II-7. Astrophysics and Astro-Glaciology

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

A novel high-resolution laser-melting sampler for discrete analyses ofion concentrations and stable water isotopic compositions in firn and icecores
Y. Motizuki,∗1 Y. Nakai,∗1 K. Takahashi,∗1 J. Hirose,∗1 Y. V. Sahoo,∗1 Y. Yano,∗1 M. Yumoto,∗2 M. Maruyama,∗2M. Sakashita,∗2 K. Kase,∗2 and S. Wada∗2Ice cores preserve past climatic changes and, in somecases, astronomical signals. Here we present a newly developed automated ice-core sampler that employs laser
melting (see Fig. 1). In our system, a hole in an ice coreapproximately 3 mm in diameter is melted and heatedwell below the boiling point by laser irradiation, and themeltwater is simultaneously siphoned by a 2 mm diameter movable evacuation nozzle that also holds the laser
ﬁber. The advantage of sampling by laser melting isthat molecular ion concentrations and stable water isotope compositions in ice cores can be measured at highdepth resolution, which is advantageous for ice cores withlow accumulation rates, such as ice cores drilled around
Dome Fuji station in Antarctica.
This device takes highly discrete samples from icecores, attaining depth resolution as small as ∼3 mm withnegligible cross contamination; the resolution can also be
set at longer lengths suitable for validating longer-term
proﬁles of various ionic and water isotopic constituentsin ice cores.
The laser beam used to melt the ice is supplied throughthe wall of the freezer container by a continuous-wave
operated Er-doped ﬁber laser (CEFL-TERA, KeopsysInc.) through optical ﬁbers (core/clad diameter =200/220 µm). The laser wavelength is 1.55 µm (nearinfrared) and the maximum output power is 10 W. The
1.55-µm wavelength takes advantage of the strong absorption bands of ice and water from 1.4–1.6 µm. In addition, because 1.55-µm lasers are commonly used in optical communication technologies, suitable optical ﬁbers
are commercially available.
To check the stability of the sampler in the −20◦ CFig. 1. Photo showing a newly-developed laser-melting icecore sampler.
∗1∗2

RIKEN Nishina Center
RIKEN Center for Advanced Photonics

Fig. 2. Photo showing an ice block after the continuous extraction of 100 meltwater samples in a stability test.

environment, we performed a continuous sampling testin which 100 vials were ﬁlled with a minimal volume(0.65 mL) of meltwater. In this test, the laser power was
set at 1.9 W, the nozzle intrusion speed was 0.52 mm/s,
the pumping speed was 5.5 mL/min, and the horizontal
and vertical pitch of the nozzle was 2.5 mm. It took 8hours 47 minutes to complete this test with no issuesthe ∼ −20◦ C environment. Figure 2 shows a dummy ice
block made up from ultrapure water (Milli-Q water) after
this stability test. We conclude that the sampling rate
will not be a bottleneck during high-throughput isotopic
and ionic ice-core analyses.
We also conducted experiments to check whether there
was any leaching of ions from inner components and tocheck the degree by which samples mixed with each otherduring continuous sample collection. We found a 2.4%
“memory eﬀect,” which is usually signiﬁcantly less than
the analytical accuracy (a few µg/L) of ion analyses byion chromatography. We conclude that internal contamination and cross contamination are negligible with thissampler.
With this new sampler design, the analysis of the2,000-year record embodied in the Dome Fuji ﬁrn core,
which took us several years, could now be ﬁnished inabout 30 working days by using two isotopic analyzers. For the ﬁrst time, we can now realistically contemplate strategic plans for cores recovered from lowaccumulation sites that include large numbers of repeated operations, such as compiling continuous 2,000year proﬁles with annual resolution of ionic and water isotopic constituents. Finally, our sampler has thecapability to proﬁle ionic and isotopic constituents atmonthly resolution to pursue intriguing transient signals,
potentially by annual layer counting.
Reference

1) Motizuki et al., submitted to Cold Reg. Sci. Technol.

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