Figure 2 . Effects of meltwater redistributionbottom), [c] is the ocean overturning in density space at 65oshelf). [a,d] are salinity anomalies for VARI-UNIF , and [b,e] are anomalies for BM-UNIF . Dotted areas indicate regions of statistically significant anomalies at a 95% confidence level from a student t -test. Squares (circles and ×’s) on [f] and [g] mark the source water locations (circles for entrainment and ×’s for exit water locations) for the shelf overflow parameterization (supplementary S3).
There are a few possible reasons why the spatially varying freshwater flux in VARI increases surface salinity over most of the Antarctic coast. First, VARI has lower freshwater fluxes over most of the Antarctic coast except in the Amundsen Sea compared toUNIF (Fig 1d). These lower freshwater fluxes can increase surface salinities along most of the Antarctic coast compared to UNIF- except on the Amundsen Sea where larger freshwater fluxes can decrease the surface waters’ salinity (Fig 2a,f). Second, surface freshwater fluxes inVARI are also redistributed meridionally to represent both ice shelf basal melting and icebergs melting away from the coast (Fig 1b,e). In other words, a portion of the freshwater flux applied along the coast in UNIF was redistributed offshore in VARI (Fig 1e). This meridional redistribution can further reduce the freshwater fluxes over most of the Antarctic coast, resulting in higher salinities inVARI .
To test to what extent zonally varying freshwater fluxes cause the salinity changes in the surface and bottom layer of VARI , we compare UNIF with BM which represents the zonally varying ice shelf basal melting without iceberg melting (Fig 1c). Zonal variations in freshwater fluxes in BM reproduce the same surface and bottom layer signals seen in VARI . In particular, BMshows higher surface salinities along most of the Antarctic shelf except in the Amundsen Sea (Fig 2b). This surface signal is carried into bottom waters (Fig 2e) through shelf overflow (Fig 2g). The Southern Ocean overturning in BM also maintains its strength, similar to theVARI case (Fig 2c). Therefore, zonally varying freshwater fluxes (Fig 1c,d, BM ) result in the same increase in AABW and surface salinities as in the case of the zonally and meridionally varying meltwater fluxes (as in VARI ). Further evaluation of the effects of iceberg melting versus ice shelf basal melting confirms that the meridional displacement of freshwater fluxes has minimal effect on AABW transport and salinity (Supplementary S5). This result suggests that zonal variation in freshwater input along the Antarctic coast is mostly responsible for increasing AABW salinity and surface salinity along the Weddell and the Ross Sea sectors in the VARI simulation, while the meridional variation has a relatively small impact, mostly in the open Weddell Sea and the Indian Ocean sectors (Fig. 2d).