Dialing down the spectrum a bit, the very low frequency (VLF: 3 kHz to 30 kHz) band starts to exhibit decent penetration of seawater, down to a depth of perhaps 20 meters."
[...]
>"Going even further down the spectrum, signals in the extremely low frequency (ELF: 3 Hz to 30 Hz) band are capable of penetrating 120 meters of seawater"
Submarines aside, this is tremendously interesting how specific mediums (in this case, salt water) either act as transducers or attenuators for different radio frequencies.
Now, when a radio frequency is influenced by some form of matter (in this case, salt water, and at higher frequencies, attenuation), it might be because the matter and the radio frequency are somehow related.
In other words, perhaps future scientists will discover that the molecules of water are resonating at a frequency which is a much higher harmonic than the radio waves that they block. And/or perhaps their frequency is somehow related to the much lower frequency radio waves that they conduct.
See, it's sort of like any attenuator can act as a conductor (or vice versa), but the frequency or set of frequencies used makes the determination as to whether the medium in question is going to attenuate or conduct...
Compare this concept to resistors in electronics.
They resist standard DC... but what about AC at a certain frequency, or pulsed DC at a certain frequency?
The higher the frequency (to a certain point when space becomes conductive and thus dissipative with respect to the circuit), the more a resistor should become a conductor...
Also, observation: The reason why distance is lost (in seawater, but also other mediums) when higher frequencies are used, is typically because power is converted into frequency, which then, in the case of a standard radio wave, expands into space as a sphere, that is, it's a inverse-square-law power loss over space.
Compare radio waves to lasers; lasers do not lose power in accord with the inverse-square-law over space...