Properties of Seawater lab

Instructions: Please fill out the worksheet attached and answer the questions below for the lab assignemnt

In this lab, we will investigate water properties including temperature, salinity, and density. We will examine temperature variations at different depths and latitudes, observe how ocean water forms distinct layers, and explore the relationship between salinity and density using measurement instruments. Additionally, we will analyze water samples from an estuary to determine salinity levels and assess potential sources of pollution. By the end of the lab, we will gain a better understanding of how seawater properties are measured and the valuable oceanographic information they provide.

After completing this lab you will be able to:

• Examine the properties of seawater, including temperature, salinity, and density.
• Analyze temperature and salinity variations to understand ocean layering.
• Work with temperature, salinity, and density data measured using analytical instruments and explore the relationships of these water parameters.
• Assess estuarine water samples for salinity levels and potential pollution sources.

Equipment and Supplies:

• Pencils and rulers

Tools and materials used:

• Mobile phone, tablet, or computer.

Instructions

1. Complete the lab assignment

• Review the instructions and begin answering the questions. The questions are embedded within the instructions for reference and will also appear when you start the untimed quiz. Your progress is saved, allowing you to continue your work at any time.
• You will be provided with a digital handout. You may download the fillable PDF file by . I suggest opening it in , which allows you to fill in the blanks. Most modern PDF readers should also work. Alternatively, you can print the handout and complete it by hand.

2. Take and submit a photo as proof of your lab work

• Take a photo of your handwritten notes, a drawing, or a screenshot of your work to document your lab progress.

Part 1 – Temperature Variations in the Ocean

The temperature of ocean water is not uniform at all latitudes or depths. Instead, it has a layered structure. These layers can be identified by measuring the temperature at different depths, creating what is known as a temperature profile of the water column (Figure 1). These profiles vary across different regions of the globe, classified as low latitudes (near the equator), mid-latitudes, and high latitudes (polar regions). The main factor controlling temperature in these profiles is the amount of sunlight reaching the ocean surface, which varies by latitude. Low latitudes receive direct sunlight year-round, warming surface waters, while high latitudes receive less energy, resulting in cooler temperatures.

Figure 1. Idealized temperature profiles for different latitudes and seasons

Watch the following video on how temperature and salinity are measured in the ocean:

Activity 1. Interpreting Ocean Temperature Profiles

In this activity, you will examine how temperature changes with depth and varies with latitude by using the provided figures to answer the questions.

Procedure:

• Examine the typical temperature profiles for different latitudes (Figure 1) and use your interpretations and the internet to answer the questions in this section.

Part 2 – Warming of the Surface Ocean

Activity 2. Ocean Temperature Experiment

In this activity, we will simulate ocean heating by using a container of water with thermometers placed at various depths to measure temperature changes. A source of light heated the water for 60 minutes and temperature changes were continuously monitored at each depth. You may observe the experimental setup in Figure 2.

Figure 2. Water container being heated by a light source

Procedure:

• Review the temperature readings for each time interval (0, 10, 20, 30, 40, 50, and 60 minutes) and depth (0 cm, 4 cm, 8 cm, and 16 cm) recorded by the digital thermometers and presented in Lab 5 Worksheet 1.
• Using the data in Lab 5 Worksheet 1, calculate the average, minimum, and maximum temperatures for each depth and enter your results in the table.
• On the grid paper in Lab 5 Worksheet 2, plot and label the data for each time interval. The graph should display seven curves, one for each recorded time point.
• Analyze the trends shown in your graph and answer the interpretation questions that follow.

Part 3 – Seawater Salinity

Salinity refers to the concentration of dissolved salts in seawater and plays a key role in determining water density. Higher salinity increases density, while lower salinity decreases it. This relationship affects ocean circulation, stratification, and marine ecosystems. Salinity is expressed in permil () and is equivalent to parts per thousand (ppt), which represent the amount of dissolved salts in water per thousand parts. For example, a salinity of 35 means there are 35 grams of dissolved salts per 1,000 grams of seawater. Coastal environments experience changing salinity due to the mixing of freshwater and seawater. In an estuary, freshwater from a river flows into the ocean, creating a salinity gradient. Near the river mouth, salinity is low (0 to 3 ), but as water moves toward the ocean (salinity of 35-38 ), it gradually increases as freshwater and seawater mix. This gradual variation in salinity strongly influences the coastal environment.

Watch the following video on how water is sampled in estuaries:

Activity 3. Determining Salinity of Water Samples

In this activity, you will act as an oceanographer studying the Coyote Estuary. This is a fragile environment where freshwater mixes with seawater. High toxin levels have been detected, and there is strong evidence of damage to the ecosystem. Griffin Chemical Company, located upriver, denies responsibility, suggesting toxins come from the Pacific Ocean. To test this claim, seawater samples were collected from different locations (Figure 3).

Figure 3. Sampling map of the Coyote Estuary

We will use the following methods to determine salinity:

Method 1: Hydrometer

A hydrometer is used to measure the density and temperature of a sample (Figure 4). When placed in water, it sinks lower in low-salinity samples and floats higher in high-salinity samples. Using the density and temperature measurements, salinity can be estimated by finding their intersection on the graph provided in Figure 5.

Figure 4. Using a hydrometer to measure density and temperature

Figure 5. Density, salinity, and temperature diagram

Method 2: Refractometer

Salinity and temperature affect seawater density. A refractometer measures how light bends through water, allowing to determine salinity (Figure 6). A few drops of the sample are placed on the prism and the transparent cover is gently closed to spread the liquid evenly. The salinity reading is obtained by looking through the eyepiece toward a light source.

Figure 6. Using a refractometer to measure salinity

Procedure:

First, we will measure density, temperature, and salinity of the provided water samples.

• Seawater samples were stored in labeled plastic containers and placed next to labeled graduated cylinders that were used for the measurements.
• The hydrometer and refractometer were always rinsed with deionized water before and after measuring each sample to prevent contamination. The wash bottle was used to direct deionized water at the instruments, and the waste was collected in a glass beaker.

• The density and temperature for each sample were measured directly from each graduated cylinder using the hydrometer (Method 1), and the results were recorded in Lab 5 Worksheet 3.
• Salinity was measured by using the plastic pipette to place a few droplets of each sample on the refractometer (Method 2). The results of each refractometer reading is shown in Figure 7. Record your results in Lab 5 Worksheet 3.

Figure 7. Refractometer readings of the samples from Coyote Estuary

Then, we will analyze our data in order to find out if the Griffin Chemical Company is the source of pollution of the estuary.

• Calculate the average salinity for each sample and record it in Lab 5 Worksheet 4.
• Refer to the map in Figure 3 to determine the distance (in kilometers) of each sample location from the chemical company, measuring from the point where chemicals would potentially enter the water near the chemical company.
• Complete Lab 5 Worksheet 4 and plot the data in Lab 5 Worksheet 5 to analyze trends. You will create two graphs on the same plot using two datasets from the table:
  • One dataset would be salinity vs distance from the chemical company.
  • Another dataset will be toxin count vs distance from the chemical company.
  • Clearly label each data set and color differently to differentiate between the two.