1. Dissolved Gasses
In Sea Water

3. Objectives
Students will be able to explain the source of and significance of dissolved gasses in ocean water.
Students will be able to describe how some marine organisms are able to utilize dissolved oxygen.
Students will understand the effects dissolved gasses have on the pH of water.

4. Photosynthesis and Respiration
Two important dissolved gasses in seawater are Carbon dioxide (CO2) and Oxygen (O2)
Two natural processes that determine the levels of dissolved CO2 and O2 are photosynthesis and respiration.

5. Photosynthesis
During the day marine algae carry out photosynthesis (making simple carbohydrates using sunlight).
6CO2 + 6H2O -> C6H12O6 + 6O2
Photosynthesis removes dissolved CO2 and adds dissolved O2, but only during the day!

6. Respiration
Respiration involves the release of energy stored in nutrients.
It is the opposite reaction to photosynthesis.
It takes place during the day and night.
Respiration adds CO2 to water.

7. CO2 and pH
Increased dissolved CO2 increases the hydrogen ion concentration, lowering the pH.
More acidic or basic?
pH fluctuates slightly during the day/night cycle. Why?

8. Dissolved Oxygen Photosynthetic algae and plants produce O2.
Some is released to the atmosphere, and some is dissolved in the sea water.
Oxygen that is dissolved in ocean water is called dissolved oxygen (DO).

9. Oxygen Intake Organisms take in DO in different ways.
Some through pores and moist cell membranes on body surface.
Some through membranes called gills.

10. DO measured in parts per million.
Ocean water can hold from 1 ppm to 12 ppm of DO.
Air holds ~200 ppm O2.

11. DO Distribution Why is there more DO at the surface?
Why is the O2 minimum zone at 1,000 m and not at the bottom of the ocean?