Abstract. To improve surface mass balance (SMB) estimates for the Greenland Ice Sheet (GrIS), we developed a 5 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 1 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 2 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 92.4 %. Sensitivity tests showed that the choice of calculation schemes for vertical water movement in snow and firn has an effect as great as 200 Gt year−1 in the GrIS-wide accumulated SMB estimates; a scheme based on the Richards equation provided the best performance.

Black carbon (BC) deposited on snow lowers its albedo, potentially contributing to warming in the Arctic. Atmospheric distributions of BC and inorganic aerosols, which contribute directly and indirectly to radiative forcing, are also greatly influenced by depositions. To quantify these effects, accurate measurement of the spatial distributions of BC and ionic species representative of inorganic aerosols (ionic species hereafter) in snowpack in various regions of the Arctic is needed, but few such measurements are available. We measured mass concentrations of size‐resolved BC (CMBC) and ionic species in snowpack by using a single‐particle soot photometer and ion chromatography, respectively, over Finland, Alaska, Siberia, Greenland, and Spitsbergen during early spring in 2012–2016. Total BC mass deposited per unit area (DEPMBC) during snow accumulation periods was derived from CMBC and snow water equivalent (SWE). Our analyses showed that the spatial distributions of anthropogenic BC emission flux, total precipitable water, and topography strongly influenced latitudinal variations of CMBC, BC size distributions, SWE, and DEPMBC. The average size distributions of BC in Arctic snowpack shifted to smaller sizes with decreasing CMBC due to an increase in the removal efficiency of larger BC particles during transport from major sources. Our measurements of CMBC were lower by a factor of ~13 than previous measurements made with an Integrating Sphere/Integrating Sandwich spectrophotometer due mainly to interference from coexisting non‐BC particles such as mineral dust. The SP2 data presented here will be useful for constraining climate models that estimate the effects of BC on the Arctic climate.

Scientifically valuable information can be learned by listening to the tiny vibrations emanating from a glacier with seismometers. However, this approach has never been employed to better understand glaciers protected from heat by a debris mantle, despite being common in the Himalayas, one of the most glacierized regions in the world. Here we installed a seismic network at a series of challenging high-altitude sites on a glacier in Nepal. Our results show that the diurnal air temperature modulates the glacial seismic noise. The exposed surface of the glacier experiences thermal contraction when the glacier cools, whereas the areas that are insulated with thick debris do not suffer such thermal stress. Thus, the unprotected ice surface bursts with seismicity every night due to cracking, which gradually damages and weathers the ice. This is the first time such processes have been observed at relatively warm temperatures and outside of the polar regions.Plain Language Summary It has been realized that much scientifically valuable information can be learned by listening to the tiny vibrations emanating from a glacier with sensitive sensors. However, due to their remoteness and the difficulties in accessing glacial environments, this approach has rarely been employed to better understand these important systems. For example, debris-covered glaciers, which are protected from heat by a debris mantle, remain to be studied despite being common in the Himalayas, one of the most glacierized regions in the world. Here we installed a seismic network at a series of challenging high-altitude sites on a glacier in Nepal. Our results show that the diurnal air temperature modulates the glacial seismic activity. A debris mantle dampens the diurnal amplitude of temperature and thus protects the ice from cyclic mechanical damage, whereas debris-free (exposed) ice experiences intensive near-surface fracturing early in the morning. This implies that the unprotected ice surface bursts with seismicity every night due to cracking, which gradually damages and weathers the ice. This is the first time such processes have been observed outside of the polar regions. These findings are in agreement with the personal experiences of climbers who felt and heard loud cracks on high-altitude glaciers at night.

We present an approach for determining the major anaerobic bacterial processes in aquifers, using the combined stable isotope ratios of major elements (C, N, and S) as net recorders of the biogeochemical reactions. The Kumamoto groundwater is constituted of two major flow systems, A-A' and B-B', within 10(3) km-scale area. Previous study [Hosono, T., Tokunaga, T., Kagabu, M., Nakata, H., Orishikida, T., Lin, I-T., Shimada, J., 2013. The use of δ(15)N and δ(18)O tracers with an understanding of groundwater flow dynamics for evaluating the origins and attenuation mechanisms of nitrate pollution. Water Res. 47, 2661-2675.] investigated the nitrate sources and extent of denitrification using [Formula: see text] and [Formula: see text] tracers. In the present study, we studied a type of denitrification (heterogenic vs. autotrophic) and occurrence of sequential anaerobic processes along the flow systems with newly measured δ(13)CDIC and [Formula: see text] . In A-A' flow system, C, N, and S isotopic compositions did not change along the flow direction. However, in B-B' flow system significant sulfate reduction (with a maximum [Formula: see text] enrichment of +55‰) occurred along with denitrification (with a maximum [Formula: see text] enrichment of +38‰) as the groundwater flowed down-gradient. Depletions in [Formula: see text] (-8‰ maximum) were found only sporadically. These observations imply that autotrophic denitrification could occur in very limited parts of the study area. Moreover, the occurrence of methanogenic reactions was suggested by the enriched δ(13)CDIC signature (+8‰ maximum) at a denitrification hotspot. By characterizing C, N, and S isotope compositional changes in wide redox range (from aerobic oxidation of organic carbon, through denitrification, to sulfate reduction, until methanogenesis), we could develop the model of C, N, and S isotopic evolutional patterns under different redox scenarios. Proposed model is useful in obtaining a comprehensive understanding of the major anaerobic bacterial processes in aquifer systems, including distinguishing between heterotrophic and autotrophic denitrification.

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 (>2.0 m a−1) 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.