Tetsuo Ohata

The application of a coupled hydrological and biogeochemical model (CHANGE) for modeling of energy, water, and CO2 exchanges over a larch forest in eastern Siberia

[1]xa0A coupled hydrological and biogeochemical model (CHANGE) that evaluates heat, water, and CO2 exchange between the biosphere and atmosphere across a spectrum of various time and space scales is described in this paper. The CHANGE model, which merges important components and functions in Arctic terrestrial ecosystems, is a process model with a self-constrained nature that is based on a complex and nonlinear interplay among hydrological, physiological, biochemical, ecological, and edaphic factors and meteorological conditions. This model was applied to a larch forest in eastern Siberia for the period of 1998–2006. A key objective was to assess the seasonal and interannual variability of the surface water, energy, and carbon fluxes over the larch forest in order to understand the responses of this ecosystem to climate change and to provide their controlling factors. Two types of simulations were performed with half-hourly and daily forcing data, and temporal correlation and other statistical measures supported the agreement between the simulations and observations. The simulated annual evapotranspiration (ET) ranged from 125 to 196 mm with a mean of 164 mm, 67% of which was contributed by transpiration. The simulated annual mean net ecosystem exchange (NEE) was −138.6 g C m−2 y−1 with a range of −79 to −195 g C m−2 y−1. The NEE variation was closely correlated with the net primary production (NPP). The simulation showed 23–43% interannual variability in heterotrophic respiration (Rh) for a mean of 273.1 g C m−2 y−1. Soil water was found to be a determinant that influences ET and CO2 fluxes in the larch forest. NEE was largely correlated to precipitation (PG). Thicker snow depth in the previous winter season contributed to higher NEE. The contribution of snow depth to NEE was significant in the dry years. The combination of summer PG and snow water resulted in higher NEE, which was found since 2004. In dry years, the access of roots to soil-thawed water alleviated soil water deficit and contributed to ecosystem net C uptake. The model sensitivity addressed the potential importance of the dynamic soil organic carbon on soil temperature.

Snow ablation in an open field and larch forest of the southern mountainous region of eastern Siberia

Abstract The southern mountainous taiga region of eastern Siberia is the runoff source area of the basins of the rivers Lena and Amur, where snowmelt discharge is an important hydrological process. To evaluate the effect of the sparse larch forest canopy on snow ablation and energy balance in the snow-pack, meteorological conditions and snow ablation were observed in a larch forest (LF) and an open field (OP). At the beginning of snowmelt, the snow water equivalent was 54.4 and 95.5 mm at OP and LF, respectively. The snow disappeared at LF three days later than at OP. Sublimation accounted for about 8% of snow ablation at both sites from 1 April to 5 May 2002, the snowmelt period. The energy balance of the snowpack at the two sites was dominated by the net all-wave radiation onto the snow surface. The difference in snowmelt between the sites was primarily caused by a difference in the net all-wave radiation. Snow surface albedo correlated with snow surface density for densities from 150 to 350 kg m−3 at both sites.

The Effect of Impurities on the Surface Melt of a Glacier in the Suntar-Khayata Mountain Range, Russian Siberia

We investigated characteristics of impurities and their impact on the ablation of Glacier No.31 in the Suntar-Khayata Mountain Range in Russian Siberia during summer 2014. Positive degree-day factors (PDDFs) obtained from 20 stake measurements distributed across the glacier’s ablation area varied from 3.00 to 8.55 mm w.e. K-1 day-1. The surface reflectivity measured with a spectrometer as a proxy for albedo, ranged from 0.09 to 0.62, and was negatively correlated with the PDDF, suggesting that glacier ablation is controlled by surface albedo on the studied glacier. Mass of total insoluble impurities on the ice surface varied from 0.1 to 45.2 g m-2 and was not correlated with surface reflectivity, suggesting that albedo is not directly conditioned by the mass of the impurities. Microscopy of impurities revealed that they comprised mineral particles, cryoconite granules, and ice algal cells filled with dark-reddish pigments (Ancylonema nordenskioldii). There was a significant negative correlation between surface reflectivity and algal biomass or organic matter, suggesting that the ice algae and their products are the most effective constituents in defining glacier surface albedo. Our results suggest that the melting of ice surface was enhanced by the growth of ice algae, which increased the melting rate 1.6 - 2.6 times greater than that of the impurity free bare-ice.

Impact of land-use changes on snow in a forested region with heavy snowfall in Hokkaido, Japan

Abstract We simulated snow processes in a forested region with heavy snowfall in Japan, and evaluated both the regional-scale snow distribution and the potential impact of land-use changes on the snow cover and water balances over the entire domain. SnowModel reproduced the snow processes at open and forested sites, which were confirmed by snow water equivalent (SWE) measurements at two intensive observation sites and snow depth measurements at the Automated Meteorological Data Acquisition System sites. SnowModel also reproduced the observed snow distribution (from the MODIS snow cover data) over the simulation domain during thaw. The observed SWE was less at the forested site than at the open site. The SnowModel simulations showed that this difference was caused mainly by differences in sublimation. The type of land use changed the maximum SWE, onset and duration of snowmelt, and the daily snowmelt rate due to canopy snow interception. Citation Suzuki, K., Kodama, Y., Nakai, T., Liston, G. E., Yamamoto, K., Ohata, T., Ishii, Y., Sumida, A., Hara, T. & Ohta, T. (2011) Impact of land-use changes in a forested region with heavy snowfall in Hokkaido, Japan. Hydrol. Sci. J. 56(3), 443–467.

Reconstruction of the depositional environment upstream of Potanin Glacier, Mongolian Altai, from pollen analysis

This study analyzed pollen in snow pits dug in September 2008 and September 2009 upstream of Potanin Glacier in the Mongolian Altai Mountains, which is a summer accumulation-type glacier, to investigate the environment for recent snow deposits. The snow pit observations in both years were carried out at sites 0 and 4, which are 3752 and 3890xa0m above sea level, respectively. Seasonal layers of the pits were identified according to the taxon of pollen scattered during different seasons. In the 2007 and 2008 layers, concentration peaks of pollen taxa scattered from spring to summer were found at the same depth. Thus, the summer melt reached the spring layer such that pollen grains in the melted layer became concentrated on the summer melt surface and caused the pollen peaks. In contrast, the concentration peaks associated with each season appeared at different depths in the 2009 layer, suggesting that the degree of melting in 2009 was less than that in 2007 and 2008. This interpretation was supported by summer temperature data (June–August) for this region. Deviations in summer air temperatures from mean monthly temperatures for the summers of 1990–2009 were negative in 2009, whereas they were positive in 2007 and 2008.

Projections of glacier change in the Altai Mountains under twenty-first century climate scenarios

We project glacier surface mass balances of the Altai Mountains over the period 2006–2100 for the representative concentration pathway (RCP) 4.5 and RCP8.5 scenarios using daily near-surface air temperature and precipitation from 12 global climate models in combination with a surface mass balance model. The results indicate that the Altai glaciers will undergo sustained mass loss throughout the 21st for both RCPs and reveal the future fate of glaciers of different sizes. By 2100, glacier area in the region will shrink by 26xa0±xa010xa0% for RCP4.5, while it will shrink by 60xa0±xa015xa0% for RCP8.5. According to our simulations, most disappearing glaciers are located in the western part of the Altai Mountains. For RCP4.5, all glaciers disappearing in the twenty-first century have a present-day size smaller than 5.0xa0km2, while for RCP8.5, an additional ~7xa0% of glaciers in the initial size class of 5.0–10.0xa0km2 also vanish. We project different trends in the total meltwater discharge of the region for the two RCPs, which does not peak before 2100, with important consequences for regional water availability, particular for the semi-arid and arid regions. This further highlights the potential implications of change in the Altai glaciers on regional hydrology and environment.

Depositional and summer snow melting features in 2007–2011 on the upstream side of Potanin Glacier, Mongolian Altai, reconstructed by pollen and oxygen isotope analysis

This study analyzed pollen in snow pits dug in late summer (2008–2011) on the upstream side of Potanin Glacier, a summer accumulation-type glacier in the Mongolian Altai, to reconstruct the recent snow depositional environment, particularly melting conditions. Annual snow pit observations were performed at sites 0 and 4 (3752 and 3890xa0m a.s.l., respectively). Seasonal layers in the pits were identified according to the presence of pollen from three taxa (Betulaceae, Pinus, and Artemisia), which have different pollen seasons typically between May and early September. The pollen-dating method was successful in snow pits where conventional methods such as ice layer dating and use of δ18O records were unreliable due to significant melting. Depths of pollen concentration peaks for the three taxa differed annually at both sites. In some years, concentration peaks of the three pollen taxa were found at different depths, but in other years, peaks associated with each taxon were found at the same depth. This difference was explained by summer temperature. Snow melting during the relatively warm summers of 2007 and 2008 caused pollen grains to concentrate on the glacier surface, producing peaks at the same depth. In contrast, snow melting during the relatively cool summer of 2009 did not substantially alter pollen grain location, and each peak thus retained its original depth. The median temperatures in 2010 and 2011 corresponded to pollen concentrating on the glacier surface at site 0 but retaining their original position at site 4.

Surface mass balance on Glacier No. 31 in the Suntar–Khayata Range, eastern Siberia, from 1951 to 2014

This study presents a 64-year (1951–2014) reconstruction of the surface mass balance of Glacier No. 31, located in the Suntar-Khayata Range of the eastern Siberia, where the ablation zone is characterized by the extensive dark ice surface. We use a temperature index-based glacier mass-balance model, which computes all major components of glacier mass budget and is forced by daily air temperature and precipitation from a nearby meteorological station. The glacier shows a mean annual mass balance of–0.35 m w.e.a–1 during the past 64 years, with an acceleration of–0.50 m w.e. a–1 during the recent years. A cumulative mass loss of the glacier is ~22.3 m w.e. over the study period, about 56% of which is observed during 1991–2014. In addition to the contribution of temperature rise and precipitation decrease to recent mass loss of the glacier, an experimental analysis, in which the clean and dark ice surfaces are respectively assumed to cover the entire ablation zone, indicates that dark ice surface, caused by insoluble impurities consisting of mineral dusts, cryoconite granules, and ice algae, plays a crucial role in the changing mass balance through enhancing melt rates in the ablation zone of the glacier.