  We discuss an action of the Grothendieck-Teichm\"{u}ller proalgebraic group
on the linear span of proalgebraic tangles, oriented tangles completed by a
filtration of Vassiliev. The action yields a motivic structure on tangles. We
derive distinguished properties of the action particularly on proalgebraic
string links and on proalgebraic knots which can not be observed in the action
on proalgebraic braids. By exploiting the properties, we explicitly calculate
the inverse image of the trivial (the chordless) chord diagram under the
Kontsevich isomorphism.
