  Clebsch potential gauge field theory for magnetohydrodynamics is developed
based in part on the theory of Calkin (1963). It is shown how the polarization
vector ${\bf P}$ in Calkin's approach, naturally arises from the Lagrange
multiplier constraint equation for Faraday's equation for the magnetic
induction ${\bf B}$, or alternatively from the magnetic vector potential form
of Faraday's equation. Gauss's equation, (divergence of ${\bf B}$ is zero), is
incorporated in the variational principle by means of a Lagrange multiplier
constraint. Noether's theorem, coupled with the gauge symmetries is used to
derive the conservation laws for (a)\ magnetic helicity (b)\ cross helicity,
(c) fluid helicity for non-magnetized fluids, and (d) a class of conservation
laws associated with curl and divergence equations, which applies to Faraday's
equation and Gauss's equation. The magnetic helicity conservation law is due to
a gauge symmetry in MHD and not due to a fluid relabelling symmetry. The
analysis is carried out for the general case of a non-barotropic gas, in which
the gas pressure and internal energy density depend on both the entropy $S$ and
the gas density $\rho$. The cross helicity and fluid helicity conservation laws
in the non-barotropic case, are nonlocal conservation laws, that reduce to
local conservation laws for the case of a barotropic gas. The connections
between gauge symmetries, Clebsch potentials and Casimirs are developed. It is
shown that the gauge symmetry functionals in the work of Henyey (1982) satisfy
the Casimir determining equations.
