Focus question: students will write the focus question in their notebooks Seawater Composition Almost anything can be found in seawater. This includes dissolved materials from Earth's crust as well as materials released from organisms. The most important components of seawater that influence life forms are salinity, temperature, dissolved gases (mostly oxygen and carbon dioxide), nutrients, and pH. Each of these is discussed below along with how it varies (or does not vary) and its influence on marine life.

Salinity map showing areas of high salinity (36 o/oo) in green, medium salinity in blue (35 o/oo), and low salinity (34 o/oo) in purple. Salinity is rather stable but areas in the North Atlantic, South Atlantic, South Pacific, Indian Ocean, Arabian Sea, Red Sea, and Mediterranean Sea tend to be a little high (green). Areas near Antarctica, the Arctic Ocean, Southeast Asia, and the West Coast of North and Central America tend to be a little low (purple).

The salinity of seawater is usually 35 parts per thousand (also written as o/oo) in most marine areas. This salinity measurement is a total of all the salts that are dissolved in the water. Many marine organisms are highly affected by changes in salinity. This is because of a process called osmosis,until an equilibrium is reached. Marine organisms respond to this as either being osmotic conformers (also called poikilosmotic) or osmotic regulators (or homeosmotic

If a marine osmotic conformer were put in fresh water (no salt), osmosis would cause water to enter its cells (to form an equilibrium), eventually causing the cells to pop (lysis). If a marine osmotic conformer were put in super salty water (greater than 35 o/oo salt) then osmosis would cause the water inside the cells to move out, eventually causing the cells to dehydrate (plasmolyze). These marine osmotic conformers include the marine plants and invertebrate animals which do not do well in areas without a normal salinity of 35 o/oo.

OSMOTIC CONFORMERS

Osmotic regulators have a variety of mechanisms to control osmosis and the salt content of their cells varies.. Marine osmotic regulators include most of the fish, reptiles, birds and mammals. These are the organisms that are most likely to migrate long distances where they may encounter changes in salinity.The fish is about 18 o/oo salt so in seawater it tends to dehydrate and constantly drinks the seawater. Special cells on the gills (called chloride cells) excrete the salt so the fish can replace its lost water. When a salmon migrates to fresh water its cells start to take on water so the salmon stops drinking and its kidneys start working to produce large amounts of urine to expell the water.

How does the temperature change at different areas? Seawater temperature map showing areas of warmer water in red and areas of cooler water is blue. White areas represent ice. Notice the upward finger of cold water in the South Pacific off of South America and the downward finger of cold water in the North Pacific off of the West Coast of the USA. The reasons for these become apparent when you learn about the major ocean currents

How are the cold blooded and warm blooded organisms are affected by the temperature and pH change? Marine algae (left) and marine green turtles (right), a reptile, are cold blooded.

The walrus (left) and dolphins (right) are warm blooded.  Warm blooded (homeothermic) marine organisms have some type of internal temperature controls to maintain a constant body temperature.  What are the other ectothermic and endothermic organisms?

What is pH and how does it affect organisms? pH is a measure of the acidity or alkalinity of a substance and is one of the stable measurements in seawater. Ocean water has an excellent buffering system with the interaction of carbon dioxide and water so that it is generally always at a pH of 7.5 to 8.5. Neutral water is a pH of 7 while acidic substances are less than 7 (down to 1, which is highly acidic) and alkaline substances are more than 7 (up to 14, which is highly alkaline). Anything either highly acid or alkaline would kill marine life but the oceans are very stable with regard to pH. If seawater was out of normal range ( ) then something would be horribly wrong.

Student Activity 1- How do you determine the pH of different substances? Students will set up the Lab Pro sensors and determine the pH of different substances- Name of the substance pH valueAcidic or Basic? Substance 1 Substance Unknown substance- ? given?

Differentiated students Activity Students will explore in groups different activities. Students will do a presentation and Summarize. Assignment- 2 Extra credits-The production of salt has an interesting history. Relate your knowledge of history to science by reporting on salt production, both ancient and Modern. Apply your knowledge of pH to our daily life and present a report.