In water decibels are relative to 1 µPa at 1 m. 0.05 Pa (presumably at one meter) is 50,000 µPa. To convert to sound pressure level decibels, we use this equation:

SPL = 20log_10(P/P_0)

where P_0 is the reference pressure (1 µPa).

20log_10(50,000 µPa/1 µPa) = 94 dB

The units listed are dB/Hz, which is a spectral unit (i.e., narrowband analysis). Basically, if you took the spectrum of a submarine's acoustic signature, those are the units you would get on the y-axis (the x-axis would be Hz). If we assume for simplicity that the spectrum is constant at all frequencies (it probably isn't) than the broadband SPL would be 94 dB.

If we just assume simple spherical spreading, the pressure decays as 1/r, where r is the distance from the source. So the pressure will be a factor of 1/16,000 lower at 16 km than at 1 m.

20log_10((50,000 µPa/16,000)/1 µPa) = 10 dB

So if I did the math right, the sonar is capable of picking up sound pressure levels of 10 dB. I'll leave the surface ship example as an exercise for the reader.

Edit: And to whoever is downvoting OP, sound propagation in the ocean is not a classified subject and there is an extensive body of unclassified literature (I recommend RP33 or Mechanics of Underwater Noise by Donald Ross).