For the last five decades the Antarctic Peninsula faces the strongest atmospheric warming on Earth with severe consequences for its glaciers, ice shelves, sea ice cover, and the surrounding marginal seas. We analyzed hydrographic data from the northwestern Weddell Sea continental shelf of three austral winters (1989, 1997, and 2006) and two summers following the last winter cruise. The whole water column north of 66S freshened by ~0.1 between the winters of the 17-year period, replaced by deep waters of the Central Bransfield Strait Basin every summer. The discussion of the causes for the salinity decrease, supported by tracer analysis, favors the increased input of glacial melt from underneath Larsen C Ice Shelf. However, the 2-m/yr melt rate, necessary for a year-by-year freshening, could be reduced to 0.38 - 1.33 m/yr due to a recent (modeled) increase of precipitation and a retreat of the sea ice cover in the northwestern Weddell Sea.