The water masses within the Weddell Sea circulate around the cyclonic Weddell Gyre. WDW (red arrows) originating from the Antarctic Circumpolar Current enters the gyre from the northeast and flows towards the ice shelf. WSDW (yellow arrows) in the Weddell Sea is renewed from the input from the Indo-Pacific sector and is locally produced by the mixture of DSW and WDW. WSBW (dark blue arrows) in the Weddell Sea is sourced primarily from the southwestern continental shelf, where the HSSW (purple arrows) formed via sea-ice freezing is exported offshore from the western side of the Ronne Ice Shelf as well as spreading down to the FRIS, leading to Ice Shelf Water (light blue arrows) formation. DSW containing HSSW, Ice Shelf Water and a small portion of modified WDW descends into the Weddell basin while mixing with WDW to form WSBW. Three hydrographic transectsA12, SR4 and A23are displayed in black lines, sitting on the Prime Meridian, across the gyre centre and over the northern boundary of the gyre, respectively. I6S transect sits further east at 30 E, marking the eastern boundary of Weddell Gyre. Temperature and salinity measurements collected by conductivity, temperature and depth (CTD) profilers are used to compute water mass area (Methods) shown in this study. The geographic locations of the Weddell Sea and southern Weddell continental shelf are marked in the inset circumpolar map with blue and red boxes, respectively.
