15.1 Composition of Seawater
Salinity
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The total amount of solid material dissolved in water
Mass of dissolved substances : Mass of the water sample
Shown in %
Most of the salt in seawater is Sodium Chloride (NaCl),
common table salt
Sources of Sea Salts
 Chemical weathering of rocks on the continents is a
source of elements found in seawater
 Reach oceans through runoff from rivers and streams
 Another source is of elements found in seawater is
from Earth’s interior
 Through volcanic eruptions, large amounts of water
vapor & other gases have been emitted into the
atmosphere
Processes Affecting Salinity
 Surface salinity varies in the ocean normally from 33% 38%
 Variations in salinity result from changes in the water
content of the solution
Continued…
 Add freshwater to saltwater
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Precipitation
Runoff from land
Icebergs melting
Sea ice melting
 Remove freshwater from saltwater
 Evaporation
 Formation of sea ice
Ocean Temperature Variation
 Ocean’s surface water temperature varies with the
amount of solar radiation it gets. (Fxn. of latitude)
 Surface waters = higher temperatures (in LL)
 Deeper waters = lower temperatures (in LL)
 Thermocline is the layer of ocean water btw 300 m –
1000 m where rapid change of temperature is seen
with depth
 Vertical barrier to many types of animals
CONTINUED…
 In HL (high latitude)…
 Surface water = cooler than in LL
 Deeper water = similar to the surface temperature
 Curve is vertical
Ocean Density Variation
 Density – mass per unit volume
 Pycnocline – layer of ocean water btw 300 m – 1000
m where there is a rapid change of density with depth
 Saltwater density is influenced by two factors…
 Salinity
 Temperature
 Most important factor affecting saltwater density
 Inversely proportional to density
Ocean Layering
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Layered according to denisty
Low density is near the surface
Higher density is near the bottom
3 layered structure
 Shallow surface mixed zone
 Transition zone
 Deep zone
Continued…
 Surface Zone
 Warmest water temperature
 Transition Zone
 Temperature falls quickly
 Distinctive layer between warm surface layer & the deep
cold layer
 Deep Zone
 Sunlight never reaches this zone
 Right above freezing
Review Questions
 What is salinity?
 Explain how latitude and sea surface temperature
relate.
 What are the 3 main zones of the ocean?
 Where would more dense water be found? Less
dense water?