Fig. 1: Circulation in PIB in 2020.

a Hydrographic observation map near PIIS from January–February 2020 overlaid on a local high-resolution bathymetry chart^28,48. White-rimmed black circles represent the positions of 2020 Conductivity-Temperature-Depth (CTD) data presented in Fig. 2. The selected CTD stations are numbered in an order of distance from PIIS. L1-L4 and IF indicate CTD observational lines aligned meridionally across PIB and along PIIS, respectively. Solid purple and green lines represent the PIIS front positions in 2009 and 2014, respectively. The solid black line indicates a new ice shelf front after the calving of the ‘B49’ iceberg (dashed blue line) from PIIS on 9 February 2020. The large solid and dotted purple circles (green circles) with arrows indicate the approximate extents of the cyclonic and anticyclonic gyres observed in 2009²⁰ (2014), respectively. These extents of gyres are referred to from Supplementary Fig. 1. Dark grey contour denotes the grounding line. b Red-faced arrows denote the ocean currents averaged over depth ranging from 30 to 300 m based on Ship-based Acoustic Doppler Profiler (SADCP) data collected in 2020, gridded into ~3 × 3 km horizontal boxes. Shading represents the dynamic height anomaly (Methods). The large solid (dotted) black circle with arrows denotes the approximate size and position of the cyclonic (anticyclonic) gyre in 2020. Small black circles denote the positions of CTD stations. c Orange-faced arrows indicate the ocean currents averaged over depth ranging from 30 to 300 m based on the Lowered Acoustic Doppler Current Profiler (LADCP) data. Colour-filled circles indicate the vertically averaged meltwater fraction above the mCDW layer.