  Flows in low Prandtl number liquid pools are relevant for various technical
applications, and have so far only been investigated for the case of pure
fluids, i.e. with a constant, negative surface tension temperature coefficient
$\partial\gamma/\partial T$. Real-world fluids containing surfactants have a
temperature dependent $\partial\gamma/\partial T > 0$, which may change sign to
$\partial\gamma/\partial T < 0$ at a critical temperature $T_c$. Where
thermocapillary forces are the main driving force, this can have a tremendous
effect on the resulting flow patterns and the associated heat transfer.
  Here we investigate the stability of such flows for five Marangoni numbers in
the range of $2.1\times 10^6 \leq Ma \leq 3.4\times 10^7$ using dynamic large
eddy simulations (LES), which we validate against a high resolution direct
numerical simulation (DNS). We find that the five cases span all flow regimes,
i.e. stable laminar flow at $Ma \leq 2.1\times 10^6$, transitional flow with
rotational instabilities at $Ma = 2.8\times 10^6$ and $Ma = 4.6\times 10^6$ and
turbulent flow at $Ma = 1.8\times 10^7$ and $Ma = 3.4\times 10^7$.
