The origin of Martian satellites is still under debate. Nevertheless, such information could give insights into the evolution of the Martian system and planetary formation processes. To address these questions, MMX (Martian Moons eXploration) will conduct spectroscopy (visible, near-infrared, Raman) and sample return from Phobos. When interpreting these spectra, an understanding of the space weathering effect is crucial. Recently, MAVEN discovered that Phobos is bombarded by oxygen ions originating from the present Martian atmosphere. However, the effect of oxygen ion irradiation on the visible, near-infrared (NIR), or Raman spectra of Phobos-like material remains uninvestigated. Therefore, in this study, we performed an exploratory oxygen ion irradiation experiment using a microwave plasma on olivine, basalt, and Phobos simulant and examined its effect on the visible/infrared/Raman spectra to be observed by the MMX mission. The irradiation experiments were conducted for 30 and 60 h. After irradiation, the reflectance of the Phobos simulant in the visible/NIR range increased nearly seven times, from 0.03 to 0.21. Raman analysis revealed the disappearance of the carbon bands, suggesting that the carbon particles contained in the simulant were oxidized by oxygen ions. For olivine, while the visible/NIR spectra show a reddening and brightening trend, suggesting oxidation of iron, the Raman spectra show a decrease in the Mg/(Fe + Mg) ratio from 93 to 87
During the Phanerozoic, the ocean repeatedly experienced periods of widespread deoxygenation known as oceanic anoxic events. Geological records from these events indicate a profound shift in marine microbial ecosystems. While cyanobacterial biomarkers are found broadly, those of anoxygenic photosynthetic green sulfur bacteria are restricted to upwelling regions or topographic highs. However, the quantitative mechanisms triggering this transition and the spatial heterogeneity of primary producers remain ambiguous. Here, using a new high-resolution one-dimensional ocean biogeochemical model explicitly incorporating a marine microbial ecosystem, we systematically evaluated the global effects of increases in riverine phosphorus input rates and sea surface temperature. We show that phosphorus-driven eutrophication and ocean warming-induced reductions in both O2 solubility and export efficiency result in surface ocean deoxygenation, leading to the restructuring of the marine microbial ecosystem. The emergence of anoxic water masses enhances denitrification and establishes a nitrogen-depleted environment, promoting the proliferation of N2-fixing cyanobacteria. With further deoxygenation, euxinic water masses develop within the photic zone, allowing green sulfur bacteria to thrive below the redoxcline, resulting in a vertical ecological segregation with oxygenic photoautotrophs and N2-fixing cyanobacteria. Moreover, an abundant supply of nutrients and H2S in upwelling regions causes more severe deoxygenation within the photic zone than in the open ocean, providing a niche suitable for green sulfur bacteria and driving a more drastic restructuring of primary producers. These findings elucidate the quantitative impacts of global climate perturbations and regional upwelling on the surface ocean, offering crucial insights into how surface ocean biogeochemistry and marine microbial ecosystems fluctuated during oceanic anoxic events.
Abstract Under global warming, precipitation is becoming less frequent but with more intense events, with little change in total precipitation amounts. These shifts have raised concerns about drying–rewetting cycles (DWCs) and their impact on soil organic matter decomposition and carbon dioxide (CO 2 ) release. Microbially derived carbon (C), such as intracellular compounds released by cell lysis and osmolyte turnover, has been considered a primary C source of DWC-induced CO 2 release. However, C released from organo–metal complexes disrupted by rapid rewetting has emerged as a significant contributor. To evaluate this contribution, we conducted incubation experiments with a single DWC. Here, we used two buried humic layer soils characterized by abundant organo–metal complexes but low microbial biomass, with two surface soils for comparison. In both buried and surface soils, the DWC consistently led to higher CO 2 release rates during incubation compared to the control. The magnitude of the increase in CO 2 release from buried humic layers exceeded the measured decreases in microbial biomass C, which represented ≤ 40% of the increase, while the amount of pyrophosphate-extractable organic C associated with organo–metal complexes was at least 90-fold greater than the DWC-induced increase. A re-analysis including data from this study and our previous study showed that the relative CO 2 release increase at DWC from control was significantly correlated with the amounts of pyrophosphate-extractable aluminum in the soils. We also observed a shift in bacterial communities in the buried soils toward a nutrient acquisition strategy adapted for rapid growth after rewetting, which may have contributed to the enhanced CO 2 release. In the present study, we suggest that organo–metal complexes, traditionally considered a stable C pool, can substantially contribute to DWC-induced CO 2 release from buried humic horizons.
Abstract Robust chronological frameworks that integrate paleomagnetic and oxygen isotope records are essential to stratigraphic correlation across diverse geological records. However, such records remain scarce for the Late Pliocene. This issue is particularly evident in the western North Pacific region around Japan, where many sedimentary basins formed below the carbonate compensation depth, yielding fewer well-preserved carbonates than those from the Atlantic Ocean. In this study, we present a high-resolution integrated chronostratigraphy of paleomagnetic and stable oxygen isotope (δ 1 8 O) records for the Late Pliocene (3.4–2.9 Ma), based on data from the marine sedimentary succession of the Chikura Group in the southernmost part of the Boso Peninsula, central Japan. In addition, we present a detailed paleomagnetic record of the upper boundary of the Kaena subchronozone and examine the behavior of the geomagnetic field during the polarity transition. Based on the benthic foraminiferal δ 1 8 O record, we developed an isotope stratigraphy corresponding to Marine Oxygen Isotope Stages (MIS) MG5 to G14, indicating that the lower Mammoth and upper Kaena boundaries correspond to MIS MG1 and G21, respectively. The relative paleointensity (RPI) record shows distinct fluctuations that correlate well with RPI variations observed in globally distributed deep-sea cores. A pronounced RPI minimum at 2.95–2.92 Ma, accompanied by unstable magnetic directions, is interpreted as a possible geomagnetic excursion or cryptochron. The upper Kaena polarity transition is characterized by rapid directional changes during an interval of reduced geomagnetic field intensity. The paleomagnetic and oxygen isotope records presented in this study provide new constraints on geomagnetic field behavior during polarity transitions and improve understanding of their timescale and structure.
Abstract Color-sorted spherical molten particles extracted from Moto-Ujina Beach sand were analyzed by inductively coupled plasma–mass spectrometry, thermal ionization mass spectrometry, micro-PIXE analysis to obtain the elemental concentrations, 235 U/ 238 U isotope ratios, and elemental concentrations and mapping, respectively. Micro-PIXE analysis was also performed for molten particles produced by fireworks, which are likely to be an artificial background for molten particles at Moto-Ujina Beach. A computer simulation was used to investigate whether the Hiroshima atomic bomb impact soil dust (mineral particles) from the near-surface could reach melting temperatures under atomic bomb fire ball-cloud conditions. The modelled temperature changes were monitored and analyzed by placing tracer particles in the explosion model calculation. The temperature rose to a maximum of approximately 1250 K (about 980 °C), which was lower than the glass particle formation temperature (2073–1673 K). The results could not determine with certainty that the particles collected at Moto-Ujina Beach derived from the A-bomb. However, even if some of the Moto-Ujina particles were formed by the atomic bomb, it would be difficult to use them as indicator materials for fallout owing to the background firework particles.
Hydropower plays a critical role in mitigating climate change by providing a renewable energy source, yet it entails significant trade-offs that impact ecological, social, and economic systems. As hydropower development intensifies in the Mekong River Basin (MRB), where only 3
Abstract Ice-nucleating particles (INPs) from mineral particles and bioaerosols in the atmosphere affect cloud properties and thus climate. Crystalline iron (Fe)-containing particles are originated from lithogenic, anthropogenic, and pyrogenic sources, whereas bioaerosols are emitted from terrestrial and marine biological sources. Atmospheric aging processes can profoundly alter the physicochemical properties of surface materials on mineral-containing (ice-active) aerosols associated with air pollution. However, crystalline Fe-containing particles from anthropogenic and pyrogenic sources are not explicitly simulated in the model prediction of INPs over the oceans, partly because our knowledge of their potentially evolving ice nucleation activity (INA) due to aging is limited. Here, we hypothesize that aged crystalline Fe-containing particles from anthropogenic and pyrogenic sources in addition to natural lithogenic sources are potentially important sources of INPs to the marine clouds over the North Pacific. After the aging processes, our atmospheric chemical transport model predicts that Fe aluminosilicate is the dominant fraction of crystalline Fe-containing particles from anthropogenic sources over the western North Pacific, suggesting an exposure of the mineral surfaces. To test this hypothesis of secondary INPs precursors, we use the model to estimate a contribution of crystalline Fe-containing particles and bioaerosols to INP concentrations that could explain ship-based measurements of potential INP concentrations at specific activation temperatures. Our model results of annual mean potential INP concentrations for aged crystalline Fe-containing particles from anthropogenic sources show the same order of magnitude as those from lithogenic sources at colder temperature (1–10 L −1 at − 30 °C) near the surface over the North Pacific. The modeled crystalline Fe-containing particles (59 ± 25%) along the cruise measurements dominate potential INP concentrations for activation temperature from − 20 to − 30 °C, compared to terrestrial (22 ± 27%) and marine bioaerosols (19 ± 23%). Among the crystalline Fe-containing particles, anthropogenic sources substantially contribute to the potential INP concentrations for activation temperature of − 30 °C during October 2–4 (30%) and November 3–5 (37%) in 2019 over the western North Pacific in downstream region of East Asian outflow. Our model results indicate nonnegligible contribution of the anthropogenic sources to annual mean INPs column concentrations up to 312 hPa from 10 to 20% over the North Pacific, given the seasonality of lithogenic sources. Our model results suggest that the contribution of the anthropogenic sources to INP concentrations is pronounced over the North Pacific in winter (from 20 to 40%) when the wind-blown dust activities are low. This study calls for further studies to elucidate the role of INPs from anthropogenic activity and open biomass burning, develop the INPs parameterization due to atmospheric aging, and revisit previously observed INP concentrations.
Abstract After the 2011 Tohoku earthquake, the dominant type of focal mechanism in the offshore forearc in Northeast Japan changed dramatically from reverse faulting to normal faulting. The aim of this study was to clarify the formation mechanism of the stress field in the offshore forearc and the changes in the mechanism caused by the 2011 Tohoku earthquake. To this end, we modeled the absolute stress field using the finite-element method considering the long-term steady plate subduction, the gravitational forces, and the gigantic earthquake cycles. The model results indicate that the shallow part of the offshore forearc exhibits a normal-fault stress state both before and after the 2011 Tohoku earthquake. This normal-fault stress field originated from the gravitational forces and the shallower bending stress due to the steady plate subduction. The deeper bending stress and frictional stress at the plate interface caused the reverse-fault stress state in the offshore forearc near the plate interface. Our results suggest that the shift in the dominant type of focal mechanism is caused primarily by the following mechanism: Reverse faulting and normal faulting are facilitated and inhibited, respectively, by interplate coupling; however, they were inhibited and facilitated, respectively, by the effects of the 2011 Tohoku earthquake. Our model does not require a reversal of the stress field across the entire offshore forearc, although such a reversal may have occurred locally. Additionally, the results suggest that the plate interface is quite weak. The magnitude of frictional stress is 5–15 MPa for a distance of 40–160 km from the trench after the 2011 Tohoku earthquake.
Abstract A positive trend in the mass term of global atmospheric angular momentum (AAM), designated as $$M_{\Omega }$$ M Ω , has been reported in previous studies but mostly analyzed from a single reanalysis dataset. In this paper, we examine the statistical significance of this trend over the period of 1950 to 2020 using four reanalysis datasets, i.e., ERA5, ERA-20C, JRA55, and NCEP/NCAR. We confirm that all of the datasets produce long-term positive trends despite some discrepancies. Moreover, all the datasets are in agreement on a positive trend over the last decade, especially over the equatorial region, suggesting an increase in equatorial air mass over the past five decades. We use a Lagrangian trajectory model to simulate changes in the interhemispheric air mass transport, whose results indicate that a mass accumulation in the equatorial region has occurred since the 1970s due mainly to transports from the Southern Hemisphere (SH). We also computed the change in the water vapor component of $$M_{\Omega }$$ M Ω ( $$\Delta M_{\Omega w}$$ Δ M Ω w ), and found that global $$\Delta M_{\Omega w}$$ Δ M Ω w contributes around 25 to 50% of the changes in global $$M_{\Omega }$$ M Ω ( $$\Delta M_{\Omega }$$ Δ M Ω ), with the largest contribution originating from the equatorial region. Although both $$M_{\Omega }$$ M Ω and $$M_{\Omega w}$$ M Ω w exhibit long-term positive trends, their statistical correlation varies across the interdecadal timescale. Particularly, a decrease in $$M_{\Omega w}$$ M Ω w is found to be inconsistent with an increase in $$M_{\Omega }$$ M Ω from the mid-1980s to the 2000s. By estimating dry air surface pressure from the difference between total surface pressure, $$p_{s}$$ p s , and water vapor surface pressure, $$p_{sw}$$ p sw , we identify that a persistent increase in dry atmosphere mass over the equatorial region might have been responsible for maintaining the positive trend of global $$M_{\Omega }$$ M Ω over the last five decades, while the contribution of $$M_{\Omega w}$$ M Ω w is also increasing over the last decade. Thus, the large positive trend in $$M_{\Omega }$$ M Ω over the last decade is likely a combined effect of the increase in dry atmosphere mass that occurred in previous decades and the current moistening of the equatorial atmosphere. These findings offer new insight into how long-term changes in atmospheric mass distribution—particularly over the equatorial region—may serve as key drivers of global $$M_\Omega$$ M Ω variability, with potential implications for large-scale circulation and Earth’s angular momentum balance.
Abstract In 2022, a “gold folding screen” (red copper leaf: copper alloy leaf containing zinc, also called Western gold leaf), which had traces of the "Black Rain" on a metal surface due to atomic bombing in August 1945, was donated to Hiroshima Peace Memorial Museum. With the cooperation of the museum, we collected and analyzed these traces. Although no radioactive particles nor anthropogenic radionuclides were detected, the red copper leaf traces dissolved by the "Black Rain" were found to be diaphanous by an optical microscopic observation. This novel finding led us to explore the "Black Rain" chemical aspect (highly oxidative) with strong “acid rain” characteristics along with presumed charcoal. This finding consists of the extremely rapid biological effects described by several witnesses after the bombings. The "Black Rain" appears to not have been a simple radioactive fallout, but a complex mixture composed of chemically reactive and oxidizing (biologically toxic) species with radioactive materials. Furthermore, the finding indicates a necessity to incorporate chemistry and aerosols into model simulations of the "Black Rain" and for deeper consideration of global environmental change scenarios, such as “nuclear winter”.
Abstract It has long been considered that dust flux reflects dryness in the source area, whereas dust grain size reflects vigor of the transport wind, although recent studies stress the importance of supply of raw materials (siliciclastic sediments) to the dust source (emission) area either by tectonic or by glacial activities in the surrounding mountainous areas. Dry areas in inland East Asia are the major sources of the dust (called Asian dust) to the northern hemisphere, and the Gobi Desert and Tarim Basin (including Taklimakan Desert) are top two sources of Asian dust at present. Dust from the Gobi Desert is dominantly carried by mid-latitude migratory cyclones at lower altitude (< 5 km) to the east, whereas dust from the Tarim Basin is mostly carried by the westerly jet at higher altitude (> 5 km) and was spread all over the northern hemisphere. These two major dust sources can be discriminated against each other by combination of provenance tracers such as electron spin resonance (ESR) signal intensity plus crystallinity index (CI) of quartz and Nd plus Sr isotopes. So, if we could know distribution of the past dust source areas and their provenance signatures in each time slices, it is possible to reconstruct the course and intensity of westerly jet and/or migratory cyclones and their changes with time from spatiotemporal distribution of fluxes and grain sizes of the dust from each source area in the North Pacific. In this review, I summarize the data on fluxes, grain sizes, and provenance of Asian dust preserved in fine-grained sedimentary sequences in proximal (desert sand and loess accumulated areas in East Asia), intermediate (East Asian marginal seas), and distal (North Pacific) areas and reconstruct their temporal changes since the late Eocene in tectonic (million years) and orbital (10 to 100 kilo-years) time scales. Then, I examine the interrelationships of those changes between proximal, intermediate, and distal areas to obtain unified view on evolution of source-to-sink processes of Asian dust and explore their control factors. I also examine the potential importance of Asian dust in global biogeochemical cycles and consequent climatic changes.
Abstract Accurate retrieval of aerosol and cloud properties is essential for improving both climate data records and trace gas observations by satellites. The Global Observing Satellite for Greenhouse gases and Water cycle (GOSAT-GW), launched on 29 June 2025, carries the Total Anthropogenic and Natural emissions mapping SpectrOmeter-3 (TANSO-3), which is designed to provide high-spectral-resolution measurements in the visible (~ 450 nm), O2 A band, and near-infrared (~ 1600 nm) regions. To prepare for operation, an aerosol and cloud retrieval algorithm was developed using Tropospheric Monitoring Instrument (TROPOMI) Level 1B data as a proxy. The algorithm retrieves the aerosol optical depth (AOD) and cloud optical depth (COD) from band 1 only from TANSO-3, and estimates the aerosol layer height (ALH) and cloud layer height (CLH) using O2–O2 absorption at 477 nm. Lookup tables were generated with the linearized pseudo-spherical vector Discrete Ordinate Radiative Transfer, and additional corrections were applied to account for relative humidity, temperature dependence, and systematic offsets in the O2–O2 absorption band. During the airborne and Satellite Investigation of Asian Air Quality (ASIA-AQ) 2024 campaign, the AODs showed good agreement with AERONET (correlation coefficient (R) = 0.781, root mean square error (RMSE) = 0.265), while comparison with Pandora SMART-s retrievals showed more moderate agreement (R = 0.444, RMSE = 0.378). ALH retrievals agreed with High Spectral Resolution Lidar-2 (HSRL-2) data within ± 1 km for AODs greater than 0.5, while under low-aerosol loading conditions the retrieved ALH became less sensitive and tended to converge toward near-surface values. COD retrievals were consistent with TROPOMI operational products, while CLH retrievals based on the O2–O2 absorption band were on average about 1 km lower than O2 A band-based results, likely due to differences in the vertical sensitivity of the two absorption bands. With further refinement in surface reflectance treatment, aerosol classification, and cloud phase detection, the algorithm will contribute to the effective use of GOSAT-GW observations for atmospheric research and air quality applications.
Abstract With the growing prevalence of landslides, risk mitigation has become critically significant. Although landslide susceptibility assessment is widely implemented globally, predicting the potential impact of landslides on human societies remains a challenge. The impact of landslides can be determined by the probability of sediment release and runout distance. This study aimed to develop a framework for evaluating the potential damage caused by landslides in an urbanized area. First, landslide occurrence susceptibility maps were produced by Artificial Neural Network (ANN), Support Vector Machine (SVM), Random Forest (RF), and Extreme Gradient Boosting (XGBoost). XGBoost is a supervised learning algorithm that implements gradient-boosted decision trees and is optimized for efficiency, scalability, and high predictive performance on large datasets. Second, an impact probability map was produced by the constrained random walk. Finally, the concept of vulnerability was integrated with the impact probability map to assess landslide risk, providing a more comprehensive understanding of landslide hazards and their potential effects on human societies. This study was conducted in an area of King County, Washington, USA, with an inventory of 2331 landslides derived from lidar imagery. Each landslide area was divided into source and deposit subareas. Fourteen parameters spanning geomorphology, geology, hydrology, and human activity were selected as conditioning factors for landslide initiation and were preprocessed to address multicollinearity before model construction. The landslide inventory map was randomly split into training (75%) and validation (25%) datasets to train the ANN, SVM, RF, and XGBoost models. Model performance was evaluated using metrics, such as the area under the curve (AUC). The results show that the XGBoost model achieved the best performance in susceptibility analysis with an overall accuracy of 0.90 and an AUC value of 0.96, followed by the RF (accuracy = 0.87 and AUC = 0.94), ANN (accuracy = 0.85 and AUC = 0.92), and SVM (accuracy = 0.85 and AUC = 0.90) models. The impact probability from the random walk method achieves an overall accuracy of 0.82 and an AUC of 0.88, demonstrating the method's effectiveness.
Abstract The ratio of P-wave to S-wave velocity (Vp/Vs) is a key indicator of subsurface fluid pressure and rock properties. However, its spatial distribution in offshore regions has been poorly constrained because of difficulties in resolving shallow seismic velocity structures, particularly Vs structures. Recent advances in distributed acoustic sensing (DAS) enable dense seismic observations even on the seafloor, improving imaging of both Vp and Vs. In this study, we estimated the spatial distribution of Vp/Vs from 25 to 85 km offshore and down to 6 km depth off Sanriku, Japan, by combining controlled-source seismic surveys for Vp and surface-wave analysis for Vs. Three distinct units with contrasting Vp and Vs values were identified. The top layer (unit-1, 0.6–2.6 km depth) shows strong spatial variations in Vp/Vs. Within 50 km from the coast (unit-1a), the spatial average is 3.33. Further offshore (50–85 km; unit-1b), a distinct vertical variation is observed, with Vp/Vs exceeding 6.00 in the uppermost layer and decreasing to approximately 3.50 in the lowermost layer. Immediately below unit-1, the second unit exhibits a significantly more uniform Vp/Vs distribution, with a spatial average of 2.84. This increased uniformity likely reflects progressive sediment compaction or a distinct change in lithology. The third unit at the depth of 1.2–6.8 km shows anomalously high Vp/Vs (spatial average of 3.27) despite high Vp (~ 4.4 km/s) at the distance range of 25–65 km from the coast, which numerical modeling attributes to seismic anisotropic structures. These findings demonstrate the utility of DAS for marine seismic imaging, fluid assessment, and other seismological analyses.
The Shikoku Basin, a Miocene back-arc basin in the Philippine Sea, hosts numerous oceanic core complexes (OCCs) that reflect melt-poor lithospheric extension. Based on bathymetric mapping, gravity and magnetic surveys, dredging, and submersible dives conducted between 2007 and 2023, we identified multiple OCCs in its southern part, including the Mado, Sui-Shin, Tosa, Sanuki, and Awa Megamullions. These OCCs expose mantle and lower crustal rocks and are associated with high mantle Bouguer anomalies, indicating thin crust. Geochemical and geochronological data from the Sui-Shin Megamullion suggest its formation immediately after rifting of the proto-Izu-Bonin arc ( 24 Ma). The Tosa Megamullion, dominated by plagioclase-peridotites with only minor gabbros, exemplifies melt-poor lithospheric conditions and may represent Hess-type oceanic crust. The spatial and temporal distribution of OCCs, including the triplet OCCs (Tosa, Sanuki, and Awa), implies multiple ridge jumps during basin evolution. These findings suggest that a significant portion of the Shikoku Basin formed largely through amagmatic or melt-poor processes, contrasting with typical mid-ocean ridge settings. The OCCs serve as tectonic windows into back-arc lithosphere evolution and provide a framework for future investigations into the role of melt supply and slab-derived fluids in shaping oceanic crustal architecture.
Back-arc basins play a crucial role in the formation of oceanic crust, similar to mid-ocean ridges. While magmatic and tectonic processes in the mature spreading stage resemble those in mid-ocean ridges, the initiation and cessation of back-arc spreading remain unclear. The Shikoku Basin and its associated remnant arc in the Philippine Sea are among the most studied back-arc systems, providing an excellent opportunity to understand the detailed processes of oceanic arc rifting and the initial stages of back-arc opening. We have recently collected bathymetry, magnetic and gravity data from the southwestern part of the Shikoku Basin. This area is characterized by a deeper basin floor and numerous oceanic core complexes with high gravity anomalies, indicating that magma-poor spreading was predominant in the initial stage. The magnetic lineation pattern is only discernible in a limited abyssal hill area, but the identified geochrons align with previous studies in the northern part of the basin and new zircon U–Pb age data from a couple of minor gabbroic samples. The morphology of closely located oceanic core complexes suggests a ridge jump. The structural features of the basin floor correlate with the morphology of the remnant arc, the Kyushu-Palau Ridge, implying that the preexisting arc crustal structure influences the style of rifting/spreading and may affect the development of ridge segmentation.
The polar region is sensitive to climate change, with concerns about the effects on ecosystems and human society. In particular, the thawing of permafrost associated with rising temperatures accelerates the microbial decomposition of organic carbon in the soil, leading to greenhouse gas emissions. Thermokarst is a landform process formed by thawing ice-rich permafrost and subsidence of the ground surface. This landform is an indicator of permafrost degradation; thus, evaluating the distribution of thermokarst is essential for understanding the impact on Arctic regions. Although assessing the thermokarst has been a labor-intensive task because of its widespread occurrence in the Arctic, automatic detection using deep learning and remote sensing techniques has been applied. However, the cost of creating training data for the specific area was challenging because thermokarst size and shape varied by region. Here, we classified thermokarst from satellite images using a recently developed method, the chopped picture method, which is suitable for identifying ambiguous and amorphous objects such as the thermokarst. This study uses high-resolution panchromatic and pan-sharpened images in eastern Siberia to evaluate the effects of differences in satellite images on classification accuracy. The training and test images were divided into 60 pixels in height and width, and each cell was classified into two categories: thermokarst topography or others. In addition, we used Global Map Data to calculate the percentage of thermokarst topography for each slope orientation (south or north) to identify the environmental conditions that facilitate the development of this topography. Results showed that our approach could clearly and automatically distinguish developed thermokarst from other landforms such as forests, lakes, and urban. Classification of thermokarst topography in panchromatic and pan-sharpened images indicated that automatic detection was possible in both images. Additionally, thermokarst topography was distributed on south-oriented slopes rather than north. This method will achieve low-cost automatic detection of thermokarst through the use of satellite data and AI. With the increase of small satellites, opportunities to utilize satellite images for observations in Arctic research will expand. Our approach will contribute to environmental monitoring in the Arctic by enabling the automatic mapping of thermokarst.
Abstract Evolution of the Shimanto accretionary complex suggests implications for the geological history of the East Asian continental margin. To better understand the tectonic evolution of the complex during Paleocene to early Miocene, we collected new petrological and geochemical data, along with U–Pb ages, from sandstones and felsic tuffs in the Murotohanto and Nabae groups in eastern Shikoku. These data clarify the depositional ages and stratigraphic architecture of the two groups, providing insight into the late Paleocene to early Miocene sequence of accretionary processes. Sandstone petrography and geochemistry reveal that the two groups have distinct provenances and demonstrate temporal variations related to the regional tectonic evolution of the continental margin. Sandstones in the Murotohanto Group contain abundant felsic igneous fragments with two detrital zircon age clusters. Cretaceous detrital zircons were supplied by erosion of the Cretaceous magmatic arc during subduction of the Izanagi–Pacific ridge (c. 60–45 Ma). Zircons with variable Permian to Cretaceous ages originated from pre-Cretaceous basement rocks and the Cretaceous arc during subduction of the relatively young Pacific Plate (c. 45–28 Ma). Sandstones from the Nabae Group exhibit petrological and geochemical characteristics indicating the influence of more mafic to intermediate igneous rocks in the source region. Detrital zircons in the Nabae Group are mainly Cretaceous and Paleogene in age, with a small number of early Miocene zircons. These zircons were supplied during erosion of the Cretaceous and Paleogene arcs, which was associated with rifting of the continental margin before opening of the Japan Sea and subduction of the Pacific Plate (c. 28–18 Ma). Transition in provenance occurred in the middle Eocene (c. 45 Ma) and the mid-Oligocene (c. 28 Ma), implying that crustal erosion extended from forearc to back-arc regions. The middle Eocene event was triggered by magmatic arc development after the Izanagi–Pacific ridge subduction, whereas the mid-Oligocene event was related to the timing of crustal uplift with regional unconformity and rifting-related magmatism in Japanese arc.
