  A new technique for on-line high resolution isotopic analysis of liquid
water, tailored for ice core studies is presented. We built an interface
between a Wavelength Scanned Cavity Ring Down Spectrometer (WS-CRDS) purchased
from Picarro Inc. and a Continuous Flow Analysis (CFA) system. The system
offers the possibility to perform simultaneous water isotopic analysis of
$\delta^{18}$O and $\delta$D on a continuous stream of liquid water as
generated from a continuously melted ice rod. Injection of sub ${\mu}$l amounts
of liquid water is achieved by pumping sample through a fused silica capillary
and instantaneously vaporizing it with 100% efficiency in a home made oven. A
calibration procedure allows for proper reporting of the data on the
VSMOW--SLAP scale. Application of spectral methods yields the combined
uncertainty of the system at below 0.1 permil and 0.5 permil for $\delta^{18}$O
and $\delta$D, respectively. This performance is comparable to that achieved
with mass spectrometry. Dispersion of the sample in the transfer lines limits
the temporal resolution of the technique. By using an optimal filtering method
we show how the measured profiles can be corrected for the smoothing effects
resulting from the sample dispersion. Considering the significant advantages
the technique offers, i.e. simultaneous measurement of $\delta^{18}$O and
$\delta$D, potentially in combination with chemical components that are
traditionally measured on CFA systems, notable reduction on analysis time and
power consumption, we consider it as an alternative to traditional isotope
ratio mass spectrometry with the possibility to be deployed for field ice core
studies. We present data acquired in the field during the 2010 season as part
of the NEEM deep ice core drilling project in North Greenland.
