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We present an elemental abundance analysis for four newly discovered ultrametal-poor stars from the Hamburg/ESO survey, with $\mathrm{[Fe/H]}\leq-4$.Based on high-resolution, high signal-to-noise spectra, we derive abundancesfor 17 elements in the range from Li to Ba. Three of the four stars exhibitmoderate to large over-abundances of carbon, but have no enhancements in theirneutron-capture elements. The most metal-poor star in the sample,HE~0233$-$0343 ($\mathrm{[Fe/H]} = -4.68$), is a subgiant with a carbonenhancement of $\mathrm{[C/Fe]}= +3.5$, slightly above the carbon-enhancementplateau suggested by Spite et al. No carbon is detected in the spectrum of thefourth star, but the quality of its spectrum only allows for the determinationof an upper limit on the carbon abundance ratio of $\mathrm{[C/Fe]} < +1.7$. Wedetect lithium in the spectra of two of the carbon-enhanced stars, includingHE~0233$-$0343. Both stars with Li detections are Li-depleted, with respect tothe Li plateau for metal-poor dwarfs found by Spite \& Spite. This suggeststhat whatever site(s) produced C either do not completely destroy lithium, orthat Li has been astrated by early-generation stars and mixed with primordialLi in the gas that formed the stars observed at present. The derived abundancesfor the $\alpha$-elements and iron-peak elements of the four stars are similarto those found in previous large samples of extremely and ultra metal-poorstars. Finally, a large spread is found in the abundances of Sr and Ba forthese stars, possibly influenced by enrichment from fast rotating stars in theearly universe.

Exploring the Origin of Lithium, Carbon, Strontium and Barium with four new Ultra Metal-Poor Stars