  We investigate chemical abundance variations along the sightlines through 13
damped Lya systems (DLA). We introduce a technique designed to identify
abundance variations in multiple velocity bins along the sightlines and perform
a series of Monte-Carlo simulations to derive quantitative limits and values.
The majority of these DLA have very uniform relative abundances: 95% c.l. upper
limits of 0.2 dex dispersion along the sightline and best fit values typically
<~0.1 dex. This surprising result indicates the gas comprising individual DLA
has similar enrichment history, nearly identical differential depletion, and
small abundance variations relating to ionization corrections. This uniformity
contrasts with stellar abundance variations observed within the Galaxy and with
the differences in abundances observed between galaxies of the Local group. It
also contrasts with variations in differential depletion along sightlines
through the SMC, LMC, and Milky Way. The results constrain the process of metal
production and dust formation in the early universe and reflect on scenarios of
galaxy formation. In terms of depletion the observations indicate a very low
porosity of significantly depleted gas, substantially lower than the filling
factor observed in present-day metal-poor galaxies. Finally, the observed
chemical uniformity may present a difficult challenge to scenarios which assume
individual DLA are comprised of multiple protogalactic clumps.

Astrophysics