Exploring Our Fluid Earth

Fig. 2.1. Salt evaporation ponds on the shores of San Francisco Bay. The bright colors are due to the different microorganisms living in the hypersaline ponds.

Image courtesy of Doc Searls

Salt evaporation ponds on the shores of San Francisco Bay illustrate a variety of processes and the connections between physical, chemical, and biological aquatic science (Fig. 2.1). In the open ponds, water evaporates—molecules of water escape from the ponds into the atmosphere. As water evaporates, salt is left behind. The more water that evaporates from the ponds, the higher the salinity of the water remaining becomes. Very salty water is called hypersaline water. Different microorganisms are able to survive and thrive in the ponds at different levels of salinity. These organisms include red and green algae and orange brine shrimp. When all of the water has evaporated from salt water, only crystallized white salt remains. This can be seen along the edge of the pond on the bottom right of Fig. 2.1. Dissolving, evaporating, crystallizing, metabolizing, photosynthesizing, and respiring—all of these are processes are made understandable by knowing how atoms and molecules interact. Water plays a special role in these processes. Understanding the chemistry of seawater leads to a better understanding of the nature of and interactions of molecular matter.

Ocean Literacy Principles

Principle 1: The earth has one big ocean with many features.
Ocean Literacy Fundamental Concept: Most of earth’s water (97 %) is in the ocean. Seawater has unique properties; it is saline, its freezing point is slightly lower than that of fresh water, its density is slightly higher, its electrical conductivity is much higher, and it is slightly basic. The salt in seawater comes from the eroding land, volcanic emissions, reactions at the seafloor and atmospheric deposition. (OLP 1e)

To build an understanding of the unique properties of seawater and how the land and the ocean interact, it is important to understand the substances dissolved in seawater. The physical, chemical, and biological interactions of seawater are affected by the types of substances dissolved in it, as well as the properties, sources, and concentrations of these substances.

These concepts will be explored in this unit through the following activities and investigations:

• Activity: Recovering Salts from Seawater
• Activity: Organizing the Elements
• Activity: Electrostatic Forces
• Question Set: Atoms, Molecules and Compounds
• Activity: Concentration and Dilution
• Question Set: Concentration
• Activity: Elemental Abundance in Nature
• Activity: Parts per Thousand
• Question Set: Using the Periodic Table to Predict Ion Formation
• Question Set: Ions in Seawater
• Question Set: Ionic Compounds
• Question Set: Salts are Ionic Compounds
• Question Set: Comparing Ionic and Covalent Compounds