Mini Lesson

Historical Ocean Salinity Data: Annual Mean Data

Historical Ocean Salinity Data: Annual Mean Data

Analyze the first of three graphs of historical ocean data in this series; this mini-lesson features salinity values using the interactive tool, FlatMap, created by NASA's Aquarius Mission. The others evaluate temperature and density for the same locations. Teachers can use the pre-plotted graphs provided here for quick-use or consider integrating the FlatMap tool in your instruction.  Flatmap allows the learner to create in-water profiles of up to six locations of salinity, temperature, and density data sets averaged over a year. These data are also downloadable as Excel files. 

Mini Lesson

Ocean Salinity:

1.  Open this link to show the interactive map of surface salinity used to create in-water profiles of how the salinity changes with depth (NOTE: Profiles of temperature and density may also be created using this tool). 

  • How did we know that map shows only surface conditions?  [The title reads Mean Salinity (psu) at 0m Depth.]
mapped locations
Credit: NASA Aquarius Annual Mean Salinity Map

2. Review the color bar with your students.  The high salinity values are in red (37 psu) and the lowest is 32 psu in blue.

    3. Help students locate the blue, green, and red dots showing key locations for maps and in-water salinity profiles

    • 5N, 24W
    • 18S, 20W
    • 62S, 34W

    4. Click the "Plot" button, located below the "Selected Location List" box. In-water profiles from these locations will appear at right. 

    Aquarius; In-Water Profiles for Salinity
    Credit: Aquarius; In-Water Profiles for Salinity

    5. Review the features of the graph with the students. Connect the locations of the different plots with the mapped image above.  

    6. Direct students to work with their peers in addressing the following question:

    How does salinity vary with depth? Describe by using evidence for the three sites. 

    Possible answers could include:

    • The blue profile - from the equatorial Atlantic Ocean (5N 24W)  - shows relatively low salinity at the surface, an increase in the top 50 meters , and then a decrease below 50 meters.
    • The green profile is located in in the central South Atlantic Ocean (18S, 20W), a region with very high surface salinity. It shows an unusual gradient with depth: salinity decreases from 37 Practical Salinity Units (psu) to 35 psu in the upper 300 meters (984 feet).
    • The red profile is from the Southern Ocean (62S, 34W), a region with low surface salinity. It's the only profile that shows a steady increase of salinity in the top 300 meters and constant salinity values below that. Of these selections, the red profile shows the least variability in salinity in the upper 300 meters. For the other locations, much of the salinity change occurs within the top 200 meters (656 feet), a salinity minimum is reached at about 1000 meters depth (3281 feet), while salinity is fairly constant below 1500 meters (4921 feet) depth.
    • You can select other locations (i.e., by clicking on the map and hitting "Plot") to see how salinity varies with depth at various locations.

    7.  Next, analyze the next mini lesson, Historical Ocean Temperature Data: Annual Mean Data, to explore the relationship of salinity and temperatures.