Bathymetric Analysis Research Articles

Habitat-driven otolith shape morphology in Oreochromis niloticus (pelagic) and Chrysichthys nigrodigitatus (benthic) from distinct zones of a tropical coastal lagoon system

This study explored the morpho-functional variations in the otoliths of Oreochromis niloticus (ON) and Chrysichthys nigrodigitatus (CN) across the Ikorodu (IKL) and Epe (EPL) regions in Nigeria's southern coastal lagoon system, with monthly sampling over twelve months. Digitized otoliths provided shape descriptors, and bathymetric analysis was conducted using the depth invariance index (DII). Remotely sensed reflectance (RSR) at 469 nm, 531 nm, and 555 nm assessed habitat productivity. Morpho-functional variations were evaluated using discriminant analysis (DA) and principal component analysis (PCA). Bathymetric analysis revealed that EPL has a deeper and more heterogeneous substratum than IKL. Additionally, Epe exhibited consistently higher RSR values than IKL. Sediment analysis showed higher clay and silt percentages in IKL and increased coarse sand in EPL, indicating distinct terrains. DA accuracy was high (ON: 92.0 %, CN: 90.8 % in cross-validation), highlighting variables such as area and circumference for ON and area, circularity, and compactness for CN. DA emphasized ellipticity, rectangularity, and roundness for ON, and form factor, compactness, circularity, and aspect ratio for CN. Higher reflectance values at EPL than at IKL indicate distinct ecological characteristics, with greater nutrient cycling and trophic productivity at EPL. Sediment analysis revealed distinct ecological heterogeneity and hydrological effects, with finer sediments in IKL indicating calmer conditions and EPL exhibiting higher energy conditions. Visualizing normal curve distributions for otolith shape descriptors in ON and CN populations revealed skewness patterns indicative of divergent adaptive features, possibly associated with habitat heterogeneity and productivity. The key otolith variables identified by DA and PCA suggest relative ecological opportunity and underscore the intricate relationships between otolith morphology and habitat variables (heterogeneity, productivity, sediment profile) in Nigeria's tropical southern lagoon system.

First Results on Lake Bathymetry of Panch-Pokhari Complex, Langtang Region, Central Nepal

The Panch-Pokhari complex, a group of five lakes, is one of the high-altitude wetlands of Nepal that has received very less attention. While these lakes hold significant religious importance, they are less known from a morpho-ecological perspective. The objective of this study is to develop a bathymetry model of the lakes through afield survey and geospatial analysis. This study generated new insights into the limnological and morphometric features of the five lakes through detailed mapping and profiling. The bathymetric analyses revealed diverse basin morphometry among the lakes, with Lake 1 being the largest, in term of its depth of 12.1 m and water volume of 208,352 m3. In contrast, Lake 5 was the smallest and the shallowest with a depth of 1.4 m and volume of 1,921 m3. This study establishes a new baseline to advance scientific understanding of the Panch-Pokhari complex. Further, integrated research combining limnological, ecological, and social aspects is recommended to support evidence-based planning for the conservation of these vital Himalayan wetlands.

Mid-ocean ridge unfaulting revealed by magmatic intrusions.

Mid-ocean ridges (MORs) are quintessential sites of tectonic extension1-4, at which divergence between lithospheric plates shapes abyssal hills that cover about two-thirds of the Earth's surface5,6. Here we show that tectonic extension at the ridge axis can be partially undone by tectonic shortening across the ridge flanks. This process is evidenced by recent sequences of reverse-faulting earthquakes about 15 km off-axis at the Mid-Atlantic Ridge and Carlsberg Ridge. Using mechanical models, we show that shallow compression of the ridge flanks up to the brittle failure point is a natural consequence of lithosphere unbending away from the axial relief. Intrusion of magma-filled fractures, which manifests as migrating swarms of extensional seismicity along the ridge axis, can provide the small increment of compressive stress that triggers reverse-faulting earthquakes. Through bathymetric analyses, we further find that reverse reactivation of MOR normal faults is a widely occurring process that can reduce the amplitude of abyssal hills by as much as 50%, shortly after they form at the ridge axis. This 'unfaulting' mechanism exerts a first-order influence on the fabric of the global ocean floor and provides a physical explanation for reverse-faulting earthquakes in an extensional environment.

Event-based soil erosion and sediment yield modelling for calculating long-term reservoir sedimentation in the Alps

ABSTRACT Among the most characteristic offsite effects of soil erosion, reservoir sedimentation is one of the longlasting problems pertaining to storage capacity and dam operations. In this work, sedimentation rates of the Fortezza reservoir in South Tyrol (Italian Alps) are analysed for nine erosive events over 14 months. Sediment rates are calculated through a modified Universal Soil Loss Equation (USLE) combined with a Sediment Delivery Ratio (SDR) module at 2.5 m resolution. The topographic factor is adjusted to the Alpine terrain, and an additional factor is included to consider the nonerodible parts of the basin. The results are validated against a 14-month sediment yield obtained by high-resolution (0.2 m) reservoir bathymetric analyses. The calculated sediment yield has an absolute deviation of 4.8% from the measured one. The results indicate that these methods can be successfully applied for the estimation of reservoir sedimentation rates in the Alps.

The depositional characteristics of turbidity current in Manila Trench: sediment provenance, geochemical elements and organic carbon burial

Turbidity currents play a significant role in sediment transport in deep ocean, profoundly impacting sedimentation in the abyssal sea. This study focused on a 375 cm long sediment core collected from the Manila Trench, revealing a distinctive 15 cm turbidite layer characterized by coarse sediment, an upward fining pattern, and a basal erosion surface. Analysis of rare earth elements and Nd isotope indicates that this turbidite layer originated from Taiwan Island. Initiated in the estuarine shelf region of southwestern Taiwan Island, the turbidity current transported substantial biogenic debris and marine fresh organic carbon into the Manila Trench. Consequently, the turbidite layer exhibited an elevated CaO content and more positive δ13C values. Despite lower TOC content in the turbidite layer due to coarse particle size, the mixture of marine fresh organic matter significantly lowered the carbon age of this layer compared to the strata both below and above it. The rapid sedimentation of the turbidite deposit led to an organic carbon burial flux comparable to the rate at which normal deep-sea sediment buries organic carbon over seven hundred years. Notably, finer sediment overlaying the turbidite layer acted as a cap, enhancing carbon sequestration within the trench. In contrast to nearby core GEO6, which documented over 11 turbidity currents, core S02 recorded only one event. Detailed bathymetric analysis highlights the crucial role of local topography in detecting and preserving turbidity currents. The insights gained from this study would advance our understanding of how turbidity currents shape and influence the deep ocean sedimentation.

Earth observation satellite data-based assessment of wetland dynamics in the Kashmir Himalaya.

Earth observation (EO) technology offers enormous opportunities to assess the magnitude and patterns of spatial variability in wetlands over time. This study aims to assessthe spatial and temporalchanges in the wetlands of the Kashmir valley using multiple remote sensing satellite data products, Geographic Information System (GIS), and field observations. Moreover, role of major factors operating at different time scales including regional geology, climate, and human activities in driving the wetland change is presented. The dynamics of the wetlands are illustrated in the occurrence, seasonality, and recurrence of surface water, land cover transitions and loss patterns particularly for the period from 1984 to 2021. Constituting about 3% (495 Km2) of the total area, substantial and variable patterns of seasonal and annual changes are exhibited by the wetlands. The main transitions of the water surface reveal that 2% of the area has changed from permanent to seasonal; 8% is lost; 15% is new seasonal; 0.12% is permanently lost; and 0.3% is new permanent. About 22% of the area reveals increase in the intensity of water surface occurrence, whereas 44% shows no change, and 34% exhibits decrease. Bathymetric analysis suggests that the average depth of the wetlands ranges between 0.6 and 16.6m. In general, alpine wetlands are relatively deeper and mostly static in their structure whereas those in the floodplain are shallow, fragmented, and showing signs of depletion during the assessment period. The results of this assessment will inform the policy on conservation and sustainability of wetlands in the Kashmir Himalaya.

Contrasting T-Phase and P-Wave Patterns from the 2015 and 2017 Eruptions of the Submarine Volcano Kick-‘em-Jenny: Influence of Cardinal Direction on Recorded First Phase Arrival

ABSTRACT Kick-‘em-Jenny (KeJ)—the most active volcano in the Lesser Antilles and located about 8 km north of Grenada—is the only known, live submarine volcano in the region. Unrest and eruption episodes are approximately decadal. Typically, a KeJ episode, which may consist of several eruptions, is short-lived and rapidly returns to quiescence, with virtually no background seismicity. Although two previous eruptions broke the surface of the sea, and some have had seismic effects felt in northern Grenada and sometimes Martinique, instrumental recordings of T phases were considered to provide firm evidence of eruptions. T phases are hydroacoustic waves that propagate efficiently in the Sound Fixing and Ranging channel allowing long-range recording. The most recent episodes occurred on 29 April 2017 and 23, 24 July 2015, with no reported surface evidence. The 2015 hr-long seismic signals, among the longest durations ever recorded, manifested differences in the first phase arrivals at some of the same recording stations suggesting a fundamental difference in T-phase wave trains’ generation at KeJ. The single eruption in the 2017 volcanic episode had a duration similar to those prior to the 2015 eruptions; however, except for the four stations in the immediate vicinity of KeJ, the detected signals propagated only as T waves. Real-time and posteruption deductions that the episodes occurred from different cardinal directions on the volcano were found to be supported by the findings from bathymetric analyses done shortly after the episodes. This characteristic enhances the KeJ profile, possibly improving real-time activity assessments in future KeJ episodes, with a view to strengthening hazard and risk communication.

Impact of coastal development on coastal morphology of Taiwan: Case studies and proposed countermeasures

When economic expansion started in the late 1970s, Taiwan was in desperate need of better infrastructure. In response, the government began construction along the coasts around the island. Many of these structures were constructed under time constraints, and their possible effects on the environment were not considered. Years later, some of the structures were found to have disrupted littoral sediment transport, resulting in the retreat of shorelines downstream. The Integrated Coastal Zone Management Plan demands the implementation of remedial measures for erosion by the responsible party in the near future. However, as morphological changes are complicated processes involving both natural and human-induced drivers, the liabilities of the parties involved are typically difficult to determine. In this study, bathymetric analysis and numerical simulation were used to assess the effects of coastal structures on coastal erosion. With the former, the rate of change of the bathymetric volume along the shore was used to identify the extent of the structural effect. The latter one is then used to clarify the respective effect of adjacent structures on coastal bathymetry. Three cases with different surroundings were considered to verify the scheme. It is suggested that range of influence of the structure should be determined in terms of coastal cells. In the case of multiple structures existing within a cell, the cost of remedial measures should be proportional to the length of the structure vertical to the coastline. Remedies to restore the continuity of longshore drift are then proposed. These results can be used to promote effective coastal zone management and prevent further deterioration.

Studies on navigational depth of a shipping channel using numerical modelling and bathymetric analysis in the Hooghly estuary, India

ABSTRACT Availability of navigational draft along the shipping channel is essential for effective freight transport of any port for its economic sustenance. Rangafala channel is one of the main channels leading to Kolkata port. The primary objective of this research work is to find the critical and vulnerable positions in the navigation channel. A Cartesian grid-based, two-dimensional, depth-averaged, finite volume model has been developed using existing bathymetry, water level, sediment data, and appropriate boundary conditions in hydrodynamic and sediment transport modelling. The developed model is first calibrated using observed velocity data, and then, it has been validated with observed water level data at the Haldia gauge station. The validated model has been simulated for 6-month boundary values, and it has been experienced that the depth-averaged model velocity is relatively high throughout the channel. The hydrodynamic and sediment transport model results suggest that the channel remains self-maintained, and only a few locations experience little deposition. Eleven years of channel bathymetric data are used to complement the simulated model results. It is observed that the required draft for navigation has always been maintained along the Rangafala channel.

Characteristic Depths, Fluxes, and Timescales for Greenland's Tidewater Glacier Fjords From Subglacial Discharge‐Driven Upwelling During Summer

AbstractGreenland's glacial fjords are a key bottleneck in the earth system, regulating exchange of heat, freshwater and nutrients between the ice sheet and ocean and hosting societally important fisheries. We combine recent bathymetric, atmospheric, and oceanographic data with a buoyant plume model to show that summer subglacial discharge from 136 tidewater glaciers, amounting to 0.02 Sv of freshwater, drives 0.6–1.6 Sv of upwelling. Bathymetric analysis suggests that this is sufficient to renew most major fjords within a single summer, and that these fjords provide a path to the continental shelf that is deeper than 200 m for two‐thirds of the glaciers. Our study provides a first pan‐Greenland inventory of tidewater glacier fjords and quantifies regional and ice sheet‐wide upwelling fluxes. This analysis provides important context for site‐specific studies and is a step toward implementing fjord‐scale heat, freshwater and nutrient fluxes in large‐scale ice sheet and climate models.

Mapping Submarine Geomorphology of the Philippine and Mariana Trenches By an Automated Approach Using GMT Scripts

Abstract This paper presents a geospatial analysis of two oceanic trenches using a GMT (Generic Mapping Tools) cartographic method that exploits the scripting approach to visualisation of their geometric shapes. To this end, the research applies the high-resolution datasets GEBCO and ETOPO1 and ETOPO5 for modelling of the submarine relief. This allows taking into account the 2D and 3D shape deviations in the geomorphology of the two selected segments of the trenches by transecting a series of the cross-section profiles. A scripting algorithm of spatial data processing based on the GMT techniques visualised the topography of the submarine objects in 2D and 3D forms and extracted the topographic data from raster grids for statistical analysis of depth using the cross-section transect profiles of both trenches. The bathymetry of the Mariana Trench was evaluated in the southern segment located near the Challenger Deep area, southwest of Guam Island, in comparison with the segment of the Philippine Trench, which was transected in the surroundings of Mindanao Island. The study presented a comparative submarine geomorphic modelling and spatial analysis of the Philippine Sea basin area. The bathymetric analysis of the relief in the Mariana and Philippine trenches showed effective performance of the GMT scripting toolset in advanced cartographic data analysis and visualisation.

Bathymetric Signatures of Submarine Forearc Deformation: A Case Study in the Nankai Accretionary Prism

AbstractLarge earthquakes and tsunamis in subduction zone forearcs occur via slip on the shallow plate boundary and upper plate faults, but the locations, geometries, and slip histories of these faults can be difficult to constrain in regions with minimal subsurface geophysical and stratigraphic data. Here, we test a new approach to quantify the submarine seafloor geomorphic response to forearc deformation in order to identify structures that contribute to active deformation, to interpret their geometry and kinematics, and to evaluate their relative rates, magnitudes, and timing of deformation. We develop a workflow that uses filtered bathymetric digital elevation models, where long wavelength topography has been removed, to isolate the slope, relief, curvature, ridgelines, and trough lines associated with faults, fault‐related folds, and slope failures. We apply these methods to the Kumano region of the Nankai accretionary prism, southeastern Japan, where existing constraints on fault geometry, kinematics, and deformation history allow us to both evaluate the efficacy of our approach and to identify the lateral continuity of deformation processes. Our bathymetric analyses yield a high‐resolution tectono‐geomorphic map of active structures and reveal along strike variations in strain accumulation and out‐of‐sequence deformation. These metrics also demonstrate the importance of a strike‐slip fault system at the seaward edge of the Kumano Basin as a primary structure that accommodates deformation and partitions strain in the Nankai forearc. These results show the utility of using a submarine tectono‐geomorphic approach to evaluate active deformation in forearcs, particularly in regions with limited geophysical and core data.

Linking land system changes (1980–2017) with the trophic status of an urban wetland: Implications for wetland management

The knowledge on urban ecosystem dynamics is being increasingly felt due to unprecedented symptoms arising out of urbanization. This study is aimed to assess land use-land cover changes (LULCCs) around a wetland ecosystem using high spatial resolution CORONA and Google Basemap satellite imageries. The imageries were processed by digitizing land cover features at 1:3000 scale in ArcGIS 10.1. The imageries were classified into nine classes, and an estimation of accuracy was performed utilizing the Kappa coefficient and error matrices. The overall accuracy obtained was 94% for the 2017 dataset. The key findings indicated a loss of 23% in the wetland area from 1980 to 2017. While in the vicinity, a significant increase in green spaces (706.2%) and roads (89.4%) was observed. Morphometric analysis revealed that the wetland has lost a surface area of 10.2ha from 1980 to 2017. The maximum length (Lmax) of the wetland was reduced by 722m while the maximum width (Wmax) decreased by 78m. Bathymetric analysis revealed that the wetland is shallow with a depth ranging from 10 to 174cm. The Carlson's Trophic State Index (TSI) of wetland ranging from 74 to 87 indicates hyper-eutrophic waters. Overall, the loss of wetland area, together with the reduction in morphometric features, low depth, and higher trophic status speak of anthropogenic pressures that are compromising the ecological integrity of this wetland. Therefore, landscape planning and governance are of pivotal importance for the conservation and management of wetland ecosystems in this region.

An Integrated Multiscale Method for the Characterisation of Active Faults in Offshore Areas. The Case of Sant’Eufemia Gulf (Offshore Calabria, Italy)

Diagnostic morphological features (e.g., rectilinear seafloor scarps) and lateral offsets of the Upper Quaternary deposits are used to infer active faults in offshore areas. Although they deform a significant seafloor region, the active faults are not necessarily capable of producing large earthquakes as they correspond to shallow structures formed in response to local stresses. We present a multiscale approach to reconstruct the structural pattern in offshore areas and distinguish between shallow, non-seismogenic, active faults, and deep blind faults, potentially associated with large seismic moment release. The approach is based on the interpretation of marine seismic reflection data and quantitative morphometric analysis of multibeam bathymetry, and tested on the Sant’Eufemia Gulf (southeastern Tyrrhenian Sea). Data highlights the occurrence of three major tectonic events since the Late Miocene. The first extensional or transtensional phase occurred during the Late Miocene. Since the Early Pliocene, a right-lateral transpressional tectonic event caused the positive inversion of deep (>3 km) tectonic features, and the formation of NE-SW faults in the central sector of the gulf. Also, NNE-SSW to NE-SW trending anticlines (e.g., Maida Ridge) developed in the eastern part of the area. Since the Early Pleistocene (Calabrian), shallow (<1.5 km) NNE-SSW oriented structures formed in a left-lateral transtensional regime. The new results integrated with previous literature indicates that the Late Miocene to Recent transpressional/transtensional structures developed in an ∼E-W oriented main displacement zone that extends from the Sant’Eufemia Gulf to the Squillace Basin (Ionian offshore), and likely represents the upper plate response to a tear fault of the lower plate. The quantitative morphometric analysis of the study area and the bathymetric analysis of the Angitola Canyon indicate that NNE-SSW to NE-SW trending anticlines were negatively reactivated during the last tectonic phase. We also suggest that the deep structure below the Maida Ridge may correspond to the seismogenic source of the large magnitude earthquake that struck the western Calabrian region in 1905. The multiscale approach contributes to understanding the tectonic imprint of active faults from different hierarchical orders and the geometry of seismogenic faults developed in a lithospheric strike-slip zone orthogonal to the Calabrian Arc.

Crustal Structure Across the Northern Region of the Islas Marías Archipelago

The tectonic interaction between the Rivera and North American plates north of the Bahía de Banderas is poorly understood. The nature of the crust and where the subduction ends in the western part of the Islas Marias Archipelago are still controversial. Based on new geophysical data provided by the TsuJal project, we present the shallow and deep crustal structure of the Rivera–North American plate contact zone along two seismic transects, TS09b and RTSIM01b, and the bathymetry obtained across the northern region of María Madre Island. Detailed bathymetric analysis allowed mapping of a series of lineaments along the study region, with two main preferred tendencies (020–050° and 290–320°) associated with the evolution of the Pacific-Rivera rise and the transform faults of the Gulf of California, respectively. The shallow structure is characterized by five sedimentary basins without deformation, whose horizons are subparallel, suggesting that the sediment deposition occurred after the extension process ended. The deep structure corresponds to a transition between oceanic crust (Rivera Plate), with an average thickness of ∼10 km to the Islas Marías Escarpment, and a thinned continental crust, whose thickness increases toward the continent until it reaches 28 km, with a dip angle of 7–10°. The absence of an accretionary prism suggests that the subduction process of the Rivera Plate beneath the North American Plate to the north of Islas Marías has ceased. In this study, we determined that the morphological expression of the northern limit of the Rivera Plate corresponds to the Islas Marías Escarpment.

Age of the volcanoes of the Columbretes Islands (Western Mediterranean)

The Columbretes Islands, compose the only volcanic archipelago in the western Mediterranean, and are located on the eastern edge of the Ebro continental shelf, 50 km to the east of the coast of the Iberian Peninsula, and constitute the emerging part of the Columbretes Volcanic Field. Only one volcanic structure is recognised on the surface, corresponding to Columbrete Grande, in which successive phases of hydromagmatic and strombolian volcanic activity are identified. The bathymetric analysis also identifies other monogenetic volcanoes, aligned according to two strikes: a main N170o E direction (formed by more than seven volcanic centres of phonolitic composition and which, at present, appears as small islets) and a second direction, N55o E (which belongs to the two volcanic centres of basic composition, one of which is Columbrete Grande). New K/Ar radiometric dating, along with the reinterpretation of the existing data and current volcanological criteria, allows two periods of main volcanic activity to be recognised: an older period with a basanitic composition (from 0.7 to 0.8 Ma) and a second period, of essentially phonolitic composition (from 0.2 to 0.3 Ma). The well-preserved morphology of submarine volcanoes indicates that volcanic activity has continued until much more recent times.

Morphological behavior of the Magdalena River delta (Colombia) due to intra and interannual variations in river discharge

Morphological conditions of river deltas define the sedimentological processes of this kind of ecosystem, which are strategic points to locate transport infrastructures, such as ports. River deltas can present morphological variations caused by natural or anthropogenic factors, affecting the navigability conditions of cargo ships. In order to guarantee feasible conditions for the navigability of river deltas and reduce economic costs caused by dredging activities, further studies are required to assess the relationship between hydrological and hydrodynamic processes with the morphodynamic behavior along the river basin. This study evaluates the hydrodynamic and morphodynamic conditions of the Magdalena River delta (Colombia) based on river discharges, water levels, and bathymetric information for the period 2006–2012. Moreover, linear-time-invariant systems (LTI) was developed to perform correlation analysis between the climatic oscillations, such as the ENSO, and the water level conditions in the Magdalena River. The bathymetric analysis showed unsteady morphological conditions along the river bed and high erosion rates during the studied period. The delta presented sedimentation conditions during El Niño years, or periods with negative discharge anomalies, and erosion rates during La Niña years, or periods with positive discharge anomalies. For intrannual scales, dry periods (January–April) presented sedimentation trends, whereas wet periods (September–December) exhibited significant erosion trends.

BATHYMETRIC AND GEOLOGICAL PROPERTIES OF THE ADRIATIC SEA

Advance in the visualization of the bathymetric and geological data from charted to digital maps and models opened the possibility to analyse data within Geographic Information System (GIS) functionalities. In this paper, bathymetric and geological properties of the Adriatic Sea were analysed using the General Bathymetric Chart of the Ocean (GEBCO) 2020 digital bathymetric model (DBM) and data from the European Marine Observation and Data Network (EMODnet). The bathymetric analysis includes depth statistics, area and volume calculation, hypsometry, and analysis of the heterogeneity of bathymetric data from the GEBCO 2020 DBM within the limits of the Adriatic defined by the International Hydrographic Organization (IHO) and 3 sub-basins delineated according to the bathymetry. The geological analysis includes seabed substrate map from EMODnet data and kilometre-scale seabed variability in the Adriatic. The GEBCO 2020 DBM shows that the Adriatic Sea is a shallow sea with a mean depth of -253 metres and over 50% of area shallower than 100 metres. The area of the Adriatic Sea is 138 516 km2 with a total volume of 35 521 km3. Patterns describing morphological variability coincide with the heterogeneity of the underlying source data of the GEBCO 2020 digital bathymetry model and major structures in the Adriatic Sea.

GEBCO GRIDDED BATHYMETRIC DATASETS FOR MAPPING JAPAN TRENCH GEOMORPHOLOGY BY MEANS OF GMT SCRIPTING TOOLSET

The study investigated geomorphology of the Japan Trench located east of Japan, Pacific Ocean. A high-resolution GEBCO Gridded Bathymetric Dataset was used for modeling, mapping and visualization. The study aimed to compare and analyse variations in the geomorphic structures of the two parts of the trench and to visualize variations in the geological, geophysical and bathymetric settings. Technically, the cartographic work was performed using scripting based on the Generic Mapping Toolset (GMT). Modelled cross-sectioning orthogonal profiles transecting the trench in a perpendicular direction were automatically digitized and graphed in the two segments. The results of the bathymetric analysis shown that the southern part is shallower: with deeper values in absolute (139 samples between –7000 to –8000 m) and statistical records (the most frequent values are within –5500 to –5800 m) comparing to the northern segment (–5300 to –5500 m). The geomorphological analysis shows a more complicated relief in the northern part of the trench, which has a higher seismic activity. The southern part has a gentler slope on the Honshu island side. The geoid modeling along the trench ranges in 0–20 mGal. The highest values are recorded by the Honshu Island (>40 mGal). The rest of the area has rather moderate undulations (20–40 mGal). The free-air marine gravity of the Sea of Japan is <40 mGal. The results include 2D and 3D graphical models, thematic cartographic maps, spatial and statistical analysis of the Japan Trench geomorphology. Tested GMT functionality can be applied to future regional bathymetric modeling of the ocean trenches. All presented maps and graphs are made using GMT scripting toolset.

Python libraries matplotlib, seaborn and pandas for visualization geospatial datasets generated by QGIS

This work aim is to perform modelling and spatial analysis of the marine geological data using combination of the QGIS and Python programming. Selecting proper cartographic software is important part of the geospatial research. QGIS provides organizing data in a GIS project for mapping and spatial visualization through vector and raster layers stored in GIS. Study area is Mariana Trench, west Pacific Ocean. A series of cross-section profiles were digitized in QGIS and used for further data processing in Python. Mariana Trench has complex geomorphic structure and unevenness in profiles stretching south-westwards. The geomorphology is subjected to various phenomena that affect its shape. These include bathymetry, geodesy, gravimetry, tectonics plates and geological settings, studied in this paper. To understand the structure of the trench, a data modelling using bathymetric analysis was performed by combination of QGIS mapping and statistical analysis in Python’s library Seaborn. Statistical data modelling aimed at the analysis of the spatial variation of the geomorphology of the trench using following methods: multiple facet grids, area charts for the data frames, regression analysis, letter- value plots, hexagonal and Kernel density estimation. The results of the geospatial data analysis show spatial unevenness of the geomorphic structure, gravimetric, geodetic and bathymetric settings of the Mariana Trench. The study demonstrated effectiveness of Python application in geographic data analysis with Python codes provided for repeatability.