(Received November 13, 2015; Accepted November 12, 2016)

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1 Geochemical Journal, Vol. 51, pp. 293 to 298, 2017 doi: /geochemj NOTE Overview of the chemical composition and characteristics of Na + and Cl distributions in shallow samples from Antarctic ice core DF01 (Dome Fuji) drilled in 2001 YUKO MOTIZUKI, 1 HIDEAKI MOTOYAMA, 2 YOICHI NAKAI, 1 KEISUKE SUZUKI, 3 YOSHINORI IIZUKA 4 and KAZUYA TAKAHASHI 1 * 1 RIKEN Nishina Center, Hirosawa 2-1, Wako , Japan 2 National Institute of Polar Research, Research Organization of Information and Systems, Midoricho 10-3, Tachikawa, Tokyo , Japan 3 Department of Environmental Sciences, Shinshu University, Asahi 3-1-1, Matsumoto , Japan 4 Institute of Low Temperature Science, Hokkaido University, Sapporo , Japan (Received November 13, 2015; Accepted November 12, 2016) Ice core samples record information about the geological history of the Earth, including past climate changes. Dome Fuji, situated at the highest point of Queen Maud Land, is considered one of the best drilling locations for procuring samples to reconstruct past climates and environments. We present here fundamental data on the concentrations of dissolved ions in shallow samples, between 7.7 m and 65.0 m depth, from the Dome Fuji ice core drilled in The measured anions were HCOO, CH 3 COO, CH 3 SO 3, F, Cl, NO 2, NO 3,, C 2 O 4, and PO 4 3, and the cations were Na +, K +, Mg 2+, Ca 2+, and NH 4 +. The temporal resolution of the depth profiles of the ion concentrations was less than one year. No significant correlations were observed among the ions except between Na + and Cl. The ion balance in the core, based on the averaged ion concentrations of the samples, was different to that of sea salt, a result consistent with the findings of previous studies. In several samples, however, synchronous concentration peaks of Na + and Cl were identified, and the Cl /Na + ratios of the corresponding samples were close to the sea salt ratio. This observation indicates the possibility that climate conditions were such that precipitation containing sea salt occurred in the Dome Fuji area. The Cl /Na + ratio of samples that did not exhibit Na + and Cl peaks in the depth profile differed from that previously reported for the covering snow. This result implies that Cl, but not Na +, was redistributed after deposition. High concentrations of in some samples may account for this alteration of Cl /Na + ratios. To interpret these observations and elucidate the climatic conditions, further studies, such as isotopic analyses of d 18 O and dd, are required. Keywords: ice core, Dome Fuji, chemical composition, ion balance INTRODUCTION Ice core samples are regarded as time capsules because they contain information on the history of the Earth, including climate changes. Dome Fuji station ( S, E; 3810 m a.s.l.) is situated at the highest point of Queen Maud Land, Antarctica, and is thus considered to be one of the best drilling locations in Antarctica for obtaining significant data with which to reconstruct past climates and environments. Kamiyama et al. (1989) examined the chemical composition and ion balance of surface snow in East Queen Maud Land around the present Dome Fuji station and showed that the chemi- *Corresponding author ( kazuyat@riken.jp) Copyright 2017 by The Geochemical Society of Japan. cal composition and ion balance of surface snow there are distinct from those of sea salt. At Dome Fuji, a shallow ice core (112.6 m) was obtained in 1993, and the concentrations of anions and cations were analysed in approximately 100 samples collected at 50-cm intervals from the ice core by Watanabe et al. (2003). In 1995 and 1996, an ice core was recovered to a depth of 2503 m, and chemical analyses were performed by Iizuka et al. (2008) on samples from eight sections to estimate past environments during the Holocene and last glacial maximum. The profile to a depth of 40 m in a shallow core, the DF01 core, drilled at Dome Fuji in November 2001, was examined by Igarashi et al. (2011) and the peaks were compared with recorded volcanic eruptions to develop an age model for the core. Subsequently, Motizuki et al. (2014) extended the age model of the DF01 core to a depth of 85 m through non-sea-salt syn- 293

2 Table 1. The average, maximum and median concentrations of ion species of 1435 samples from Dome Fuji ice core (mg/l) (minimum concentrations of all species were less than detection limits) F - CH 3 COO - HCOO - MSA Cl - NO 2 - NO 3-2- C 2 O 4 2- PO 4 3- Na + K + Mg 2+ Ca 2+ NH 4 + average maximum median D.L D.L.: detection limits. chronization with a shallow core drilled near Kohnen station that had been dated by annual layer counting, and established the chronology from AD 1900 back to AD 1. Despite these partial chemical analyses of Dome Fuji ice cores, no systematic analyses or core chemistry in conjunction with high-resolution sampling (e.g., about one year per sample) has yet been performed on these Antarctic cores. In this study, precise ion chromatographic measurement of anions and cations in samples collected between the depths of 7.7 m and 65.0 m from the Dome Fuji ice core DF01 were performed. This depth interval corresponds to a period of approximately 1300 years. In this paper, we examine the chemical composition and ion balances in these samples, which have a time resolution of slightly less than one year, and consider some basic geochemical implications of the results. SAMPLES AND EXPERIMENTAL PROCEDURE The ice core DF01, after drilling at Dome Fuji station, immediately cut into 50-cm segments and then transported to the National Institute of Polar Research (NIPR), Japan. We examined the DF01 ice core segments extracted between the depths of 7.7 m and 65.0 m. These segments were further cut into longitudinal sections approximately 3 4 cm long. According to the chronological studies by Igarashi et al. (2011) and Motizuki et al. (2014), each 3 4 cm segment should generally correspond to a time period of slightly less than one year. Before the analyses, the surface (thickness >3 mm) of each sample was scraped off with a ceramic knife in a clean-air bench to prevent contamination. Each ice sample was then stored in a clean, dust-free plastic bag until chemical analysis. The samples were prepared in a freezer laboratory, and a total of 1435 samples were obtained for the analysis in the present study. Anions and cations in the samples were analysed by using ion chromatography (ICS2000 system for anions and Dionex 500 system for cations). The anions HCOO, CH 3 COO, CH 3 SO 3, F, Cl, NO 2, NO 3, SO 4, C 2 O 3 4, and PO 4 were measured by a gradient technique, and the cations Na +, K +, Mg 2+, Ca 2+ +, and NH 4 were measured by an isocratic method. The analytical errors were estimated to be 5% or less. RESULTS AND DISCUSSION In most samples, the concentrations of each ion were observed to range from 10 to 200 mg/l, and the ph range was about In Table 1, the average concentrations of ions are listed with the maximum and the median values. The depth profiles of the dominant ions (Na +, Cl and SO 4 ) are shown in Fig. 1. We compared the average relative abundance of cations and anions in the ice core samples with that in sea salt (Fig. 2). In sea salt, the main ions are Na + and Cl, whereas in the DF01 ice core samples and alkaline earth ions were markedly abundant. This result shows that most of the precipitation at Dome Fuji during the period represented by these samples did not reflect the composition of sea salt, and hence the precipitation at Dome Fuji site contains some different components from sea salt or could be metamorphosed after precipitation. This is basically consistent with the result of Kamiyama et al. (1989), who investigated the ionic balance of surface snow in East Queen Maud Land, and those of Watanabe et al. (2003), whose data from the Dome Fuji ice core drilled in 1993 did not indicate any influence from the sea. Kamiyama et al. (1989) also analysed the concentration of tritium fallout from nuclear bomb tests conducted in the 1960s, a primarily stratospheric signal, and compared the concentration to those reported for other locations in Antarctica; the highest tritium level was found around the Dome Fuji site. On the basis of their results, Kamiyama et al. (1989) proposed that ions in snow samples from the high inland plateau in East Queen Maud Land were not directly transported via the troposphere but were instead transported from the stratosphere. Fourré et al. (2006), who summarized available tritium data with their newly obtained results in snow samples from Arctic and Antarctic polar caps, showed that samples from Dome Fuji contain significantly high levels of tritium, although Fourré et al. (Table 1: Fourré et al., 2006) misreported one of Dome Fuji tritium values as pertaining to Dome C; their result implies that precipitation around Dome Fuji might reflect 294 Y. Motizuki et al.

3 Fig. 1. Depth profiles of the dominant ions. Chemical characteristics in shallow samples from Antarctic ice core DF01 295

Overview of chemical composition K + NH 4 + Mg 2+

- NO - 3 Na + Cl - Average ion concentrations of DF01

(left) Relative ion composition of the DF01 ice core,

samples. (right) Relative ion composition of sea salt.

correlations were found between dominant cationanion

4 Overview of chemical composition K + NH 4 + Mg 2+ Organic aci id Mg K Ca2+ Ca 2+ Na + 2- Cl - NO - 3 Na + Cl - Average ion concentrations of DF01 samples (7.7m-65.0m) Sea salt Fig. 2. (left) Relative ion composition of the DF01 ice core, based on the average concentrations (meq/l) in 1435 samples. (right) Relative ion composition of sea salt. Fig. 3. Scatter plots of Na + vs. Cl concentrations and vs. Cl concentrations in 1435 samples. a) Na + vs. Cl. b) vs. Cl. conditions in the stratosphere. Among the 15 ions measured in this study, no significant correlations were found between dominant cationanion pairs except between Na + and Cl, whose correla- tion coefficient was The depth profiles of the ion concentrations displayed several characteristics. One of the dominant ion species in the samples was. Several peaks were recognized (Fig. 1); as reported by 296 Y. Motizuki et al.

5 Igarashi et al. (2011) and Motizuki et al. (2014), these peaks are signals of volcanic eruptions. Sulphur injected into the atmosphere by a huge volcanic eruption has subsequently become incorporated, as sulphuric acid, into snow that fell on Antarctica. In the depth profiles of Na + and Cl concentrations (Fig. 1), several synchronous Na + and Cl peaks were observed. A scatter plot of the concentrations of Na + against those of Cl shows that the samples exhibiting synchronous Na + and Cl peaks in the depth profiles plot close to the sea salt mixing line (i.e., a Cl /Na + ratio of 1.8; Fig. 3-a), dashed line). Suzuki et al. (2002, 2003) and Bertler et al. (2005) reported that the concentrations of Na + and Cl in surface snow decrease exponentially with increasing distance from the Antarctic coast, and that the effect of sea salt can hardly be recognized around Dome Fuji. Similarly, Kamiyama et al. (1989) reported that the ion balance in surface snow around Dome Fuji site is different to that of seawater. Therefore, precipitation containing sea salt does not ordinarily reach the interior of Antarctica under the prevailing climatic conditions. The results obtained in this study imply, however, that sudden changes in climatic conditions around Antarctica, occurring at the times corresponding to the depths where the synchronous Na + and Cl peaks were observed in the ice core profiles, caused precipitation in this interior region to contain abundant sea salt. Fujita and Abe (2006) examined stable isotopes of hydrogen and oxygen in the daily precipitation at Dome Fuji in 2003 and reported that 11 precipitation events (on 18 days) accounted for 47% of the annual accumulation of snow. These heavy snowfalls occurred under specific conditions (i.e., relatively higher air temperature, stronger wind speeds, and higher air pressure), and, moreover, they exhibited d-excess values (defined as d-excess = dd 8d 18 O) close to that of the meteoric water line. These findings suggest that the direct vapour transfer from coastal areas to the area around Dome Fuji occurred during these heavy snowfall events. Therefore, it is possible to infer the occurrence of climate changes causing precipitation containing sea salt to fall in inland parts of Antarctica from high-resolution depth profiles of Na + and Cl concentrations. Further careful investigation of depth profiles of Na + and Cl concentrations is required. Furthermore, Na + and Cl concentrations were correlated with each other in most samples, excluding those with the synchronous peaks (Fig. 3-a), dotted line). The Cl /Na + ratio of the samples on the correlation line was 1.36, which was lower than that of sea salt (the Cl /Na + ratio is 1.8). Newberg et al. (2005) reported the Cl depletion in sea salt particles for the north-eastern Pacific Ocean. If the sea salt components might be subject to such depletion of Cl through atmosphere during the transportation to Dome Fuji site, the precipitation at Dome Fuji might have exhibited lower Cl /Na + ratio than sea salt. However, for the Cl /Na + ratio of the snow covering at Dome Fuji, Suzuki et al. (2003) reported 3.4 and Iizuka et al. (2016) reported 2.6. These observed data were higher than that of sea salt. Therefore, it should be necessary to take account of some metamorphism which reduced the Cl /Na + ratio for the samples in the ice core after the precipitation. Fujita et al. (2016) examined layered firn collected from several sites at Dome Fuji (DF93, DF99 and DFS10) and suggested that, in the presence of sulphate, Cl ions are much more mobile than Na + in ice; as a result, the Cl distribution is smoothed, becoming relatively homogeneous, whereas Na + is fixed to sulphate. In the studied DF01 core, was the dominant anion with concentrations exceeding 250 mg/l in many parts of the depth profile (Fig. 1). Moreover, on a scatter plot of against Cl (Fig. 3-b)), the Cl concentrations fall within a narrow range in samples containing high concentrations of. If the hypothesis of Fujita et al. (2016) is correct, then the Cl /Na + ratios in samples with relatively high concentrations of would be altered after precipitation by the smoothing of Cl concentrations across samples, leading to the Cl /Na + ratios similar to those observed in this study. The samples for which Na + and Cl plot along the sea salt mixing line contained relatively low concentrations of. Thus, in those samples containing a sea salt component, because the concentrations were not very high, the Cl /Na + ratios of the precipitation are considered preserved. Further detailed studies of the relationship between Na + and Cl in the DF01 core are required to confirm this hypothesis. In addition, isotopic analyses of d 18 O and dd should help to elucidate the climatic conditions responsible for the synchronous Na + and Cl peaks in the depth profiles. SUMMARY Chemical analyses of the DF01 ice core samples collected at intervals of 3 4 cm, each corresponding to slightly less than one year, yielded the following significant findings. 1. The ion balance of the averaged ion concentrations differed from that of sea salt. 2. Several characteristic Na + and Cl concentration peaks were observed in the depth profiles, and the Cl / Na + ratio of these peaks indicated the presence of a strong sea salt component. This observation implies that some critical climatic change occurred to cause precipitation with an enhanced sea salt component to fall in the Dome Fuji area. 3. In most samples, excluding those exhibiting the synchronous Na + and Cl peaks in the depth profiles, Na + and Cl were correlated, but the Cl /Na + ratios differed Chemical characteristics in shallow samples from Antarctic ice core DF01 297

6 from both the sea salt mixing line and the previously reported ratios in the surface snow at the core site. 4. It is probable that the Cl /Na + ratios were altered after precipitation by the re-distribution of Cl, but not Na +, in ice with a high concentration of. Detailed analyses of ions and isotopes are required to investigate further the relationship between Na + and Cl and possible effects of changes of climatic conditions. The data of Na +, Cl and, which will be accessible from the Dome Fuji Ice Core Consortium, are expected to contribute significantly to scientific studies using data in ice cores from the polar regions. Acknowledgments We thank the Dome Fuji Ice Core Consortium for providing the ice core examined in this study. We are grateful to M. Kitagawa (RIKEN), T. Kobayashi (NIPR), and M. Igarashi (NIPR/RIKEN) for their help in obtaining the data by ion chromatography. We also thank S. Fujita for enlightening discussion. YM acknowledges support from the Funding Program for Next Generation World-Leading Researchers (NEXT Program, Grant Number GR098) initiated by the Council for Science and Technology Policy and the Japan Society for the Promotion of Science (JSPS) and a Grant-in-Aid for Scientific Research (A) (Grant Number ) from JSPS to fulfil this study. REFERENCES Bertler, N., Mayewski, P. A., Aristarain, A., Barrett, P., Becagli, S., Bernardo, R., Bo, S., Xiao, C., Curran, M., Qin, D., Dixon, D., Ferron, F., Fisher, H., Frey, M., Frezzotti, M., Fundel, F., Genthon, C., Gragnani, R., Hamilton, G., Handley, M., Hong, S., Isaksson, E., Kang, J., Ren, J., Kamiyama, K., Kanamori, S., Kärkäs, E., Karlöf, L., Kaspari, S., Kreutz, K., Kurbatov, A., Meyerson, E., Ming, Y., Zhang, M., Motoyama, H., Mulvaney, R., Oerter, H., Osterberg, E., Proposito, M., Pyne, A., Ruth, U., Simões, J., Smith, B., Sneed, S., Teinilä, K., Traufetter, F., Udisti, R., Virkkuka, A., Watanabe, O., Williamson, B., Winther, J.-G., Li, Y., Wolff, E., Li, Z. and Zielinski, A. (2005) Snow chemistry across Antarctica. Ann. Glaciology 41, Fourré, E., J.-Baptiste, P., Dapoigny, A., Baumier, D., Petit, J.- R. and Jouzel, J. (2006) Past and recent tritium levels in Arctic and Antarctic polar caps. Earth Planet. Sci. Lett. 245, Fujita, K. and Abe, O. (2006) Stable isotopes in daily precipitation at Dome Fuji, East Antarctica. Geophys. Res. Lett. 33, L Fujita, S., Goto-Azuma, K., Hirabayashi, M., Hori, A., Iizuka, Y., Motizuki, Y., Motoyama, H. and Takahashi, K. (2016) Densification of layered firn of the ice sheet at Dome Fuji, Antarctica. J. Glaciology, doi: jog ; published online: 21 March Igarashi, M., Nakai, Y., Motizuki, Y., Takahashi, K., Motoyama, H. and Makishima, K. (2011) Dating of the Dome Fuji shallow ice core based on a record volcanic eruption from AD1260 to AD2001. Polar Sci. 5, Iizuka, Y., Horikawa, S., Sakurai T., Johnson, S. D., Dahl- Jensen, J., Steffensen, P. and Hondoh, T. (2008) A relationship between ion balance and the chemical compounds of salt inclusions found in the Greenland Ice Core Project and Dome Fuji ice cores. J. Geophys. Res. 113, D Iizuka, Y., Ohno, H., Uemura, R., Suzuki, T., Oyabu, I., Hoshina, Y., Fukui, K., Hirabayashi, M. and Motoyama, H. (2016) Spatial distributions of soluble salts in surface snow of East Antarctica. Tellus 68B, ( tellusb.v ). Kamiyama, K., Ageta, Y. and Fujii, Y. (1989) Atmospheric and depositional environments traced from unique chemical compositions of the snow over an inland high plateau, Antarctica. J. Geophys. Res. 94, 18,515 18,519. Motizuki, Y., Nakai, Y., Takahashi, K., Igarashi, M., Motoyama, H. and Suzuki, K. (2014) Dating of a Dome Fuji (Antarctica) shallow ice core by volcanic signal synchronization with B32 and EDML1 chronologies. The Cryosphere 8, Newberg, J. T., Matthew, B. M. and Anastasio, C. (2005) Chloride and bromide depletions in sea-salt particles over the northeastern Pacific Ocean. J. Geophys. Res. 110, D06209, doi: /2004jd Suzuki, T., Iizuka, Y., Matsuoka, K., Furukawa, T., Kamiyama, K. and Watanabe, O. (2002) Distribution of sea salt components in snow cover along the traverse route from the coast to Dome Fuji station 1000 km inland at east Dronning Maud Land, Antarctica. Tellus 54B, Suzuki, T., Iizuka, Y., Furukawa, T., Matsuoka, K., Kamiyama, K. and Watanabe, O. (2003) Spatial variability of chemical tracers in surface snow along the traverse route from the coast to 1000 km inland at east Dronning Maud Land, Antarctica. Chinese J. of Polar Science 14, Watanabe, O., Kamiyama, K., Motoyama, H., Fujii, Y., Igarashi, M., Furukawa, T., Goto-Azuma, K., Saito, K., Kanamori, S., Kanamori, N., Yoshida, N. and Uemura, R. (2003) General tendencies of stable isotopes and major chemical constituents of the Dome Fuji ice core. Mem. Natl. Inst. Polar Res., Spec. 57, Y. Motizuki et al.

Supplement of Ice core evidence for a 20th century increase in surface mass balance in coastal Dronning Maud Land, East Antarctica

Supplement of The Cryosphere, 10, 2501 2516, 2016 http://www.thecryosphere.net/10/2501/2016/ doi:10.5194/tc1025012016supplement Author(s) 2016. CC Attribution 3.0 License. Supplement of Ice core evidence