"Volume of Informal Certs"

[KA]

I've been chasing the death of a relative, but with no luck. As he was a Master Mariner I have looked at the GRO Marine Deaths Indices, which may  have yielded results.

There is an entry

Gibson (1852) Male (see Vol. of Informal Certs).

Does anybody know what this volume is?  Where is it?  And how I can access it?  I'm not near enough to the Records Office to visit.

Regards

KA