Fig. 3: Indicators of a regime shift in heat flux efficiency beneath the Petermann Ice Shelf.

Along-fjord summer mean temperature (a), salinity (b), and flow (c) for the control experiment for the section shown in Fig. 1b. Mean isopycnals (solid black lines) are overlaid at equal intervals of 0.2 kg/m³. The 27.9 kg/m³ isopycnal corresponds to the dense Atlantic Water that contacts the grounding line. For the same section, changes (δ) in summer mean temperature (d), salinity (e), and flow (f) for the discharge (Q_sg) experiment Q_sg-present relative to control are shown. Black stippled lines in panels d and e indicate the zero temperature and salinity difference contour, respectively. In panel f, solid black lines and stippled green lines depict the mean isopycnals for the control and Q_sg-present experiments, respectively, plotted at equal intervals of 0.2 kg/m³. In each panel, the Petermann Ice Shelf grounding line (at ca. 600 m depth) is on the right margin, and the open ocean is to the left. Vertical magenta line in panels (a, b, d, and e) shows the transect location closest to the model node ca. 10 km from the grounding line (Fig. 1b) at which the vertical profile of summer mean temperature (g) and salinity (h) are shown for the control, Q_sg-present, Q_sg-median, and Q_sg-RCP 8.5 experiments (Table 1). i Laterally integrated summer mean vertical overturning profile¹⁷ [in Sverdrup (Sv)] for all the experiments (Table 1) for the section shown in Fig. 1b. Positive [Sv] values correspond to (laterally integrated) inflow, and negative [Sv] values correspond to (laterally integrated) outflow across the section.