
• Underwater volcanic eruptions.
• Organisms that live in the water.

Temperature and Dissolved Gases

• Warmer water can hold less gas than cold water.
• Cold water at high-latitudes tend to absorb gas.
• Warm, tropical water tends to release gas.

Ocean as a Carbon Sink

• Ocean contains 60 times more CO2 than the atmosphere.
• Dissolved CO2 can remain in the ocean for thousands for years.
• Some carbon is incorporated into shells of marine organisms -> sediments -> sedimentary rock.
• CO2 is a greenhouse gas – helps regulate global climate.

Ocean water is…

• 96.5% water
• 3.5% dissolved solids

Solids Dissolved in the Ocean

• Chlorine
• Sodium
• Magnesium
• Sulfur
• Calcium
• Potassium
• Trace Elements

      (≈70 other elements in very small amounts)

• Ex – gold, zinc, phosphorus, iodine

Sources of Dissolved Solids

• Volcanic eruptions
• Chemical weathering of rock on land
• Chemical reactions between sea water and newly-formed sea-floor rocks


• Concentration of dissolved salts
• Measured in parts per thousand (‰)
• Ex – If 1,000g of ocean water held 35g of salt, the salinity would be 35(3.5%).
• Salinity of fresh water is <1‰ (<0.1%).
• Measured by electrical conductivity.
• Higher salinity = better conductivity.

Affected by…

• Evaporation (Salt is left behind)
• Precipitation (Fresh water is added)
• Freezing (Salt is left behind)


• Depends on location and depth.
• Surface Water
• Heated by Sun.
• Heat distributed downward by mixing
• Waves & Currents
• Fairly constant, down to 100 - 300m.
• Equatorial water:  ≈30oC.
• Polar water:  -1.9o(freezing point).
• Pack Ice – sea ice that completely covers an area of the ocean.
• Insulates water below.
• Thermocline
• A layer (in a body of water) in which temperature drops with increased depth faster than it does in other layers.
• Warmer water in surface layer is less dense, so it can’t mix with deeper water.
• The thermocline marks the boundary.
• Deep Water
• Temp ≈2oC.
• Deep ocean currents flow slowly beneath warm surface currents.
• Holds more dissolved gasses than warm surface water.


• Ratio of mass to volume.
• Expressed as g/cm3 (solids & liquids) g/L (gases).
• Pure water = 1 g/cm3
• Ocean water = 1.020 to 1.029 g/cm3.

• More dissolved solids = more dense.
• Colder temps = more dense.  (To a certain point!)


• Most colors are absorbed by water.
• Red is absorbed fastest.
• Blue tends to be reflected.
• Makes ocean look blue.
• Phytoplankton absorbs red and blue light, reflects green.
• Changes color of ocean.
• Many crustaceans have red pigments, which does not show up underwater.

Chapter 24, Section 2 - Life in the Oceans                                                                                                                                          

Nutrient Cycling

• Organisms help to cycle nutrients and dissolved gases in/out of the ocean water.
• While alive, organisms absorb…
• Carbon
• Hydrogen
• Oxygen
• Sulfur
• Nitrogen
• Phosphorus
• Silicon
• When they die, bacteria digest their remains and release the nutrients back into the water.


• Organisms die, sink to the bottom, and decay.
• Deep water = nutrient storage.
• Upwelling – Movement of deep, cold, nutrient-rich water to the surface.
• Occurs when wind causes surface water to move offshore.  (This draws the cold water up.)
• Opposite convection!
• This brings nutrients to the surface for use.

Marine Food Webs

Most marine organisms live in the upper 100m of water.
Sunlight => Photosynthesis


Free-floating, mainly microscopic, organisms in aquatic habitats.
Form the base of the food web.


Organisms that swim actively in ocean water.
Ex. – Fish, dolphins, squid.


Organisms that live on the ocean floor.
Ex. – Plants, crabs, sea stars, clams.

Ocean Environments

Benthic Zone

The bottom of the ocean (or other bodies of water).
Intertidal – between high & low tide lines.
Sublittoral – on the continental shelf, continually submerged.  (Kelp, algae.  Sea stars, brittle stars, sea lilies)
Bathyal – on the continental slope, down to 4000m.  (Few plants.  Octopi, sea stars, brachiopods)
Abyssal – 4,000 to 6,000m.  No sunlight.  (sponges and worms)
Hadal – Ocean trenches, deeper than 6,000m.  Mainly unexplored.  (Life thought to be scarce.)
Pelagic Zone

The region of a body of water above the benthic zone.

Neritic – Area above the continental shelf.  Abundant light, low pressure, moderate temps.  (Lots of plankton & nekton – fish & seafood!)
Oceanic – Area beyond continental shelf.  Four layers, based on depth.
Epipelagic – sunlit & full of life.

Decreasing sunlight/ life as you get deeper.

Chapter 24, Section 3 - Ocean Resources                                                                                                                                          


• Process of removing salt from ocean water.
• Methods
1. Distillation
• Water is heated, causing it to evaporate.
• Water vapor is cooled, fresh water collected.
§ Requires a lot of energy (expensive).
2. Freezing
• Water is frozen, ice collected and melted.
§ Uses 1/6 the energy of distillation.
3. Reverse Osmosis
• High pressure & special filters are used to separate salt from water.

Mineral & Energy Resources

• Salt
• Petroleum & Natural Gas
• Found in deposits along continental margins.
• ≈ ¼ of the world’s oil is mined offshore.
• Nodules
• Lumps of minerals on the abyssal (deep-ocean) floor.
• May contain Mn, Fe, Cu, Ni, Co, phosphates.
• Hard to get…
• Very deep water.
• Outside of country boundaries à political issues.
• Trace Minerals
• Extracted directly from water.
• Magnesium & bromine.
• Concentration of most dissolved minerals is too small for extraction to be cost-effective.


1. Fishing
• Important source of food, worldwide.
• Overfishing can cause fish populations to collapse.
• Governments manage fishing with limit, size and season laws.
2. Aquaculture
• Raising aquatic plants/animals for human use/consumption.
• Ex. – Catfish, salmon, oysters, shrimp.
• Pollution can be an issue (affects/created by farm).
• Ocean farms produce more food than agricultural farms – they can farm at various depths          (instead of just on the surface).


• Ocean as a dumping ground…
• Garbage
• Sewage
• Nuclear waste
• The ocean naturally dilutes and destroys wastes.
• Increased human population produces waste faster than the ocean can break it down.
• Coastal areas at greatest risk => closest to source.
• In some places, fish are unsafe to eat.