How do the pressure variations with depth affect our ability to explore the ocean? In particular, what are some of the challenges of scuba diving?

Answer 1

the ambient pressure increases by one atmosphere for every 10 m of depth

nitrogen (≈ 80% of the air) goes into solution in the blood at elevated pressures , and acts as an intoxicant
... air mixtures where the nitrogen is replaced by helium and/or argon are used when deep diving to prevent "nitrogen narcosis"

gases dissolved in the blood under elevated pressure must be allowed to come out of solution slowly to prevent bubbles forming in the circulatory system and other tissues
... a condition called "the bends" or "caissons disease"

scuba divers are taught to "never rise faster than your exhaust bubbles"
... they also make stops at various depths when ascending to "decompress"