## Lab 8.2 – How do DO levels correlate to seawater temperatures?

Fundamental concept: Compare expected and observed relationship between dissolved oxygen and water temperature
Estimated time to complete
: 45 minutes
Data skills preparation: Lab 2.1 – Time series, Lab 2.5 – Vertical sections
Materials needed: None

In this activity we will add a new data set collected over the same time at the same place, seawater temperature. We will look for patterns in how these two data sets may correlate with each other.

Because we are now looking at two variables you may wish to review how they can be related to each other. Where do we find cold water in the ocean? Where do we find warm water? Where do we find higher levels of dissolved oxygen? Where do we find lower levels of dissolved oxygen?

Use the graph to answer the following questions. When you hover over a data point, a box will pop up with more information. You can turn zoom and out of areas of the graph using the slider bar located below the diagram.

### Interpretation Questions

1. How many periods of prolonged low temperatures (less than 10°C for more than two days) do you see in these data?
2. Compare the two interactive graphs. What do you notice about the trends in temperature and DO?
3. Does DO change at the same pace (rapid or slow) as the seawater temperature?
4. Describe the typical “textbook” relationship between temperature and dissolved oxygen. If you had a beaker of water and you heated it up, as the temperature went up would the dissolved oxygen level in the water increase or decrease?
5. Does the pattern shown in the graphs fit the relationship you described in question 4? Explain why or why not.

### Application Questions

1. In a general way, where in the ocean do you expect colder water to occur, and where in the ocean do you expect warmer water?
2. The following figure shows us seawater temperature along a transect across the shelf by Endurance Glider #384, near our study area. The colors represent different temperatures. The seawater temperature data we are examining was collected in approximately 25 m of water. Use this vertical section graph (Figure 8.2.1) to estimate the expected temperature of seawater off the Oregon coast at 25 m below the surface. Complete this statement: The water temperatures at this depth are greater than ______°C.
1. The temperature data shown in the interactive time series graph at the top of this activity was collected at a depth of approximately 25 m. Review your answer to Quick Check question #4 to find the minimum temperature of the time series. Then locate that temperature on the vertical section graph color scale (Figure 8.2.1) and complete this statement: The coldest water temperatures observed in our interactive data set above are equivalent to the temperature of water observed at _____ m depth in the vertical section.
2. Use the information from the vertical sections (Figure 8.2.1; Application questions 7-8) to formulate a hypothesis as to why the seawater temperature and dissolved oxygen content changed in the pattern you observed in the time series graphs (Interpretation questions 1-5). What other sorts of data might be needed to test your hypothesis? If you are having trouble developing a hypothesis, you may wish to review the concepts and quick check questions in the Lab 8 introduction.