Lab 7.2 – What is the relationship between Chlorophyll-a and other abiotic variables?

Estimated time to complete: 45 minutes
Materials needed: None

Primary production (chlorophyll-a) is influenced by a number of abiotic variables. What can you observe about the relationship between primary production and irradiance, SST, salinity, and nitrate in the temperate Atlantic Ocean?

Use the graph to answer the following questions. You can turn on and off different variables to compare to chlorophyll-a (click the box next to the variables listed below the graph). You also can adjust the date range shown by using the slider bar.


Orientation questions

  1. Examine each abiotic variable and note the following: How does the variable vary by season? During which month(s) does it tend to be higher? How high on average? During which month(s) does it tend to be low? How low on average?
    • Irradiance
    • SST
    • Salinity
    • Nitrate (phytoplankton need a variety of nutrients; in this exercise we examine one of them, nitrate)

Interpretation questions

  1. Which dataset(s) are most strongly tied to the seasons?
  2. Which dataset(s) are least strongly tied to the seasons?
  3. Compare primary production to each of the abiotic variables; do you notice any relationship? For each of the following variables, describe any relationships with chlorophyll-a you observe.

    • Irradiance
    • Temperature
    • Salinity
    • Nitrate
  4. Synthesize your observations by explaining which factors lead to the pattern of primary production shown. Explain why chlorophyll-a and the three abiotic variables are related in this manner. What is responsible for these patterns and relationships? How do the different variables affect each other? How does that result in the pattern of chlorophyll-a (primary production) shown?

Assessment question

  1. Select one variable. Imagine that it either increased or decreased dramatically. Predict the changes that would occur or not occur in all of the other variables.