## Lab 2.4 – Vertical sections

Fundamental concept: Variability in the data, finding trends
Estimated time to complete: 30 minutes
Materials needed (none)

### How can the data from lots of station profiles be combined into one easy to read graph?

How can the data from lots of station profiles be combined into one easy to read graph? Station profiles show the structure of the water column well, but they do that at just one place. Sometimes oceanographers need to know how the structure changes across the ocean, across the continental shelf, or across a bay. A data product called a vertical section provides a way to show the data from lots of station profiles making it easy to look at the change in structure in space. One OOI data set used this type of data to help unravel the reason the crabs on the Oregon coast were dying. Let’s take a look at a vertical section and see how it is related to station profiles. This will give you the tools you need to do the Anoxia module (Lab 8), and discover how, and why, changing water conditions kills crabs and fish on the Oregon continental shelf.

Vertical sections show changes in a property (such as temperature in the one below) by using either color coding or contour lines, or both. So they are similar to contoured or color coded bathymetry maps, but they use color to show the value of some property (in this case temperature) other than water depth. Look at the figure. Note how the sea surface is at the top, and water depth increases as you go down. Horizontal distance is on the x-axis. So the figure essentially represents a vertical wall of water, as if the ocean were sliced top to bottom and one side of the slice is shown. Vertical sections use contouring to map the changes in a property on this vertical surface. The figure below shows a slice of temperature at the edge of the continental shelf of the Coastal Pioneer array, measured by a glider in February 2017.

Figure 2.4.1 Contour graph of temperature at shelf break

1. In the vertical section, which colors represent warm water?  Which represents cool water?
2. Describe the change in temperature from surface to bottom, based on this color coding, near the left side of the vertical section. This is over the outer continental shelf.
3. Describe the change in temperature from surface to bottom on the right side of the vertical section. This is in deeper water over the continental slope. The water column is much deeper than 180 meters, but the glider stopped at that depth.
4. Would you say that there is a consistent trend in the way the temperature changes with depth?

Next, we will make a more precise assessment of the variation in temperature with depth in the vertical section. The figure below is a copy of the temperature vertical section measured by a Pioneer array glider, with two stations (A and B) marked.

Figure 2.4.2 Temperature contour graph

Imagine that we collected a station profile at location A. Draw a station profile graph with depth on the y-axis and temperature on the x-axis. If you need assistance with plotting this graph, see the animation at the bottom of this page. When you are done, click the link below to check your answer.

1. Now draw a station profile for location B. The portion of the water column near the surface with uniform temperature is called the surface mixed layer. The surface mixed layer at station A extends to 50 m deep. How deep is the surface mixed layer at Station B?
2. Below the surface mixed layer, temperature changes rapidly with depth. This is called the thermocline. At what depth does the temperature stop changing rapidly as depth changes? In other words, if you could dive into this part of the ocean, at what depth would you stop experiencing a lot of temperature change?
3. In the vertical section, how do the colors show us depths with rapidly changing temperature vs. uniform temperature? How do the contour lines show us this same information?