Rapid Alkalization in Lake Inawashiro, Fukushima, Japan: Implications for Future Changes in the Carbonate System of Terrestrial Waters

The global carbon cycle, one of the important biogeochemical cycles controlling the surface environment of the Earth, has been greatly affected by human activity. Anthropogenic nutrient loading from urban sewage and agricultural runoff has caused eutrophication of aquatic systems. The impact of this eutrophication and consequent photosynthetic activity on CO₂ exchange between freshwater systems and the atmosphere is unclear. In this study, we focused on how nutrient loading to lakes affects their carbonate system. Here, we report results of surveys of lakes in Japan at different stages of eutrophication. Alkalization due to photosynthetic activity and decreases in PCO₂ had occurred in eutrophic lakes (e.g., Lake Kasumigaura), whereas in an acidotrophic lake (Lake Inawashiro) that was impacted by volcanic hot springs, nutrient loading was changing the pH and carbon cycling. When the influence of volcanic activity was stronger in the past in Lake Inawashiro, precipitation of volcanic-derived iron and aluminum had removed nutrients by co-precipitation. During the last three decades, volcanic activity has weakened and the lake water has become alkalized. We inferred that this rapid alkalization did not result just from the reduction in acid inputs but was also strongly affected by increased photosynthetic activity during this period. Human activities affect many lakes in the world. These lakes may play an important part in the global carbon cycle through their influence on CO₂ exchange between freshwater and the atmosphere. Biogeochemical changes and processes in these systems have important implications for future changes in aquatic carbonate systems on land.     

Fractional-order derivative and time-dependent viscoelastic behaviour of rocks and minerals

A general constitutive equation for viscoelastic behaviour of rocks and minerals with fractional-order derivative is investigated. This constitutive law is derived based on differential geometry and thermodynamics of rheology, and the fractional order of derivative represents the degree of time delay. Analyzing some laboratory experimental data of high temperature deformation of rocks and minerals such as halite, marble and orthopyroxene, we propose how to determine the orders of fractional derivative for viscoelastic behaviours of rocks and minerals. The order is related to the exponents for the temporal scaling in the relaxation modulus and the stress power-law of strain rate, i.e., the non-Newtonian flow law, and considered as an indicator representing the macroscopic behaviour and microscopic dynamics of rocks.     

Seasonal changes in camera-based indices from an open canopy black spruce forest in Alaska,and comparison with indices from a closed canopy evergreen coniferous forest in Japan

Evaluation of the carbon, water, and energy balances in evergreen coniferous forests requires accurate in situ and satellite data regarding their spatio-temporal dynamics. Daily digital camera images can be used to determine the relationships among phenology, gross primary productivity (GPP), and meteorological parameters, and to ground-truth satellite observations. In this study, we examine the relationship between seasonal variations in camera-based canopy surface indices and eddy-covariance-based GPP derived from field studies in an Alaskan open canopy black spruce forest and in a Japanese closed canopy cedar forest. The ratio of the green digital number to the total digital number, hue, and GPP showed a bell-shaped seasonal profile at both sites. Canopy surface images for the black spruce forest and cedar forest mainly detected seasonal changes in vegetation on the floor of the forest and in the tree canopy, respectively. In contrast, the seasonal cycles of the ratios of the red and blue digital numbers to the total digital numbers differed between the two sites, possibly due to differences in forest structure and leaf color. These results suggest that forest structural characteristics, such as canopy openness and seasonal forest-floor changes, should be considered during continuous observations of phenology in evergreen coniferous forests.     

Galerkin boundary integral equation method for spontaneous rupture propagation problems: SH-case

We develop a Galerkin finite element boundary integral equation method (GaBIEM) for spontaneous rupture propagation problems for a planar fault embedded in a homogeneous full 2-D space. A 2-D antiplane rupture propagation problem, with a slip-weakening friction law, is simulated by the GaBIEM. This method allows one to eliminate the strong singularities from the integral representation of the traction, and to separate explicitly the expression for the traction into an instantaneous component; static and time-dependent components with weakly (logarithmic) singular kernels; and a dynamic component and a quasi-static component, with continuous, bounded, kernels. Simulated results throw light into the performance of the GaBIEM and highlight differences with respect to that of the traditional, collocation, boundary integral equation method (BIEM). Both methods converge with a power law with respect to grid size, with different exponents. There is no restriction on the CFL stability number for the GaBIEM since an implicit, unconditionally stable method is used for the time integration. The error of the approximation increases with the time step, as expected, and it can remain below that of the BIEM.     

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 cleanand 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.     

Identification of 1771 Meiwa Tsunami deposits using a combination of radiocarbon dating and oxygen isotope microprofiling of emerged massive Porites boulders

The Meiwa Tsunami, one of the largest tsunamis recorded in historical documents in Japan struck Ishigaki Island and neighboring islands of the Ryukyu Arc in April 1771 AD, killing more than 12 000 people. An enormous number of massive Porites coral boulders are scattered on the shore and in the reef moat of eastern Ishigaki Island. Although these boulders likely were cast ashore by the Meiwa Tsunami, a detailed examination has not yet been conducted. When the marine reservoir effect is taken into account, one of mode values of calibrated radiocarbon dates possibly corresponds to the time of the 1771 event. However, the range of calibrated radiocarbon ages indicates that the transport of the boulders cannot be ascribed solely to the tsunami. Oxygen isotope microprofiling, which indicates sea-surface temperature variation, was therefore conducted to further investigate the mechanism of transport. The results suggest that the skeletal growth of most coral colonies was interrupted in summer or autumn; hence, tropical storms and typhoons are also very likely to be agents of transport. Thus, by combining radiocarbon dating with oxygen isotope microprofiling to investigate Porites coral boulders, it is possible to separate paleotsunami boulders from those transported by storm events as far as tsunamis occurred during the non-storm season.     

Ice core record of Be over the past millennium from Dome Fuji, Antarctica: A new proxy record of past solar activity and a powerful tool for stratigraphic dating

The cosmogenic nuclide ¹⁰Be was analyzed by using accelerator mass spectrometry on an ice core drilled at the Dome Fuji station, inland Antarctica, for 700–1900 yr CE. The measured concentration of ¹⁰Be in the Dome Fuji ice core and the derived ¹⁰Be flux show similar fluctuations, with both increasing at known solar-activity minima over the last millennium in agreement with earlier observations of ¹⁰Be and ¹⁴C. Based on the similar nature of the ¹⁰Be flux to the reconstructed ¹⁴C production rate patterns, a ¹⁰Be–¹⁴C correlation age model for the Dome Fuji ice core was successfully constructed. This age model agrees well with the initial version of the tephrochronology of the core. The ¹⁰Be-flux record contains information on variability in the amount of cosmic radiation incident on the atmosphere, which is mainly attributable to high-frequency change in solar activity and low-frequency background intensity adjustment of the geomagnetic field. High-resolution ¹⁰Be analyses of the Dome Fuji ice cores promise to provide potentially important information on the history of cosmic radiation intensity over the past several hundred thousand years.     

Overview of NOPACCS (Northwest Pacific Carbon Cycle Study)

The Northwest Pacific Carbon Cycle Study (NOPACCS) was a program aimed at investigating the carbon cycle of the North Pacific Ocean, which can be thought of as a large reservoir of carbon dioxide. NOPACCS was also aimed at estimating the North Pacific's capacity as a carbon sink. Project design, scientific results, and data availability, and subsequent projects resulting from this project are also described in this review. Studies of the upper ocean processes focused on the latitudinal differences in the fugacity of carbon dioxide; and on the detail of plankton community structures. Intermediate water was studied in relation to the formation of North Pacific Intermediate Water and the amount of accumulated anthropogenic carbon. The sedimentation process, past carbon cycle and coral reefs were also studied during the project. A preliminary, overall view of the carbon cycle of the North Pacific was drawn from the results of the project and compared to global values.     

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