What does the term gradient describe in diving terms?

The term gradient in diving refers to the difference between the internal partial pressure and the external partial pressure of a gas. This concept is crucial for understanding how gases behave under pressure when divers ascend or descend in water. In diving, as a diver goes deeper, the external pressure increases, affecting the gases in the body, particularly nitrogen, which is absorbed by tissues.

As a diver ascends, the external pressure decreases, and the gases that were absorbed must be released safely to avoid complications like decompression sickness. Understanding this gradient helps divers plan their ascents and any necessary decompression stops to allow gases to safely leave the body, thus minimizing risks associated with changes in pressure during a dive.

The other options describe different aspects of diving not related to the definition of gradient in this context. For example, temperature differences do not directly relate to gas behavior, buoyancy measures relate to the diver's ability to float or sink, and surrounding water pressure is a notion associated with depth but not specifically with the internal and external gas pressures.