# Topography of the Aleutian Trench south-east off Bowers Ridge, Bering Sea, in the context of the geological development of North Pacific Ocean

Polina Lemenkova

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Polina Lemenkova. Topography of the Aleutian Trench south-east off Bowers Ridge, Bering Sea, in the context of the geological development of North Pacific Ocean. Baltica: An International Yearbook for Quaternary Geology and Palaeogeography, Coastal Morphology and Shore Processes, Marine Geology and Recent Tectonics of the Baltic Sea Area, 2021, 34 (1), pp.27-46. 10.5200/baltica.2021.1.3. hal-03237945

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# Topography of the Aleutian Trench south-east off Bowers Ridge, Bering Sea, in the context of the geological development of North Pacific Ocean

Lemenkova, P. 2021. Topography of the Aleutian Trench south-east off Bowers Ridge, Bering Sea, in the context of the geological development of North Pacific Ocean. *Baltica, 34 (1)*, 27–46. Vilnius. ISSN 0067-3064.

Manuscript submitted 5 August 2020 / Accepted 3 April 2021 / Available online 20 June 2021

© Baltica 2021

**Abstract.** The research is focused on the topographic modelling and mapping of the Aleutian Trench. The study area is situated in the Bering Sea, a marginal sea located northernmost of the Pacific Ocean, between Alaska and Kamchatka Peninsula. The geological setting of the region is characterized by the subduction of the oceanic Pacific Plate below the continental North American Plate. Other features include high seismic activity along the Aleutian island arcs bordering the oceanic seafloor. The objective of this paper is to explore the interaction between the geophysical setting affecting the relief of the seafloor by using geoinformation techniques and geological analysis. In the hypothesis of this study, variations in the geophysical fields as independent variables are reflected in the morphology of the seafloor, which can be observed using data visualization by the advanced cartographic scripting solutions. The open source high-resolution topographic map (ETOPO1), marine free-air gravity and Bouguer gravity anomaly data were used and integrated to investigate the potential correlation between the geophysical, geological, tectonic and topographic settings of the Bering Sea. Our main method includes bathymetric mapping of the area with publicly available bathymetric data using GMT. Materials include open source data: ETOPO1 raster grid with 1 arc-minute resolution, EGM96 gravity and vector contour layers of GMT. The research included complex thematic mapping of the region, including topographic, contour, geodetic and geophysical mapping, 3D modelling and geomorphological plotting of the 30 cross-section segments of the trench located SE off the Bowers Ridge. According to the processed ETOPO1 dataset, the minimal depth is -8480 m and the mean is -3089.154 m. The geoid undulations model shows that the majority of the gravity values lie in the interval between -10 and 20 m with the lowest values along the trench. The statistical histogram shows that the most common depth value in the segment of the Aleutian Trench is -4800 m, occurring 1722 times. The profile linear trend modelling was done with four different approaches of the regression model (y = f(x) + e) by weighted least squares (WLS) with arguments: 1) $m_2t = a + bt$ (polynomial model degree one); 2) $m_3t = a + bt + ct^2$ (polynomial model degree two); 3) $m_4t = a + bt + ct^2 + d\cos2\pi*t + \sin2\pi*t$ (polynomial model with Fourier series one); and 4) additional plotting residuals. Surface modelling was performed using xyz modelling from the ASCII data enlarging fragment towards SE of the Bowers Ridge. The tested functionality of modules of GMT presented an effective cartographic scripting toolset enabling a precise topographic mapping and 3D modelling. The paper contributes to a more detailed understanding of the Pacific Ocean seafloor bathymetry, more specifically of the selected segment of the Aleutian Trench near Bowers Ridge area.

**Keywords:** GMT; cartography; geology; 3D modelling; geophysics; gravity

<figure><img src="image_3.png" /></figure>
INTRODUCTION

Understanding the geomorphic form and shape of
the deep-sea trenches is crucial for modelling their
geophysical and geological phenomena, because dif-
ferent shapes affected by the lithosphere movements
reveal details in the tectonic evolution of the region.
Various factors affect the formation of deep-sea
trenches, among which are tectonic plate movement,
subduction dynamics of the underlying slab into the
deep mantle seismic activities in the study area, e.g.
submarine earthquakes (Shepard 1963), and geologi-
cal phenomena identifying the characteristics of the
submarine geomorphology of the trench based on ge-
ological data modelling and submarine geomorpholo-
gy (Tibaldi, Bonali 2017; Lemenkova 2018a, 2018b;
Yogodzinski et al. 2015; Münker et al. 2004).

The seafloor is constantly deforming under the
impact of plate tectonic processes modelling the
shape of the ocean floor. This activity is one of the
fundamental issues of the marine geology. However,
proper techniques to map the marine environment
and bathymetry visualizing and modelling deep-sea
regions are still developing (Wadge 1992; Schenke,
Lemenkova 2008; Suetova et al. 2005; Lemenkova
2019a, 2019b; Wessel, Smith 1991). The study of
the submarine landforms, such as oceanic trenches,
has technical limitations due to the often remote and
inaccessible location of the study object. Therefore,
machine learning data modelling algorithms are an
effective tool for marine mapping. This study uses
Generic Mapping Tools (GMT), a cartographic tool-
set for mapping seafloor regions using shell scripts

and developed methodology (Wessel, Smith 1991;
Lemenkova 2019c, 2019d).

A particular challenge in the geospatial mapping
of the seafloor are the dynamic processes that lead to
the formation of the landforms. Submarine geological
modelling should therefore encompass not only the
landforms of the trench, but also its explicit links with
tectonics, seismicity in the study area, earthquakes re-
peatability and magnitude, oceanological parameters
(current direction and strength) and lithology (nature
and properties of the underlying rocks).

With this study we address the question why the
geophysical setting affects the relief of the seafloor
and investigate interaction among free-air marine
gravity, the dependence of topographic position along
the trench on the varying geoid gravity values and the
trend of the bathymetry profiles. The geoinformation
techniques and geological analysis were used to solv-
ing the problem of geospatial analysis and coherency
of the multi-source data used in this study.

Hence, the aim of this study is to explore the in-
teraction between the geophysical setting affecting
the relief of the seafloor by investigating the factors
of regional geological evolution, tectonic history and
variability in regional geophysical fields which great-
ly influenced the depth and landforms of the seafloor
affecting the lithosphere in the southern region of the
Bering Sea. The goal of the performed geomorpho-
logical mapping of the Bering Sea submarine regions
is to visualize the seafloor landforms and features of
the selected segment of the Aleutian Trench by using
a multi-disciplinary approach of the scripting carto-
graphic techniques and geological analysis.

<figure><img src="image_4.png" /><figcaption>Fig. 1 Topographic map of the Bering Sea basin and the Aleutian Arc. Source: author</figcaption></figure>
According to the hypothesis of this study, varia-
tions in the geophysical fields as independent vari-
ables are reflected in the morphology of the seafloor,
which can be observed using data visualization by the
advanced cartographic scripting solutions. Automated
mapping by means of GMT makes geospatial analysis
more effective today, since it enables to more focus on
the geological data analysis rather than on technical
aspects of the GIS-based mapping routine. Since the
GMT is an open source toolset, the required material
resources for cartographic processing only consist of
the installed GMT and the collected data. Therefore,
this study presents several code snippets to explain
the efficient methods of GMT in more details.

The added value of this paper contributing to the
existing studies on the Bering Sea consists in the
novel approaches by cartographic scripting solving
the needs to distinguish the geomorphology of the
Aleutian Trench. Deep-sea trenches have a wide vari-
ety of geomorphological shapes that can be analysed
through the cross-section techniques: slope steepness
(smooth, steep, gentle slope), convex, asymmetric,
V-formed, U-formed, and so on. Therefore, since not
all deep-sea trenches are the same, it is important to
model and map them to distinguish their unique ge-
ometry by using advanced cartographic solutions.

Rapid evolution of mapping approaches presents
changed ways of mapping that makes the cartographic
data processing more effective through faster work-
flow and more accurate maps based on the machine-
based graphics. Modern map production often faces a
strong time pressure and high requirements for map
quality. This can be done by the application of GMT
though its scripting paradigm, which consists in its
logical and automated procedures of modular syntax.

Understanding the geomorphology of the oce-
anic trenches and surrounding seafloor is crucial in
the comprehension of the Earth's tectonic evolution.
Knowing the geomorphology of the deep-sea trench-
es assists in solving the problems of the correlation
among factors affecting its formation, which can be
formulated in the key questions: How do the tectonic
plates movements shape the general morphology of
the deep-sea trench? How do the seismicity and vol-
canism in the area of the trench increase the sedimen-
tation intake and accumulation which may change
the present form of the trench (e.g. sediment-starved
or sediment-filled)? How does the particle size and
load intensity contribute to the filling of the trench by
sediments? Since the individual features of the gradi-
ent and the depth of the slopes of each trench vary,
what are the major factors that shape the current form
of the trench (caused by the tectonic movements and
lithosphere processes in each particular region of the
trench)? Finally, the ocean currents velocity also con-
tributing to sedimentation may be a subject of addi-

tional studies with regard to the deep-sea trenches.

Since the middle of the 20th century along with
rapid technological development of the bathymetric
survey, the oceanic seafloor shape and morphology
were largely used and discussed by scientific com-
munities (Frohlich et al. 1982; Lundgren et al. 1995;
Mortera-Gutiérrez et al. 2003; Vasquez et al. 2015;
Beniest et al. 2016, 2018; Johnson et al. 2017; Beni-
est 2017; Dumke et al. 2018). Then, the progress in
methods of data analysis and cartographic visualiza-
tion introduced a new relationship between oceanic
seafloor and tectonic history: seafloor spreading and
formation of the submarine landforms (Fisher et al.
1987; Ely et al. 2016; Leat et al. 2016; Beniest et al.
2017; Schmid et al. 2020; Beniest, Schellart 2020;
Lemenkova 2021a; Cloetingh et al. 2021).

Qualitative visualization of the spatial raster grids
introduced the notion of conceptual neighbourhood
(Freksa 1991), which refers to the geological, geo-
physical and topographic datasets aimed to identify
correlations with the geomorphological landform
of the trench corresponding to their spatial relation-
ships (Pullar, Egenhofer 1988). Particularly, the re-
lationship between geological setting, distribution
of tectonic lineaments, properties of rocks (density,
magmatism) underlying seafloor, oceanic geophys-
ics and submarine geomorphology was not hence-
forward representable using a linear rapport because
of their complex properties and nature. Accurate and
systematic mapping of geomorphological features of
the oceanic seafloor and deep-sea trenches based on
high-resolution datasets (such as ETOPO1) provides
a factual dataset for geomorphological interpretation
and analysis of such correlation between topographic
features, geophysical and geological setting.

A combined representation of the topographic
and geophysical relationships with a comparison of
the geomorphological modelling is a non-straightfor-
ward task from both cognitive geological and techni-
cal cartographic points of view. Some of these tasks
are linked to the perceiving and representing geomor-
phological phenomena as 2D and 3D spatial models
and overlaying gravimetric datasets with topographic
maps. In this sense, a GMT-based visualization pro-
vides an appropriate description of the geographic
relationships that apply in spatial dimensions by ad-
justing cartographic projections, grid dimensions,
comparative and statistical analysis of the results.

The submarine geomorphological mapping exer-
cise of this paper aims at visualizing and analysing
landform features based on the combination of com-
puter-based modelling and plotting through GMT
and published literature of the geological setting of
the study area located in the Bering Sea and Aleutian
Trench. Variations in geomorphic local and regional
features include variable seabed texture fabric: breaks
and smooth changes in the slope, conical and linear local depressions and/or submarine ridges. The GMT-based mapping of the geomorphological features of the Aleutian Trench in a selected digitized segment is undertaken at a consistent resolution (1 arc minute grid of ETOPO1) appropriate for the project which enabled to map in details of complex landforms. Larger scales were used for enlarged maps to better visualize the segment of the Bowers Ridge.

The Bering Sea, compared to other marginal seas of the Pacific Ocean is worth special attention due to its contrasting topography. The differences in bathymetry of the submarine margin of the continent are notable in western and eastern parts of the Bering Sea which depends on the age of the crystalline basement.

## REGIONAL SETTING

### Topographic location

The studies feature is the Aleutian Trench, an oceanic trench located in the Bering Sea, a marginal sea situated in the northernmost part of the Pacific Ocean (Udintsev *et al.* 1959; Murray 1945). The Aleutian Island Arc is placed on a submarine ridge separated from the Kamchatka Peninsula by the deep (> 4000 m) Kamchatka Strait. The topography of the Aleutian Island Arc is dissected by a long, narrow elevated feature that extends along the trench with relative heights between 400 and 1000 m, dividing the Aleutian Island Arc into several blocks. The geomorphology of the continental slope is characterized by a rather steep, stepped ledge with valleys and blocks. The seafloor of the southern Bering Sea reaches depths up to 3000 to 3300 m, where it smoothly transforms to the flat seafloor bottom of the Aleutian and Commandor basins with depths of 3700 to 4000 m, separated by a block of the Shirshov Ridge (depth of 3000 m).

Variations in the topography of the continental margin are contrasting in western and eastern parts of the Bering Sea, which depends on the age of the crystalline basement. The shelf of the Mesozoic platform of Chukotka, which connects to the shelf of the Mesozoic platform of Alaska, has a considerable width (up to 500–600 km) presenting a vast erosional plain formed in Beringia, then levelled by processes of abrasion and accumulation during flooding in the Pleistocene. The surface of the plain lies at depths of 80–120 m, and the outer edge of the shelf at depths of 120–180 m. The thickness of the sedimentary cover of the Bering Sea shelf is uneven: up to 3–4 km in the depressions of the Mesozoic platform basement, interrupted by several islands (St. Lawrence, St. Matthew, permafrost-covered volcanic island Nunivak, Pribilof Islands and the Diomede Islands). A different

morphology of the continent's underwater margin is observed along Cenozoic of the Koryak Highlands and Kamchatka. Shelf abrasion terrace is narrow there, only 20–50 km, with depths up to 120–180 m. The continental slope is steep with many small submarine canyons. The sedimentary cover on the shelf and the slope is very thin, so that the foundation exposed in many places.

### Geological setting

The Aleutian Island Arc is a huge mountain structure with a complex double structure separating the basin of the Bering Sea from the Pacific Ocean. Its mountain range stretches from the shores of North America to the shores of Eurasia in the form of a crescent arc with a radius of ca. 1500 km, with a centre near Cape Navarin. The ridge of the Aleutian Islands is mostly submarine and only appears above sea level by its peaks – by the Commander Islands and Aleutian ridges, Alaska and Kenai peninsulas. The total length of the Aleutian Island Arc reaches 3000 km.

The Aleutian Islands include rocks of many ages and types: hornfels, hornblende gneiss, slate, schist, granulite, granodiorite, varieties of granite (biotite and hornblende granite). The metamorphic rocks of Palaeozoic age in western Aleutians have undergone recrystallization. The presence of crystalline rocks of continental type proves that a large land mass must have existed in the vicinity in the Mesozoic or Palaeozoic times. The bedrock source of the boulders in western Aleutian Islands was not seen and may not be exposed. Therefore, the relative ages of the granitic and metamorphic rocks could not be definitely determined (Coats 1956). The granitic rocks might be younger however, because most of them lack directional textures, proving that they have not been metamorphosed.

The crystalline basement surface of the Mesozoic structures on the Alaskan Shelf of the Bering Sea forms an extensive marginal depression where the seafloor surface gradually sinks to the edge of the shelf, reaching depths of ca. 3000 m, gradually deepening further to the seafloor bottom of the basin (Kurnosov 1981). According to the magnetic anomalies, the basin of the Bering Sea formed during the Mesozoic and is a relic of the ancient Kula Plate according to the palaeotectonic reconstructions (Gorbatov *et al.* 2000).

The flat bottom of the Aleutian Trench seafloor is filled with sediments. According to the data of deep-water drilling (Udintsev 1987), the sediment stratum is represented by two layers. The lower layer has an age from Late Cretaceous to Late Miocene. It is composed of the hemipelagic sediments consisting of clay and silt-sized grains of terrigenous origin, biogenic material from the Aleutian Island Arc and marine or-
ganisms. This layer is consistently overlying the oceanic crystalline basement, gently inclined towards the foot of the Aleutian arc slope. The thickness of this layer is 200–400 m. The upper layer is represented by the horizontally accumulated turbidite deposits that unconformably overlie the hemipelagic sediments of the lower layer forming the wedges containing the deposits. The age of the sediments is from the Late Miocene to the present time, with thickness gradually increasing westwards from 1000 to 3000 m. The west end of the Aleutian Island Arc is separated from the continent by the Kamchatka Strait with depths over 4000 m (Udintsev 1987).

The basement surface of the Cainozoic structures of the Aleutian Island Arc and the coast of Kamchatka sinks along a steep ledge towards the seafloor bottom with depths ranging from 5000 to 7000 m (Udintsev et al. 1963). The depths of the crystalline basement surface in the Aleutian Trench are ca. 1000 m higher compared to the present topography (Udintsev 1972). The metamorphic granite layer is absent on the seafloor of the marginal Bering Sea, as proved both by geophysical data analysis and results of the deep-sea drilling (Artyushkov et al. 1984; Udintsev 1987). Instead, a basaltic, or other type of volcanic, layer is located below the sedimentary cover. The Conrad and Moho discontinuity extends beneath the island arc and submarine elevations (Torne et al. 2020).

The geological composition of the andesitic substrate in Aleutian Trench results from the melts of the subducted Pacific oceanic crust (Kay 1978). The most widespread rocks in the region of the Aleutian Islands include high alumina andesite, basalt and intrusions of gabbro and granodiorite. Clay minerals found in the rocks include smectite, illite, chlorite (Kim et al. 2015). The upper crust lithology is composed of the metamorphic rocks in the granulite (or amphibolite) facies of metamorphism and magmatic intrusions. The crust transitions from oceanic to continental arc in the Aleutian Islands region (Fliedner, Klemperer 2000; Holbroock et al. 1999). The Aleutian Island Arc separated the Mesozoic Aleutian Basin and the Paleogene arcs of the Shirshov Ridge located on the eastern border of the Commander Basin, and the Bowers Ridge from the ocean bed. A young Commander Basin of the Bering Sea began to form in the rear of the arising island arcs in response to rising of asthenospheric material and the extension of the crust.

The geological historical processes contributed to the environmental uniqueness of the Aleutian Islands area (Rathburn et al. 2009). The granite, metamorphic and sedimentary lithologies are derived from the Alaskan continental margin, while igneous clasts could be derived from volcanic sources surrounding the Bering Sea (Dadd, Foley 2016). The striped pattern of magnetic anomalies is stretching from the

region of the Aleutian Island Arc and trending approximately east-west is found south of the Aleutian Trench (Hayes, Heirtzler 1968). The magnetic anomalies are located along the axial parts of anticlinal folds and are caused by the deep blocks of the basalt layer (as in bathymetry) and variations in the chemistry or magnetism of the rocks in the Aleutian Island region, as studied in various works (Bingham, Stone 1972; Watts, Talwani 1974; Cande 1976). The striped pattern of magnetic anomalies is also observed parallel to the Aleutian Island Arc at the seafloor bottom of the Bering Sea basin.

## Tectonic evolution

The tectonic history of the Aleutian Island Arc is deeply connected with Kuril-Kamchatka Trench, because the Aleutian Island Arc collides with the Kuril-Kamchatka Arc in the area of the Cape Kamchatka peninsula (Freitag et al. 2001). The Aleutian transform fault separated the Kronotskiy terrain block from the Pacific Plate during the major event in the tectonic history of the Pacific region which was a plate reorganization that occurred ca. 50 Ma (Vaes et al. 2019; Seton et al. 2015; Müller et al. 2016). The Bering Sea is located in an area where the Pacific Plate subducts under the North American Plate. During the Early Cretaceous, subduction of the Pacific Plate below the North America Plate initiated. This subduction is still ongoing presenting an example of ocean-ocean convergent zones in the region where currently the Bering Sea is located. The large and old Pacific Plate moves in N–NW direction with respect to North America where it is subducted beneath the southern Alaska and the Aleutian Island Arc (Drewes et al. 1961). The Aleutian and Commander Islands are colliding with the Kamchatka Peninsula Cape. The collision was initiated after the changed direction of plate motion in the Middle Eocene (ca. 40 Ma), with the last collision episodes having started recently (Gaedicke et al. 2000). During the Mesozoic and Tertiary, the Kamchatka–Aleutian junction was affected by the subduction in Kronotskiy subduction zone and collision of the Kronotskiy arc against North-East Eurasia margin (Hanna et al. 2020), leading to the formation and developing of four structural assemblages of the Kronotskiy arc terrane, which are characterized by the precollisional deformations in the accretionary wedge, the fore-arc basin and volcanic belt, and syn-collisional deformation of the entire Kronotskiy terrane and deformations in the foreland basin (Alexeiev et al. 2006).

The Aleutian Island Arc is classified as an accreting margin (Jicha, Kay 2018) with most of the arc having a well-developed frontal prism that formed in the Plio-Pleistocene. The Central Aleutian volcanic
<figure><img src="image_5.png" /><figcaption>**Fig. 2** Contour map of the study area. Source: author</figcaption></figure>

front migrated 30–60 km northwards since the formation of the arc massif completed in the late Eocene. The Aleutian Trench has a weak coupling between the surface tectonic plate and subducting slabs (Yoshida 2017).

## Seismicity and earthquakes

The Aleutian region is known for its seismic activity. In 1946, the seismicity of the Aleutian region caused a very severe tsunami (Bai *et al.* 2018), but other tsunamis originated in the Aleutian region affect far located regions (Ryan *et al.* 2014). Studies on the seismicity, earthquake sources and effects distribution in the region of the Aleutian Islands are presented in previous studies (Ekstrom, Engdahl 1989; Engdahl, Billington 1986). The seismic belt stretches along the NW and W margins of the Pacific Ocean and continues along the island arcs from the Aleutian Islands to New Zealand. In its central part, several seismically active zones are observed according to the direction of the island arcs in the western part of the Pacific Ocean. More detailed studies on the seismicity of the Aleutian Island Arc area are provided in relevant existing publications (Boyd *et al.* 1995; Liakopoulou-Morris *et al.* 1995; Estabrook *et al.* 1997; Gorbatov *et al.* 2001; López, Okal 2006).

There is a high seismic activity along the island arcs bordering the oceanic crust. Besides weak earthquakes, also some strong earthquakes with magnitudes of 7.0–8.5 and with hypocenters located under the island arcs with focal planes of 50–70° occurred (Litvin 1987). Using data from Harvard CMT catalogue since 1977, Mortera-Gutiérrez et al. (2003) re-

ported three classes of focal mechanisms along the Aleutian Trench for the shallow, large earthquakes (<60 km depth with moment magnitudes Mw >4.5): (1) thrusting events of the interplate zone, (2) strike-slip fault events in the upper plate of the Aleutian Ridge, and (3) normal faulting events on the STS of the oceanic plate. That said, north of the Aleutian Trench most earthquakes point at thrust faulting. The depths of the earthquake hypocenters vary from 200–250 km to 600–700 km. Well-defined hypocenters reach depths of 200–300 km, with occasional hypocenters with greater depths (>500 km).

The thickness of the Earth's crust in the Bering Sea region varies and exceeds 30 km on the continental margin, is ca. 25 km thick under the Aleutian Island Arc, and only <10–12 km under the seafloor basin (Udintsev *et al.* 1980). The Earth's crust in the Commander depression is represented by almost a single velocity layer of 6.5 km/s. The Aleutian basin itself consists of two layers with velocities of 3.7–5.5 and 6.8–7.2 km/s, with Moho velocities of 8.0 km/s. The thickness of the Earth's crust in the Aleutian Trench is reduced to 8 km with velocities at 4.5–5.5 and 6.3–6.6 km/s (Litvin 1987).

## MATERIALS AND METHODS

### Data Listing

The precision in collecting, sorting and organizing data is the key for getting high-quality geospatial data, which will greatly influence the research output and final quality (Smith 1993; Wessel, Watts 1988). The data used in this research include vector
layers embedded in the GMT (coastlines) and high-resolution downloaded raster datasets: ETOPO1, xyz topographic and gravity datasets from the open public repositories of the USGS.

In this research, high-resolution geodata were
collected from the United States Geological Survey
(USGS) open source database geoid data EGM-96
(Lemoine et al. 1998), marine free-air gravity data
(Sandwell, Smith 1997) and available embedded
Geo-Information Systems (GIS) layers of the Generic
Mapping Tools (GMT) (Wessel, Smith 1996; Smith,
Sandwell 1997).

Mapping with GMT

This work is technically based on using the GMT,
a cartographic scripting toolset, which has certain ad-
vantages over the existing traditional GIS, e.g. Map-
Info, Erdas Imagine, QGIS, ArcGIS, widely used
in the geosciences (Klaučo et al. 2013, 2014, 2017;

Lemenkova *et al.* 2012). The scripting approach of the GMT is based on machine algorithms that can process data which results in printing quality and aesthetic values of the cartographical outputs. The layouts of the GMT are accurate with respect to the cartographic projection and scale.

GMT includes a formal programming foundation,
i.e. a certain kind of scripting language with a set of
minimal operators and flags required for the manipu-
lation with cartographic commands, set-up regional
projections and local adjustment (e.g. legends, grids,
ticks, annotations). The main software used for this
study is Generic Mapping Tools with various modules
of which the functionality is described in the software
documentation and release announcement (Wessel,
Smith 1995; Wessel et al. 2013). GMT enables plot-
ting of visual cartographic variables including (Bertin
1983) position, size, shape, value, colour, orientation,
and texture of the cartographic elements.

The simplicity, clearness of graphic expression

<figure><img src="image_6.png" /><figcaption>**Fig. 3** Modelling 3D mesh grid of the Aleutian Islands and Aleutian Trench area. Source: author</figcaption></figure>
and readability of maps is achieved through a detailed adjustment of the annotation fonts and cartographic elements. A wide variety of colour palettes (contrast- ing, neighbouring or complementary colours) sup- ported by GMT enables to select the most suitable

colours for representing continuous surfaces (gravity,
geoid, topography) to balance graphic arts and techni-
cal methods for representing geographic phenomena
(Imhof 1965). As a result, a special kind of aesthetics
and beauty is inherent to a map plotted by GMT.

<figure><img src="image_7.png" /><figcaption>Fig. 4 Geoid model of the Bering Sea basin. Source: author</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Fig. 5 Marine free-air gravity map of the Bering Sea basin. Source: author</figcaption></figure>
The maps, using GMT, and the cartographic visualization presented in this paper are made according to the theoretical cartographic principles. These principles include the concept of semiotics and its three subdivisions (Freitag 1971): syntaxics, that is, a syntax of a map; semantics, that is, producing a map with meaning and cartographic elements (Claramunt, Thériault 1996); and pragmatics, that is, the organization, general layout and contexts of the map layouts. Special GMT modules that are designed for plotting elements and base elements are ‘pslegend’ and ‘psbasemap’. The general bathymetric map of this study is the ETOPO1 bathymetric 1 arc-minute resolution grid (Amante, Eakins 2009). The ETOPO1 global relief model was modelled with the ‘grdimage’ module of GMT (Fig. 1).

The initial grid was subset using the GMT module ‘grdcut’, which cuts off the region from the grid file within a window of 154°W – 220°W and 40°N – 65°N and saves it to the NetCDF format. The main drawing models used were: ‘pscoast’ module for mapping coastal lines and contours, ‘psscale’ module for mapping the colour legend, and ‘pstext’ module to add textual explanations on the map. The isolines were plotted with 1 m interval and annotations every 5 m using the GMT ‘grdcontour’ module.

The bathymetry was visualized using the ‘geo’ colour palette. The original data was derived from the sea-surface satellite altimetry measurements and

ocean soundings provided by global geospatial sources (Amante, Eakins 2009). Therefore, the ETOPO1 includes existing bathymetry data and uses interpolated gravity values elsewhere. Based on an analysis of the ETOPO1 map (Fig. 1), the suitable segment was selected for plotting sample data on cross-section profiles and the series of the profiles was plotted for topographic analysis. Specifically, the segment was plotted as a line from start to end points (red thick points shown in Fig. 7) with the following coordinates: 180°W, 49.9°N to 172.0°W, 51.0°N.

Representing geological and geophysical data and the tectonic setting of the Barents Sea in one, referenced, map requires the understanding of their relationships within an integrated framework of the combined data in a GMT project. Combining several GMT modules allowed the computation and visualization of 2D and 3D models of the Aleutian Trench. The 3D map also includes a mesh model (Fig. 3), which shows that the study area rotated 165°/45° overlapping the contour map of the geoid. Several GMT modules were used following previous studies (Lemenkova 2020c), grdcut, grd2cpt, grdcontour, pscoast, grdview, logo, psconvert, in order to add cartographic elements on the map listed and summarized in Table 1.

The automated digitizing of the geomorphological profiles was done using the ‘grdtrack’ module of GMT. The simulation was programmed using GMT syntax using the ETOPO1 raster dataset as a base map.

<figure><img src="image_9.png" /><figcaption>Marine free-air vertical gravity anomaly for the Aleutian Trench area</figcaption></figure>

**Fig. 6** Modelling free-air vertical marine gravimetry of the Bering Sea. Source: author
The model includes a systematic drawing of a cross-section consisting of 30 segments to evaluate the geomorphology of the Aleutian Trench. The cross-section (180.0°W 49.9°N (start point) 172.0°W 51.0°N (end point)) is 400 km long with 30 segments that are 2 km long and oriented perpendicular to the WSW-ENE oriented major cross-section (Fig. 7b). The segments are spaced 20 km apart (Fig. 7). From the start to end point of the major cross-section there is a set of points at which the perpendicular, 2-km wide segments were made. The distance between each two is 20 km. In total, there are 30 of the segments visualized in Fig. 7 as thin yellow lines parallel to each other with a 2 km distance between them. These segments were plotted automatically by GMT. The modelling consists of drawing a median line (red line on Fig. 7) and calculating error bars and an interval of the threshold (grey area) for the statistical dataset for all the segments (Fig. 7) using the GMT ‘convert’ module. The bathymetry was then mathematically modelled for line curvature (Fig. 8) and statistically processed (Fig. 9).

The coastlines, ticks and directional rose were added on the map using the GMT ‘pscoast’ module.

The NetCDF grid format was processed as a grid file (Rew, Davis 1990). The cartographic routine includes adding the basic elements on the map, including ticks, gridlines, directional rose, legend and choosing a suitable projection. Further technical details are described in previous publications (Lemenkova 2019f, 2020b, 2021b). 3D modelling was done using the GMT ‘grdview’ module.

The CryoSat-2 and Jason-1 and gravity models are used to support geophysical investigations, geological prognosis as well as the geological resources management. The data included a raster grid developed by Lemoine *et al.* (1998) and tested methodology (Lemenkova 2020a). The GMT script used for modelling gravity includes the ‘grdimage’ and ‘img2grd’ modules. The combination of the GMT modules for modelling allows a proper visualization of the thematic maps.

To assist in the identification of the geomorphology of the Aleutian Trench, the bathymetric ETOPO1 data were contoured at 500 m intervals using the GMT module ‘grdcontour’ (Fig. 2). The geomorphic analysis process in GMT module ‘trend1d’ was applied to build statistical trends with four functional

<figure><img src="image_10.png" /><figcaption>**Fig. 7** Automatic digitizing of the cross-section profile in the study area. Source: author</figcaption></figure>
approaches (Fig. 8) and visualization of the median and mean profiles (Fig. 7 and Fig. 8). The results of the surface modelling (Figs 10 and 11) were used by modelling an xyz dataset. The grid was smoothened prior to use by applying the 'blockmean' module of the GMT: it interpolated the original values in the table by a smoothing algorithm. The most important

codes from the GMT scripts for modelling and mapping are presented and summarized in Table 1.

## Statistical modelling with GMT

Statistical data modelling is an important tool for the analysis of data in geosciences (Lemenkova

<table><caption>**Table 1** Summary of the GMT modules and examples of codes used for mapping</caption><thead><tr><td>GMT module</td><td>Code snippet from the GMT script</td><td>Practical aim (purpose)</td></tr></thead><tbody><tr><td>gmtset</td><td>gmt set FORMAT_GEO_MAP = dddF MAP_FRAME_PEN = dimgray \ MAP_FRAME_WIDTH = 0.1c \</td><td>Setting up general parameters of GMT (fonts, language, layout offset, style of coordinates, etc.)</td></tr><tr><td>img2grd</td><td>img2grd grav_27.1.img -R154/220/40/65 -GgravAT.grd -T1 -I1 -E-S0.1 -V</td><td>Conversion of the image which extracts a subset of the img file in Mercator projection</td></tr><tr><td>grd2cpt</td><td>gmt grd2cpt geoid.egm96.grd -Crainbow > geoid.cpt</td><td>Generating colour palette (here: example for geoid)</td></tr><tr><td>grdimage</td><td>gmt grdimage at_relief.nc -Catocean.cpt -R154/220/40/65 -JM6i -P-I + a15 + ne0.75 -Xc -K > $ps</td><td>Raster image visualization</td></tr><tr><td>pscoast</td><td>gmt pscoast -R -J -P -V -W0.25p -Df -B + t"Geoid gravitational regional model: Aleutian Trench area" -Bxg3f4a8 -Byg3f2a4 -O -K >> $ps</td><td>Plotting coast lines</td></tr><tr><td>grdcontour</td><td>gmt grdcontour geoid.egm96.grd -R -J -C2 -A5 -Wthinnest, dimgray -O -K >> $ps</td><td>Adding isolines</td></tr><tr><td>psbasemap</td><td>Add grid with major and minor lines gmt psbasemap -R -J -Bpxg12f6a12 -Bpyg5f5a5 -Bsxg6 -Bsyg5 -B + t"Bathymetry of the Aleutian Trench and coastal land topography" -O -K >> $ps</td><td>Adding base cartographic elements (grid, major and minor ticks, title and subtitle, scale, directional rose)</td></tr><tr><td>psscale</td><td>gmt psscale -R -J -CgravAT.cpt \ -Dg142/40+w11.0c/0.5c+v+o0.7/0i+m1 \ -Bxg100f20a100+l"Marine free-air gravity anomaly colour scale" \ -I0.2 -By+lmGal -O -K >> $ps</td><td>Adding scale bar on the map</td></tr><tr><td>pstext</td><td>gmt pstext -R -J -N -O -K \ -F+jTL+f7p,5,black+jLB+a-270 -Gwhite@40 \ >> $ps << EOF 172.0 56.0 Shirshov Ridge EOF</td><td>Adding text on the map (left: example for annotating the Shirshov Ridge)</td></tr><tr><td>logo</td><td>gmt logo -Dx6.2/-2.2+0.1i/0.1i+w2c -O -K >> $ps</td><td>Placing logo of GMT below the map</td></tr><tr><td>psrose</td><td>gmt psrose tableA2.txt -i1,4 -R0/1/0/360 \ -A7r -S1.0in \ -Glightsteelblue1 -Bx0.2g0.2 \ -By30g30+l"Bathymetric data distribution by cross-section profiles" \ -B + t"Aleutian Trench: Rose diagram on the cross-section profiles" + gghostwhite \ -M0.5c + e+gred2+n1c \ -W0.1p,red \ -Cm \ -UBL/-15p/-65p -Vv -K > $ps</td><td>Plotting rose diagram</td></tr><tr><td>pshistogram</td><td>gmt pshistogram table2.txt -i4 -R-8200/1000/0/20 -JX4.8i/2.4i -X3.6i \ -Bpxg1000a1000f100 + l"Bathymetry (m)" \ -Bpyg5a5f2.5 + l"Frequency distribution"+u"%" -Bsyg2.5 \ -BWSne + t"Aleutian Trench: Histograms of the depths values on the cross-section profiles"+gghostwhite -Gpowderblue \ -D+f6p,4 -L0.1p, dimgray -Z1 -W250 -N0+pred -N1+pblue -N2 + pgreen \ -O -K >> $ps</td><td>Plotting statistical histograms</td></tr><tr><td>pslegend</td><td>gmt pslegend -R -J -Dx1.0/-2.6+w5.0c+o-1.0/0.5c \ -F + pthick + ithinner + gwhite \ --FONT_ANNOT_PRIMARY = 8p -O -K << EOF >> $ps S 0.3c v 0.5c red 0.01c 0.6c Mean and standard deviation S 0.3c v 0.5c green 0.01c 0.6c LMS mode and scale S 0.3c v 0.5c blue 0.01c 0.6c Median and L1 scale EOF</td><td>Adding Legend</td></tr><tr><td>psconvert</td><td>gmt psconvert BathymetryAT.ps -A0.2c -E720 -Tj -Z</td><td>Converting the PostScript file to graphical format (e.g. JPG, TIFF). Example: to JPG with 720 dpi resolution, 0.2 cm margins</td></tr><tr><td>trend1d</td><td>gmt trend1d -Fxmr stackA2.txt -Np2,f1 + l1 > modelAT.txt</td><td>Modelling regression line</td></tr><tr><td>psxy</td><td>gmt psxy -R-200/200/-2000/1000 -J -Bpxag100f10 -Bsxg50 -Bpyaf+u"m" -Bsyg1000 -BWSne+gmintcream -W0.1 -Sc0.05c \ -Gred modelAT.txt -i0,2 -Y5.0c -O -K >> $ps</td><td>Plotting graph</td></tr><tr><td>echo</td><td>echo "m@-5@-(t) = a + b\267t + c\267t@+2@++ d\267cos(2@~p@~t) + e\267sin(2@~p@~t)" | gmt pstext -R -J \ -F + f12p + cBL -Dj0.1i -Gcornsilk -O -K >> $ps</td><td>Adding annotations on the graph by Unix 'echo' utility and ASCII numeral system of Octal codes (the example is for texts in Fig. 8)</td></tr><tr><td>gdalinfo</td><td>gdalinfo at_relief.nc -stats</td><td>GDAL utility for inspecting the grid (min/max values)</td></tr></tbody></table>
<figure><img src="image_11.png" /><figcaption>**Fig. 8** Modelling trends for the relief of the mean cross-section profile. Source: author</figcaption></figure>

2021c; Davis 2002; Lemenkov, Lemenkova 2021). Proper data interpretation should include testing several algorithms, selecting appropriate approaches and statistical packages (Jones *et al.* 2014). For this study, available techniques are used to model histograms (Lemenkova 2019e). The median derived the cross-section of the trench and shows the statistical visualization of the median stacked profiles with error bars (Fig. 7a).

## RESULTS

The slopes of the Aleutian ridge have a complex stepped-block structure (Figs 7 and 8) with numerous ridges and canyons running parallel to the trench. The Aleutian Trench extends beyond the island arc on both sides, reaching the continental slopes of the Kamchatka Peninsula and Alaska. The seafloor of the trench is formed by a chain of the narrow depressions
with a rather flat seafloor bottom. The greatest depths are found in the centre of the trench (maximum depth is 8480 m). The depth of the processed ETOPO1 bathymetric data along the chosen profile ranges from -8480 m (bathymetry) to 5738 m (terrain areas).

The geoid gravitational model shows that the majority of the gravity values lie in the interval between -10 to 20 mGal with the lowest values along the trench. The most common depth value in the study area is 4800 m, occurring 1722 times. Four modelling approaches for the profile linear trend modelling were tested for the regression model (Fig. 8) ($y = f(x) + e$) by weighted least squares (WLS) with arguments: 1) $m_2 t = a + bt$ (polynomial model degree one); 2) $m_3 t = a + bt + ct^2$ (polynomial model degree two); 3) $m_4 t = a + bt + ct^2 + d\cos2\pi*t + e\sin2\pi*t$ (polynomial model with Fourier series one); 4) additional plotting residuals. Finally, surface modelling was performed using xyz modelling from the ASCII data.

A clear correlation between the marine free-air gravity anomalies and the submarine topography can be seen in the Bering Sea. The free-air gravity anomaly of the Aleutian Basin and the Commander Basin have slightly positive free-air anomalies, the Shirshov Ridge and Bowers Ridge have moderately positive free-air anomalies, the Commander Islands and the Aleutian Islands have strong positive anomalies, and the Aleutian Trench is marked by strong negative anomalies (<- 100 mGal).

The Bouguer anomaly increases with a decreasing thickness of the Earth's crust from the continental margin to the seafloor of the Bering Sea basin. However, contrasting with the background of the intense

positive anomalies of the seafloor of the Bering Sea basin, the submarine ridges Shirshov Ridge and Bowers Ridge are characterized by low Bouguer gravity anomaly values. This indicates a relative increase in the thickness of the Earth's crust below both ridges. Sharp gradients of marine free-air gravity anomalies are observed in the zone of the Aleutian Island Arc and the Aleutian Trench. There, the trench is characterized by a rather moderate positive free-air gravity anomaly which is much smaller than the anomaly of the oceanic seafloor.

The topographic modelling shows a highly detailed distribution of the bathymetric data along the segments of the cross-section (Fig. 9). The topographic analysis shows that the shelf of the Bering Sea is very wide in the NE and narrows towards NW. This controls the asymmetry in the bathymetry of the ocean floor. The surface of the shelf is mostly horizontal, with minimal bathymetric variation; however, in some areas there are locally some small valleys and elevations observed. The prevailing depths of the bathymetric features are about 60 to 90 m, reaching 120 to 140 m depth at the outer edge.

The statistical inventory of the bathymetric data is summarized in a histogram (Fig. 9) and shows that depths with ranges between 5600 and 5400 m occur 1106 times (8%); depths with ranges between 5400 and 5200 m occur 846 times (7%); and depths with ranges between 4900 and 5200 m occur 1297 times (11%). The highest values of 4900 and 4700 m occur 1722 times (13.2%). Significantly low values demonstrated shallow areas with depth ranges between 4500 and 3000 m with occurrence of below 200 (all

<figure><img src="image_12.png" /><figcaption>Bathymetric data distribution by cross-section profiles</figcaption></figure>

<figure><img src="image_13.png" /></figure>

GMD 2019 Jun 29 17:13:40

<figure><img src="image_14.png" /><figcaption>Aleutian Trench: Histograms of the depths values on the cross-section profiles</figcaption></figure>

**Fig. 9** Histogram chart showing the bathymetric data distribution (depths) by the profiles. The statistical inventory shows that depths with ranges between 5600 and 5400 m occur 1106 times (8%); depths with ranges between 5400 and 5200 m occur 846 times (7%); depths with ranges between 4900 and 5200 m occur 1297 times (11%). The highest values of 4900 and 4700 m are with 1722 occurrences (13.2%). Much lower values demonstrated shallow areas with depth ranges between 4500 and 3000 m with occurrence below 200 (all of them less than 2.5%). Values with ranges shallower than 500 m belong to the shelf areas near the Aleutian Islands adjusting the trench. Source: author
Surface modelling of the topography along the Aleutian Trench

Modelling: GMT surface module, tension factor of the continuous curvature splines 0.25
Input raw table data: global 1-min grid resolution in ASCII XYZ-format, applied blockmean filter.
Output spatial model: 30-sec grid spacing in netCDF format, shading azimuth gradient: 45°

<figure><img src="image_15.png" /><figcaption>**Fig. 10** Topographic surface modelling of the Bowers Ridge from the ASCII xyz data. Source: author</figcaption></figure>

Surface modelling of the gravity along the Aleutian Trench

Modelling: GMT surface module, tension factor of the continuous curvature splines 0.25
Input raw table data: global 1-min grid resolution in ASCII XYZ-format, applied blockmode filter.
Output spatial model: 30-sec grid spacing in netCDF format

<figure><img src="image_16.png" /><figcaption>**Fig. 11** Surface modelling of the gravity over Bowers Ridge from the ASCII xyz data. Source: author</figcaption></figure>
of them less than 2.5%). Values with ranges shallow-
er than 500 m belong to the coastal shelf areas near
the Aleutian Islands adjusting the trench. A geomor-
phic analysis (Figs 8 and 3) shows that the NW of the
trench, on the side of the island arc, has a steeper and
shorter slope, with a series of marine terraces.

DISCUSSION

The geophysical mapping of the Bering Sea and geo-
morphological modelling of the selected segment of the
Aleutian Trench was demonstrated using the GMT car-
tographic scripting toolset. The newly presented maps
of the Aleutian Trench region support the hypothesis on
the impacts of geophysical and tectonic evolution af-
fecting the modern structure of the seafloor, which are
indicated as differences in topographic shapes and vari-
ability of depth along the Aleutian Trench. The com-
plexity of the geomorphic landforms and the response
of topography to the impacts from geophysical proc-
esses and geological evolution presenting interactions
between these factors in the basin of the Bering Sea is
a challenging task to evaluate in a simplified way. The
variability of the topography of the Bering Sea is nota-
ble on the presented maps. The basin of the Bering Sea
is contrasting with its shelf (NE region) and outlined by
the 3000 m isoline. It has the notable submarine uplifts:
Shirshov Ridge, Bowers Ridge and Aleutian Island Arc
which separate it to the western, eastern and southern
parts, respectively: the Aleutian Basin, the Commander
Basin and the Bowers Basin (Fig. 1).

The seafloor of these basins is presented by the
accumulative abyssal plain. The maximum depths are
3887 m in the Aleutian Basin, 3828 m in the Com-
mander Basin, and 3500 m in the Bowers Basin. The
geomorphology of the Shirshov and Bowers Ridges
has a fault block structure with asymmetric steep
slopes and destructed surface levelled by the abra-
sion processes in the geological past. The bathymetry
of the both ridges varies from 500 to 1000 m, with
minimum depths of 559 m for the Shirshov Ridge and
256 m for the Bowers Ridge.

A subsequent analysis of the Bering Sea region
seafloor in the context of geophysical and topograph-
ic setting showed that an effective cartographic model
of the submarine topographic landforms depends on
a range of factors presenting the interaction between
the geophysical, geological and tectonic factors shap-
ing the trench form. Besides, important are techni-
cal characteristics of the models themselves defined
using GMT parameters, the geographic context in
which models are placed (since western and eastern
parts of the Pacific Ocean present trenches of various
depths and shapes), and the interactions between data
and cartographic approaches used for data processing
(data formats, data resolution, data origin).

Visualizing submarine geomorphology provided
the context and guidance for further geological and
oceanographic discussions regarding hadal trench
shape, occurrence of terraces, steepness of the slopes,
location of canyons, as well as their distribution. The
major results of the profile are the maximum depth
of the trench of 8480 m, the asymmetric continental
shelf, which is wider in the E and NE and much nar-
rower in the W and SW. The geoid modelling shows
that the majority of the geoid values lie in the interval
between 10 to 20 mGal with the lowest values along
the trench that proves the deficit of the landmasses
in the depression of the trench. The analysis of the
marine free-air gravity shows the data range from
the minimum at -284.919 mGal to the maximum at
529.791 mGal with the mean at 5.037 mGal.

The major negative values of gravity lie exact-
ly along the trench areas (including both Aleutian
and Kuril-Kamchatka trenches visible on the map
in Fig. 5), as well as along the Emperor Seamounts
Chain and the Bowers Ridge and north of the Com-
mander Basin (all values are coloured deep purple in
Fig. 5). This seems to indicate regional coherency of
the geophysical anomaly fields with bathymetry and
topographic distribution of the negative and positive
landforms in the basin of the Bering Sea. On the con-
trary, higher values of gravity (bright red colours in
Fig. 5) clearly correspond to the distribution of the
topographic landmasses in the Aleutian Trench.

The main result of our analysis is that bathymetry
is distributed unequally along the study area in the
trench, according to major distributions of the land-
forms and with respect to the location of the Aleutian
Island Arc and Aleutian Trench having the crescent-
arc geometric form in the south of the Bering Sea. The
selected cross-section demonstrates that repeatability
of depths variation between 5600 and 5400 m is 8%;
repeatability of depth between 5400 and 5200 m is
in approximately the same frequency of 7%; repeat-
ability of depth between 4900 and 5200 m is 11%;
and the highest values of 4900 and 4700 m occur in
13.2%, which are the most often values. Much lower
values demonstrated shallow areas with depth ranges
between 4500 and 3000 m with occurrence less than
2.5%. The values with ranges shallower than 500 m
belong to the shelf areas near the Aleutian Islands ad-
justing the trench.

These results show that the geomorphology, geo-
logical setting and geophysical data are connected,
because the model of the trench topographic shape
represents a complex non-linear system depending on
the approximated functionality of the variety of fac-
tors, such as geophysical, tectonic and geologic as the
major driving forces sculpturing submarine bathym-
etry, with considerable uncertainty in the conditions
of impact factors.
CONCLUSIONS

The geomorphology of the seafloor is driven by
complex interactions among prevailing tectonic and
geological settings as the most important factors con-
tributing to the actual shape of the seabed. Some re-
gional patterns in this correlation regarding the Aleu-
tian Trench were noted, such as, for instance, a strong
role of landmass distribution in gravity anomalies:
negative and positive values in gravity grids mirror-
ing the isolines of the depressions and islands in the
seafloor topography, respectively.

Besides, the geological setting and tectonic evolu-
tion of the region are largely influenced by the geo-
physical process of tectonic plate subduction in which
the Pacific Plate subducts under the North American
Plate, forming a convergent boundary with the trench-
arc system (Aleutian Trench and Aleutian Island Arc).
The complexity of these tectonic processes consequent-
ly involved a series of faults and had a pronounced in-
fluence on the seafloor bathymetry across the Bering
Sea, enabling to analyze their consequences for the
topographic variability of the seafloor.

The paper discussed both methodological algo-
rithms of the mapping and analysis of the geological
evolution and characteristics of the study area based
on the previous works. Traditionally, bathymetric
mapping includes data of the sub-bottom echo sound-
er or swath bathymetric surveying (Kuhn et al. 2006;
Gauger et al. 2007); however, this work demonstrated
the use of the scripting approaches of the GMT used
for the processing of the open source data on topogra-
phy and geophysics of the Bering Sea region. Future
work can consider the results of this paper illustrating
the relationship between the geomorphology of the
trench and the geological and geophysical setting.

The results of this study included the compiled
bathymetry, gravity and geoid data obtained from the
open access sources of geoinformation and applied the
global grids for the region of the Bering Sea and Aleu-
tian Trench in the North Pacific Ocean. The results of
mapping and geomorphological cross-section model-
ling of the Aleutian Trench, as well as those derived
from general statistical calculation of histograms (based
on the 30 topographic segments of the cross-section of
the Aleutian Trench) demonstrate a substantial varia-
tion of submarine topography of the seafloor reflecting
geophysical conditions reflected in the varying values of
marine free-air gravity anomalies (Faye's), vertical grav-
ity anomalies, and the gravitational model of geoid.

The produced maps show high-resolution geo-
metric features and shapes (observed using the map
based on the 15-arc second resolution GEBCO grid).
Several presented models and maps describe the geo-
logical, geophysical and geomorphic modelling of the
study area, including an outline of the shell scripting,

the model, and visualized maps. Advantages of the
GMT demonstrated in the presented paper consist in
its high efficiency for the cartographic workflow.

Geomorphological modelling through cross-sec-
tioning and thematic geophysical mapping and geol-
ogy and geomorphology interpretation revealed com-
plex features such as fracture zones, ridges, abyssal
plain and hills, seamounts and guyots on the seabed
of the Bering Sea and in the Aleutian Trench. Visual-
izing submarine geomorphology provided the context
and guidance for further geological and oceanograph-
ic discussions regarding hadal trench shape, occur-
rence of terraces, steepness of the slopes, location of
canyons, as well as their distribution.

ACKNOWLEDGEMENTS

I am deeply grateful to Dr. Anouk Beniest (Assistant
Professor from Vrije Universiteit Amsterdam, Nether-
lands) for careful reading, thoughtful review and nu-
merous constructive comments regarding geology and
tectonics. Her suggestions on methodology and critical
remarks about the structure of the manuscript signifi-
cantly improved the initial version of this manuscript
and some of the maps. I also highly appreciate the re-
view and feedback of one anonymous reviewer. This
research has been implemented in the framework of
the Project No. 0144-2019-0011, Schmidt Institute of
Physics of the Earth, Russian Academy of Sciences.

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