## Lab 8.1 – What trends or patterns can you observe in dissolved oxygen levels in the ocean at this location?

Fundamental concept: Describe variation of dissolved oxygen over time and compare to vertical variation
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 examine OOI data concerning the amount of dissolved oxygen (DO) in the seawater over a few weeks a few kilometers away from the area where the Oregon Department of Fish and Wildlife filmed the dying crabs in the crab pot. We will look at real data to see if our general understanding of where oxygen is in the ocean, and how it may vary through time, match observations at the Oregon continental shelf location.

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 zoom in and out of areas of the graph using the slider bar.

### Interpretation Questions

1. Most organisms need a DO concentration of 2 mg/L or above to be able to live. Below this concentration, we consider conditions to be “hypoxic,” and if DO falls to approximately 0 mg/L, conditions are “anoxic.” Click the “Draw 2 mg/L Threshold Line” box beneath the graph to bring up a line that marks 2 mg/L, the threshold for hypoxic conditions. Characterize conditions on the seafloor over the weeks that these data were collected. Was hypoxia common, rare, or non-existent during this time?
2. How many longer-term (longer than two days) hypoxic events happened during the interval covered by these data?
3. Use the slider bar to look in more detail at the hypoxic event that started on June 3. For how many days does DO remain below the hypoxia threshold?

### Application Questions

1. What are some ways ocean water becomes oxygenated? Would these processes operate in the same way in all parts of the ocean? What are some differences you might see with depth?
2. Based on depth and temperature, make a hypothesis about which depths of the ocean would be well-oxygenated and which depths would not be.

The following figure (Fig. 8.1.1a below) shows us seawater properties along a transect across the Oregon shelf. These graphs are called vertical sections and show us how temperature, salinity, and dissolved oxygen change with depth along a transect. You may have encountered similar plots if you have worked through Lab 2.5 previously. The data in the vertical sections below were collected by Endurance Glider #384, near our study site. You can see the glider position in relation to our study site in Fig. 8.1.1b: the glider moved from 100km offshore towards our study site closer to shore.

1. For this part of the exercise, we will focus on how dissolved oxygen varies with depth, which we can see on the third panel of Figure 8.1.1a below. Do these real-word data support your hypotheses from questions 4-5? Why or why not?

Figure 8.1.1a. Vertical sections collected by a glider in the Endurance Array.

Figure 8.1.1b. Position of the glider, color-coded by time, during collection of the transects shown in Figure 8.1.1a. Black diamonds show the locations of OOI platforms in the Endurance Array. The time series data of dissolved oxygen that you viewed at the top of this page was collected at the Oregon Inshore Surface Mooring at 44.7°N, 124.0°W (the marker closest to the coast of Oregon).