  We present and discuss results from time-distance helioseismic measurements
of meridional circulation in the solar convection zone using 4 years of Doppler
velocity observations by the Helioseismic and Magnetic Imager (HMI) onboard the
Solar Dynamics Observatory (SDO). Using an in-built mass conservation
constraint in terms of the stream function we invert helioseismic travel times
to infer meridional circulation in the solar convection zone. We find that the
return flow that closes the meridional circulation is possibly beneath the
depth of $0.77 R_{\odot}$. We discuss the significance of this result in
relation to other helioseismic inferences published recently and possible
reasons for the differences in the results. Our results show clearly the
pitfalls involved in the measurements of material flows in the deep solar
interior given the current limits on signal-to-noise and our limited
understanding of systematics in the data. We also discuss the implications of
our results for the dynamics of solar interior and popular solar dynamo models.
