[meteorman81 (OP)]

We dont know what provides the water source.  there are no streams running into it and no known springs.  We always said that it was just ground water and tends to fluctuate regularly with dry, wet climates.  There is a 12" drain pipe that runs vertically then turns and runs approximately 100 yards to a second, larger pond.

[CliffordK]

I don't have any comparison.
And, we don't have any place to go ice fishing around here.

I'm a bit surprised at the temperatures of 37°F at the surface, and 40°F at the bottom.

I would have anticipated that the temperature just below the ice would have been 32°F to perhaps 34°F (0°C to +1°C).

I would think that 37°F (+2 to +3°C) would be enough to melt the ice at the surface.

Steel pipe at the outlet?

Perhaps there is a spring, or the end of "drainage tile" under the middle of the pond.  Or some Kryptonite?

I am a little puzzled about how you describe such a vertical hole. 

If the weather has been consistent with refreezing, the freezing or lack thereof would give you more indication of what is happening.