Stable isotope 13C/12C ratios of organic carbon in sediments and in particulate organic carbon (POC) change from typically marine values in Groswater Bay to those of terrestrial soils in Goose Bay along an offshore–onshore transect in Hamilton Inlet, southeastern Labrator. The δ13C values in POC collected from close to the water surface change relatively little in Lake Melville, indicating that the integrity of the runoff plume is maintained as it spreads in Lake Melville. The organic carbon isotope ratios in POC collected from the near-bottom waters are similar to those of surficial sediments.Downcore δ13C values reflect paleo-oceanographic changes in Hamilton Inlet during and since deglaciation. In two sediment cores that reached sufficiently old sediments (10 000 years BP), the δ13C values change toward the bottom of the cores to values similar to those of the terrestrial organic carbon in soils, signifying greater terrestrial influence during deglaciation and during the early Holocene.According to the history of postglacial isostatic readjustment of the area, Lake Melville basin was more open to the marine waters during the early postglacial marine incursion because of deeper channels leading into Lake Melville. As a consequence, evidence for greater marine influence during that time should be found in sediment cores. The lack of evidence for the deposition of marine organic carbon brought in by the marine counterflow waters suggests a proximal glaciomarine environment in the Lake Melville basin. Glacial runoff diluted the basin waters, and it is possible that the whole inner Labrador Shelf was relatively fresh during that time.