  Hydrogen ($\delta$2H) and oxygen ($\delta$18O) isotopes of water extracted
from speleothem fluid inclusions are important proxies used for paleoclimate
reconstruction. In our study we use a cavity ring-down laser spectroscopy
system for analysis and modified the approach of Affolter et al. (2014) for
sample extraction. The method is based on crushing of small sub-gram speleothem
samples in a heated and continuously water-vapour purged extraction line. The
following points were identified:
  Injection of reference water shows a precision (1$\sigma$) of 0.4-0.5 permil
for $\delta$18O values and 1.1-1.9 permil for $\delta$2H values for water
amounts of 0.1-0.5 $\mu$l, which improves with increasing water amount to
0.1-0.3 permil and 0.2-0.7 permil, respectively, above 1 $\mu$l. The accuracy
of measurements of water injections and water-filled glass capillaries crushed
in the system is better than 0.08 permil for $\delta$18O and 0.3 permil for
$\delta$2H values. The reproducibility (1$\sigma$) based on replicate analysis
of speleothem fluid inclusion samples with water amounts > 0.2 $\mu$l is 0.5
permil for $\delta$18O and 1.2 permil for $\delta$2H values, respectively.
Isotopic differences between the water vapour background of the extraction
system and the fluid inclusions have no significant impact on the measured
fluid inclusion isotope values if they are within 10 permil for $\delta$18O and
50 permil for $\delta$2H values of the background. Tests of potential
adsorption effects with inclusion free spar calcite confirm that the isotope
values are unaffected by adsorption for water contents of about 1 $\mu$l (fluid
inclusion) water per g of carbonate or above.
  Fluid inclusion analysis on three different modern to late Holocene
speleothems from caves in northwest Germany resulted ...
