  The prediction of the PLANCK-constrained primordial lithium abundance in the
Universe is in discordance with the observed Li abundances in warm Population
II dwarf and subgiant stars. Among the physically best motivated ideas, it has
been suggested that this discrepancy can be alleviated if the stars observed
today had undergone photospheric depletion of lithium. The cause of this
depletion is investigated by accurately tracing the behaviour of the lithium
abundances as a function of effective temperature. Globular clusters are ideal
laboratories for such an abundance analysis as the relative stellar parameters
of their stars can be precisely determined. We performed a homogeneous chemical
abundance analysis of 144 stars in the metal-poor globular cluster M30, ranging
from the cluster turnoff point to the tip of the red giant branch. NLTE
abundances for Li, Ca, and Fe were derived where possible. Stellar parameters
were derived by matching isochrones to the observed V vs V-I colour-magnitude
diagram. Independent effective temperatures were obtained from automated
profile fitting of the Balmer lines and by applying colour-T_eff calibrations
to the broadband photometry. Li abundances of the turnoff and early subgiant
stars form a thin plateau that is broken off abruptly in the middle of the SGB
as a result of the onset of Li dilution caused by the first dredge-up.
Abundance trends with effective temperature for Fe and Ca are observed and
compared to predictions from stellar structure models including atomic
diffusion and ad hoc additional mixing below the surface convection zone. The
comparison shows that the stars in M30 are affected by atomic diffusion and
additional mixing. After applying a conservative correction for atomic
diffusion, we find an initial Li abundance of A(Li) = $2.48\pm0.10$ for the
globular cluster M30.
