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Session Five  --  Seaweeds
Session Five  --  Seaweeds


Salinity refers to how much salt there is dissolved in water.

      When rain falls from the sky, it falls as fresh water.  The drops may have a few dust motes in them. and sometimes a little carbonic acid if carbon dioxide from the air has dissolved in the water, but it is pretty pure, and is used by animals and plants on land.  However, despite the steady fall of rain on our planet for billions of years, most of the water on earth is salty, and in the sea.

     What happened?

     Over billions of years, rain fell on the land as well as the oceans.  As the raindrops came in contact with the rocks and soil on land, substances, such as sodium, potassium and calcium, dissolved in the water.  When the water returned to the sea as runoff, it carried the dissolved substances with it.  

     When the water evaporated to go through the water cycle again, it left the heavier molecules of the dissolved substances behind.  Gradually these heavier molecules accumulated in the oceans and changed the salinity of the water.

    The proportion of salt to sea water is 3.5% by weight right now.  That's about a pound of salt to every 3 and a quarter gallons of water.

    When you think about all that water in the ocean -- there must be many, many tons of salt dissolved in it!

     There are different kinds of salts in the water, but the most common salt is sodium chloride, which we call table salt.


10.    Major elements present in constant ratios

>       "Law" of constant proportions

>       Sodium/magnesium always 8.3 for any salinity

>       Sodium/calcium always 25.9

>       Chloride/sulfate always 7.1

>       Happens because water in oceans mixes quickly: in one to two thousand years


4.  "It's dead, Jim."
False again.  It's teaming with life!  Plankton, algae, brine shrimp, and brine flies form the base of a food pyramid that supports one of the largest biomasses on the North American continent.  Vast numbers of birds flock here.  Take a drive out to the Bear River Migratory Bird Refuge and see for yourself.  The whole system is delicate, however, and needs our protection, as evidenced by occasional die-backs or epidemics.

1. "It stinks!"
The Great Salt Lake itself doesn't really stink.  This is a shore phenomenon that is experienced when one is downwind wading out along the mud flats or in the cities on windy days.  Under-muds get churned up by breaking waves.  These muds are rich in organics from brine flies, fly eggs, brine shrimp, algae , etc. which are being decomposed by bacteria in an oxygen-poor environment (a reduction-zone) which gives up a gas that smells a lot like rotten eggs -- Hydrogen Sulfide (H2S). This odor is released and carried by the winds.  So, what does it actually smell like sailing out on "The Great Salt?"  Sailors can tell you.  It is a salty-sea smell, a lot like the ocean!

3. "It's too salty."
At 12-25% salinity, the Great Salt Lake is one of the saltiest seas in the world.


brine shrimp eat a green alga that grows there.  Can survive hot and freezing temperatures. diapause in winter for eggs


Dead Sea

While the salinity of the oceans is 35 grams per liter, in the Dead Sea it reaches 350 to 370 grams per liter, making swimmers extremely buoyant.

Although aquatic life is not possible in these conditions,


or maybe 340 g per liter?

  • The lysocline is the line below which the water is undersaturated with respect to carbonate. It is also called the "CCD" (carbonate compensation depth), and it is a challenge for organisms with calcitic shells. It generally lies 3-4 Km below the surface but may be shallower in shallower waters.


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Photos from archives at Biology Department, University of Bowling Green, Ohio
from NOAA
© 1996,1997, 1998, 1999, 2000, 2002, 2003.   Elizabeth Anne Viau. All rights reserved. This material may be used by individuals for instructional purposes but not sold. Please inform the author if you use it at .