Part 4—Analyze Graphs to Predict the Bloom

Examine the changes in water temperature, density, and salinity at each of the four buoy locations.

• Observe how each parameter changed at the surface and at depth over the year.
• Consider what you learned about stratification and mixing and how these conditions can be detected on your graphs.
• Compare your graphs with the vertical profiles for each season in Part 1. Do you see how each graph represents the annual cycle of mixing and stratification?
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Stratification, or layering, is indicated when the water temperature, salinity and density lines begin to separate, usually in July and August.

Interpret your graphs for each location to understand what was happening to the water column throughout the year and when a bloom might occur. Use the following questions to guide you in making a prediction about the timing and location of the spring bloom for 2009. Refer back to Part 1, or consult other resources as necessary.

• Generally, how do water temperatures change with increasing depth?
• How does salinity change with increasing depth?
• How does density change with increasing depth?
• What do your density graphs look like during times that the water column is mixed? How do the lines on the density graph change as the water becomes stratified?
• Knowing that blooms occur when phytoplankton have ready access to sunlight and nutrients in a floating surface layer, make a prediction of the month or week that a bloom might occur for each buoy location.
• Does your predicted bloom date vary by buoy location? Consider where each buoy is located in the Gulf of Maine. Can you explain any differences in predicted bloom dates based on the buoy locations?
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Water temperatures are more constant at deeper depths. When the water column is mixed, the variables (water temperature, density and salinity) are all pretty close. As the water column stratifies these variables diverge. This usually occurs in the months of July and August.