Answer:
Explanation:The condition that would cause the salinity of ocean water to decrease is option D: a river flowing into the sea.
When a river flows into the ocean, it brings fresh water from land sources into the saltwater environment. This fresh water has a lower salinity compared to the ocean water. As the river water mixes with the ocean water, it dilutes the overall salinity, resulting in a decrease in salinity levels.
Rivers carry various substances, including sediments and dissolved minerals, from land to the sea. These substances mix with the ocean water, altering its composition and reducing its salinity. The higher the flow rate of the river, the greater the dilution effect on the ocean water's salinity.
This phenomenon can be observed in areas where large rivers, such as the Amazon or the Mississippi, flow into the ocean. The influx of freshwater from these rivers contributes to the formation of estuaries, which are transitional zones where saltwater and freshwater mix. Estuaries typically have lower salinity levels due to the influence of the river's freshwater input.
It is important to note that the other options, such as high rates of evaporation, freezing of glaciers, or extremely hot weather, would not cause a decrease in ocean water salinity. In fact, these conditions can contribute to increasing salinity levels.