The graphs below show the change in temperature and salinity of a region of ocean as an instrument is lowered below the surface. Depth is measured in kilometers below the surface, temperature in degrees Celsius, and salinity in parts per thousand. Image of two graphs. The left graph has the x axis labeled temperature degree C ranging from 0 to 10. The y axis is labeled depth below surface, km, ranging from negative 1.8 to 0. The line on graph goes up vertically starting at about 2 degree C on the x axis and negative 1.9 km on the y axis. The vertical line goes up staying at about 2 degree C and climbs from negative 1.9 km to about negative 0.8 km. The line starts to shift right at negative 0.6 km. The line shifts to the right from 2 degree C to 5 degree C. The line shifts to right more starting at negative 0.5 km and reaches 10 degree C around negative 0.2 km. The line continues up vertically after negative 0.2 km. The right graph has the x axis labeled salinity ranging from 33.8 to 34.6. The y axis is labeled depth below surface, km, ranging from negative 1.8 to 0. The line on the graph starts at 34 on the x axis and 0 km on the y axis. The line starts to shift to the right at negative 0.1 km and levels out at 34.2 on the x axis. At negative 0.2 km the line shifts to the left and continues to shift left until it reaches negative 0.5 km. The line starts to shift to the right again at negative 0.6 and continues to shift right until it reaches negative 1.9 km on the y axis and 34.6 on the x axis.
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What is the most valid conclusion based on the data?

The water in the ocean gets warmer as the salinity increases.
Higher salinity at shallow depths prevents the ocean from freezing.
Low concentrations of salt in the deep ocean keep the water cold.
Salinity is less stable at shallower depths than at deeper depths.