Faculty Profiles - FUJITA, Koji

Papers - FUJITA, Koji

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Use of Water Balance and Tracer-Based Approaches to Monitor Groundwater Recharge in the Hyper-Arid Gobi Desert of Northwestern China Reviewed International coauthorship

Akiyama T, Kubota J, Fujita K, Tsujimura M, Nakawo M, Avtar R, Kharrazi A

Environments Vol. 5 ( 5 ) page： 55 - 15 2018.5

Language：English Publishing type：Research paper (scientific journal)

The groundwater recharge mechanism in the hyper-arid Gobi Desert of Northwestern China was analyzed using water balance and tracer-based approaches. Investigations of evaporation, soil water content, and their relationships with individual rainfall events were conducted from April to August of 2004. Water sampling of rainwater, groundwater, and surface water was also conducted. During this period, 10 precipitation events with a total amount of 41.5 mm, including a maximum of 28.9 mm, were observed. Evaporation during the period was estimated to be 33.1 mm. Only the soil water, which was derived from the heaviest precipitation, remained in the vadose zone. This is because a dry surface layer, which was formed several days after the heaviest precipitation event, prevented evaporation. Prior to that, the heaviest precipitation rapidly infiltrated without being affected by evaporation. This is corroborated by the isotopic evidence that both the heaviest precipitation and the groundwater retained no trace of significant kinetic evaporation. Estimated δ-values of the remaining soil water based on isotopic fractionation and its mass balance theories also demonstrated no trace of kinetic fractionation in the infiltration process. Moreover, stable isotopic compositions of the heaviest precipitation and the groundwater were very similar. Therefore, we concluded that the high-intensity precipitation, which rapidly infiltrated without any trace of evaporation, was the main source of the groundwater.

DOI： 10.3390/environments5050055

Asynchrony between Antarctic temperature and CO2 associated with obliquity over the past 720,000 years Reviewed International coauthorship Open Access

Ryu Uemura, Hideaki Motoyama, Valérie Masson-Delmotte, Jean Jouzel, Kenji Kawamura, Kumiko Goto-Azuma, Shuji Fujita, Takayuki Kuramoto, Motohiro Hirabayashi, Takayuki Miyake, Hiroshi Ohno, Koji Fujita, Ayako Abe-Ouchi, Yoshinori Iizuka, Shinichiro Horikawa, Makoto Igarashi, Keisuke Suzuki, Toshitaka Suzuki, Yoshiyuki Fujii

Nature Communications Vol. 9 ( 1 ) page： 961 2018.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Nature Publishing Group

The δD temperature proxy in Antarctic ice cores varies in parallel with CO2 through glacial cycles. However, these variables display a puzzling asynchrony. Well-dated records of Southern Ocean temperature will provide crucial information because the Southern Ocean is likely key in regulating CO2 variations. Here, we perform multiple isotopic analyses on an Antarctic ice core and estimate temperature variations at this site and in the oceanic moisture source over the past 720,000 years, which extend the longest records by 300,000 years. Antarctic temperature is affected by large variations in local insolation that are induced by obliquity. At the obliquity periodicity, the Antarctic and ocean temperatures lag annual mean insolation. Further, the magnitude of the phase lag is minimal during low eccentricity periods, suggesting that secular changes in the global carbon cycle and the ocean circulation modulate the phase relationship among temperatures, CO2 and insolation in the obliquity frequency band.

DOI： 10.1038/s41467-018-03328-3

NHM-SMAP: Spatially and temporally high-resolution nonhydrostatic atmospheric model coupled with detailed snow process model for Greenland Ice Sheet Reviewed Open Access

Masashi Niwano, Teruo Aoki, Akihiro Hashimoto, Sumito Matoba, Satoru Yamaguchi, Tomonori Tanikawa, Koji Fujita, Akane Tsushima, Yoshinori Iizuka, Rigen Shimada, Masahiro Hori

Cryosphere Vol. 12 ( 2 ) page： 635 - 655 2018.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Copernicus GmbH

To improve surface mass balance (SMB) estimates for the Greenland Ice Sheet (GrIS), we developed a 5ĝ€̄km resolution regional climate model combining the Japan Meteorological Agency Non-Hydrostatic atmospheric Model and the Snow Metamorphism and Albedo Process model (NHM-SMAP) with an output interval of 1ĝ€̄h, forced by the Japanese 55-year reanalysis (JRA-55). We used in situ data to evaluate NHM-SMAP in the GrIS during the 2011-2014 mass balance years. We investigated two options for the lower boundary conditions of the atmosphere: an offline configuration using snow, firn, and ice albedo, surface temperature data from JRA-55, and an online configuration using values from SMAP. The online configuration improved model performance in simulating 2ĝ€̄m air temperature, suggesting that the surface analysis provided by JRA-55 is inadequate for the GrIS and that SMAP results can better simulate physical conditions of snow/firn/ice. It also reproduced the measured features of the GrIS climate, diurnal variations, and even a strong mesoscale wind event. In particular, it successfully reproduced the temporal evolution of the GrIS surface melt area extent as well as the record melt event around 12 July 2012, at which time the simulated melt area extent reached 92.4ĝ€̄%. Sensitivity tests showed that the choice of calculation schemes for vertical water movement in snow and firn has an effect as great as 200ĝ€̄Gtĝ€̄year-1 in the GrIS-wide accumulated SMB estimates
a scheme based on the Richards equation provided the best performance.

DOI： 10.5194/tc-12-635-2018

Review of the status and mass changes of Himalayan-Karakoram glaciers Reviewed International coauthorship Open Access

Mohd Farooq Azam, Patrick Wagnon, Etienne Berthier, Christian Vincent, Koji Fujita, Jeffrey S. Kargel

Journal of Glaciology Vol. 64 ( 243 ) page： 61 - 74 2018.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Cambridge University Press

We present a comprehensive review of the status and changes in glacier length (since the 1850s), area and mass (since the 1960s) along the Himalayan-Karakoram (HK) region and their climate-change context. A quantitative reliability classification of the field-based mass-balance series is developed. Glaciological mass balances agree better with remotely sensed balances when we make an objective, systematic exclusion of likely flawed mass-balance series. The Himalayan mean glaciological mass budget was similar to the global average until 2000, and likely less negative after 2000. Mass wastage in the Himalaya resulted in increasing debris cover, the growth of glacial lakes and possibly decreasing ice velocities. Geodetic measurements indicate nearly balanced mass budgets for Karakoram glaciers since the 1970s, consistent with the unchanged extent of supraglacial debris-cover. Himalayan glaciers seem to be sensitive to precipitation partly through the albedo feedback on the short-wave radiation balance. Melt contributions from HK glaciers should increase until 2050 and then decrease, though a wide range of present-day area and volume estimates propagates large uncertainties in the future runoff. This review reflects an increasing understanding of HK glaciers and highlights the remaining challenges.

DOI： 10.1017/jog.2017.86

A 60 Year Record of Atmospheric Aerosol Depositions Preserved in a High-Accumulation Dome Ice Core, Southeast Greenland Reviewed Open Access

Yoshinori Iizuka, Ryu Uemura, Koji Fujita, Shohei Hattori, Osamu Seki, Chihiro Miyamoto, Toshitaka Suzuki, Naohiro Yoshida, Hideaki Motoyama, Sumito Matoba

Journal of Geophysical Research: Atmospheres Vol. 123 ( 1 ) page： 574 - 589 2018.1

Language：English Publishing type：Research paper (scientific journal)

©2017. American Geophysical Union. All Rights Reserved. The Southeastern Greenland Dome (SE-Dome) has both a high elevation and a high accumulation rate (1.01 m we yr−1), which are suitable properties for reconstructing past environmental changes with a high time resolution. For this study, we measured the major ion fluxes in a 90 m ice core drilled from the SE-Dome region in 2015 and present the records of annual ion fluxes from 1957 to 2014. From 1970 to 2010, the trend of nonsea-salt (nss) SO42− flux decreases, whereas that for NH4+ increases, tracking well with the anthropogenic SOx and NH3 emissions mainly from North America. The result suggests that these fluxes reflect histories of the anthropogenic SOx and NH3 emissions. In contrast, the decadal trend of NO3− flux differs from the decreasing trend of anthropogenic NOx emissions. Although the cause of this discrepancy remains unclear, it may be related to changes in particle formation processes and chemical scavenging rates caused by an increase in sea salt and dust and/or a decrease in nssSO42−. We also find a high average NO3− flux (1.13 mmol m−2 yr−1) in the ice core, which suggests a negligible effect from postdepositional NO3− loss. Thus, the SE-Dome region is an excellent location for reconstructing nitrate fluxes. Over a decadal time scale, our NO3− flux record is similar to those from other ice cores in Greenland high-elevation sites, suggesting that NO3− concentration records from these ice cores are reliable.

DOI： 10.1002/2017JD026733

Surface lowering of the debris-covered area of Kanchenjunga Glacier in the eastern Nepal Himalaya since 1975, as revealed by Hexagon KH-9 and ALOS satellite observations Reviewed Open Access

Damodar Lamsal, Koji Fujita, Akiko Sakai

CRYOSPHERE Vol. 11 ( 6 ) page： 2815 - 2827 2017.12

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：COPERNICUS GESELLSCHAFT MBH

This study presents the geodetic mass balance of Kanchenjunga Glacier, one of the largest debris-covered glaciers in the easternmost Nepal Himalaya, which possesses a negative mass balance of -0.18 +/- 0.17mw.e.a(-1) for the 1975-2010 study period, estimated using digital elevation models (DEMs) generated from Hexagon KH-9 and ALOS PRISM stereo images. Accurate DEMs, with a relative uncertainty of +/- 5.5 m, were generated from the intensive and manual editing of triangulated irregular network (TIN) models on a stereo MirrorTM/3D Monitor. The glacier ice-flow velocity field was also calculated using a feature-tracking method that was applied to two ALOS orthoimages taken in 2010. The elevation differences between the two DEMs highlight considerable surface lowering across the debriscovered area, and a slight thickening in the accumulation area of Kanchenjunga Glacier between 1975 and 2010. The magnitude and gradient of surface lowering are similar among the six glacier tributaries, even though they are situated at different elevations, which may reflect variations in the iceflow velocity field. The pattern of surface lowering correlates well with the ice-flow velocity field over the debriscovered portion of the main tributary, suggesting that the glacier dynamics significantly affect surface lowering by altering the emergence velocity along the glacier, particularly in the compressive ablation area. Surface-lowering patterns partially correspond to the supraglacial pond area fraction of the glacier, with enhanced surface lowering observed in areas that possess a larger pond area fraction. These findings support the hypothesis that supraglacial ponds may intensify ice wastage and play a key role in the heterogeneous surface lowering of debris-covered glaciers. The estimated mass loss of Kanchenjunga Glacier is moderate compared with other debris-covered glaciers in neighboring Himalayan regions, which may be due to the lower pond area fraction of Kanchenjunga Glacier relative to other glaciers.

DOI： 10.5194/tc-11-2815-2017

Seasonal-Scale Dating of a Shallow Ice Core From Greenland Using Oxygen Isotope Matching Between Data and Simulation Reviewed Open Access

Ryoto Furukawa, Ryu Uemura, Koji Fujita, Jesper Sjolte, Kei Yoshimura, Sumito Matoba, Yoshinori Iizuka

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 122 ( 20 ) page： 10873 - 10887 2017.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

A precise age scale based on annual layer counting is essential for investigating past environmental changes from ice core records. However, subannual scale dating is hampered by the irregular intraannual variabilities of oxygen isotope (delta O-18) records. Here we propose a dating method based on matching the delta O-18 variations between ice core records and records simulated by isotope-enabled climate models. We applied this method to a new delta O-18 record from an ice core obtained from a dome site in southeast Greenland. The close similarity between the delta O-18 records from the ice core and models enables correlation and the production of a precise age scale, with an accuracy of a few months. A missing delta O-18 minimum in the 1995/1996 winter is an example of an indistinct delta O-18 seasonal cycle. Our analysis suggests that the missing delta O-18 minimum is likely caused by a combination of warm air temperature, weak moisture transport, and cool ocean temperature. Based on the age scale, the average accumulation rate from 1960 to 2014 is reconstructed as 1.02 m yr(-1) in water equivalent. The annual accumulation rate shows an increasing trend with a slope of 3.6 mm yr(-1), which is mainly caused by the increase in the autumn accumulation rate of 2.6 mm yr(-1). This increase is likely linked to the enhanced hydrological cycle caused by the decrease in Arctic sea ice area. Unlike the strong seasonality of precipitation amount in the ERA reanalysis data in the southeast dome region, our reconstructed accumulation rate suggests a weak seasonality.

DOI： 10.1002/2017JD026716

Contrasting glacier responses to recent climate change in high-mountain Asia Reviewed Open Access

Akiko Sakai, Koji Fujita

SCIENTIFIC REPORTS Vol. 7 ( 1 ) page： 13717 2017.10

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

Recent studies of Asian glaciers have shown that glaciers in eastern Karakoram and West Kunlun have been slightly gaining mass while those in nearby Jammu Kashmir and Himalayas are losing mass, at rates of more than 0.5 m w.e.yr(-1) and about 0.3 m w.e.yr-1, respectively. Two possible explanations have been proposed for this difference in glacier behaviour: spatial heterogeneity in climate change (climatic forcing) or differing glacier responses to climate change (glacier response). However, neither explanation has strong supporting evidence. Here, we examine the glacial response by calculating the mass-balance sensitivity to temperature change in high-mountain Asia. In support of the glacier-response explanation, we find a strong correlation between observed glacier surface-elevation changes and mass-balance sensitivity of glaciers. The high coefficient of determination (R-2 = 0.61) suggests that spatially heterogeneous mass-balance sensitivity has more explanatory power than regionally different climate change for the recent contrasting glacier fluctuations in the high mountain Asia.

DOI： 10.1038/s41598-017-14256-5

Downwasting of the debris-covered area of Lirung Glacier in Langtang Valley, Nepal Himalaya, from 1974 to 2010 Reviewed Open Access

Takayuki Nuimura, Koji Fujita, Akiko Sakai

QUATERNARY INTERNATIONAL Vol. 455 page： 93 - 101 2017.10

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Despite the widespread shrinkage of debris-covered Himalayan glaciers in recent decades, the underlying processes driving these changes are poorly understood. This study presents recent mass-balance data for the debris-covered area of Lirung Glacier in Langtang Valley, Nepal Himalaya, constrained using multi-temporal, remotely sensed digital elevation models calibrated to in situ GPS survey data, and surface-flow velocity data from phase-only correlation. The results indicate surface lowering of between -1.3 and -1.8 m a(-1) during the study period ( 1974-2010), with accelerated glacier thinning after 2000. Similarly, we observed a decline in emergence velocity in the upper debris-covered area since 2000. We argue that this deceleration plays a key role in surface lowering, in contrast to declining surface mass balance, which we suggest is a residual effect of emergence velocity and surface lowering. Taken together, our findings indicate that the recent increase in surface lowering is attributable to the declining flux of ice from the upper to lower debris-covered areas of Lirung Glacier. Furthermore, this pattern suggests that downwasting of the upper debris-covered area will be augmented by a positive feedback between surface lowering and decelerated flow velocity. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.

DOI： 10.1016/j.quaint.2017.06.066

Topographic controls on the debris-cover extent of glaciers in the Eastern Himalayas: Regional analysis using a novel high-resolution glacier inventory Reviewed

Sunal Ojha, Koji Fujita, Akiko Sakai, Hiroto Nagai, Damodar Lamsal

QUATERNARY INTERNATIONAL Vol. 455 page： 82 - 92 2017.10

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

To better understand the influence of topography on the formation of Himalayan debris-covered glaciers, we manually digitized 5301 glaciers, covering an area of 5691 +/- 893 km(2), from high-resolution Advanced Land Observing Satellite imagery, and identified 842 debris-covered glaciers with a debris-covered area of 3839 +/- 753 km(2). This estimation of the debris-covered area of these glaciers is a novel approach in the Eastern Himalayas. We investigated the relationship between the debris-covered area and the corresponding potential debris supply (PDS) slopes for the debris-covered glaciers across the region. The PDS slopes on the southern side show better correlation with their debris-covered area formation than those situated on the northern side of the Himalayan barrier, with this correlation weakening toward the western massifs. Further investigation showed that PDS slopes oriented SE to Wexert a stronger control on the formation of debris-covered areas, which is related to the diurnal freezeethaw cycle on the southern slope of the mountain barrier. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.

DOI： 10.1016/j.quaint.2017.08.007

Evaluating the Scale and Potential of GLOF in the Bhutan Himalayas Using a Satellite-Based Integral Glacier-Glacial Lake Inventory Reviewed

Hiroto Nagai, Jinro Ukita, Chiyuki Narama, Koji Fujita, Akiko Sakai, Takeo Tadono, Tsutomu Yamanokuchi, Nobuhiro Tomiyama

GEOSCIENCES Vol. 7 ( 3 ) page： 77 2017.9

Language：English Publishing type：Research paper (scientific journal) Publisher：MDPI AG

A comprehensive glacier-glacial lake inventory was developed for the Bhutan Himalayas based on satellite observations between 1987-1990 and 2006-2011. In total, 733 lakes (covering 82.6 km(2)) were delineated between 4000 and 6000 m a.s.l. and their relationships to associated glaciers were documented. Using this new inventory, the scale and potential for glacial lake outburst flooding (GLOF) based on multiple criteria was examined. This included a history of connectivity characteristics of glacial lakes to mother glaciers, potential flood volumes, and debris-cover of mother glaciers in addition to the conventional criteria of expansion rate and lake size. The majority of the lakes with high expansion rates (more than double in size) and large areas (> 0.1 km(2)) met the conditions of being continuously in contact with a mother debris-covered glacier for nearly 20 years. Based on these multiple criteria, two lakes were identified as having potential for large-scale GLOF. Potentially dangerous glacial lakes listed in the International Centre for Integrated Mountain Development (ICIMOD) study were re-visited, and some overlaps with the glacier-glacial lake inventory were found.

DOI： 10.3390/geosciences7030077

Debris-covered glacier anomaly? Morphological factors controlling changes in the mass balance, surface area, terminus position, and snow line altitude of Himalayan glaciers Reviewed

Franco Salerno, Sudeep Thakuri, Gianni Tartari, Takayuki Nnimura, Sojiro Sunako, Akiko Sakai, Koji Fujita

EARTH AND PLANETARY SCIENCE LETTERS Vol. 471 page： 19 - 31 2017.8

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

What are the main morphological factors that control the heterogeneous responses of debris covered glaciers to climate change in the southern central Himalaya? A debate is open whether thinning rates on debris covered glaciers are comparable to those of debris free ones. Previous studies have adopted a deterministic approach, which is indispensable, but is also limiting in that only a few glaciers can be monitored. In this context, we propose a statistical analysis based on a wider glacier population as a complement to these deterministic studies. We analysed 28 glaciers situated on the southern slopes of Mt. Everest in the central southern Himalaya during the period 1992-2008. This study combined data compiled by three distinct studies for a common period and population of glaciers for use in a robust statistical analysis. Generally, surface gradient was the main morphological factor controlling the features and responses of the glaciers to climate change. In particular, the key points that emerged are as follows. 1) Reduced downstream surface gradient is responsible for increased glacier thinning. 2) The development of supraglacial ponds is a further controlling factor of glacier thinning: where supraglacial ponds develop, the glaciers register further surface lowering. 3) Debris coverage and thickness index were not found to be significantly responsible for the development of supraglacial ponds, changes in elevation, or shifts in snow line altitude. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2017.04.039

Anomalous winter-snow-amplified earthquake-induced disaster of the 2015 Langtang avalanche in Nepal Reviewed Open Access

Koji Fujita, Hiroshi Inoue, Takeki Izumi, Satoru Yamaguchi, Ayako Sadakane, Sojiro Sunako, Kouichi Nishimura, WalterW. Immerzeel, Joseph M. Shea, Rijan B. Kayastha, Takanobu Sawagaki, David F. Breashears, Hiroshi Yagi, Akiko Sakai

NATURAL HAZARDS AND EARTH SYSTEM SCIENCES Vol. 17 ( 5 ) page： 749 - 764 2017.5

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：COPERNICUS GESELLSCHAFT MBH

Coseismic avalanches and rockfalls, as well as their simultaneous air blast and muddy flow, which were induced by the 2015 Gorkha earthquake in Nepal, destroyed the village of Langtang. In order to reveal volume and structure of the deposit covering the village, as well as sequence of the multiple events, we conducted an intensive in situ observation in October 2015. Multitemporal digital elevation models created from photographs taken by helicopter and unmanned aerial vehicles reveal that the deposit volumes of the primary and succeeding events were 6.81 +/- 1.54 x 10(6) and 0.84 +/- 0.92 x 10(6) m(3), respectively. Visual investigations of the deposit and witness statements of villagers suggest that the primary event was an avalanche composed mostly of snow, while the collapsed glacier ice could not be dominant source for the total mass. Succeeding events were multiple rockfalls which may have been triggered by aftershocks. From the initial deposit volume and the area of the upper catchment, we estimate an average snow depth of 1.82 +/- 0.46m in the source area. This is consistent with anomalously large snow depths (1.28-1.52 m) observed at a neighboring glacier (4800-5100ma.s.l.), which accumulated over the course of four major snowfall events between October 2014 and the earthquake on 25 April 2015. Considering long-term observational data, probability density functions, and elevation gradients of precipitation, we conclude that this anomalous winter snow was an extreme event with a return interval of at least 100 years. The anomalous winter snowfall may have amplified the disastrous effects induced by the 2015 Gorkha earthquake in Nepal.

DOI： 10.5194/nhess-17-749-2017

State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling Reviewed Open Access

Kenji Kawamura, Ayako Abe-Ouchi, Hideaki Motoyama, Yutaka Ageta, Shuji Aoki, Nobuhiko Azuma, Yoshiyuki Fujii, Koji Fujita, Shuji Fujita, Kotaro Fukui, Teruo Furukawa, Atsushi Furusaki, Kumiko Goto-Azuma, Ralf Greve, Motohiro Hirabayashi, Takeo Hondoh, Akira Hori, Shinichiro Horikawa, Kazuho Horiuchi, Makoto Igarashi, Yoshinori Iizuka, Takao Kameda, Hiroshi Kanda, Mika Kohno, Takayuki Kuramoto, Yuki Matsushi, Morihiro Miyahara, Takayuki Miyake, Atsushi Miyamoto, Yasuo Nagashima, Yoshiki Nakayama, Takakiyo Nakazawa, Fumio Nakazawa, Fumihiko Nishio, Ichio Obinata, Rumi Ohgaito, Akira Oka, Jun'ichi Okuno, Junichi Okuyama, Ikumi Oyabu, Frederic Parrenin, Frank Pattyn, Fuyuki Saito, Takashi Saito, Takeshi Saito, Toshimitsu Sakurai, Kimikazu Sasa, Hakime Seddik, Yasuyuki Shibata, Kunio Shinbori, Keisuke Suzuki, Toshitaka Suzuki, Akiyoshi Takahashi, Kunio Takahashi, Shuhei Takahashi, Morimasa Takata, Yoichi Tanaka, Ryu Uemura, Genta Watanabe, Okitsugu Watanabe, Tetsuhide Yamasaki, Kotaro Yokoyama, Masakazu Yoshimori, Takayasu Yoshimoto

SCIENCE ADVANCES Vol. 3 ( 2 ) page： e1600446 2017.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER ASSOC ADVANCEMENT SCIENCE

Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instabilitywith bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets.

DOI： 10.1126/sciadv.1600446

A firn densification process in the high accumulation dome of southeastern Greenland Reviewed Open Access

Yoshinori Iizuka, Atsushi Miyamoto, Akira Hori, Sumito Matoba, Ryoto Furukawa, Takeshi Saito, Shuji Fujita, Motohiro Hirabayashi, Satoru Yamaguchi, Koji Fujita, Nozomu Takeuchi

ARCTIC ANTARCTIC AND ALPINE RESEARCH Vol. 49 ( 1 ) page： 13 - 27 2017.2

Language：English Publishing type：Research paper (scientific journal) Publisher：INST ARCTIC ALPINE RES

We examine a firn core from a dome in southeast Greenland that exhibits distinct firn densification. The ice was-20.9 degrees C at 20 m depth, and the core gives an average accumulation rate of 1.0 m w.e. yr(-1) in water equivalent. However, the close-off density of 830 kg m(-3) occurs at 83.4-86.8 m depth, which is about 20-m shallower than that obtained from two empirical models. Where the density p > 750 kg m(-3), the densification appears faster than that from the empirical models. As a result, compared to the empirical coefficient, the actual compactive viscosity coefficient is nonlinear and decreases at p > 750 kg m(-3), indicating that the fun with a higher density is softer than that from the empirical result. We argue here that the high accumulation rate creates a high overburden pressure in a short time. Thus, the relative softness of the firn may arise from (1) there being not enough time to form bonds between grains as strong as those in a lower accumulation-rate area, and similarly, (2) the dislocation density in the firn being relatively high.

DOI： 10.1657/AAAR0016-034

Precipitation regime and stable isotopes at Dome Fuji, East Antarctica Reviewed

Dittmann A, Schlosser E, Masson-Delmotte V, Powers JG, Manning KW, Werner M, Fujita K

Atmospheric Chemistry and Physics Vol. 16 ( 11 ) page： 6883-6900 2016.6

Glacier area shrinkage in eastern Nepal Himalaya since 1992 using high-resolution inventories from aerial photographs and ALOS satellite images Reviewed

Ojha S, Fujita K, Asahi K, Sakai A, Lamsal D, Nuimura T, Nagai H

Journal of Glaciology Vol. 62 ( 233 ) page： 512-524 2016.4

Abrupt and moderate climate changes in the mid-latitudes of Asia during the Holocene Reviewed

Aizen EM, Aizen VB, Takeuchi N, Mayewski PA, Grigholm B, Joswiak DR, Nikitin SA, Fujita K, Nakawo M, Zapf A, Schwikowski M

Journal of Glaciology Vol. 62 ( 233 ) page： 411-439 2016.4

Inconsistent relations among major ions and water stable isotopes in Antarctic snow under different accumulation environments Reviewed

Hoshina Y, Fujita K, Iizuka Y, Motoyama H

Polar Science Vol. 10 ( 1 ) page： 1-10 2016.3

Heterogeneity in supraglacial debris thickness and its role in glacier mass changes of the Mount Gongga Reviewed

Zhang Y, Hirabayashi Y, Fujita K, Liu SY, Liu Q

Science China Earth Sciences Vol. 59 ( 1 ) page： 170-184 2016.1

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