Fig. 1: Overview of the Filchner-Ronne Ice Shelf system.
a Map of Filchner-Ronne hot-water drilled boreholes (Site 5, FSW, FSE, FNE1, & FNE2) and High Salinity Shelf Water (HSSW) production regions, (b) located south of the Warm Deep Water (WDW) that circulates along the continental slope in the southern Weddell Sea. a Contours: water column thickness (m); open ocean colors: anomalous sea ice formation rate (SFR) after 2015 compared with all years since 2002; blue (green) squares (crosses): ship-based CTD stations in front of the Filchner Ice Shelf in 2018 (2017); Vectors indicate time-averaged current meter observations from the lowest (black) and highest (white) instrument in the water column and legends showing a 2 cm s−1 (10 cm s−1) scale for the Filchner sites (Site 5). Colored arrows indicate inferred pathways and transformation from HSSW into ISW in the Berkner mode (green to purple) and in the Ronne mode (orange to blue). c Monthly and 36-month low-pass filtered time series of Southern Annual Mode (SAM) and (d) relative SFR anomalies, area-averaged over the orange polygon in front of Ronne Ice Shelf. Black lines: linear trend; blue dots: enhanced SFR events greater than 1σ (green dashed line) above the time average; blue (red) letters: years of dominantly Ronne (Berkner) mode water masses in the Filchner Trough21,22. Black (grey) crosses in (a) indicate significant correlations between low-pass filtered time series of local SFR anomalies and SAM at 99% (95%) confidence level. Color shaded areas in (c & d) indicate the 15 year period (orange and green) relative to which the spatial pattern of SFR anomalies (green only) is computed that is shown in (a).
