Oceanographers conducted an investigation to determine how variations in seawater salinity… — ACT

Oceanographers conducted an investigation to determine how variations in seawater salinity affect the vertical settling rates of marine micro-calcite ( $CaCO_3$ ) particles. Synthetic seawater samples were prepared at four salinity levels ( $30\ \text{PSU}$ , $33\ \text{PSU}$ , $35\ \text{PSU}$ , and $38\ \text{PSU}$ ). In each trial, micro-calcite particles of uniform diameter ( $50\ \mu\text{m}$ ) were dropped into a $1\text{-meter}$ vertical settling column maintained at a constant water temperature of $20^\circ\text{C}$ . The elapsed transit time required for each particle to sink through the $1\text{-meter}$ distance was recorded to calculate its terminal sinking velocity.

Match each experimental component from the investigation to its correct variable classification.

Seawater salinity levels ( $30\ \text{PSU}$ , $33\ \text{PSU}$ , $35\ \text{PSU}$ , and $38\ \text{PSU}$ )Independent Variable
Calculated terminal sinking velocity of the micro-calcite particlesDependent Variable
Water temperature ( $20^\circ\text{C}$ ) and particle diameter ( $50\ \mu\text{m}$ )Controlled Variables

Answer

Seawater salinity matches the Independent Variable; calculated terminal sinking velocity matches the Dependent Variable; and water temperature along with particle diameter match the Controlled Variables.

Seawater salinity is the independent variable because it is the condition deliberately varied (

30\text{--}38\ \text{PSU}

) by the oceanographers. Terminal sinking velocity is the dependent variable because it is the outcome measured in response to those salinity variations. Water temperature (

20^\circ\text{C}

) and particle diameter (

50\ \mu\text{m}

) are controlled variables because they were kept fixed across all trials to isolate the effect of salinity.

Step-by-Step Solution

Identify the parameter systematically manipulated by the researchers across experimental trials.

The oceanographers prepared water samples at four specific salinity values (

30\ \text{PSU}

33\ \text{PSU}

35\ \text{PSU}

, and

38\ \text{PSU}

), making salinity the independent variable.

The independent variable is the factor intentionally altered to test its effect on the system.

Identify the response or output measured as a result of changing the manipulated parameter.

The transit time was measured and used to determine terminal sinking velocity, making sinking velocity the dependent variable.

The dependent variable represents the measured outcome that changes in response to the independent variable.

Identify physical conditions maintained without change across all test runs.

Water temperature (

20^\circ\text{C}

), particle size (

50\ \mu\text{m}

), and settling distance (

1\text{ meter}

) were held identical in every trial, making them controlled variables.

Controlled variables are kept constant to ensure that observed variations in sinking velocity are caused solely by changes in salinity rather than confounding physical factors.

Key Concept

Identifying Independent, Dependent, and Controlled Variables

Estimated Time:2m 0s

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