  We describe the flows and morphological dynamics of topological defect lines
and loops in three-dimensional active nematics and show, using theory and
numerical modelling, that they are governed by the local profile of the
orientational order surrounding the defects. Analysing a continuous span of
defect loop profiles, ranging from radial and tangential twist to wedge $\pm
1/2$ profiles, we show that the distinct geometries can drive material flow
perpendicular or along the local defect loop segment, whose variation around a
closed loop can lead to net loop motion, elongation or compression of shape, or
buckling of the loops. We demonstrate a correlation between local curvature and
the local orientational profile of the defect loop, indicating dynamic coupling
between geometry and topology. To address the general formation of defect loops
in three dimensions, we show their creation via bend instability from different
initial elastic distortions.
