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New long Chandra grating observations of the O supergiant $\zeta$ Pup shownot only a brightening of the x-ray emission line flux of 13 per cent in the 18years since Chandra's first observing cycle, but also clear evidence - at morethan four sigma significance - of increased wind absorption signatures in itsDoppler-broadened x-ray emission line profiles. We demonstrate this withnon-parametric analysis of the profiles as well as Gaussian fitting and thenuse the line-profile model fitting to derive a mass-loss rate of $2.47 \pm 0.09\times 10^{-6}$ Msun/yr, which is a 40 per cent increase over the valueobtained from the cycle 1 data. The increase in the individual emission linefluxes is greater for short-wavelength lines than long-wavelength lines, aswould be expected if a uniform increase in line emission is accompanied by anincrease in the wavelength-dependent absorption by the cold wind in which theshock-heated plasma is embedded.

Chandra spectral measurements of the O supergiant $\zeta$ Puppis indicate a surprising increase in the wind mass-loss rate over 18 years