Ⅱ-7. Astrophysics and Astro-Glaciology

RIKEN Accel. Prog. Rep. 53

Commissioning of a prototype novel laser melting sampler for analyzing
ice cores with high depth resolution and high throughput
Y. Motizuki,∗1 Y. Nakai,∗1 M. Yumoto,∗2 M. Maruyama,∗2 K. Takahashi,∗1 K. Kase,∗2 S. Wada,∗2 J. Hirose,∗1 andY. Yano∗1A new facility for analyzing ice cores is being developed jointly by the Astro-Glaciology Research Group(AGRG) of RIKEN Nishina Center and the Photonics Control Technology Team of RIKEN Center for Advanced Photonics in a room (50 m2 ) at Wako Campus.
The mission of this facility is to analyze ice cores withhigh depth (temporal) resolution and high throughput
to obtain concentration proﬁles of various isotopes such−as 18 O/16 O and various ions such as SO2−
4 and NO3 .
The ice cores that we study have been drilled by
the Japanese Antarctic Research Expedition (JARE)
around Dome Fuji (DF) station in East Antarctica, andthe current JARE project to obtain the third Japanese
deep ice core, which is expected to contain information
up to more than a million years ago, has been approved
and is in progress. We aim at investigating the longterm history of climate change from the viewpoints of
the relation with solar activities and volcanic eruptions.
We also seek traces of supernovae in our galaxy and its
explosion rate as our ﬁnal goal.
In our facility, a low-temperature (LT) room, i.e., aprefabricated freezer container (3 m wide × 5 m long× 3 m high), has been installed, and its inside has been
kept at −20◦ C. Outside the LT room, two sets of isotope
analyzers have been equipped at room temperature; weplan to add the newest ion chromatography system here
in the near future.
The application of the laser melting method on ice
cores to obtain samples is the ﬁrst in the world. Figure 1 depicts a schematic of the prototype laser melting
sampler. The sampler consists of a continuous-wave ﬁberlaser (λ = 1.55 µm), an optical ﬁber (core diameter =200 µm, our originally designed nozzle (2 mm outer ϕ),a sampling buﬀer system with an electromagnetic valve,
and a computer that controls the positions of the sampling nozzle and the motorized stage on which an ice coreis placed. This system makes it possible to analyze ice
cores at a high depth resolution of ∼2 mm scale, whichcorresponds to a temporal resolution of ∼1 month in thecase of a DF ice core. Our system is also applicable to a
1-year resolution (∼3 cm) when sampling is performedin the direction of core depth.

Fig. 1. Schematic of the ice-core laser melting sampling system.
∗1∗2Fig. 2. Left ﬁgure shows a photo of melting ice with thenozzle intruding the dummy ice (bottom right) and theinside buﬀer being ﬁlled (bottom left). The right shows
a ﬁlled vial.

In Fig. 1, the laser beam delivered by the opticalﬁber irradiates the target ice-core surface, and 1.5 mL ofmelted water (suﬃcient volume for our precision analysis) is sucked up through the nozzle and transported
into our original SUS vial bottle by a peristaltic tube
pump at a pressure drop of 1 atm. The nozzle and tube
are kept above 0◦ C by the heaters installed inside thenozzle assembly.
We succeeded in continuous sampling into the vials
using this prototype sampler. Figure 2 shows the result: the holes were vertically made as small as 2 mm ϕon a dummy ice block (ρ = 0.9 g/cc) by laser melting.
For this purpose, a laser beam with a power of ∼1.3 W
was irradiated, and the nozzle intruding speed was set
to 0.40 mm/s. The eﬃciency of collecting melted water
was estimated to be ∼100%. As the ﬁrst step, we set ourtarget sampling time for a vial to 20 min, which was determined in concordance with the measurement time of
one sample by a single isotope analyzer using the AGRGprotocol developed based on our isotope measurements.
By choosing optimum apparatus parameters and by using an automated multi -nozzle system that has alreadybeen equipped in our system, we plan to attain a higher
throughput to handle many sample vials.
Our new technique has some advantages in comparison with the standard heater-melting continuous ﬂow
analysis method.1) They are as follows: 1) samplingzones are discrete to avoid mixing with each other, 2)
the amount of sampling ice can be adequately minimized, and 3) fragile low-density ice cores are also applicable because the portion of a core is placed horizontally (Fig. 1). Making the most of these merits, we havestarted to perform our ﬁrst application on Antarctic ice
to study if there appear seasonal variations in the wellestablished temperature proxy (18 O/16 O) for the ﬁrst
time in the past ∼30 years for direct comparison withthe temperature measured in the area.
We are grateful to Michio Sakashita for supporting uswith laser ﬁber treatment and Yu Vin Sahoo for preparing clear dummy ice blocks suitable for our experiments.
Reference

RIKEN Nishina Center
RIKEN Center for Advanced Photonics

1) e.g., R. Dallmayr et al., Bull. Glaciol. Res. 34, 11 (2016).
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