Transcript Seawater Properties - Marine Biology Honors

Seawater Properties
Seawater
• How did the water get
salty?
1. Chemical
weathering of rocks
on land
2. From the Earth’s
interior
Salt Composition
• 6 ions make up over
98% of the solids in
seawater
• Sodium and Chloride
account for 85% of
those solids.
Salinity
• Is defined as: the total
amount of salt dissolved
in seawater.
• Average salinity of the
ocean is 35 ‰ or 35 parts
per thousand.
• Salinity is also expressed
in grams/liter.
• Changes in salinity are
controlled by the addition
(rain or snow) or removal
(evaporation or freezing)
of pure water.
Temperature (T), Salinity (S)
and Density (D)
• Temperature varies greatly in the
ocean (between -2 ºC to 30 ºC).
This has a strong influence on
density.
• Density is mass/volume. It is
measured in g/cm3, g/ml or g/L.
• A Hydrometer is the instrument
used to determine density.
• Salinity and temperature affect
the density of water (as salinity
and temperature decrease,
density increases).
TSD Diagram
Ideal Aquarium Conditions
• Temperature: 25-26.6ºC
• Salinity: 35 parts per thousand (ppt), ‰
• Density: 1.020-1.024 g/cm3
Dissolved gasses
• 3 most important
gasses in the ocean:
– Oxygen
– Carbon Dioxide
– Nitrogen
• Gasses dissolve
better in cold water.
• Marine animals affect
the amount of
dissolved gasses in
the ocean.
Dissolved Oxygen (D.O.)
• 0-9 mg/L in seawater.
• 21% in atmosphere.
• Major source of D.O. is
photosynthesis.
• 50% of atmospheric O2
is from diffusion from the
ocean.
• At the surface an
increase in temperature
or salinity = decrease in
the amount of D.O. that
can be dissolved.
Transparency
• Seawater is relatively
transparent so sunlight
can penetrate fairly deep
into the ocean (which
helps plants to grow).
• Transparency depends
on what is suspended
and dissolved in the
water.
• Different colors of light
penetrate to different
depths of the ocean.
Blue light penetrates the
deepest, red light the
least.