We measured the hydrogen and oxygen isotope composition (δ2H and δ18O) of precipitation and stream water from the Soft Plume River at multiple spatiotemporal scales on sub-Antarctic Marion Island, Indian sector of the Southern Ocean. Monthly precipitation δ2H and δ18O values ranged from -43.7‰ to -14.7‰ and from -7.0‰ to -3.3‰ (n=13), respectively. Stream water values ranged from -48.0‰ to -25.4‰ for δ2H and from -7.6‰ to -4.0‰ for δ18O (n=92). The monthly precipitation data yielded a local meteoric water line with the equation δ2H=8.4δ18O+11.4. There was no clear seasonality in isotope composition present in precipitation and stream water. Along the stream, no significant difference was observed between sites. However, δ2H and δ18O values were lower and more variable at the highest site. This is probably the result of the ‘amount effect’, where more precipitation fell at a higher elevation compared with a downstream site in the catchment. The findings illustrate spatiotemporal patterns in precipitation and stream water isotopes and provide insight into mechanisms affecting their composition on sub-Antarctic Marion Island.