Question

exam lesson name: introduction to oceanography
exam number: 700793rr
exam guidelines
exam instructions

question 15 of 20 :
select the best answer for the question

1. which of the following is the most likely to occur if the temperature of seawater decreases?

○ a. the speed of sound will decrease due to the decreasing salinity of seawater
○ b. the speed of sound will increase due to the decreasing density of seawater.
○ c. the speed of sound will increase due to the increasing density of seawater.
○ d. the speed of sound will decrease due to the increasing density of seawater.

□ mark for review (will be highlighted on the review page)

Explanation:

1. Recall the relationship between seawater temperature, density, and sound speed: As seawater temperature decreases, its density increases.
2. Analyze the effect of density on sound speed in a medium: In general, sound speed in a medium is related to the medium's density (and elasticity). For seawater, an increase in density (with other factors like salinity and pressure considered, but here temperature - density is key) leads to an increase in sound speed? Wait, no—wait, actually, the formula for sound speed in seawater is approximately \( c = 1448.96+4.591T - 5.304\times10^{-2}T^{2}+2.374\times10^{-4}T^{3}+1.340(S - 35)+1.630\times10^{-2}D+1.675\times10^{-7}D^{2}-1.025\times10^{-2}T(S - 35)-7.139\times10^{-13}TD^{3}\), where \( T \) is temperature (°C), \( S \) is salinity (psu), and \( D \) is depth (m). But a simpler way: when temperature decreases, density increases. And from the formula, as \( T \) decreases, the first - order term \( 4.591T \) decreases, but also density (related to \( D \) - but more directly, for a given depth, lower temperature means higher density). Wait, actually, the speed of sound in a fluid is given by \( c=\sqrt{\frac{K}{

ho}}\), where \( K \) is bulk modulus and \(
ho \) is density. In seawater, as temperature decreases, the bulk modulus \( K \) increases more than the density \(
ho \) increases, so the net effect is that sound speed decreases? Wait, no, let's think again. Wait, no—when temperature decreases, seawater becomes more dense. But the bulk modulus (a measure of compressibility) also changes. However, the correct relationship is: as seawater temperature decreases, the speed of sound decreases, and as density (due to temperature decrease, since lower temp -> higher density) increases, how does that affect? Wait, the formula from oceanography: the speed of sound in seawater increases with increasing temperature, increasing salinity, and increasing pressure (depth). So if temperature decreases, sound speed decreases. Now, why? Because the main factor here is temperature. But let's check the options:

• Option A: Talks about salinity decreasing, but the question is about temperature decreasing, so A is wrong.
• Option B: Says density decreases with temperature decrease, but temperature decrease leads to density increase, so B is wrong.
• Option C: Says sound speed increases with density increase, but from the formula, lower temperature (higher density) leads to lower sound speed, so C is wrong.
• Option D: Says sound speed decreases due to increasing density (from temperature decrease). This matches the relationship: lower temperature -> higher density -> lower sound speed (since the effect of temperature on sound speed is dominant, and the density increase here is due to temperature decrease, and the net effect is lower sound speed).

Answer:

D. The speed of sound will decrease due to the increasing density of seawater.