  We study the temperature dependence of the magnetic penetration depth in a 3D
topological superconductor (TSC), incorporating the paramagnetic current due to
the surface states. A TSC is predicted to host a gapless 2D surface Majorana
fluid. In addition to the bulk-dominated London response, we identify a $T^3$
power-law-in-temperature contribution from the surface, valid in the
low-temperature limit. Our system is fully gapped in the bulk, and should be
compared to bulk nodal superconductivity, which also exhibits power-law
behavior. Power-law temperature dependence of the penetration depth can be one
indicator of topological superconductivity.
