An Improved Continuous Flow
Analysis System for High-Resolution
Field Measurements on Ice Cores
P A T R I K R . K A U F M A N N , * , † , ‡
U R S F E D E R E R , † , ‡ M A N U E L A . H U T T E R L I , §
M A T T H I A S B I G L E R , |
S I M O N S C H U¨ P B A C H , † , ‡ U R S R U T H , ⊥
J O C H E N S C H M I T T , † , ‡ , ⊥ A N D
T H O M A S F . S T O C K E R † , ‡
Climate and Environmental Physics, Physics Institute,
University of Bern, Bern, Switzerland, Oeschger Centre for
Climate Change Research, University of Bern, Bern,
Switzerland, British Antarctic Survey, Cambridge, United
Kingdom, Centre for Ice and Climate, Niels Bohr Institute,
University of Copenhagen, Denmark, and
Alfred-Wegener-Institute for Polar and Marine Research,
Bremerhaven, Germany
Received March 20, 2008. Revised manuscript received July
18, 2008. Accepted July 29, 2008.
Continuous flow analysis (CFA) is a well-established method
to obtain information about impurity contents in ice cores as
indicators of past changes in the climate system. A section of
an ice core is continuously melted on a melter head supplying
a samplewater flowwhich is analyzed online. This provides high
depth and time resolution of the ice core records and very
efficient sample decontamination as only the inner part of the
ice sample is analyzed. Here we present an improved CFA
systemwhichhasbeentotally redesigned inviewofasignificantly
enhanced overall efficiency and flexibility, signal quality,
compactness, and ease of use. These are critical requirements
especially for operations of CFA during field campaigns, e.g.,
inAntarcticaorGreenland.Furthermore,anoveldevicetomeasure
the total air content in the ice was developed. Subsequently,
the air bubbles are now extracted continuously from the sample
water flow for subsequent gas measurements.
Introduction
Ice cores provide a wealth of information about past climate
(1, 2), reaching back as far as 800 kyr in time. The diversity
of dissolved and particulate impurities deposited on ice sheets
provides an opportunity to obtain information on changes
in atmospheric transport and chemistry, strengths of sources
and sinks, and depositional effects (3-5).
Over the past years, continuous flow analysis (CFA)
systems have become a standard in ice core analyses (6-11).
This is due to the very fast and efficient decontamination of
the sample and the high depth resolution that can be achieved
over the full length of a deep ice core, in a fraction of the time
compared to that required for discrete sampling methods.
In CFA, a longitudinal subsection of an ice core is melted
continuously on a melter head, located in a cold environment,
while the sample is separated into inner and outer sample
flows providing efficient decontamination of the sample
(9, 10, 12, 13). The inner sample section, which consists of
the meltwater and bubbles from enclosed air in the ice, is
continuously pumped into a warm laboratory for online
analyses. Different analysis techniques can be used in a CFA
system. Apart from the methods used in this work, mass
spectrometers (7-9), fast ion chromatographs (FIC) (6, 11),
or other techniques (14) can be connected to a CFA melting
device.
The CFA system developed at the University of Bern, based
on earlier work (12, 13) and several innovations described
here, has been successfully used to obtain ice core records
in the frame of the recent major European ice core projects
in Antarctica (e.g., refs3, 15). However, the original CFA setup
has been lost during ship transport from Antarctica. This
gave us the chance to design a new system in a rigorous field
deployable way and to include several innovations: novel
measuring units have been introduced and existing ones
have been improved.
Past fieldwork has shown the need for a compact, modular,
robust, and transportable CFA system with temperature
stabilization. In situ analysis of ice cores in the field is
advantageous as the ice samples do not have to be transported
and hence the risk of additional fractures is avoided. This is
technically very important for the feasibility of the continuous
melting procedure, and scientifically to get high-resolution
records with fewer gaps. Furthermore, the risk of contami-
nation (e.g., HCHO) is reduced.
In this publication we describe new measuring units for
CFA such as the analysis of the total air content (TAC) and
insoluble dust particle concentration and size distribution
(16). The CFA system now also features a continuous air
extraction unit, offering the possibility of subsequent gas
analysis. Until now, the air in the melt flow originating from
the ice has been released without scientific benefit, although
these bubbles contain valuable information about the
composition of the past atmosphere (17, 18). In addition, a
novel technique for total organic carbon (TOC) has been
developed. However, its description is beyond the scope of
this publication and is provided in a separate publication
(26). Furthermore, several improvements or innovations
concerning traditional Bern CFA units (12) are described
briefly. To demonstrate the capability of our improved CFA
system we present measurements of TAC, dust, Na+, Ca2+,
NH4+, NO3-, SO42-, H2O2, HCHO, and the electrolytical
conductivity on a sequence of the North Greenland Ice Core
Project (NGRIP) ice core.
In addition to the innovations of the present work, the
major goal was to completely redesign the whole system in
order to improve the overall efficiency, signal stability,
robustness, automation, and ease of use. Hence, discussion
of the system is organized in preassembled units: melting
unit, sample distribution unit, and analysis unit.
Melting Unit
From the ice core, a sample with a typical cross section of
32 × 32 mm2 and a length between 1.0 and 1.65 m is cut and
then vertically placed above a heated melter head in a PTFE-
coated aluminum tray, which guides the ice during melting.
The whole melting unit is rack-mounted and located in a
cold environment at around -20 °C. It also contains a LCD
display and control buttons to monitor and control the CFA
system from the cold laboratory.
* Corresponding author e-mail: kaufmann@climate.unibe.ch;
phone: +41 (0)31 631 4465; fax: +41 (0)31 631 8742.
† Climate and Environmental Physics, Physics Institute, University
of Bern.
‡ Oeschger Centre for Climate Change Research, University of Bern.
§ British Antarctic Survey.
| University of Copenhagen.
⊥ Alfred-Wegener-Institute for Polar and Marine Research.
Environ. Sci. Technol. 2008, 42, 8044–8050
8044 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 21, 2008 10.1021/es8007722 CCC: $40.75  2008 American Chemical Society
Published on Web 10/04/2008

Compared to earlier versions of the melter head (12, 13),
the new design allows a larger sample rate and a more steady
melting process. It has already proven its reliability by melting
several 1000 m of ice cores. The melter head is now made
of copper plated with electroless nickel (5 µm) and gold (2
µm) to provide a chemically inert surface with good thermal
conductivity. The surface is divided into two concentric parts
(Figure FS2 in the Supporting Information, SI), but only the
sample water from the inner part (diameter of 24 mm) is
used for analysis. To prevent contamination efficiently, a
small meltwater overflow from the inner toward the outer
part is guaranteed (7, 8). This is achieved by pumping less
sample water from the inner part than available at the chosen
melting speed.
Due to the enlargement six concentrically arranged drain-
off holes are used, instead of one central hole. They are
connected to a PEEK-manifold by connection tubes as short
as possible, but of identical length, in order to minimize
sample dispersion. From the manifold a PFA tube (1.55 mm
i.d., 1/8′′ o.d., Omnilab) leads to the warm laboratory. An
additional six tubes from the outer part ensure drainage of
the discarded meltwater which could be used for further
investigations (e.g., for contamination insensitive isotope
measurements (19)).
To maintain a constant melting rate of typically 3.5 cm/
min, the melter head is kept at constant temperature (typically
20 °C). A thermostat (dTron16, JUMO) is connected to an
electrical cartridge heater of 400 W (Electrolux) in the center
of the copper body to provide heat coaxial to the ice sample.
The melt progress is registered by an optical encoder (Baumer
Electric) connected to a weight lying upon the ice sample,
which applies additional pressure to maintain a uniform
melting speed also toward the end of a measurement.
Distribution Unit
In the distribution unit, the sample meltwater from the melter
head is conveyed by a peristaltic pump with Tygon tubing
(both Ismatec) at a rate of typically ∼15.2 mL/min (Figure
1), adjusted to the melting speed. It is naturally segmented
by air bubbles coming from enclosed air in the ice which
account for approximately 10% of the volume. A custom-
built bubble detector is scanning the segmented flow in the
PFA tubing before it enters the debubbler, providing infor-
mation about TAC (see Analysis section). The debubbler is
hermetically sealed to ambient air, and its volume (∼300 µL)
is optimized to reduce sample dispersion but still prevent
any air bubbles entering the analysis systems. The rate of the
overflow is given by the difference of the inflow and the
water consumption of all measuring units.
The final separation of air and water in the overflow takes
place in the degassing unit through a gas-permeable hy-
drophobic membrane (Accurel, Microdyn) where a helium
flow outside the Accurel is used as carrier gas (7). It is
important to pressure-decouple the degassing unit from the
entire liquid chemistry flow system, as it affects the flow
rates. This is achieved with an additional buffer volume, which
is open to atmospheric pressure (∆p in Figure 1). The bubble
detector, the debubbler, the buffer volume and the degassing
unit are mounted inside a temperature stabilized box (25 (
0.02 °C).
After the debubbler, a master valve (080T-Series, BioChem
Valve) determines whether sample water or blank flows
FIGURE 1. The flow system of the CFA analysis system. Meltwater flow from the melting unit is divided by the use of a closed debubbler
into a bubble-free sample water flow and an air-containing overflow. The latter is led to a gas extraction unit for further gas analysis,
while the sample water passes through the master valve and is distributed to the measuring units. Abbreviations and symbols: total air
content (TAC), Solenoid valves (small white circles), bubble detectors (BD, black ellipses), pressure gauge (p), pump tubes and flow
directions (arrow boxes), flow rates in mL/min (numbers in the arrow boxes), Accurel micro porous membrane debubbler (small gray
boxes), fluorimetric detection (FD), absorption detection (AD), standard solution (Sta), reagent (Rea), carrier solution (Car), buffer solution
(Buf), waste (W), immobilized enzyme reactor (IMER), cation exchange column (CEC), multicomponent calibration solution (MCS), buffer
volume for pressure decoupling (∆p), and back pressure coil (bp-coil). Furthermore, lengths and temperatures (if heated or cooled) of
mixing and reactor coils, and wavelengths of the different detections are indicated in the figure. Descriptions of additional items are given
in the text.
VOL. 42, NO. 21, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 8045