What contributes to variability in DSC sound speed in relation to depth?

Variability in sound speed in the deep sound channel (DSC) is significantly influenced by water salinity. Sound speed in seawater is affected by temperature, pressure (which changes with depth), and salinity. As depth increases, salinity can vary due to factors such as freshwater inflows or oceanic features like thermohaline circulation. Higher salinity generally increases the sound speed, while lower salinity has the opposite effect.

Understanding the interplay between salinity and depth is crucial for applications like underwater acoustics and oceanographic studies, as sound speed directly influences how sound travels through water. The other options may relate to environmental conditions that affect the ocean's surface or aquatic life but do not directly influence the intrinsic sound speed variations with depth in the DSC as salinity does.