1. Ocean Water
Earth Science Ch. 15

2. 15.1 The Composition of Seawater
Seawater consists of about 3.5% dissolved minerals that are collectively called salts.
Salinity: solid material dissolved in water.
Salinity is the ratio of the mass of dissolved substances to the mass of the water sample.
Salinity is expressed in parts per thousand (0/00).
The average salinity of seawater is 350/00
Most of the salt in seawater is NaCl.
Cl: 55%, Na: 31%, Other elements: 14%

4. Processes that decrease salinity by adding fresh water
Sources of Sea Salts
Chemical weathering of rocks on the continents. The salts enter the ocean by runoff
Volcanic eruptions
Processes that decrease salinity by adding fresh water
Precipitation
Runoff from land
Melting of icebergs and sea ice
Processes the increase salinity by removing fresh water
Evaporation
Formation of sea ice

5. Ocean Temperature Variation
The ocean’s surface water temperature is affected by the amount of solar radiation received, which is primarily due to latitude.
The angle of the sun’s rays at different latitudes affects the intensity of solar radiation.
Higher latitudes (near the poles) have lower surface temperatures because of the lower angle of the sun’s rays.
Lower latitudes (near the equator) have higher surface temperatures because of the higher angle of the sun’s rays.

6. Surface water generally have higher temperatures than deeper waters.
Low latitudes
temperatures are high near the surface
The temperature decreases rapidly with depth.
This area of rapid decrease in temperature is called the thermocline

7. High latitudes
the temperature of the water at the surface is similar to that in deep water.
Ocean water at high latitudes has no themocline.
Water that has no thermocline is called isothermal.

9. Ocean Density Variation
Density differences cause a layering effect in oceans.
Seawater density is affected by 2 main factors: salinity and temperature
An increase in salinity increases seawater density. Increases in salinity increase buoyancy.
An increase in temperature decreases seawater density.
Of the 2 factors, temperature has a greater influence on density.
Cold water with high salinity would have the greatest density.

10. Density of ocean water varies with depth. Low latitudes
density dramatically rises with depth in an area is called the pycnocline.
High latitudes
density is similar throughout the water column. There is no pycnocline.

11. General patterns in ocean water
Temperature
Decreases with depth
Due to lack of solar energy
Thermocline: largest decrease
Salinity
Due to less evaporation
Halocline: largest decrease
Density
Increases with depth
Due to surrounding water pressure
Pycnocline: largest increase

12. Oxygen Dissolved Nutrients Solar Energy Life
Decreases with depth due to lack of photosynthetic organisms and consumption of oxygen by organisms at the surface
Dissolved Nutrients
Decreases with depth due to use by organisms at the surface
Solar Energy
Decreases with depth due to lack of sunlight
Life
Decreases with depth due to lack of oxygen and nutrients available

14. Ocean Layering The ocean is layered according to density.
Low density water is found near the surface and high density water is found below.
The highest density water is found at the greatest ocean depths.
The open ocean has a 3 layered structure:
Shallow surface mixed zone
Higher temperatures and mixing by waves and currents
Transition zone
Temperature drops quickly
Deep zone
No sunlight, freezing, high density

15. Layering only occurs in low latitude regions.
In high latitude regions cold, high-density water forms at the surface, sinks, and forms a deep ocean current that travels toward the equator.
The water at the equator moves toward the higher latitudes by surface currents which are generated by winds.
This entire process is caused by convection
Cools – sinks – heats – rises

18. 15.2 Diversity of Ocean Life
The success of marine organisms in the ocean depends on 3 factors:
Ability to avoid predators
Ability to find food
Ability to cope with challenges of their environment

19. Classification of Marine Organisms
Marine organisms can be classified according to where they live and how they move.
They are classified as either:
Plankton – floaters (algae, bacteria, small animals)
Nekton – swimmers
Benthos – bottom dwellers (sea stars, crabs)
Most marine organisms live in the sunlit surface of the ocean where photosynthesis is possible.
Photosynthesis
H2O + CO2 + sunlight = O2 and C6H12O6
Organisms that undergo photosynthesis provide food and produce oxygen.
Algae are an important source of oxygen

21. Hydrothermal vents Found along the mid ocean ridge
Water very hot and saturated with minerals
The precipitation of the minerals gives the water the appearance of black smoke
Chemicals from the vents are an energy source for bacteria
The bacteria produce sugars and food that enable them and other organisms to survive in this extreme environment

23. Marine Life Zones
3 factors are used to divide the ocean into distinct marine life zones:
Availability of sunlight
Distance from shore
Water depth

24. Availability of sunlight
The part of the ocean into which sunlight penetrates is called the photic zone
The photic zone is the area where light is strong enough for photosynthesis to occur.
Phytoplankton which produce food that feed most ocean life are found in this zone

25. Distance from shore Intertidal zone Neritic zone Oceanic zone
Region between high and low tides
Very harsh place to live due to changing conditions
Neritic zone
Covers the continental shelf
Shallow enough for sunlight to reach the ocean floor
Large number of species
Oceanic zone
Deep ocean
Lower levels of nutrients and smaller populations

26. Water depth Pelagic zone Benthic zone Abyssal zone
Open ocean of any depth
Animals swim or float freely
Benthic zone
Any sea bottom surface
Animals that attach to, crawl upon, or burrow into the seafloor
Abyssal zone
Includes the deep ocean floor
Extremely high water pressure, constantly low temperatures, no sunlight, and sparse life.

28. 15.3 Ocean Productivity Primary productivity
Production of organic compounds from inorganic substances through photosynthesis or chemosynthesis
Two factors influence a region’s photosynthetic productivity: nutrients and sunlight
Primary producers need nutrients such as nitrogen, phosphorus, and iron
The most abundant marine life exists where there are ample nutrients and sunlight

29. Oceanic feeding relationships
Phytoplankton, plants, and bacteria are the main oceanic producers
Only a small percentage of energy taken in at any level is passed on to the next level because energy is lost as heat at each level
The producer’s biomass in the ocean is much greater than the biomass of top consumers

30. Trophic levels
Chemical energy stored in ocean producers is transferred to the other organisms through feeding
Zooplankton are herbivores that consume phytoplankton
Larger herbivores feed on brown algae and marine plants that grow near the shore
The herbivores are eaten by carnivores
Each of these feeding stages is called a trophic level

31. Transfer efficiency
The transfer of energy between trophic levels is very inefficient
Only 2% of the light energy absorbed is stored as chemical energy and made available to the first trophic level
After the first level only about 10% is available for the next level

32. Food chains and food webs
A food chain is a sequence of organisms through which energy is transferred starting with the primary producer, then the herbivore, then the consumer
More often than food chains, a food web is formed where the consumers can feed on a number of different animals, each of which feeds on a variety of organisms
Food webs show how the success or failure of one population could affect other populations

34. How Does El Niño Work?
In normal years, the winds tend to blow from east to west across the waters of the tropical Pacific. The easterly winds push the surface waters westward across the ocean. In turn, this causes deeper, colder waters to rise to the surface. This "upwelling" of deep ocean waters brings with it the nutrients that otherwise would remain near the bottom. The fish populations living in the upper waters are dependent on these nutrients for survival.
During El Niño years, the winds weaken, causing the upwelling of deep water to cease. The consequent warming of the ocean surface further weakens the winds and strengthens El Niño. As the ocean warms, the warmer water shifts eastward and so do the clouds and thunderstorms that produce heavy rainfall along the equator. This results in changes in jet streams (winds aloft), which lead to dry conditions in Indonesia and Australia, and floods in Peru and Ecuador. El Niño events occur on average every 3 to 5 years.