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Earth Systems:
Notes- Section 15.2
Salinity
 Salinity is defined as the amount of dissolved _____________ in _________________.
 Oceanographers express salinity as ___________ of salt per______________ of water, or
parts per thousand (ppt).
• The total salt content of seawater averages 35 ppt, or _______%.
 From the map, where is the salinity (in parts per thousand) the highest?
________________________________ Where is it the lowest?
__________________________________________
Seawater
• Essentially____________ and a complex solution of _____________.
• These salts comprise approximately _________% (by weight) of seawater.
• This percentage may appear small but the quantities of salt in the ocean are enormous.
• If all the ocean water was evaporated, there would still be a layer of salt_____ m thick
covering the entire ocean floor.
Seawater’s Elements
• Several elements can be found in this complex solution of salts in seawater.
• The most abundant salt is ________________, otherwise known as common table salt
(NaCl).
• Sodium chloride comprises almost ______% of all the elements in the salt solution.
• Sodium chloride combined with the next three most abundant salts:
__________________________, ______________ and _____________________
comprise about 99% of the elements found in seawater.
• However, the traces of the remaining elements are very important in maintaining the
necessary chemical environment for _______ in the sea.
Regional Changes
• In subtropical regions where rates of _____________exceed those of
_________________, salt left behind by the evaporation of water molecules accumulates
in the surface layers of the ocean. There, salinity can be as high as _______ ppt.
• In equatorial regions where precipitation is abundant, salinity is lower. Even lower
salinities of _____ or ____ ppt occur in Polar Regions where seawater is diluted by
melting sea ice.
• The more precipitation (or water), the ________ salinity
 (likewise, the less precipitation/water, the _____________ salinity)
Diversity of Salinity Levels
• In areas where evaporation is far greater than precipitation, such as the ___________
________ or _____ ________, the salinity levels may exceed _____%.
• In contrast, areas which are supplied by a lot of fresh water via rivers or precipitation,
such as the _________ _______, the salinity level is often below ______%.
• Generally, the salinity levels of the open ocean range from ______% to ______%.
• The lowest salinity often occurs where _________ ________ empty into the oceans,
creating areas of water called _____________
Sources and Removal of Sea Salts
• What is the primary source of the salt in the sea?
• The chemical weathering of the rocks on the continent is delivered to the oceans by
streams and rivers at an estimated ______ billion tons annually.
• Although, rivers continually add salts to the oceans, the ________ of seawater is not
_________.
•
•
•
This is because the salts are being ____________just as quickly as they are being added.
Water evaporates from seawater and leaves __________ salt behind.
Marine organisms remove ions from seawater to build ___________, bones, and
___________.
• As organisms die, their _______ _________ accumulate on the seafloor and become part
of the bottom sediments.
• Winds can also pick up salty droplets from breaking waves and deposit the ______
further inland.
Physical Properties of Seawater – Density
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• Freshwater has a maximum density of _____ g/cm .
• Because salt ions add to the overall mass of the water in which they are dissolved, they
increase the _______________ of the water.
• Seawater is denser than _______________, and its density increases with salinity.
• Temperature also affects density - __________ water is denser than warm water.
• Because of salinity and temperature variations, the density of seawater ranges from
3
3
__________ g/cm to __________ g/cm .
• Is it easier to float in the ocean or in Lake Allatoona? __________________ Why?
__________________
Physical Properties of Seawater- Freezing Point
• Variations in ___________ cause the freezing point of seawater to be somewhat lower
than that of ____________. Freshwater freezes at 0°C.
• Because salt ions interfere with the formation of the crystal structure of ice, the freezing
point of seawater is -2°C.
• Why to people put salt on icy sidewalks and roads?
__________________________________________________________________ At
what temperature is the salt most effective? ____________________________
Physical Properties of Seawater- Absorption of Light
• Light only penetrates the upper 100 m of seawater. Below that depth, everything is ____.
• In the darkness of the deep ocean, some organisms including some fish, shrimp, and crab,
are _______.
• Other organisms attract prey by producing light, called_____________, through a
chemical reaction.
Ocean Temperature Layering
• Ocean surface temperatures range from _____°C in polar waters to 30°C in equatorial
regions, with the average surface temperature being _____°C.
• Ocean water temperatures, however, decrease significantly with depth.
• Deep ocean water is always ______, even in tropical oceans. It ranges from 0°C to 3°C.
• Beneath roughly 100 m, temperatures decrease continuously with depth to around
______°C at 1000 m. The dark waters below 1000 m have fairly uniform temperatures
of less than 4°C.
• Based on these temperature variations, the ocean can be divided into _______ layers.
1) The first is a relatively warm, sunlit surface layer approximately _____ m thick.
2) The second is a transitional layer known as the ___________, which is characterized by
rapidly decreasing temperatures with depth.
3) The third layer is a cold and dark bottom layer with temperatures near ____________.
• In general, ocean layering is caused by ____________ differences.
• Because cold water is more dense than ______ ________, cold water sinks to the
bottom, while less-dense, _______ _________ is found near the ocean’s surface.