Lab 7 – Instructor Guide

You are here: / / / Lab 7 – Instructor Guide

Lab 7 – Water Masses and Ocean Circulation
Instructor Guide

This lab introduces the concepts of water masses that are characterized by distinct densities due to their temperature and salinity.  In a series of four scaffolded activities, it introduces students to important water masses, how oceanographers distinguish them, and how they are part of ocean circulation. The activities should be completed in order, although the instructor can stop the lab after any particular activity if the necessary learning outcomes have been met. The activities are intended for undergraduate students in Introductory Oceanography courses (for either marine science majors or non-science majors). 

Approximate time involved:

  • Each of the 4 activities may take 30-60 minutes for students to explore, discuss and complete the assigned questions.
  • Instructors should plan to implement one activity per 50 or 60 minute lecture course, or
  • Activities could be assigned in a 3-hour computer lab, or
  • Activities could be assigned as a weekly homework assignment.

Learning outcomes

After completing this lab students will be able to:

  • LO1. Demonstrate basic data literacy in graph interpretation by identifying changes in temperature, salinity and density through time, with water depth, and among water masses.
  • LO2. Describe how variation in water masses at a location can be identified and the impact these variations have on marine organisms.
  • LO3. Interpret a TSD diagram to identify water masses in the ocean.
  • LO4. Predict locations that are sources of deep-water thermohaline circulation and provide evidence to confirm this process. 
Learning Outcome Activity 1 Activity 2 Activity 3 Activity 4
Outcome 1 Introduced  Guided Practice Applied Applied
Outcome 2 Introduced Guided Practice Applied Applied
Outcome 3 N/A N/A Introduced Guided Practice and Applied
Outcome 4 N/A N/A N/A Introduced and Guided Practice

Materials needed

None

LAB 8 student Answer Sheet form

What students should know before this activity

  • Data Skills: how to read and interpret time series graphs and vertical sections 
  • The definition of density and how temperature and salinity impact density (see Lab 6)
  • What processes will increase salinity and what processes will decrease salinity
  • Solar heating varies with season and latitude

What instructors should know before this activity

  • Density is defined as mass per unit volume of a substance. Water density is usually measured in grams per cubic centimeter.
  • The three primary factors that determine seawater density are pressure, temperature and salinity.
    • The pressure effect is usually small since the water molecule is nearly incompressible.
    • Water density is very sensitive to temperature change. There is an inverse relationship between seawater density and temperature. As seawater temperature increases, density decreases. This results from the volume change in water as it is heated and cooled.
    • When salts are dissolved in water, the density of the water increases as salts have a greater density than water and add more mass than volume.
  • Temperature of the surface ocean is primarily determined by solar heating. Wind mixing distributes heat to deeper depths.
  • Salinity is determined at the surface by the processes that add water to the ocean and decrease salinity (glaciers and ice sheets melting, precipitation, run-off) and processes that remove water from the ocean and increase salinity (ice forming, evaporation)
  • There are many different combinations of temperature and salinity that produce the same seawater density. This can be illustrated in a temperature-salinity or T-S diagram. Oceanographers use T-S diagrams to identify the vertical structure of the water column and water masses.

Scientific Background

  • Review the formula for density and how salinity and temperature impact density
  • Review the processes that increase and decrease both temperature and salinity and how these vary across latitudes and with seasons

 

Teaching Notes

Introduction and Lab 7.1

  • Students may need to be encouraged to think about how Gulf Stream intrusions may impact species native to New England
    •  review the terms native versus non-native/ invasive species
  • Students struggle to understand the top graph that shows vertical profiles over time and how to interpret them.
    • Compare and contrast them with vertical profiles to show how time is added as an additional variable in a vertical section.
    • It may help to show them how you can create a vertical profile graph from a vertical section graph (see Lab …)and relate that to this visualization.

Lab 7.2

  • Be sure to focus on that BOTH salinity and temperature affect density.. Students may struggle to realize that if temperature is higher and salinity is higher (as is true for Gulf Stream water), density may not change much.
    • Point out that the density line graph does not show a large change on May 8-12th when the salinity and temperature data indicates Gulf Stream water
    • This concept will be highlighted in Lab 7.3
  • The end of this activity introduces a cutting edge new technology called the Imaging FlowCytobot (IFCB).

Lab 7.3

  • Some students struggle with the TSD diagrams and you may need to go over how to read these with the students. Here is a helpful video:   

Lab 7.4

Optional Pre-Lab Activities:
Pre/post-lab Assessment Questions:
  1. TBD
Extensions:
  • TBD

Associated Resources:

  • TBD