Temperature fluctuations in a half-zone liquid bridge of molten silicon were measured under precisely controlled oxygen partial pressure in the ambient atmosphere. A transition from a mode with non-periodic fluctuations in temperature to one with periodic fluctuations occurred when the oxygen partial pressure at the inlet was increased from 3.5 x 10(-7) to 1.8 x 10(-5) MPa. The transition indicates that the absolute temperature coefficient of surface tension decreases with increasing oxygen partial pressure at the silicon surface.