Whether neutrinos are Majorana or Dirac particles is an open question. Theoretically, it is also possible that neutrinos are pseudo-Dirac, which are fundamentally Majorana fermions, but essentially act like Dirac fermions in most experimental settings due to extremely small active-sterile mass splitting. However, they can be differentiated through active-sterile oscillations with an astrophysical baseline. In this talk, we will show that the recent identification of ultra-high energy neutrino sources by the IceCube Neutrino Observatory provides us with such an astrophysical baseline, thus improving the reach of terrestrial experiments by more than a billion for the mass-squared difference.