Sea level oscillations associated with both the 2010 Chile and 2011 Japan tsunamis were recorded in the coastal waters of King George Island off the west coast of Antarctica with an online coastal mooring system. The Chile tsunami arrived at the detection site within around five hours of the earthquake. The largest wave (84.4 mm) was measured 27 hours after the first arrival. In contrast, the Japan tsunami was detected around 26 hours after the earthquake, and the maximum wave height (180.8 mm) was observed around 11 hours after the initial wave. The energy level of the earthquake and the direction of energy propagation are probably the two most significant causes of the comparatively high amplitudes of the 2011 Japan tsunami, despite the fact that its epicentre was much further away than that of 2010 Chile tsunami. The sea level oscillations associated with the tsunami increased the level of mixing of seawater in the shallow Antarctic coastal waters and influenced the environment temporarily.