Sulfur isotope ratios of organic sulfur (δ³⁴S_org), degrees of pyritization (DOP) and sulfurization (DOS) in sediments were analyzed to reveal the organic sulfur compositions and their relationships with iron sulfides in a penguin-affected lake Y2 and a pristine Yanou Lake (YO) at Ardley Island and Fildes Peninsula, Antarctica, respectively. The depleted δ³⁴S_org values in Y2 sediments of 1-15 cm indicated a high proportion of ³⁴S-depleted diagenetic organic sulfur (S_diag) in total sulfur. Meanwhile, the high DOS in Y2 sediments of 8-15 cm indicated a concurrent sulfurization of iron and the organic matter, likely due to the high availability of active iron in this layer. The observed much enriched δ³⁴S_org in Y2 sediments of 48-56 cm corresponding to the period of high penguin populations, which indicated that large external inputs of penguin guanos result in a rapid increase in ³⁴S-enriched biological organic sulfur (S_bio) in the sediments, and exceeds the S_diag that from the internal sulfur transformations. The depleted δ³⁴S_org in YO sediment of 28 cm indicates a high proportion (95.4%) of ³⁴S-depleted S_diag which was from strong sulfurization of organic matter, corresponding to the strongest sulfate reduction in this layer. Meanwhile, the high DOP in YO sediment of 28 cm indicated a concurrent formation of pyrite sulfur and the sulfurization of organic matter in this layer, due to the high available precursors of hydrogen sulfide and/or intermediate species of sulfur from the sulfate reduction. Our study indicates that the components of organic sulfur are coupled tightly with organic matter and reactive iron and provides a direct implication for the depositions of organic matter and thus the potential climatic and environmental effects in regional aquatic ecosystems.