PADI Divemaster Certification Practice Exam

What effect might calm winds have on visibility in the water after an upwelling?

1. Increased visibility due to fewer waves

2. Decreased visibility due to plankton growth

3. Stable visibility due to a lack of turbulence

4. No effect on visibility

The correct answer is: Decreased visibility due to plankton growth

Calm winds following an upwelling can lead to decreased visibility due to the nutrient-rich waters stirred up from the ocean floor. During an upwelling, the movement of water brings nutrients like phytoplankton and other microscopic organisms closer to the surface. These organisms can proliferate rapidly in the enriched environment created by upwelling. When winds are calm, there is less mixing of the water, which allows these plankton and other particles to settle or remain in the water column without being dispersed. As the concentration of plankton increases, the water can become more turbid, which can reduce visibility. In this context, while calm winds may prevent further turbulence that might otherwise clear the water, they allow the effects of the upwelling to dominate, leading to a scenario where increased plankton growth contributes to reduced visibility. Thus, this illustrates how the ecological dynamics of water can interact with physical conditions to affect visibility underwater.