Axial Poynting flux interpolated along field lines rooted in the swirling structure shown in Fig. 2 traced from seed points at a height of 6 Mm. Poynting flux directed in the positive s-direction is positive, while Poynting flux directed in the negative s-direction is negative. The two populations of field lines are colored in red and blue depending on the magnetic field patch in which they are rooted at the loop footpoint at the right. The color-coding is the same as in Fig. 4. The dotted black line is drawn at a constant value of zero. The thick dashed red and blue lines show the averaged Poynting flux per flux patch, while the dashed black line shows the average taken over all traced field lines. For a discussion, see Sects. 3.1 and 4.3.