Faculty Profiles - FUJITA, Koji

Papers - FUJITA, Koji

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Modelling the development and decay of cryoconite holes in northwestern Greenland Reviewed

Yukihiko Onuma, Koji Fujita, Nozomu Takeuchi, Masashi Niwano, Teruo Aoki

The Cryosphere Vol. 17 ( 8 ) page： 3309 - 3328 2023.8

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

Abstract. Cryoconite holes (CHs) are water-filled cylindrical holes with cryoconite (dark-coloured sediment) deposited at their bottoms, forming on ablatingice surfaces of glaciers and ice sheets worldwide. Because the collapse of CHs may disperse cryoconite on the ice surface, thereby decreasing theice surface albedo, accurate simulation of the temporal changes in CH depth is essential for understanding ice surface melt. We established a novelmodel that simulates the temporal changes in CH depth using heat budgets calculated independently at the ice surface and CH bottom based onhole-shaped geometry. We evaluated the model with in situ observations of the CH depths on the Qaanaaq ice cap in northwestern Greenland during the2012, 2014, and 2017 melt seasons. The model reproduced the observed depth changes and timing of CH collapse well. Although earlier models haveshown that CH depth tends to be deeper when downward shortwave radiation is intense, our sensitivity tests suggest that deeper CH tends to form whenthe diffuse component of downward shortwave radiation is dominant, whereas CHs tend to be shallower when the direct component is dominant. Inaddition, the total heat flux to the CH bottom is dominated by shortwave radiation transmitted through ice rather than that directly from theCH mouths when the CH is deeper than 0.01 m. Because the shortwave radiation transmitted through ice can reach the CH bottom regardless ofCH diameter, CH depth is unlikely to be correlated with CH diameter. The relationship is consistent with previous observationalstudies. Furthermore, the simulations highlighted that the difference in albedo between ice surface and CH bottom was a key factor for reproducingthe timing of CH collapse. It implies that lower ice surface albedo could induce CH collapse and thus cause further lowering of the albedo. Heatcomponent analysis suggests that CH depth is governed by the balance between the intensity of the diffuse component of downward shortwave radiationand the turbulent heat transfer. Therefore, these meteorological conditions may be important factors contributing to the recent surface darkening ofthe Greenland ice sheet and other glaciers via the redistribution of CHs.

DOI： 10.5194/tc-17-3309-2023

A long-term mass-balance reconstruction (1974–2021) and a decadal in situ mass-balance record (2011–2021) of Rikha Samba Glacier, central Himalaya Reviewed International coauthorship

Tika Ram Gurung, Rijan Bhakta Kayastha, Koji Fujita, Sharad Prasad Joshi, Anna Sinisalo, James D. Kirkham

Journal of Glaciology Vol. 69 ( 276 ) page： 723 - 736 2023.8

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

Abstract

Despite their importance for regional water resource planning and as indicators of climate change, records of in situ glacier mass balance remain short and spatially sparse in the Himalaya. Here, we present an updated series of in situ mass-balance measurements from Rikha Samba Glacier, Nepal, between 2011 and 2021. The updated in situ mass balance is −0.39 ± 0.32 m w.e. for this period. We use an energy-mass balance model to extend the annual mass-balance series back to 1974. The model is forced using daily meteorological variables from ERA5-Land reanalysis data that is linearly bias-corrected using observations from an automatic weather station situated near the glacier terminus. The modeled mass balance is consistent with the in situ mass-balance series measured 2011–2021 and with previous glaciological and geodetic estimates. The model results indicate a mass balance of −0.56 ± 0.27 m w.e. a<sup>−1</sup> over the reconstruction period of 1974–2021, which is comparable to the mass losses experienced by other Himalayan glaciers during this time. An assessment of the sensitivity of the glacier mass balance to meteorological forcing suggests that a change in temperature of ±1 K has a stronger effect on the calculated mass balance compared to a ±20% change in either precipitation, or relative humidity, or solar radiation.

DOI： 10.1017/jog.2022.93

DOI： 10.1017/jog.2022.93

Other Link： https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143022000934

AsiaPEX: Challenges and Prospects in Asian Precipitation Research Reviewed International coauthorship

Toru Terao, Shinjiro Kanae, Hatsuki Fujinami, Someshwar Das, A. P. Dimri, Subashisa Dutta, Koji Fujita, Azusa Fukushima, Kyung-Ja Ha, Masafumi Hirose, Jinkyu Hong, Hideyuki Kamimera, Rijan Bhakta Kayastha, Masashi Kiguchi, Kazuyoshi Kikuchi, Hyun Mee Kim, Akio Kitoh, Hisayuki Kubota, Weiquang Ma, Yaoming Ma, Millind Mujumdar, Masato I. Nodzu, Tomonori Sato, Z. Su, Shiori Sugimoto, Hiroshi G. Takahashi, Yuhei Takaya, Shuyu Wang, Kun Yang, Satoru Yokoi, Jun Matsumoto

Bulletin of the American Meteorological Society Vol. 104 ( 4 ) page： E884 - E908 2023.4

Language：English Publishing type：Research paper (scientific journal) Publisher：American Meteorological Society

Abstract

The Asian Precipitation Experiment (AsiaPEX) was initiated in 2019 to understand terrestrial precipitation over diverse hydroclimatological conditions for improved predictions, disaster reduction, and sustainable development across Asia under the framework of the Global Hydroclimatology Panel (GHP)/Global Energy and Water Exchanges (GEWEX). AsiaPEX is the successor to GEWEX Asian Monsoon Experiment (GAME, 1995-2005) and Monsoon Asian Hydro-Atmosphere Scientific Research and Prediction Initiative (MAHASRI, 2006-2016). While retaining the key objectives of the aforementioned projects, the scientific targets of AsiaPEX focus on land-atmosphere coupling and improvements to the predictability of the Asian hydroclimatological system. AsiaPEX was designed for both fine-scale hydroclimatological processes occurring at the land surface and the integrated Asian hydroclimatological system characterized by multiscale interactions. We adopt six approaches including observation, process studies, scale interactions, high-resolution hydrological modeling, field campaigns, and climate projection, which bridge gaps in research activities conducted in different regions. Collaboration with mesoscale and global modeling researchers is one of the core methods in AsiaPEX. We review these strategies based on the literature and our initial outcomes. These include the estimation and validation of high-resolution satellite precipitation, investigations of extreme rainfall mechanisms, field campaigns over the Maritime Continent and Tibetan Plateau, areas of significant impact on the entire AsiaPEX region, process studies on diurnal to interdecadal scale interactions, and evaluation of the predictabilities of climate models for long-term variabilities. We will conduct integrated observational and modeling initiative, the Asian Monsoon Year (AMY)-II around 2025-2028, whose strategies are the sub-regional observation platforms and integrated global analysis.

DOI： 10.1175/BAMS-D-20-0220.1

DOI： 10.1175/bams-d-20-0220.1

Other Link： https://journals.ametsoc.org/downloadpdf/journals/bams/aop/BAMS-D-20-0220.1/BAMS-D-20-0220.1.xml

Up-glacier propagation of surface lowering of Yala Glacier, Langtang Valley, Nepal Himalaya Reviewed International coauthorship

Sojiro Sunako, Koji Fujita, Takeki Izumi, Satoru Yamaguchi, Akiko Sakai, Rijan Bhakta Kayastha

Journal of Glaciology Vol. 69 ( 274 ) page： 425 - 432 2023.4

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

Abstract

We quantify the surface elevation changes along Yala Glacier in Langtang Valley, Nepal Himalaya, since 1981 using geodetic methods to understand the recent evolution and current state of small debris-free glaciers across the region. We analyse differential global positioning system measurements and aerial stereo imagery that were acquired along Yala Glacier in 2007, 2009, 2012 and 2015 to generate digital elevation models for each calculation period. Continuous surface lowering has mainly been observed across the down-glacier area during the calculation periods, although a large degree of variability exists, with this lowering trend propagating up-glacier in recent years. The area-weighted glacier mass balances range from −0.98 ± 0.27 to −0.26 ± 0.30 m w.e. a<sup>−1</sup> for the five calculation periods (1981–2007, 2007–2009, 2009–2012, 2012–2015 and 2007–2015). These calculated mass-balance data reveal that Yala Glacier has undergone accelerated mass loss since the late 2000s, which is consistent with the results of previous in situ measurement and remote-sensing studies.

DOI： 10.1017/jog.2022.118

DOI： 10.1017/jog.2022.118

Other Link： https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143022001186

Multiscale Processes Leading to Heavy Precipitation in the Eastern Nepal Himalayas Reviewed International coauthorship

Hidetaka Hirata, Hatsuki Fujinami, Hironari Kanamori, Yota Sato, Masaya Kato, Rijan B. Kayastha, Madan L. Shrestha, Koji Fujita

Journal of Hydrometeorology Vol. 24 ( 4 ) page： 641 - 658 2023.4

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：American Meteorological Society

Abstract

The processes underlying heavy rainfall in the higher elevations of the Himalayas are still not well-known despite its importance. Here, we examine the detailed process causing a heavy rainfall event, observed by our rain gauge network in the Rolwaling valley, eastern Nepal Himalayas, using ERA5 reanalysis and a regional cloud-resolving numerical simulation. Heavy precipitation (112 mm day<sup>−1</sup>) was observed on July 8, 2019, at Dongang (2790 m above sea level). Most of the precipitation (81 mm) occurred during 19–23 local time (LT). The synoptic-scale environment is characterized by a monsoon low-pressure system (LPS) over northeastern India. The LPS lifted moisture upward from the lower troposphere and then horizontally transported it into the eastern Nepal Himalayas within the middle troposphere, increasing the content of the water vapor around Dongang. A mesoscale convective system passed over Dongang around the time of the intense precipitation. Numerical simulation showed surface heat fluxes prevailed under the middle tropospheric (~ 500hPa) southeasterly flow associated with the LPS around a mountain ridge on the upwind side of Dongang until 19 LT, enhancing convective instability. Topographic lifting led to the release of the enhanced instability, which triggered the development of a mesoscale precipitation system. The southeasterly flow pushed the precipitation system northward, which then passed over Dongang during 20–22 LT, resulting in heavy precipitation. Thus, we conclude that the heavy precipitation came from the multiscale processes such as three-dimensional moisture transport driven by the LPS and the diurnal variation in heat fluxes from the land surface.

DOI： 10.1175/JHM-D-22-0080.1

DOI： 10.1175/jhm-d-22-0080.1

Other Link： https://journals.ametsoc.org/downloadpdf/journals/hydr/aop/JHM-D-22-0080.1/JHM-D-22-0080.1.xml

Evolution of snow algae, from cosmopolitans to endemics, revealed by DNA analysis of ancient ice Reviewed International coauthorship International journal

Takahiro Segawa, Takahiro Yonezawa, Ryo Matsuzaki, Hiroshi Mori, Ayumi Akiyoshi, Francisco Navarro, Koji Fujita, Vladimir B. Aizen, Zhongqin Li, Shuhei Mano, Nozomu Takeuchi

The ISME Journal Vol. 17 ( 4 ) page： 491 - 501 2023.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

Recent studies of microbial biogeography have revealed the global distribution of cosmopolitans and dispersal of regional endemics, but little is known about how these processes are affected by microbial evolution. Here, we compared DNA sequences from snow/glacier algae found in an 8000-year-old ice from a glacier in central Asia with those from modern snow samples collected at 34 snow samples from globally distributed sites at the poles and mid-latitudes, to determine the evolutionary relationship between cosmopolitan and endemic phylotypes of snow algae. We further applied a coalescent theory–based demographic model to the DNA sequences. We found that the genus Raphidonema (Trebouxiophyceae) was distributed over both poles and mid-latitude regions and was detected in different ice core layers, corresponding to distinct time periods. Our results indicate that the modern cosmopolitan phylotypes belonging to Raphidonema were persistently present long before the last glacial period. Furthermore, endemic phylotypes originated from ancestral cosmopolitan phylotypes, suggesting that modern regional diversity of snow algae in the cryosphere is a product of microevolution. These findings suggest that the cosmopolitans dispersed across the world and then derived new localized endemics, which thus improves our understanding of microbial community formation by microevolution in natural environments.

DOI： 10.1038/s41396-023-01359-3

DOI： 10.1038/s41396-023-01359-3

Other Link： https://www.nature.com/articles/s41396-023-01359-3

A WIGGLE-MATCHED 297-YR TREE-RING OXYGEN ISOTOPE RECORD FROM THAILAND: INVESTIGATING THE <sup>14</sup>C OFFSET INDUCED BY AIR MASS TRANSPORT FROM THE INDIAN OCEAN Reviewed International coauthorship

Masaki Sano, Nathsuda Pumijumnong, Koji Fujita, Masataka Hakozaki, Fusa Miyake, Takeshi Nakatsuka

Radiocarbon Vol. 65 ( 2 ) page： 505 - 519 2023.4

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

ABSTRACT

Regional offsets from Northern Hemisphere radiocarbon (<sup>14</sup>C) calibration curves are widely recognized for monsoon Asia and often hinder accurate <sup>14</sup>C dating. In this paper, we explore the possible linkage between summer monsoon intensity and <sup>14</sup>C offsets using tree-ring δ<sup>18</sup>O and <sup>14</sup>C data from Thailand. We developed a 297-yr floating tree-ring δ<sup>18</sup>O chronology comprising seven teak log-coffin samples from the Ban Rai rock shelter site, northwestern Thailand. The outermost ring of our chronology was estimated to date from 358–383 CE, within a 95.4% (2σ) probability range, based on a total of 10 <sup>14</sup>C measurements that were wiggle-matched against a mixed calibration curve evenly weighted from the IntCal20 and SHCal20 curves. Backward trajectory analysis showed that an intensified (weakened) summer monsoon detected in a modern tree-ring δ<sup>18</sup>O chronology was most likely to be induced by increased (decreased) air mass transport from the tropical Indian Ocean, which is an area of intense upwelling where the <sup>14</sup>C concentration is lower than the atmospheric <sup>14</sup>C level. However, partly because of the limited sample size and dating uncertainty, the direct linkage between the tree-ring δ<sup>18</sup>O series and <sup>14</sup>C records obtained from our teak log-coffin samples could not be statistically verified.

DOI： 10.1017/RDC.2023.14

Climate and Surface Mass Balance at Glaciar Perito Moreno, Southern Patagonia Reviewed International coauthorship

Masahiro Minowa, Pedro Skvarca, Koji Fujita

Journal of Climate Vol. 36 ( 2 ) page： 625 - 641 2023.1

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：American Meteorological Society

Abstract

The mass budget of southern Patagonian glaciers is characterized by an extreme amount of surface ablation. To understand the processes controlling surface mass balance, we analyzed in situ data including meteorological variables and ablation stakes for the 25 years between 1996 and 2020 near the terminus of Glaciar Perito Moreno in southern Patagonia in South America. The mean annual temperature has increased over the study period at a rate of 0.2°C decade<sup>−1</sup>. An energy-balance model was applied to calculate a point surface mass balance, based on meteorological records. The average point surface mass balance is estimated to be −16.3 m water equivalent (w.e.) yr<sup>−1</sup> between 1996 and 2020, decreasing at a rate in the range from −0.4 to −0.9 m w.e. yr<sup>−1</sup> decade<sup>−1</sup>. The greatest contribution to the surface energy balance was due to the sensible heat flux, and its variation drove the surface mass balance variation. The meteorological and surface mass balance records were compared with the Southern Annular Mode and El Niño–Southern Oscillation, which change the atmospheric circulation over southern Patagonia and influence surface mass balance near the terminus of the glacier. Our long-term dataset investigates the detailed meteorological conditions and surface mass balance and their connection with the large-scale climate variability over the last 25 years, reported for the first time in Patagonia.

DOI： 10.1175/JCLI-D-22-0294.1

DOI： 10.1175/jcli-d-22-0294.1

Other Link： https://journals.ametsoc.org/downloadpdf/journals/clim/36/2/JCLI-D-22-0294.1.xml

Increased oceanic dimethyl sulfide emissions in areas of sea ice retreat inferred from a Greenland ice core Reviewed

Yutaka Kurosaki, Sumito Matoba, Yoshinori Iizuka, Koji Fujita, Rigen Shimada

Communications Earth & Environment Vol. 3 ( 1 ) page： 327 2022.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

Ocean phytoplankton are an important source of dimethyl sulfide, which influences marine cloud formation. Model studies suggest that declines in Arctic sea ice may lead to increased dimethyl sulfide emissions, however observational support is lacking. Here, we present a 55-year high-resolution ice core record of methane sulfonic acid flux, an oxidation product of dimethyl sulfide, from the southeast Greenland Ice Sheet. We infer temporal variations in ocean dimethyl sulfide emissions and find that springtime (April–June) fluxes of methane sulfonic acid correlate well with satellite-derived chlorophyll-a concentration in the Irminger Sea. Summertime (July–September) methane sulfonic acid fluxes were 3 to 6 times higher between 2002–2014 than 1972–2001. We attribute this to sea ice retreat day becoming earlier and a coincident increase in chlorophyll-a concentration in the adjacent open coastal waters.

DOI： 10.1038/s43247-022-00661-w

DOI： 10.1038/s43247-022-00661-w

Other Link： https://www.nature.com/articles/s43247-022-00661-w

Multi-decadal monsoon characteristics and glacier response in High Mountain Asia Reviewed International coauthorship

T E Shaw, E S Miles, D Chen, A Jouberton, M Kneib, S Fugger, T Ou, H-W Lai, K Fujita, W Yang, S Fatichi, F Pellicciotti

Environmental Research Letters Vol. 17 ( 10 ) page： 104001 - 104001 2022.10

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

Abstract

Glacier health across High Mountain Asia (HMA) is highly heterogeneous and strongly governed by regional climate, which is variably influenced by monsoon dynamics and the westerlies. We explore four decades of glacier energy and mass balance at three climatically distinct sites across HMA by utilising a detailed land surface model driven by bias-corrected Weather Research and Forecasting meteorological forcing. All three glaciers have experienced long-term mass losses (ranging from −0.04 ± 0.09 to −0.59 ± 0.20 m w.e. a<sup>−1</sup>) consistent with widespread warming across the region. However, complex and contrasting responses of glacier energy and mass balance to the patterns of the Indian Summer Monsoon were evident, largely driven by the role snowfall timing, amount and phase. A later monsoon onset generates less total snowfall to the glacier in the southeastern Tibetan Plateau during May–June, augmenting net shortwave radiation and affecting annual mass balance (−0.5 m w.e. on average compared to early onset years). Conversely, timing of the monsoon’s arrival has limited impact for the Nepalese Himalaya which is more strongly governed by the temperature and snowfall amount during the core monsoon season. In the arid central Tibetan Plateau, a later monsoon arrival results in a 40 mm (58%) increase of May–June snowfall on average compared to early onset years, likely driven by the greater interaction of westerly storm events. Meanwhile, a late monsoon cessation at this site sees an average 200 mm (192%) increase in late summer precipitation due to monsoonal storms. A trend towards weaker intensity monsoon conditions in recent decades, combined with long-term warming patterns, has produced predominantly negative glacier mass balances for all sites (up to 1 m w.e. more mass loss in the Nepalese Himalaya compared to strong monsoon intensity years) but sub-regional variability in monsoon timing can additionally complicate this response.

DOI： 10.1088/1748-9326/ac9008

DOI： 10.1088/1748-9326/ac9008

Other Link： https://iopscience.iop.org/article/10.1088/1748-9326/ac9008/pdf

Editorial: Debris-covered glaciers: Formation, governing processes, present status and future directions Invited International coauthorship

Shukla Aparna, Nicholson Lindsey, Banerjee Argha, Fujita Koji, Quincey Duncan J.

Frontiers in Earth Science Vol. 10 2022.9

Land- to lake-terminating transition triggers dynamic thinning of a Bhutanese glacier Reviewed International coauthorship

Yota Sato, Koji Fujita, Hiroshi Inoue, Akiko Sakai, Karma

The Cryosphere Vol. 16 ( 6 ) page： 2643 - 2654 2022.7

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

Abstract. There have been rapid increases in both the number andexpansion of the proglacial lakes across High Mountain Asia. However, therelationship between proglacial lakes and glacier dynamics remains unclearin the Himalayan region. Here we present the surface elevation, flow-velocity changes, and proglacial lake expansion of Thorthormi and Luggeglaciers in the Lunana region, Bhutanese Himalaya, during the 2000–2018period using photogrammetry and GPS survey data. The lake expansion andsurface lowering rates and flow-velocity field of Lugge Glacier, alake-terminating glacier, have remained approximately constant since 2000.Conversely, there have been accelerated proglacial lake expansion and a2-fold increase in the thinning rate of Thorthormi Glacier since 2011, aswell as a considerable speed-up in the flow-velocity field(>150 m a−1). We reveal that the lake formation and transition of ThorthormiGlacier from a land- to lake-terminating glacier have triggered glacierspeed-up and rapid thinning via a positive (compressive) to negative(extensional) change in the emergence velocities. This study provides thefirst evidence of dynamic glacier changes that are associated withproglacial lake formation across the Himalayan region.

DOI： 10.5194/tc-16-2643-2022

DOI： 10.5194/tc-16-2643-2022

Other Link： https://tc.copernicus.org/articles/16/2643/2022/tc-16-2643-2022.pdf

Mass Balance of Four Mongolian Glaciers: In-situ Measurements, Long-Term Reconstruction and Sensitivity Analysis Reviewed International coauthorship International journal

Purevdagva Khalzan, Akiko Sakai, Koji Fujita

Frontiers in Earth Science Vol. 9 page： 785306 2022.1

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Frontiers Media SA

This study describes the <italic>in situ</italic> observed and modeled mass balances of four representative glaciers in the Mongolian Altai Mountains. Mass-balance stakes and automatic weather stations (AWS) were installed along each glacier to obtain the <italic>in situ</italic> mass balances and meteorological variables. We calibrate the ERA5 meteorological variables using the observed values, then estimate the precipitation parameters to obtain the observed point mass balances using an energy- and mass-balance model. We evaluate the mass-balance profile and glacier-wide mass balance via a mass-balance model using the calibrated ERA5 data and estimated precipitation parameters to fill in the spatial and temporal gaps in the stake networks and AWS measurements. We demonstrate that almost all of the observed mass balances have been in a negative state since 2003. We also reconstruct the long-term mass balances for the 1980–2018 period, which range from −760 to −160 mm water equivalent under the different climatic conditions (annual precipitation varies from 190 to 860 mm). We further evaluate the mass-balance sensitivities to temperature and precipitation changes. We confirm that both sensitivities correlate significantly with the annual precipitation; increased precipitation yields more negative sensitivity to temperature changes and less positive sensitivity to precipitation changes.

DOI： 10.3389/feart.2021.785306

Soluble salts in deserts as a source of sulfate aerosols in an Antarctic ice core during the last glacial period Reviewed International journal

Ryu Uemura, Kosuke Masaka, Yoshinori Iizuka, Motohiro Hirabayashi, Hitoshi Matsui, Risei Matsumoto, Miki Uemura, Koji Fujita, Hideaki Motoyama

Earth and Planetary Science Letters Vol. 578 page： 117299 - 117299 2022.1

Ice core drilling on a high-elevation accumulation zone of Trambau Glacier in the Nepal Himalaya Reviewed International coauthorship International journal

Akane Tsushima, Morihiro Miyahara, Tetsuhide Yamasaki, Nao Esashi, Yota Sato, Rijan B. Kayastha, Ang J. B. Lama Sherpa, Masaki Sano, Koji Fujita

Annals of Glaciology Vol. 62 ( 85-86 ) page： 353 - 359 2021.9

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Cambridge University Press (CUP)

<title>Abstract</title>We drilled an 81.2-m-long ice core in the accumulation area (5860 m a.s.l.) of Trambau Glacier in the Rolwaling region during October–November 2019. The drilling operation was conducted with a lightweight electro-mechanical drill system after two reconnaissance fieldworks in 2017 and 2018, during which two shallow firn cores were drilled with a hand auger. The drill system and ice core samples were transported by helicopters at a high elevation of 6000 m a.s.l. A further challenging issue was the ice core transportation between Nepal and Japan, as no regular commercial flight was available for the frozen samples. The addition of dry ice imported from India immediately prior to leaving Nepal allowed the ice core samples to be successfully transported to a cold room in Japan, and remain in a frozen state. Stratigraphic observations during the drilling operation suggest the drill site has been affected by melting and refreezing.

DOI： 10.1017/aog.2021.15

Anthropogenic Impacts on Tropospheric Reactive Chlorine Since the Preindustrial Reviewed International coauthorship International journal

Shuting Zhai, Xuan Wang, Joseph R. McConnell, Lei Geng, Jihong Cole‐Dai, Michael Sigl, Nathan Chellman, Tomás Sherwen, Ryan Pound, Koji Fujita, Shohei Hattori, Jonathan M. Moch, Lei Zhu, Mat Evans, Michel Legrand, Pengfei Liu, Daniel Pasteris, Yuk‐Chun Chan, Lee T. Murray, Becky Alexander

Geophysical Research Letters Vol. 48 ( 14 ) page： e2021GL093808 2021.7

Twice‐Daily Monsoon Precipitation Maxima in the Himalayas Driven by Land Surface Effects Reviewed International coauthorship International journal

Hatsuki Fujinami, Koji Fujita, Nobuhiro Takahashi, Tomonori Sato, Hironari Kanamori, Sojiro Sunako, Rijan B. Kayastha

Journal of Geophysical Research: Atmospheres Vol. 126 ( 13 ) 2021.7

Physically Based Summer Temperature Reconstruction From Melt Layers in Ice Cores Reviewed International journal Open Access

Koji Fujita, Sumito Matoba, Yoshinori Iizuka, Nozomu Takeuchi, Akane Tsushima, Yutaka Kurosaki, Teruo Aoki

Earth and Space Science Vol. 8 ( 7 ) 2021.7

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：American Geophysical Union (AGU)

Previous reconstructions of summer temperatures from ice cores have relied on a statistical relationship between a melt layer and temperature observed at nearby stations. This study presents a novel method for reconstructing summer temperatures from melt layers in ice cores using an energy balance model that incorporates heat conduction and meltwater refreezing in the firn. We use the seasonal patterns in the ERA-Interim reanalysis data set for an ice core site to calculate the amounts of refreezing water within the firn under various summer mean temperature (SMT) and annual precipitation conditions, and prepared calibration tables containing these three variables. We then estimate the SMTs from the refreezing amount and annual accumulation, both of which can be obtained from an ice core. We apply this method to four ice cores that were recovered from sites with different climates: two sites on the Greenland Ice Sheet, one in Alaska, and one in Russian Altai. The reconstructed SMTs show comparable variations with those of observed temperatures at nearby stations. The nonlinear relationship between SMT and melt layer thickness differs between sites, indicating that a single linear approximation cannot be employed to estimate SMT. Sensitivity analyses suggest that the annual temperature range, amount of annual precipitation, and firn albedo (which is a time-invariant value in the model) significantly affect the relationship between SMT and melt layer thickness. This new method provides an alternative to existing approaches and yields an independent estimate of SMT from ice cores that have been affected by melting.

DOI： 10.1029/2020EA001590

Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020EA001590

Variations in mineralogy of dust in an ice core obtained from northwestern Greenland over the past 100 years Reviewed International coauthorship International journal Open Access

Naoko Nagatsuka, Kumiko Goto-Azuma, Akane Tsushima, Koji Fujita, Sumito Matoba, Yukihiko Onuma, Remi Dallmayr, Moe Kadota, Motohiro Hirabayashi, Jun Ogata, Yoshimi Ogawa-Tsukagawa, Kyotaro Kitamura, Masahiro Minowa, Yuki Komuro, Hideaki Motoyama, Teruo Aoki

Climate of the Past Vol. 17 ( 3 ) page： 1341 - 1362 2021.6

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

Abstract. Our study is the first to demonstrate a
high-temporal-resolution record of mineral composition in a Greenland ice
core over the past 100 years. To reconstruct past variations in the sources
and transportation processes of mineral dust in northwestern Greenland, we
analysed the morphology and mineralogical composition of dust in the SIGMA-D
ice core from 1915 to 2013 using scanning electron microscopy (SEM) and
energy-dispersive X-ray spectroscopy (EDS). The results revealed that the
ice core dust consisted mainly of silicate minerals and that the composition
varied substantially on multi-decadal and inter-decadal scales, suggesting
that the ice core minerals originated from different geological sources in
different periods during the past 100 years. The multi-decadal variation
trend differed among mineral types. Kaolinite, which generally formed in
warm and humid climatic zones, was abundant in colder periods (1950–2004),
whereas mica, chlorite, feldspars, mafic minerals, and quartz, which
formed in arid, high-latitude, and local areas, were abundant in warmer
periods (1915–1949 and 2005–2013). Comparison to Greenland surface
temperature records indicates that multi-decadal variation in the relative
abundance of these minerals was likely affected by local temperature changes
in Greenland. Trajectory analysis shows that the minerals were transported
mainly from the western coast of Greenland in the two warming periods, which
was likely due to an increase in dust sourced from local ice-free areas as a
result of shorter snow/ice cover duration in the Greenland coastal region
during the melt season caused by recent warming. Meanwhile, ancient deposits
in northern Canada, which were formed in past warmer climates, seem to be the
best candidate during the colder period (1950–2004). Our results suggest
that SEM–EDS analysis can detect variations in ice core dust sources during
recent periods of low dust concentration.

DOI： 10.5194/cp-17-1341-2021

Ice Cliff Dynamics of Debris-Covered Trakarding Glacier in the Rolwaling Region, Nepal Himalaya Reviewed International coauthorship International journal Open Access

Yota Sato, Koji Fujita, Hiroshi Inoue, Sojiro Sunako, Akiko Sakai, Akane Tsushima, Evgeny A. Podolskiy, Rakesh Kayastha, Rijan B. Kayastha

Frontiers in Earth Science Vol. 9 2021.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Frontiers Media SA

Ice cliffs can act as “hot spots” for melt on debris-covered glaciers and promote local glacier mass loss. Repeat high-resolution remote-sensing data are therefore required to monitor the role of ice cliff dynamics in glacier mass loss. Here we analyze high-resolution aerial photogrammetry data acquired during the 2007, 2018, and 2019 post-monsoon seasons to delineate and monitor the morphology, distribution, and temporal changes of the ice cliffs across the debris-covered Trakarding Glacier in the eastern Nepal Himalaya. We generate an ice cliff inventory from the 2018 and 2019 precise terrain data, with ice cliffs accounting for 4.7 and 6.1% of the debris-covered area, respectively. We observe large surface lowering (&gt;2.0 m a<sup>−1</sup>) where there is a denser distribution of ice cliffs. We also track the survival, formation, and disappearance of ice cliffs from 2018 to 2019, and find that ∼15% of the total ice cliff area is replaced by new ice cliffs. Furthermore, we observe the overall predominance of northwest-facing ice cliffs, although we do observe spatial heterogeneities in the aspect variance of the ice cliffs (ice cliffs face in similar/various directions). Many new ice cliffs formed across the stagnant middle sections of the glacier, coincident with surface water drainage and englacial conduit intake observations. This spatial relationship between ice cliffs and the glacier hydrological system suggests that these englacial and supraglacial hydrological systems play a significant role in ice cliff formation.

DOI： 10.3389/feart.2021.623623

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