Surjectivity of the total Clifford invariant and Brauer dimension
  Merkurjev's theorem--the statement that the 2-torsion of the Brauer group is represented by Clifford algebras of quadratic forms--is in general false when the base is no longer a field. The work of Parimala, Scharlau, and Sridharan proves the existence of smooth complete curves over local fields, over which Merkurjev's theorem is equivalent to the existence of a rational theta characteristic. Here, we prove that for smooth curves over a local field or surfaces over a finite field, replacing the Witt group by the total Witt group of all line bundle-valued quadratic forms recovers Merkurjev's theorem: the 2-torsion of the Brauer group is always represented by even Clifford algebras of line bundle-valued quadratic forms. 
Asher Auel
math.AG math.NT