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The five deeps: The location and depth of the deepest place in each of the world's oceans


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The exact location and depth of the deepest places in each of the world’s oceans is surprisingly unresolved or at best ambiguous. Out of date, erroneous, misleading, or non-existent data on these locations have propagated uncorrected through online sources and the scientific literature. For clarification, this study reviews and assesses the best resolution bathymetric datasets currently available from public repositories. The deepest place in each ocean are the Molloy Hole in the Fram Strait (Arctic Ocean; 5669 m, 79.137° N / 2.817° E), the trench axis of the Puerto Rico Trench (Atlantic Ocean; 8408 m 19.613° N / 67.847° W), an unnamed deep in the Java Trench (Indian Ocean; 7290 m, 11.20° S / 118.47° E), Challenger Deep in the Mariana Trench (Pacific Ocean; 10,925 m, 11.332° N / 142.202° E) and an unnamed deep in the South Sandwich Trench (Southern Ocean; 7385 m, 60.33° S / 25.28° W). However, discussed are caveats to these locations that range from the published coordinates for a number of named deeps that require correction, some deeps that should fall into abeyance, deeps that are currently unnamed and the problems surrounding variable and low-resolution bathymetric data. Recommendations on the above and the nomenclature and definition of deeps as undersea features are provided.
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The ve deeps: The location and depth of the deepest place in each of the
world's oceans
Heather A. Stewart
, Alan J. Jamieson
British Geological Survey, Lyell Centre, Research Avenue South, Edinburgh EH14 4AP, UK
School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE1 7RU, UK
Deepest places
Hadal zone
Oceanic trenches, ve oceans
The exact location and depth of the deepest places in each of the world's oceans is surprisingly unresolved or at
best ambiguous. Out of date, erroneous, misleading, or non-existent data on these locations have propagated
uncorrected through online sources and the scientic literature. For clarication, this study reviews and assesses
the best resolution bathymetric datasets currently available from public repositories. The deepest place in each
ocean are the Molloy Hole in the Fram Strait (Arctic Ocean; 5669 m, 79.137° N/2.817° E), the trench axis of the
Puerto Rico Trench (Atlantic Ocean; 8408 m 19.613° N/67.847° W), an unnamed deep in the Java Trench (Indian
Ocean; 7290 m, 11.20° S/118.47° E), Challenger Deep in the Mariana Trench (Pacic Ocean; 10,925 m,
11.332° N/142.202° E) and an unnamed deep in the South Sandwich Trench (Southern Ocean; 7385 m, 60.33° S/
25.28° W). However, discussed are caveats to these locations that range from the published coordinates for a
number of named deeps that require correction, some deeps that should fall into abeyance, deeps that are
currently unnamed and the problems surrounding variable and low-resolution bathymetric data.
Recommendations on the above and the nomenclature and denition of deeps as undersea features are provided.
1. Introduction
Much of the world's ocean, in particular the open ocean, deep-sea
and polar regions are profoundly inaccessible. Their great depths, re-
moteness and immense size also renders exploration and the mapping
of undersea features an ongoing laborious process and as such only a
small fraction has been bathymetrically mapped (Weatherall et al.,
2015;Mayer et al., 2018). Yet humankind has always had great en-
thusiasm for not only discovering new territories and features but
naming them in pursuit of cultural ownership and in order to establish
their place within the known landscape. Therefore, in addition to the
political and economic advantages associated with exploration, there is
an underlying curiosity-driven, subjective appreciation of the Earths
landscape. Furthermore, within sometimes arbitrary topographical ca-
tegories, humans are intrinsically drawn to those at the ends of any
given extreme. Fascination and inspiration is habitually drawn from the
highest mountain, the longest river, the biggest ocean, the deepest
trench, amongst many others at national, intercontinental or global
levels. These world-record places are part of the heritage of humankind
and not only tell us a lot about the planet in which we inhabit but
provide the platform for awe and wonder.
Through relative ease of accessibility there is a far greater body of
knowledge about the terrestrial landscape than that of our undersea
landscapes, and indeed, the oceans are still often referred to as the last
frontier on Earth. Yet looking at any large scale map of the seaoor, our
knowledge regarding depth and morphology appears complete.
However, much of the water depth information is derived from satellite
altimetry rather than acoustic surveys (Smith and Sandwell, 1997;
Becker et al., 2009) and as such there are dramatic variations in the
resolution of our mapping of the seaoor. This variation is not only
born from the dierence in ever-evolving technological capability but
the collation of information spanning very long timescales. The im-
mense area occupied by the ocean makes a complete high resolution up-
to-date map a long way o, but within the current body of marine
geomorphological mapping it would be reasonable to assume we have
as much of an understanding of where the deepest places are as we do
the highest mountains, however, this has not been the case.
Satellite altimetry-derived global bathymetry datasets have re-
presented a signicant advancement in large-scale ocean mapping
(Harris et al., 2014), yet only provide a generalised view of the shape of
the seaoor (Smith and Sandwell, 1997;Becker et al., 2009), as they do
not provide sucient resolution to perform robust geomorphometric
analyses (Lecours et al., 2016). They provide general estimates of water
depths and coarsely lls gaps between sparse ship soundings (Smith and
Received 18 July 2018; Received in revised form 5 July 2019; Accepted 7 July 2019
Corresponding author.
E-mail address: (H.A. Stewart).
Earth-Science Reviews 197 (2019) 102896
Available online 09 July 2019
0012-8252/ © 2019 British Geological Survey, a component body of UKRI 'BGS © UKRI 2018'. Published by Elsevier B.V. This is an open access article under the
CC BY license (
Sandwell, 1997;Becker et al., 2009), but it is, however, less precise
than single-beam echosounder-derived data and has far less resolution
than multibeam echosounder systems.
A recent study (Mayer et al., 2018) reviewed the General Bathy-
metric Chart of the Oceans (GEBCO_2014; global
compilations of bathymetric data and concluded that despite the ap-
pearance of complete global coverage of ocean depths, these datasets
are deceptive as modern interpolation and visualization techniques
produce apparently complete representations of ocean depth from ap-
parently sparse data points. When the GEBCO_2014 dataset is inter-
rogated and divided into its resolution of 30 arc-second grid cells
(926 m at the equator), approximately 82% of the grid cells do not
include a single depth measurement (Weatherall et al., 2015), in other
words, the percentage of the seaoor that has been constrained by
measured data or pre-prepared grids that may contain some inter-
polated values is < 18% (Weatherall et al., 2015;Mayer et al., 2018).
The most recent calculation of the ocean's mean and median depth
is 3897 and 3441 m respectively (Weatherall et al., 2015), however, the
average horizontal resolution at those water depths is about 8 km
(Mayer et al., 2018). Depths > 3000 m account for 75.3% of the world's
oceans, an area covering 230,910,385 km
, of which 85% of it is un-
charted (equal to 69% of the entire ocean; Mayer et al., 2018). This
means asking simple questions like where are the deepest places in the
world?or what is the maximum depth of each ocean, very dicult to
answer with condence as the intricacies of seaoor morphology are
largely unresolved and exacerbated at ever greater depths.
1.1. Peaks and troughs
Mountains provide extremely topographically diverse high altitude
environments (Ives et al., 1997) and are found on every continent
culminating at the highest place on the earth, Mount Everest, at 8848 m
above sea level (Gruen and Murai, 2002). It is widely recognised that
mountains are of signicant global importance in recognition of the
interrelationships of high elevation ecosystems, the people who inhabit
them, and as centres for biodiversity (Barthlott et al., 1996;Ives and
Messerli, 1990).
From a human perspective, one of the great mountaineering chal-
lenges is to climb the seven summits, meaning the highest mountain
on each of the seven continents. Alternatively there are the eight-
thousanderswhich are the 14 independent mountains > 8000 m above
sea level. There are however slight variations in what are considered
the highest points. The ambiguity arises in regards to the denition of a
continent, for example, whether only mainland Australia is used or the
larger region of Oceania. There are also ambiguities in relation to the
exact altitude of some of these mountains, for example, when a
mountain is situated a signicant distance from the coast, sea level is
often dicult to dene. Even detailed surveys of Mount Everest range
from 8840 m to 8850 m which emphasizes the uncertainties in the re-
corded heights and has remained problematic for some time (de Graa-
Hunter, 1955;Gruen and Murai, 2002;Mishra et al., 2015).
The highest summits of the world are analogous with the deepest
places in the ocean. The maritime equivalent to the seven summits
include the deepest point in each ocean, or the ve deeps(Fig. 1), and
similar to the eight thousanders, there are ve locations that exceed
10,000 m water depth: the ten thousanders.A common statement in
popular marine science is that the Mariana Trench is so deep that Mount
Everest would t inside it with a mile to spare, but there are other simi-
larities between these two unique places. The Himalayas are 2400 km
long and the Mariana Trench is 2550 km long, scientists have had
problems in both measuring the exact height above sea level of Mount
Everest (Mishra et al., 2015) and the exact depth of the Challenger Deep
in the Mariana Trench (e.g. Gardner et al., 2014;van Haren et al., 2017)
and both are considered the ultimate end pointsin exploration
(Piccard and Dietz, 1961).
1.2. Underlying rationale
The problems of dening these maritime end points in the pursuit of
exploration based on unreliable data is exemplied by the 2011 an-
nouncement that the company Virgin Oceanic were constructing a full
ocean depth manned submersible. DeepFlight Challenger, is anticipated
to explore the deepest point in each ocean, a challenge akin to the
seven summits. The press release stated that they planned to dive the
Mariana Trench (Pacic Ocean, 11,033 m), Molloy Deep (Arctic Ocean,
5608 m), Puerto Rico Trench (Atlantic Ocean, 8605 m), South Sandwich
Trench (Southern Ocean, 7235 m) and the Diamantina Trench (Indian
Ocean, 8047 m). However, by interrogating publically available global
compilations of bathymetric data and peer-reviewed literature, it is
concluded that none of these water depths are correct: Challenger Deep
in the Mariana Trench is not > 11,000 m deep (10,925 m; van Haren
et al., 2017), the Puerto Rico Trench and Diamantina Trench are
somewhat shallower (8408 and 70907100 m respectively), and the
South Sandwich Trench and Molloy Hole are deeper (8183 and 5669 m
respectively), than the depths cited in the DeepFlight Challenger press
release. Furthermore, the Diamantina Trench is not a trench, it is a
fracture zone (as per guidelines for naming undersea features listed by
the International Hydrographic Organization and the Intergovern-
mental Oceanographic Commission (IHO-IOC), see Holcombe, 1977),
and is not the deepest place in the Indian Ocean which is actually lo-
cated within the Java Trench (7290 m). Also, much of the South
Sandwich Trench is in the Atlantic Ocean with the location for the
deepest point in the trench recorded as being of a latitude of 55°S, and
thus short of the 60°S boundary between the Atlantic and Southern
oceans. Thus placing their South Sandwich Trench dive site in the South
Atlantic Ocean and not the Southern Ocean as advertised.
The sources of these erroneous depths are not easily traced to the
original citation and are often so widespread in literature and popular
internet sites that they are dicult to correct (Table 1). The depth of
11,034 m for the Challenger Deep originates from the Soviet expedition
on-board the ship Vityaz in 1957 although there is doubt surrounding
the sound velocity correction for their echosounder data (discussed in
Gardner et al., 2014). A deep> 11,000 m water depth has never been
found in subsequent surveys utilising more advanced technology (e.g.
Nakanishi and Hashimoto, 2011), yet the depth record persists. Web-
sites like Wikipedia complicate matters further, for example, the entry
for the Diamantina Fracture Zone refers to it as a Trench and states it is
not the deepest place in the Indian Ocean (7079 m) but directs the
reader to the Diamantina Deep, apparently located within the Dia-
mantina Fracture Zone and states it is the deepest point in the Indian
Ocean at 8047 m water depth. Other entries state that the Litke Deep
(350 km north of Svalbard) is the deepest point in the Arctic Ocean
(5449 m), while asserting that the Molloy Deep (5669 m) is not the
deepest point in the Arctic Ocean as it is located in the Fram Strait, but
does not cite any primary literature. However, the Fram Strait is within
the Arctic Ocean, as stated when the reader is taken to the Arctic Ocean
entry on the same website. These examples are given solely to illustrate
the incongruences of data at the time of writing.
Furthermore, there are also discrepancies when global compilations
of bathymetric data are interrogated. For example, using Geographic
Information System (GIS) software to study large-scale trench topo-
graphy derived from GEBCO_2014 can often lead to erroneous depths
and locations. Examples of this include the Kuril-Kamchatka Trench,
whereby GEBCO_2014 bathymetry places the deepest point at 44.07°
N/150.18° E at 10,542 m (Jamieson, 2015) but a recent expedition on
the RV Sonne, equipped with an EM122 multibeam echosounder failed
to nd depths > 9500 m (Brandt, 2016). Similarly, on the same vessel
with the same multibeam echosounder system, an expedition transiting
the Indian Ocean acquired data over the Wallaby-Zenith Fracture Zone
with an estimated water depth of 7700 m (extracted from GEBCO_2014
data). However, the EM122 bathymetric data revealed the maximum
water depth of the fracture zone to be a little over 6500 m (A. J.
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
Jamieson personal observation; Werner et al., 2017). These examples
demonstrate that global compilations, although include many areas of
high-resolution, shipborne bathymetric soundings, also include areas
where data are sparse and this must be taken into account during
subsequent analyses.
The main objective of this study was to assess and locate the deepest
points within the Arctic, Atlantic, Indian, Pacic and Southern oceans
using the best data currently available via open access repositories.
Deepsare conned areas that represent the deepest point of a trench,
fracture or basin. The focus of this study was to determine not only the
location of these deeppoints but to assess the quality of the data
available and to assign a condence value to those locations. The study
was incentivised by the forthcoming 5-Deeps Expedition(www. on the Deep Submergence Support Vessel (DSSV)
Pressure Drop to dive a new 11,000 m rated 2-man submersible, the
Deep Submergence Vehicle (DSV) Limiting Factor, to the deepest point in
each ocean.
2. Materials
2.1. Data sources
A data mining exercise was undertaken to search for publically
available bathymetry data which included multibeam echosounder
bathymetry acquired by scientic research cruises, single-beam echo-
sounder bathymetry data acquired by both research and commercial
vessels. Where no better data are available, global compilations from
the GEBCO_2014, the International Bathymetric Chart of the Southern
Ocean (IBCSO) and International Bathymetric Chart of the Arctic Ocean
(IBCAO) were used. These latter three data sources utilised satellite
altimetry in areas where data are sparse (e.g. the Shuttle Radar
Topography Mapping 30 arc sec database (SRTM30_PLUS) altimetry-
derived bathymetry (Becker et al., 2009)).
The most comprehensive publically available bathymetry were de-
rived from the Global Multi-Resolution Topography (GMRT Synthesis; which comprises tiled, multiresolution, bathy-
metry datasets complete with source citations (Ryan et al., 2009). Each
gridded tile set involves computing weighted averages of depth esti-
mates at the nodes for each grid tile, designed to ensure preservation of
Fig. 1. Map showing the global location of the ve deepest point of the ve oceans. All data sourced from the Global Multi-Resolution Topography Synthesis (Ryan
et al., 2009).
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
the data whilst avoiding introduction of data artefacts in the resultant
Digital Elevation Model (DEM) (Ryan et al., 2009). The GMRT Synthesis
also comprises gridded seaoor depths where multibeam bathymetry
data are absent (30 arc sec resolution which equates to approximately
1 km) derived from GEBCO_2014 (Weatherall et al., 2015). Another
source of bathymetric data is the National Oceanic and Atmospheric
Administration National Centers for Environmental Information
(NOAA-NCEI) (;NOAA National Centers for
Environmental Information (2004)) which is the United States national
archive for multibeam echosounder data with the ability to create
binary grids of the data in an area of interest able to be imported into
ArcGIS. ArcGIS grids of the bathymetry data were produced at the re-
solution of the dataset with additional layers of bathymetric contours,
slope, and aspect derived from the bathymetry data and were generated
in ArcGIS using the spatial analyst extension and Benthic Terrain
Modeler (Walbridge et al., 2018).
2.1.1. Arctic Ocean
The Arctic Ocean is the smallest and shallowest of the world's ve
major oceans. This water body is completely surrounded by the con-
tinents of Asia, North America, Europe and the island of Greenland. The
Molloy Hole is located in the Fram Strait between Greenland and
Svalbard, and is considered to represent the southern node of the
Molloy seaoor spreading area (Freire et al., 2014). The deepis
broadly circular with a relatively featureless seaoor topography
(Fig. 2). Terminal slide deposits from the Molloy Slide, the deepest
Table 1
List of the many published depths and location of potential sites for the deepest point in each ocean. For the deepest point in the Pacic Ocean the vessel and year of
survey are given in italics where known. The precision in latitude and longitude is replicated from the source material cited although it should be noted that the
accuracies of both modern and historical single-beam and multibeam echosounders and navigation systems, mean that a number of the positions published have an
unreasonable level of accuracy (e.g. 0.000001 implies the position is known to one millionth of a degree, or 10 cm).
Ocean Feature Latitude Longitude Depth (m) Source
Arctic Molloy Hole 79.136667° N 2.816667° E 5669 Klenke and Schenke (2002);Klenke and Schenke (2006a, 2006b)
79.141° N 2.798° E 5573 Jakobsson et al. (2012)
79.166667° N 2.833333° E 5770 Bourke et al. (1987)
79.141667° N 2.783333° E 5669 Thiede et al. (1990)
Atlantic Milwaukee Deep (Puerto Rico Trench) 19.58333° N 66.5° W 8740 GEBCO Gazetteer
19.6° N 68.31667° W 8710 Lyman (1954)
Puerto Rico Trench 19.773° N 66.928° W 8526 Stewart and Jamieson (2018)
Indian Java Deep 9.315193° S 108.905716° E 7725 or 7450 GEBCO Gazetteer
Java Trench 11.1710° S 118.4669° E 7204 Stewart and Jamieson (2018)
Diamantina Deep (Diamantina
Fracture Zone)
35° S 104° E 8047 GEBCO Gazetteer
Dordrecht Deep (Diamantina Fracture
33.42° S 101.48° E 7079 GEBCO Gazetteer
Diamantina Fracture Zone 34.807° S 102.567° E 7324 Stewart and Jamieson (2018)
Pacic Challenger Deep (Mariana Trench) 11.332417° N 142.20205° E 10,925 ± 12 van Haren et al. (2017)
RV Sonne 2016
11.329903° N 142.199305° E 10,984 ± 25 Gardner et al. (2014)
USNS Sumner 2010
11.326344° N 142.187248° E 10,994 ± 40 Gardner and Armstrong (2011)
USNS Sumner 2010
11.371° N 142.593° E 10,920 ± 5 Nakanishi and Hashimoto (2011)
Kairei 1998/99
11.373333° N 142.591667° E 10,920 ± 10 GEBCO Gazetteer
11.382° N 142.4376° E 10,744 Fryer et al., 2003
MR1 1997
11.3349° N 142.1967° E 10,896 KAIKO remotely operated vehicle (ROV) (2002) cited in Todo et al. (2005)
11.368333° N 142.59° E 10,903 Bowen et al. (2009)
ROV Nereus
11.3767° N 142.5833° E 10,989 Taira et al. (2005)
Hakuho-Maru 1992
11.3767e N 142.5833° E 10,890 Taira et al. (2004)
11.339° N 142.22° E 10,938 ± 10 Fujioka et al. (2002)
Kairei 1998
11.373337° N 142.59167° E 10,933 Fujimoto et al. (1993)
Hakuho-Maru 1992
11.373337° N 142.59167° E 10,920 ± 10 S/V Takuyo of the Hydrographic Department of the Japan Maritime
Safety Agency (1984) (Hydrographic Department, 1984)
11.333° N 142.197° E 10,915 ± 10 R.L. Fisher (pers comm. In Nakanishi and Hashimoto (2011)) Thomas
Washington 1975 and 1980
11.333° N 142.197° E 10,915 ± 20 Fisher and Hess (1963)
Spenser F. Baird 1977
11.333° N 142.197° E 10,850 ± 20 Fisher and Hess (1963)
Stranger 1959
11.34833° N 142.191667° E 11,034 ± 50 Vityaz 1957
11.316667° N 142.25° E 10,863 ± 35 Carruthers and Lawford (1952)
Challenger VIII 1951
11.400° N 143.267° E 8184 Thomson and Murray (1895)
HMS Challenger 1875
Southern South Sandwich Trench 56.243° S 24.836° W 8125 Stewart and Jamieson (2018)
Meteor Deep (South Sandwich
55.6667° S 25.9167° W 8325 Zhivago (2002)
55.67° S 25.92° W 8428 Allaby (2009)
Unnamed Deep (South Sandwich
60° S 24° W 7235 Untraceable source but cited in Wikipedia (
Note GEBCO Gazetteerrefers to the IHO-IOC GEBCO Gazetteer of Undersea Feature Names.
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
mass-wasting deposit in the northern Atlantic and Arctic Ocean, are
present in the northern portion of the Molloy Hole marking the
downslope limit of the slide (Freire et al., 2014). The headwall of the
slide is located east of the Molloy axial rift valley to the north of the
Molloy Hole (Freire et al., 2014). The Molloy Hole was previously
known as the Molloy Deep, although it is noted here that in order to
meet standardisation guidelines set by the Sub-Committee on Undersea
Feature Names (SCUFN) feature name compilation of GEBCO the term
Molloy Deepwas changed to Molloy Hole(Klenke and Schenke,
2002). To comply with the SCUFN the term Molloy Holeis used here.
The rst comprehensive bathymetric dataset of the Molloy Hole was
published by Klenke and Schenke (2002) based on multibeam echo-
sounder data acquired by the R/V Polarstern between 1984 and 1997.
These data were gridded at 100 m resolution (Fig. 2) and formed the
basis of an updated bathymetric chart of the Fram Strait (Klenke and
Schenke, 2006a) and were available to download from the Pangaea
world data centre (;Klenke and Schenke, 2006b).
Subsequently Freire et al. (2014) published a study using processed
multibeam echosounder data acquired in 2009 at a resolution of 30 m
whereby the older data collated by Klenke and Schenke (2006b) was
used to inll the gaps where the 2009 data were absent. The Freire et al.
(2014) dataset was not available for this study from public repositories
such as GMRT Synthesis, NOAA-NCEI or Pangaea. IBCAO version 3.0
(Jakobsson et al., 2012) includes the area of the Molloy Hole, com-
prising a base grid of 2 km resolution (from version 2.0; Jakobsson
et al., 2008), with higher resolution datasets (mainly multibeam
echosounder and Olex), merged onto the base grid at a resolution of
500 m (see Jakobsson et al., 2012 and references therein for detailed
methodology). Using the IBCAO source identication grid it is revealed
that multibeam echosounder data were included in the compilation
covering the Molloy Hole and subsequently gridded at 500 m resolu-
tion. Multibeam echosounder data gridded at 100 m resolution as spe-
cied by Klenke and Schenke (2006b) were utilised for the purposes of
this study.
Reported maximum water depths for Molloy Hole are 5573 m in the
IBCAO compilation (Jakobsson et al., 2012), 5669 m as determined by
Thiede et al. (1990) and Klenke and Schenke (2002, 2006a) (Fig. 2;
Table 1), and 5770 m by Bourke et al. (1987) (Fig. 2;Table 1).
2.1.2. Atlantic Ocean
The Atlantic Ocean is the second largest of the world's oceans,
bounded to the north by the Arctic Ocean and by the Southern Ocean to
the south. The continents of North and South America, and Africa and
Europe bound the Atlantic Ocean to the west and east respectively.
Harris et al. (2014) report the maximum water depth of the North
Atlantic Ocean as 8620 m using Shuttle Radar Topography Mapping
30 arc sec database (SRTM30_PLUS, see Becker et al. (2009) for details).
The deepest part of the Atlantic Ocean is thought to be the Milwaukee
Deep within the roughly east-west oriented Puerto Rico Trench, located
around 120 km north of the island of Puerto Rico (Lyman, 1954)
(Fig. 3). The Puerto Rico Trench is around 810 km in length and has
formed where the North American and Caribbean plates slide (strike-
slip plate boundary) past each other with only a small component of
subduction (on the eastern boundary resulting in the Lesser Antilles
volcanic island arc). The Caribbean plate is drifting eastward at ap-
proximately 20 mm per year relative to the North American plate (De
Mets et al., 2010). The small component of subduction has resulted in a
wider and unusually smooth seaoor west of ~65° W underlain by
normal fault bounded blocks (ten Brink, 2005) that manifest morpho-
logically as a small number of elongated ridges along the trench bottom
and an absence of conned deeps. East of ~65° W the trench is nar-
rower with the seaoor morphology revealing a number of escarpments
descending stepwise into the trench axis (ten Brink, 2005). A complex
interplay of faulting related to reactivation of an existing tectonic fabric
and bend-related faulting of the subducting plate in the eastern section
of the Puerto Rico Trench forms a network of trench-axis grabens, or
conned deeps, as has been documented in other subduction settings
(e.g. Masson, 1991;Stewart and Jamieson, 2018). Such features are
absent in the western portion of the Puerto Rico Trench.
Data from both the GMRT Synthesis and NOAA-NCEI portal were
compared to ensure the same surveys were included in both data
compilations. Both compilations included multibeam echosounder data
Fig. 2. Map of the Molloy Hole within the Fram Strait with
the locations of published deeps(red circles) and the deepest
point determined by Klenke and Schenke (2002) (white
star = 5669 m water depth) (Table 1). The outer rim of the
Molloy Hole lies at 2700 m water depth (white contour). The
deepest section of the Molloy Hole is dened by the 5600 m
contour (blue contour). All other contours at 100 m intervals
(between 2700 and 5600 m water depth). Illumination from
270° at an altitude of 35°. (For interpretation of the references
to colour in this gure legend, the reader is referred to the
web version of this article.)
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
from eight surveys between 1996 and 2015, with the resultant DEM
gridded at 60 m resolution (Fig. 3). The DEM is inlled with data de-
rived from the GEBCO_2014 global bathymetry dataset.
Documented maximum depths of the Milwaukee Deep vary from
8740 m as published in the IHO-IOC GEBCO Gazetteer of Undersea
Feature Names, 8710 m as recorded by Lyman (1954), and 8526 m as
determined by Stewart and Jamieson (2018) from analysis of the
GEBCO_2014 global bathymetry dataset (Fig. 3;Table 1).
2.1.3. Indian Ocean
The Indian Ocean is bounded by the continents of Asia and Africa to
the north and west respectively, Australia to the east and by the
Southern Ocean to the south. There are two areas that have been his-
torically claimed as the deepest point in the Indian Ocean; the Java
(Sunda) Trench and the Diamantina Fracture Zone (e.g. Kopp et al.,
2009, 2013; IHO-IOC GEBCO Gazetteer). Due to very similar estimated
depths and the variation in those estimated depths, both the Java
Trench and the Diamantina Fracture Zone are considered in this study.
The Java Trench, also known as the Sunda Trench, is located south
and west of the islands of Java and Sumatra in the eastern Indian
Ocean, and is in excess of 3200 km in length. The trench is formed as
the Indo-Australian Plate subducts beneath the Eurasian Plate, at a rate
of between 60 and 73 mm per year (De Mets et al., 2010).
The only publically data available covering the deepest portions of
the Java Trench were the GEBCO_2014 global bathymetric compilation
available at a resolution of 30 arc sec (Fig. 4A).
The documented maximum depths vary from 7725 m or 7450 m in
the Java Deep as recorded in the IHO-IOC GEBCO Gazetteer of
Undersea Feature Names, Harris et al. (2014) reporting the maximum
water depth as 7318 m, and a maximum depth of 7290 m determined
by Stewart and Jamieson (2018) from the GEBCO_2014 global bathy-
metry dataset (Fig. 4A; Table 1). These two locations are 1067 km apart
therefore it can be concluded that there is still debate as to the location
of the deepest point of the Java Trench.
The Diamantina Fracture Zone is located southwest of Australia and
formed as the Australian and Antarctic continents separated and is in
excess of 3400 km in length. Two data sources were available for the
Diamantina Fracture Zone: multibeam bathymetry data available from
Geoscience Australia and the GMRT Synthesis (Fig. 5A). Both datasets
were interrogated for this review and were gridded at 110 m resolution
with the Geoscience Australia data comprising single tracks of
multibeam echosounder data. The GMRT Synthesis DEM incorporates
the Geoscience Australia data as well as a survey from 2004 on-board
the research vessel Nathaniel B. Palmer that runs along the axis of the
fracture zone. The GMRT Synthesis DEM is inlled with data derived
from the GEBCO_2014 global bathymetry dataset.
Documented maximum depths vary from 8047 m in the Diamantina
Deep and 7079 m in the Dordrecht Deep as recorded in the IHO-IOC
GEBCO Gazetteer of Undersea Feature Names and 7324 m as de-
termined by Stewart and Jamieson (2018) from the GEBCO_2014 global
bathymetry dataset (Fig. 5A; Table 1).
2.1.4. Pacic ocean
The Pacic Ocean is the largest of the world's ve oceans and ex-
tends from the Arctic Ocean to the Southern Ocean and is bounded to
the east by North and South American continents, and to the west by
Australasia and the continent of Asia. The Mariana Trench is located
southeast of the island of Guam and east of the Mariana Islands and is
up to 10,925 m deep (van Haren et al., 2017), is 2550 km in length with
a mean width of 70 km (Angel, 1982)(Fig. 6). The trench is formed as
the Pacic Plate subducts beneath the Mariana Arc system, part of the
Philippine Plate, to the west. This study encompasses only the wes-
ternmost portion of the Mariana Trench, oriented roughly west-east.
Two datasets, available from the NOAA-NCEI and the GMRT
Synthesis, covering the southernmost area of the Mariana Trench were
compared. The multibeam echosounder data includes three surveys
undertaken by the U.S. Naval Oceanographic Oce USNS Sumner in
2010, the RV Melville in 2001, and the Thomas Washington in 1986.
GEBCO_2014 is used to inll areas where multibeam echsounder data
are absent with ArcGIS grids of the multibeam bathymetry data pro-
duced at a grid size of 120 m for the Mariana Trench (Fig. 6).
A number of expeditions have visited the Mariana Trench in search
of the deepest point with > 18 known published depths (e.g. Table 1)
including the 1957 Vityaz recorded depth of 11,034 m (Taira et al.,
2004). The rst precise depth was published as 10,915 ± 10 m by
Fisher and Hess (1963) using TNT charges and a controlled depth re-
corder during two expeditions to the region in 1959 and 1962 as many
echosounders of the period could not operate in such deep water
(Gardner et al., 2014). Over the following 25 years a number of ex-
peditions determined the depth to be within 10,920 ± 10 m which is
the value cited in the IHO-IOC GEBCO Gazetteer of Undersea Feature
Names. More recently however, van Haren et al. (2017) have provided
Fig. 3. Map of the Puerto Rico Trench with the published Milwaukee Deep locations (red circles) (Table 1) and the deepest point of the trench determined by this
study (white star = 8408 m water depth). The 6000 m depth contour is shown in white. The deepest section of the trench is dened by the 8000 m contour (blue). All
other contours at 500 m intervals (between 6000 and 8000 m water depth). Illumination from 20° at an altitude of 25°. (For interpretation of the references to colour
in this gure legend, the reader is referred to the web version of this article.)
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
an updated position and maximum depth for Challenger Deep, super-
seding that published by Gardner et al. (2014), using data acquired in
2010 with a Kongsberg EM122 multibeam echosounder, a deepest
sounding of 10,925 ± 12 m (Table 2). The van Haren et al. (2017)
study suggests that the observed discrepancy with the Gardner et al.
(2014) depth is related to the application of the correct sound velocity
prole, which is essential for accurate depth determination. Gardner
et al. (2014) used Sippican Deep Blue Expendable Bathythermographs
(XBTs) to determine the sound velocity for the upper 760 m, whereas
van Haren et al. (2017) utilised a shipborne SBE911plus Conductivity
Temperature Depth (CTD) that extended down to 8000 m below sea
surface. Use of the XBTs whereby the sound velocity is extrapolated
from 760 m below sea surface to 12,000 m water depth (as is required
for the multibeam system used) is not equivalent to a sound velocity
prole derived from 8000 m of data. Furthermore the van Haren et al.
(2017) data are comparable to those acquired by Nakanishi and
Hashimoto (2011) who although were operating a less accurate mul-
tibeam echosounder, also had CTD data to full ocean depth for de-
termining the sound velocity.
2.1.5. Southern Ocean
The Southern Ocean extends from the northern coast of Antarctica
to a latitude of 60° S as dened by the International Hydrographic
Organization (IHO). The South Sandwich Trench, is a large arcuate
subduction trench that spans both the South Atlantic and Southern
oceans formed by the subduction of the southernmost section of the
South American Plate beneath the South Sandwich Plate at a rate of
6578 mm per year (Smalley et al., 2007). The South Sandwich Islands
are the resultant volcanic arc, situated on the South Sandwich Plate.
The trench is 965 km long and attains a maximum published depth in
the Meteor Deep (Maurer and Stocks, 1933;Table 1). The Meteor Deep
is located north of 60° S, around 100 km northeast of Zavodovski Island
located at a latitude of between ca. 55.67° S and 56.24° S depending on
which published location is believed. As has been highlighted in this
paper previously, the South Sandwich Trench straddles the boundary
between the Atlantic and Southern oceans. Therefore two respective
deepswere sought after during the course of this study, each side of
the 60° S boundary (as per the recognised latitudinal boundary of the
IHO). Examination of both the GMRT Synthesis and the NOAA-NCEI
compilations revealed that few high-resolution datasets have been up-
loaded to public repositories (Fig. 7).
The IBCSO was initiated as a GEBCO regional mapping project with
the goal of compiling the rst bathymetric model covering the entire
Southern Ocean south of 60° S. The rst version was published in 2013
with a resolution of 500 m based on a polar stereographic projection
with true scale at 65° S referenced to the WGS84 ellipsoid (Arndt et al.,
2013). The dataset was compiled using data from hydrographic oces,
scientic research institutions and data centres and includes single-
beam and multibeam bathymetry data, regional bathymetric models,
digitised soundings from nautical charts and satellite-based predicted
bathymetry in the deep-sea where sounding data are sparse. Note
that > 80% of the Southern Ocean is not yet mapped even at a re-
solution of 500 m (Arndt et al., 2013).
In addition, the British Antarctic Survey (BAS) have published a
1:750,000 bathymetry map compiled from a variety of dierent data
sources (Leat et al., 2016). The BAS published map covers the area of
the South Sandwich subduction system situated in the East Scotia Sea,
South Atlantic, between ca. 55.1° S and 61.9° S, and 24° W and 32° W.
The primary data are multibeam echosounder bathymetry collected
from scientic cruises undertaken by BAS, Alfred Wegener Institute
(AWI) and the Centre for Marine and Environmental Sciences
(MARUM), University of Bremen. This is supplemented by older data
Fig. 4. (A) Map of the deepest section of the Java Trench with the locations of published deeps(red circles) (Table 1). The 6000 m depth contour is shown in white.
The deepest section of the trench is dened by the 7000 m contour (green). All other contours at 200 m intervals (between 6000 and 7200 m water depth) (B) Inset
map of the identied deep within the Java Trench with the deepest point determined during this study (white star = 7290 m water depth) which is within 3 km of the
published deepest point by Stewart and Jamieson (2018). The outer rim of the deep lies at 6900 m water depth (black contour). The 7200 m contour is coloured blue.
For location of inset map see the red box in Fig. 4A. Illumination from 45° at an altitude of 35°. (For interpretation of the references to colour in this gure legend, the
reader is referred to the web version of this article.)
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
from a BAS towed sonar survey (MR1) and single-beam data collected
by scientic surveys and commercial shing vessels. Where no data
existed from these sources, global compilations from GEBCO_2014 and,
below 60° S, the IBCSO were used; both these datasets use satellite al-
timetry in areas where data are sparse. Gridded datasets were re-
sampled to 200 m resolution and then converted to point data with the
nal product produced via a weighted process given the variety of data
resolutions available (Leat et al., 2016).
Even with the recent mapping eort and compilation exercises un-
dertaken by both BAS and IBCSO, there are few high-resolution data
available to robustly analyse from the South Sandwich Trench.
Therefore the GEBCO_2014 data were interrogated for this area of in-
terest. Note that the east-west trending fracture zone that intersects the
southernmost extent of the South Sandwich Trench generally does not
exceed around 6000 m water depth therefore was discounted as an area
of interest in this study.
Published maximum depths in the Meteor Deep vary from 8428 m to
8325 m as reported in a number of publications (e.g. Allaby, 2009;
Zhivago, 2002) although the original source of this sounding cannot be
traced. Other published maximum depths for this trench include
8264 m (Maurer and Stocks, 1933;Heezen and Johnson, 1965) for
Meteor Depth, and 8125 m at a position to the south as determined by
Stewart and Jamieson (2018) from the GEBCO_2014 global bathymetry
dataset (Fig. 7;Table 1). The deepest point south of 60° S, located
within the southernmost extent of the South Sandwich Trench attains a
maximum depth of 7235 m (Fig. 7;Table 1).
2.2. Condence levels
With regard to the condence assessment a value of 1is given to a
location with high condence that has a suite of good quality multi-
beam echosounder bathymetry data as evidence to the accuracy of the
location of the deep. A value of 2is given where either the multibeam
echosounder bathymetry data is of poor quality containing a number of
bathymetric artefacts, or the position is based on best available single-
beam bathymetry data. A value of 3is given where the location is
based on global data compilations with low resolution data. A hydro-
graphic survey will be essential to conrm the exact position and depth
for the deepshould a condence value of 3have been assigned in this
Upon assessment of the data available for the ve-deeps from data
repositories and through global bathymetry compilations, the most
comprehensive data available was over the Challenger Deep. Given the
volume of high-resolution data available, and the in depth analysis on
the error associated with soundings from depths exceeding 10,000 m
(e.g. Gardner et al., 2014;van Haren et al., 2017), a condence value of
1is assigned to the van Haren et al. (2017) site which represents the
most up-to-date location and depth for Challenger Deep. Conversely, a
condence value of 3was awarded to the Java and South Sandwich
trenches reecting that these areas are only covered by low-resolution
global bathymetry products. Data from the Puerto Rico Trench are
awarded a condence value of 2as although the maximum depth
recording is 8540 m within the available data, inspection of the data
reveal that possible soundings > 8400 m water depth were individual
data spikes extending > 100 m below the surrounding sea bed and no
condence value can be assigned to these points. Finally, data from the
Molloy Hole in the Arctic Ocean were also assigned a condence value
of 2reecting the resolution of the multibeam data available (Klenke
and Schenke, 2006a) and agreement between studies as to the location
and depth of the deepest point (Thiede et al., 1990;Klenke and
Fig. 5. (A) Map of the deepest section of the Diamantina Fracture Zone with the locations of published deeps(red circles) (Table 1). The 6000 m depth contour is
shown in white. The deepest section of the feature is dened by the 7000 m contour (blue). All other contours at 200 m intervals (between 6000 and 7000 m water
depth) (B) Inset map of Dordrecht Deep with the deepest point determined during this study (white star = between 7090 and 7100 m water depth) which is within
4 km of the published GEBCO Gazetteer location for Dordrecht Deep. The outer rim of Dordrecht deep lies at 5300m water depth (pink contour). The 7000 m contour
is coloured blue. All other contours at 100 m intervals (between 5300 and 7000 m water depth). For location of inset map see the red box in Fig. 5A. Illumination from
45° at an altitude of 25°. (For interpretation of the references to colour in this gure legend, the reader is referred to the web version of this article.)
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
Schenke, 2002, 2006a).
2.3. Uncertainty
The accuracies of both modern and historical single-beam and
multibeam echosounders, as well as navigation systems, is an inter-
esting subject although it is beyond the scope of this paper.
Multibeam echosounder systems are frequently tailored for each
individual survey dependent on water depth, weather, whether there is
a need to optimise the bathymetric data over backscatter intensity data
or vice versa, and so on. Individual aspects such as beam angle (e.g.
older systems were xed beam and the operator could simply cut the
outer beams compared to modern systems whereby you can alter the
angle where you keep all beams but within a narrower angle), system
calibration, and motion sensor and gyro accuracy (which are subse-
quently applied to the data). Many of these settings are not system-
atically recorded, or if they are, the information is contained in grey
literature which is rarely available online. Aspects such as the appli-
cation of an accurate sound velocity prole are crucial during data
acquisition and any subsequent data processing. Sound velocity was
one of the crucial dierences between the Gardner et al. (2014) and van
Haren et al. (2017) maximum depths for the Challenger Deep in the
Mariana Trench.
Given the example parameters listed above and the fact that few of
Fig. 6. Map of the deepest section of the Mariana Trench with the deepest point, located in Challenger Deep, determined by van Haren et al. (2017) indicated by the
white star (10,925 m water depth). Note that due to clustering of the published deepslocations it was not possible to display them all (Table 1). The 6000 m depth
contour is shown in white. The 10,500 m contour is shown in blue with the deepest soundings located in the westernmost of the 3 basins. All other contours at 500 m
intervals (between 6000 and 10,500 m water depth). Illumination from 350° at an altitude of 35°. (For interpretation of the references to colour in this gure legend,
the reader is referred to the web version of this article.)
Table 2
List of locations that based on the best available data that constitute the deepest places in each ocean, the ve-deeps. Note that the deepest point in the South
Sandwich Trench is south of 60° S and not the published location for Meteor Deep.
Ocean Area Location Latitude Longitude Anticipated Depth (m) Condence
Pacic Mariana Trench Challenger Deep 11.332° N 142.202° E 10,925 ± 12 1
Indian Java Trench Unnamed Deep 11.20° S 118.47° E 7290 3
Southern South Sandwich Trench Unnamed Deep South of 60°S 60.33° S 25.28° W 7385 3
Atlantic Puerto Rico Trench Milwaukee Deep 19.613° N 67.847° W 8408 2
Arctic Fram Strait Molloy Hole 79.137° N 2.817° E 5669 2
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
these are recorded consistently for inclusion in a study such as this, a
robust examination of system uncertainty for all published depths
would be the subject of another review. Likewise, the accuracy of na-
vigational systems, the impact of using dierent projections, datum and
ellipsoids during data acquisition, processing and subsequent analyses
are not addressed here.
3. Results
Upon assessing the nominal location for each of the ve-deeps there
are some oceans that were treated slightly dierent from others. For
example, there is no doubt that Challenger Deep in the Mariana Trench
is the deepest point in the Pacic Ocean (Gardner et al., 2014;van
Haren et al., 2017) and that the Puerto Rico Trench is the deepest place
in the Atlantic Ocean. However, in the latter the exact depth of the
deepest point, known as Milwaukee Deep(Lyman, 1954), required
reassessment. The deepest point in the Southern Ocean, the South
Sandwich Trench, oered two locations: the deepest point in the trench,
or Meteor Deep(Allaby, 2009), which is north of the 60° S boundary
and a currently unnamed deep which is the deepest point of the trench
south of the 60° S boundary. In the Arctic Ocean, the Molloy Hole, in
the Fram Strait (Bourke et al., 1987;Thiede et al., 1990;Klenke and
Schenke, 2002, 2006a;Jakobsson et al., 2012) was investigated
whereas online reports of the Litke Deep being the deepest point were
discarded as data analysis revealed that the Litke Deep only achieves a
maximum water depth of ~4000 m. The deepest point in the Indian
Ocean is contentious as it is often reported as being either the Java
Trench at 9° S to 11° S or the Diamantina Fracture Zone further south at
33° S to 35° S. To assess and establish which is indeed deeper than the
other, both were included in this study, and in the Diamantina Fracture
Zone two separate locations for the deepest place were investigated
(Dordrecht Deep and Diamantina Deep).
3.1. Arctic Ocean
Klenke and Schenke (2002) compared multibeam echosounder
bathymetry from their study (100 m grid) with that of an earlier version
of the IBCAO (1 arc minute grid; Jakobsson et al., 2000) and found that
the mean dierence between the two datasets was around 52 m (about
2% of the depth) with the multibeam data registering systematically
Fig. 7. Map of the South Sandwich Trench with the published deeplocations (red circles) (Table 1). Meteor Deepis labelled with the deepest points of the trench
determined by this study (white stars) with their associated depth in italics (Table 2 and Table 3). The 6000 m depth contour is shown in white. The deepest sections
of the trench are dened by the 8000 m contour (blue). All other contours at 200 m intervals (between 6000 and 8000 m water depth). Illumination from 270° at an
altitude of 35°. (For interpretation of the references to colour in this gure legend, the reader is referred to the web version of this article.)
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
deeper primarily due to the dierence between grid resolutions.
The fourth published maximum water depth for the feature (Bourke
et al., 1987) is located ca. 3 km to the north of the other three points.
Three published locations for the deepest point (Thiede et al., 1990;
Klenke and Schenke, 2002;Klenke and Schenke, 2006a, 2006b;
Jakobsson et al., 2012) are within 880 m of each other laterally. The
fourth published location for the deepest point (Bourke et al., 1987) for
the Molloy Hole plots around 3 km to the north of the other three
The position for the deepest point of the Molloy Hole is likely within
the 880 m grouping of four published locations with the maximum
water depth and geographic location reported by Klenke and Schenke
(2002, 2006a, 2006b), based on multibeam bathymetry data, used in
this study (Fig. 2;Table 2).
3.2. Atlantic ocean
The three published deepest points from within the Puerto Rico
Trench are all located in the westernmost section of the trench, within
190 km of each other. The available data reveal depth soundings con-
sistently shallower than those published with the deepest of those being
8740 m. This study report a signicantly shallower depth of 7450 m for
that coincident location, a median ridge within the trench axis. Lyman
(1954) reports a depth of 8710 m, whereas this study reports a coin-
cident depth of 8370 m for that location. Finally the Stewart and
Jamieson (2018) maximum water depth of 8536 m coincides with an
8300 m depth in the dataset used in this study.
The dierences between these water depths is largely a result of
data availability at that particular time of publication and available
technology. The Lyman (1954) depth pertains to soundings acquired on
board the Theodore N. Gill in 1952 using an early echo-sounder system.
The Stewart and Jamieson (2018) study utilised the GEBCO_2014
global compilation with a resolution of 30 arc sec. Subsequently, pub-
lically available multibeam echosounder data coincides with all three of
these published geographic locations resulting in an improvement in
the understanding of the morphology and bathymetry of this trench.
An area of relatively featureless, at sea bed located west of 67.5°
W, encompassed by the 8400 m contour was identied during this study
using the multibeam echosounder data downloaded for this study.
Unlike most other trenches, that culminate in a single localized deep,
the deepest area of the Puerto Rico Trench presents more of an elon-
gated depression, bounded by the 8400 m contour, around 13 km long
by 3 km wide which makes identifying the deepest point dicult. This
depression hosts a maximum water depth of 8408 m and is located
approximately 40 km east of the Lyman (1954) position for the Mil-
waukee Deep (Fig. 3;Table 2).
3.3. Indian Ocean
The location of the two published Java Trench deeps, where the
maximum depths are reported as 7725 m or 7450 m (depending on the
source; Table 1) are incorrect. Furthermore, the location given for the
Java Deep is located on the overriding plate, distal to the trench axis,
with water depths of ~1910 m according to GEBCO_2014 (Fig.4A).
The maximum water depth in the Java Trench is 7290 m located in a
conned deep 3 km south of the Stewart and Jamieson (2018) location
(Fig. 4B; Table 2) that was derived from the GEBCO_2014 global
bathymetry dataset. This currently unnamed deep is the deepest point
of the Indian Ocean.
By plotting the location of these recorded depths against the
GEBCO_2014 global bathymetry dataset it becomes obvious that the
published location of the Diamantina Deep (IHO-IOC GEBCO Gazetteer
of Undersea Feature Names), where the maximum recorded water
depths are reported as exceeding 8000 m is incorrect due to positional
inaccuracies and over-estimated water depths. Furthermore, the loca-
tion given for the Diamantina Deep is outside the fracture zone entirely
with water depths of around 5300 m at that location. It is clear that
given the best resolution data available for this study, the deepest water
depths will be found in the Dordrecht Deep.
Dordrecht Deep is a bathymetric depression approximately 80 km
by 95 km in size located within the axis of the fracture zone. The deep
varies in water depth from 5300 m to 7099 m with two discreet basins
that exceed 7000 m water depth with the data indicating the deepest
point should be located in the northernmost depression (Fig. 5B;
Table 3).
3.4. Pacic Ocean
Data from this study reveal three depressions that locally exceed
10,500 m water depth (Fig. 6). It is the westernmost one of these that is
the deepest at 10,925 ± 12 m (van Haren et al., 2017;Table 2). Given
the volume of high-resolution data available and the in depth analysis
on the error associated with soundings from depths exceeding 10,000 m
by authors such as van Haren et al. (2017) and Gardner et al. (2014)
there is little doubt that this is the deepest point within the Mariana
3.5. Southern Ocean
Three deepswere identied north of 60° S all within 18 m max-
imum water depth of each other (Fig. 7 and Fig. 8AC; Table 3). One
unnamed deepwas identied south of 60° S (Fig. 7 and Fig. 8D;
Table 2). The most commonly reported depth for the Meteor Deep is
8428 m (Fig. 7;Table 1), however, when interrogating the GEBCO_2014
dataset the two geographic locations for that deep are 400 m distance
apart and register as 7124 and 7145 m water depth based on the
GEBCO_2014 compilation. This is a signicant discrepancy and the
published locations do not coincide with the three deepsidentied in
this study (Fig. 7;Table 3). Similarly, the maximum water depth pub-
lished for the section of the trench located south of 60° S, is documented
as 7235 m (Fig. 7;Table 1). This is coincident with 5540 m water depth
based on the GEBCO_2014 dataset with this inconsistency likely due to
erroneously published coordinates plotting this position signicantly
distant from the trench axis.
4. Discussion
It is perhaps unsurprising that the site with the highest condence is
the Challenger Deep in the Mariana Trench as by the very prestige of
being the deepest place in the world has led to extra scrutiny as to the
exact depth and mapping eort. The review of eorts discussed in
Gardner et al. (2014) and the renement of van Haren et al. (2017)
Table 3
List of additional sites in the Indian and Southern Oceans that are of potential interest for future study to prove or refute the deepest point of those oceans.
Ocean Area Location Latitude Longitude Anticipated Depth (m) Condence
Indian Diamantina Fracture Zone Dordrecht Deep 33.452° S 101.468° E 70907100 2
Atlantic South Sandwich Trench North of 60°S - 1 55.39° S 26.41° W 8165 3
Atlantic South Sandwich Trench North of 60°S - 2 56.26° S 24.83° W 8183 3
Atlantic South Sandwich Trench North of 60°S - 3 57.52° S 24.00° W 8170 3
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
places the deepest point in Challenger Deep, the Mariana Trench, the
Pacic Ocean and indeed the world at 11.332° N/142.202° E with a
depth of 10,925 ± 12 m. This has been realised through a high level of
multibeam echosounder data acquisition carried out by researchers in
the US and Japan (e.g. Fujioka et al., 2002;Fryer et al., 2003;Nakanishi
and Hashimoto, 2011;Gardner et al., 2014;van Haren et al., 2017).
The Milwaukee Deep (Puerto Rico Trench), the Molloy Hole (Fram
Strait) and the Dordrecht Deep (Diamantina Fracture Zone) were as-
signed a condence value of 2as the available bathymetry data is of
lower quality and contain bathymetric artefacts (Table 2 and Table 3).
In the case of the Milwaukee Deep, the current location is likely erro-
neous due there being no geomorphological distinction between this
location and rest of the trench oor (known as Brownson Deep) and
therefore requires correction, or rather the name simply falls into
abeyance. However, this study conrms that the deepest area of this
trench comprises an elongated depression, within the 8400 m contour
of which the deepest point is approximately 40 km east of the Lyman
(1954) position for the Milwaukee Deep.
In the case of the Molloy Hole, it appears the deepest point is in the
vicinity of 79.137° N/2.817° E (Klenke and Schenke, 2002), the lower
condence level is purely a result of the resolution of the multibeam
echosounder data publically available and not a reection that another,
deeper point lies elsewhere. The ambiguity in identifying the deepest
point in the Molloy Hole is in part due to the relatively featureless
topography of the seaoor of the deep. It is not a fracture zone or
subduction trench, but rather a at bottomed circular depression
lacking in a compact, clearly conned deep.
Both the published depth and location for the Diamantina Deep
appear to be erroneous, there are no areas indicated to be > 8000 m
and given coordinates do not even fall within the fracture zone (and is
only 5300 m when the underlying data were interrogated). Therefore,
the location for the Diamantina Deep needs to be revised. In the
Dordrecht Deep, it appears the deeper of the two interior depressions is
the one to northwest (Table 3). The Dordrecht Deep is proposed here as
the deepest site of the Diamantina Fracture Zone and is still included in
this study given how close the estimated depths are to the Java Deep in
the Java Trench (7100 and 7290 m respectively). Though, there is a
note of caution given the similar water depths estimated for the Java
and Dordrecht deeps therefore a multibeam echosounder survey will be
required to settle this unequivocally thereby establishing the deepest
point in the Indian Ocean. Also, within the Java Trench, the published
deepis instead located on the overriding plate rather than the trench
axis. It is recommended that either the term Java Deepfalls into
abeyance, or is corrected to a nearby depression (7258 m water depth at
10.38° S/110.35° E), or is reassigned the position reported in this study
at 7290 m water depth. Furthermore, depending on the source, occa-
sionally Java Deep means the deepest point, sometimes it refers instead
to the whole of the Java Trench. Likewise other literature refer to this
Fig. 8. Detailed maps of the deepsidentied within the South Sandwich Trench during this study from north to south. (A) The 8165 m deep. (B) The 8183 m deep.
(C) The 8170 m deep. (D) The 7385 m deeplocated south of 60° S latitude. Selected contour lines are displayed for illustrative purposes (6000 m is black, 7000 m is
blue, 8000 m is green, 8100 m is red). The deepest points determined during this study are indicated by the white stars. For bathymetry colour ramp and the
geographic location see the corresponding white stars see Fig. 7. Illumination from 270° at an altitude of 35°. (For interpretation of the references to colour in this
gure legend, the reader is referred to the web version of this article.)
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
trench as the Java Trench (e.g. Southward et al., 2002), Sunda Trench
(e.g. Nalbant et al., 2005), or the Sunda-Java Trench (e.g. Whittaker
et al., 2007) and thus there is scope to clarify this by using the two
terms for the trench and deep, perhaps Sunda for the trench after the
larger biogeographical region of Sunda, and the Java Deep after the
smaller Indonesian Island of Java.
Perhaps the most problematic site of all is the Southern Ocean's
South Sandwich Trench. Firstly, to represent the deepest point in the
Southern Ocean, technically the point must be south of 60° S, making
the depression at 60.33° S/25.28° W (7385 m depth) the deepest point
in the Southern Ocean, but by no means the deepest point of the South
Sandwich Trench. Dening the deepest point of this trench is compli-
cated, largely due to low quality bathymetric data but also in that there
are three potential deepsnorth of 60° S all within 18 m maximum
water depth of each other (8165, 8170, and 8183 m). A modern mul-
tibeam echosounder system, if properly calibrated and with a proximal
sound velocity prole, is capable of collecting accurate depth soundings
with a minimum uncertainly of between 0.2% and 0.5% water depth
dependent on signal-to-noise ratio and pulse length. Therefore, all three
of the potential maximum depths within the South Sandwich Trench
are within the uncertainty of a multibeam echosounder system and only
acquisition of high-resolution data will determine the precise location
of the deepest point of the trench. The published depths for the Meteor
Deep is 8428 m, however, there were two locations given for this site,
400 m apart, with coincident depths from sourced data of 7124 and
7145 m respectively. Also, the published location for Meteor Deep does
not coincide with any of the three unnamed deepsidentied in this
study. Note that the identied depression south of 60° S that represents
the deepest place in the Southern Ocean, is also unnamed.
5. Deeps as named features
According to the IHO-IOC guidelines for naming undersea features,
deepsare dened as a localized depression within the connes of a
larger feature, such as a trough, basin or trench. It used to be depth
specic and dened as a well dened deepest area of a depression of
the deep-sea oor which applies when soundings exceed 3000 fathoms
[5486 m](Wiseman and Ovey, 1953). The naming of deepswas once
thought to not oer anything useful scientically and was simply
spurred by the desire to name features and the British National Com-
mittee on Ocean Bottom Features suggested that the term should fall
into abeyance (Wiseman and Ovey, 1954). As recent as 1990, the IHO-
IOC committee reported that many named features such as cap,deep
and swellhave generally accepted historical usage, but do not re-
commend any wider use of such terms in new names (Bouma, 1990).
Deeps are however back in the list of accepted names for undersea
features by the IHO-IOC. In fact in 2014, a 5400 m deep depression in
the Kermadec Trench was ocial accepted as the Crean Deep, despite
it being nearly 5000 m shallower than the trench in which it resides.
Therefore, the tendency of naming deeps in general is perhaps still
not completely resolved. For example, the Izu-Bonin and Tonga tren-
ches have one clear deep each, the Ramapo Deep and the Horizon Deep
respectively (Fisher, 1954) and the Kermadec has the single Scholl Deep
(IHO-IOC GEBCO Gazetteer of Undersea Feature Names). However, the
South Sandwich has one named, the Meteor Deep (Herdman et al.,
1956), but clearly there are three other well dened deepsof similar
depth, size and morphology (Fig. 8AC) without names, plus the issues
of what constitutes the deepest point in the Southern Ocean as dis-
cussed above. In other instances there are multiple deeps within one
large-scale topographic feature such as the Peru-Chile Trench with the
Milne-Edwards, Krümmel, Haeckel and Richards deeps (Zeigler et al.,
1957), and the Puerto Rico Trench with Brownson and Milwaukee
deeps (Lyman, 1954) and a somewhat spurious Gilliss deep (George and
Higgins, 1979). Albeit a number of these only appear informally in
scientic literature and are seemingly not ocially recognised (and are
likely the source of dubious contributions that led to the sentiments of
Wiseman and Ovey (1954) and Fisher (1987)). To the contrary, the
Mariana Trench has, in addition to Challenger Deep, two other distinct
deeps; the Sirena and the Nero deeps (Fryer et al., 2003). Interestingly,
of all the deeps mentioned in this paragraph, only Challenger, Horizon
and Scholl are recognised in the IHO-IOC GEBCO Gazetteer of Undersea
Feature Names, furthermore, the Java Deep is recognised but represents
the entire Java Trench, and not simply the deepest point or by the of-
cial denition of a deep.
To bring some clarity to this, the analogy with mountain summits
can again be made. In the instance of mountains, there can be only one
summit, the highest point, which in deep trenches should be mirrored
in the naming of the deep. This works well as a descriptor where a
feature, in this case mostly trenches, have one clear deepest point. But
in the terrestrial nomenclature for mountain summits, any other ob-
vious protrusion that does not constitute the highest point is labelled a
peak, to dierentiate it from the summit (or parent peak). A similar
model could be used in the very deepest parts of the ocean to provide a
coherent nomenclature between the very deepest points, and other
distinct depressions that may be of interest to scientists or explorers.
The current system of coining all depressions deepsunderwater is akin
to calling every peak on a mountain range the summit.
In mountain ranges, topographic prominence is intuitively used to
establish a single mountain or peak against what could be otherwise
construed as a complex ridge system. This method distinguishes
mountains from lesser peaks by the height above the highest saddle
connecting it to a higher summit. A common denition of a mountain is
having an altitude with a 300 m prominence (or ~ 7% relative pro-
minence) over the surrounding ridge. Again a similar system of topo-
graphic prominence should be considered to clarify features such as
those within some of the trenches in this study and others, where there
is clearly a deepest point, but other shallower depressions and to con-
rm or refute the presence of more dubious deeps.
6. Conclusions
Based on the best resolution bathymetric datasets currently avail-
able from public repositories, the deepest points in each ocean are the
Molloy Hole in the Fram Strait (Arctic Ocean; 5669 m, 79.137° N/
2.817° E), the trench axis of the Puerto Rico Trench (Atlantic Ocean;
8408 m 19.613° N/67.847° W), an unnamed deep in the Java Trench
(Indian Ocean; 7290 m, 11.20° S/118.47° E), Challenger Deep in the
Mariana Trench (Pacic Ocean; 10,925 m, 11.332° N/142.202° E) and
an unnamed deep in the South Sandwich Trench (Southern Ocean;
7385 m, 60.33° S/25.28° W). The locations are located within the
Exclusive Economic Zone (EEZ) of Norway, Dominican Republic,
Indonesia, Federated States of Micronesia, and Britain (British Antarctic
Territory), respectively. The Diamantina Fracture Zone is in an area
beyond national jurisdiction (ABNJ).
There are however caveats to these conclusions. The deepest point
in the Southern Ocean is not the deepest point in the South Sandwich
Trench, but rather the deepest point south of 60° S. The location of the
deepest point in that trench could be any one of three potential loca-
tions none of which coincide with the published location of the Meteor
Deep, which is erroneously attributed to be the deepest point of that
trench. The similarity in depth between the three contender deeps,
combined with the poor quality of currently available data does not
guarantee this would be the deepest overall point in the trench. Only
acquisition of high-resolution bathymetric data would conrm this.
The deepest point in the Atlantic Ocean, the Milwaukee Deep, in the
Puerto Rico Trench does not exist under the denition of the IHO-IOC
guidelines. This trench actually comprises an elongated area of rela-
tively featureless seaoor bounded by the 8400 m bathymetric contour.
Furthermore, this elongated depression represents what has historically
been sub-divided into the Brownson and the Milwaukee deeps (Lyman,
1954), and as such, these two names should be omitted given none of
these form a dened topographic deep. There is also no evidence to
H.A. Stewart and A.J. Jamieson Earth-Science Reviews 197 (2019) 102896
suggest the Gilliss Deep exists as a feature (George and Higgins, 1979).
In the Indian Ocean, if the Diamantina Deep is to remain a feature
name, the location must be corrected to fall within the Fracture Zone
although it is unclear as to where exactly to move this location to as the
original reference has proven dicult to trace. This study has con-
rmed that the deepest point of the Diamantina Fracture Zone is the
Dordrecht Deep with an updated geographic position at 33.452° S/
101.468° E and a maximum water depth of between 7090 and 7100 m.
Given the low quality of bathymetry data in this area, and that of the
Java Trench, there is still a possibility that the Dordrecht Deep could be
the deepest point in the Indian Ocean.
It is clear that many of these deeps identied are currently unnamed
(particularly in the Southern and Indian Ocean), and there are a
number that are either required to have their coordinates updated
based on the data now available or indeed be omitted altogether (e.g.
Meteor and Java deeps, and the Puerto Rico Trench deeps respectively).
Furthermore we encourage the wider uptake of the correct name for the
Molloy Hole in the literature and that IHO-IOC consider clarifying the
Java/Sunda/Java-Sunda Trench nomenclature problem. Additionally,
the IHO-IOC should consider resolving the ambiguity between the term
deepsbeing used to dene the deepest point exclusively versus a
collective term for all depressions regardless of depth.
The salient nding of this study is that at an inter-ocean level there
is a reasonable grasp on where the deepest places in each ocean are.
However, the detail remains elusive with exact coordinates and setting
within a particular topographical feature poorly understood in the
majority of cases with the exact depth also remaining ambiguous. It is
hoped that initiatives such as the Seabed 2030 project (Mayer et al.,
2018), high prole privately funded exploration, and the continuing
upward trend in scientic work at such depths (e.g. Jamieson, 2018)
will resolve these matters for future generations of explorers, scientists
and everyone in between to engage.
A.J.J. conceived the study incentivised by the forthcoming 5-Deeps
Expeditionon the DSSV Pressure Drop nanced by Caladan Oceanic LLC
(USA). H.A.S. undertook data analysis and both authors contributed
equally to the production of the manuscript. The authors thank two
anonymous reviewers for their critical reviews of the manuscript.
H.A.S. was supported in this research by the British Geological Survey
(BGS) Ocean Geoscience Team and publishes with the permission of the
Executive Director of the BGS (United Kingdom Research and
Innovation). The authors declare no competing nancial interests.
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... The Indian Ocean is geomorphologically complex, hosting subduction trenches, seamounts, ridges, plateaus, coral atolls, fracture zones and hydrothermal vents. The Indian Ocean is largely bounded by canyon-incised continental slopes (Daniell et al., 2010;Harris et al., 2014) that in places can plunge from the coast to > 7,000 m deep (Stewart and Jamieson, 2019). Numerous expeditions and institutional efforts in the last two centuries have contributed greatly to our knowledge of coastal marine biodiversity within the Indian Ocean (Wafar et al., 2011). ...
... Contemporary marine science has acknowledged the global importance of understanding Indian Ocean biodiversity for habitat management and are focussing efforts on, for example, coral reefs (Sheppard, 1998;Wafar et al., 2011;McClanahan and Muthiga, 2016) and seamount associated pelagic communities (Rogers, 2016;Rogers et al., 2017), typically in the upper 3,000 m. However, the average depth of the Indian Ocean is 3,741 m (Eakins and Sharman, 2020) and hosts vast areas, particularly in the East Indian Ocean, that exceed 6,000 m (e.g., the Wharton Basin, Java Trench, and the Wallaby-Zenith and Diamantina fracture zones; Jamieson, 2015;Stewart and Jamieson, 2019;Bongiovanni et al., 2021;Weston et al., 2021). ...
... Furthermore, the exact depth of other features, for example the Wallaby-Zenith Fracture Zone, has been substantially corrected from the original satellite altimetryderived to new multibeam echosounder-derived bathymetry (Weston et al., 2021). In fact, during the search for the deepest point in the Indian Ocean for the 2019 Five Deeps Expedition (Jamieson, 2020) it was not clear if the Java Trench or Diamantina Fracture Zone was deeper (Stewart and Jamieson, 2019). After conducting multibeam transects at both features, the Five Deeps Expedition demonstrated that the Java Trench holds the deepest point in the Indian Ocean, with of depth of 7,187 ± 13 m at an unnamed deep at 11.129 • S/114.942 ...
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The Java Trench is the only subduction trench in the Indian Ocean that extends to the hadal zone (> 6,000 m water depth), and except for sevenbenthic trawls acquired around the 1950s, there has been little to no sampling at hadal depths undertaken since. In 2019, we undertook a 5-day expedition comprising a scientific dive using a full ocean depth-rated submersible, the DSV Limiting Factor , seven hadal-lander deployments, and high-resolution bathymetric survey. The submersible performed a video transect from the deepest point of the trench, up a 150 m high near-vertical escarpment located on the forearc, and then across a plateau at a depth of ∼7,050 m to make in situ observations of the habitat heterogeneity and biodiversity inhabiting these hadal depths. We found the Java Trench hadal community to be diverse and represented by 10 phyla, 21 classes, 34 orders and 55 families, with many new records and extensions in either depth or geographic range, including a rare encounter of a hadal ascidian. The submersible transect revealed six habitats spanning the terrain. The deepest trench axis comprised fine-grained sediments dominated by holothurians, whereas evidence of active rock slope failure and associated talus deposits were prevalent in near-vertical and vertical sections of the escarpment. Sediment pockets and sediment pouring down the steep wall in “chutes” were commonly observed. The slope terrain was dominated by two species in the order Actiniaria and an asteroid, as well as 36 instances of orange, yellow, and white bacterial mats, likely exploiting discontinuities in the exposed bedrock, that may indicate a prevalence of chemosynthetic input into this hadal ecosystem. Near the top of the escarpment was an overhang populated by > 100 hexactinellid (glass) sponges. The substrate of the plateau returned to fine-grained sediment, but with a decreased density and diversity of epifauna relative to the trench floor. By providing the first visual insights of the hadal habitats and fauna of the Java Trench, this study highlights how the habitat heterogeneity influences patchy species distributions, and the great benefit of using a hadal-rated exploratory vehicle to comprehensively assess the biodiversity of hadal ecosystems.
... However, knowledge gaps are present. This gap is readily seen with recently resolved uncertainty with the deepest location in each ocean and poorly resolved bathymetric maps (Stewart and Jamieson, 2019). Further, vast swathes of the hadal zone remain unexplored and unstudied (Jamieson, 2018), especially with non-subduction features and hadal features outside the Pacific Ocean (Stewart and Jamieson, 2019;Weston et al., 2021). ...
... This gap is readily seen with recently resolved uncertainty with the deepest location in each ocean and poorly resolved bathymetric maps (Stewart and Jamieson, 2019). Further, vast swathes of the hadal zone remain unexplored and unstudied (Jamieson, 2018), especially with non-subduction features and hadal features outside the Pacific Ocean (Stewart and Jamieson, 2019;Weston et al., 2021). Meanwhile, the Mariana Trench has undergone an immense degree of scrutiny regarding simply how deep it is (Fujimoto et al., 1993;Gardner et al., 2014;van Haren et al., 2017;Bongiovanni et al., 2021;Greenaway et al., 2021). ...
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The hadal zone is a cluster of deep-ocean habitats that plunge to depths of 6000–11000 m below sea level. Research of the deepest marine zone has occurred on a disjunct timeline and slower than shallower zones. Over the past 20 years, research efforts have surged with greater sampling capabilities and an expansion of expeditions. We aimed to assess the state of hadal science by quantitively assessing the publishing landscape. We applied a topic modelling approach and fit a Latent Dirichlet Allocation model for 12 topics to 520 abstracts from peer-reviewed papers, reviews, and conference proceedings available on the Web of Science's Core Collection between 1991 and 2021. The model outputs were analysed with ecological modelling approaches to identify the main lines of research, track trends over time, and identify strengths and gaps. We found that hadal science is occurring across all five broad disciplines of oceanography and engineering. Hadal research has exponentially grown in the past 30 years, a trend that shows no signs of slowing. The expansion is most rapidly occurring to understand the biogeochemistry of trenches, the functions of microbial communities, and the unique biodiversity inhabiting these ecosystems, and then the application of ‘omics techniques to understand hadal life. The topic trends over time are largely driven by available technology to access and sample the deepest depths and not necessarily the pursuit of specific scientific questions, i.e. the hadal research topics are bounded by the capabilities of available exploratory vehicles. We propose three recommendations for future hadal research: (1) conduct multifeature studies that include all hadal geomorphologies across their depth range, (2) establish a programme for seasonal or long-term sampling, and (3) strengthen cross-disciplinary research. This continued acceleration in hadal research is pertinent for this last marine frontier given its vulnerability to multiple anthropogenic pressures and cascading threats from global change.
... Of the 38 oceanic trenches, 28 are located in the Pacific Ocean generated by the Ring of Fire (Fig. 4). There are no oceanic trenches in the Arctic Ocean in which the deepest water depth is −5669 m (Stewart and Jamieson, 2019). To provide physiographical properties of each oceanic trench the bathymetric data from Kioka et al. (2019aKioka et al. ( , 2019b was used for the Japan Trench, Leat et al. (2014Leat et al. ( , 2016 for the South Sandwich Trench, and GEBCO 2020 Grid (GEBCO Bathymetric Compilation Group, 2020) for the other oceanic trenches. ...
... They have also highlighted the significant uncertainty in estimating depth and location of deepest place mainly due to the measurement uncertainty, precise sound velocity estimation and data processing in the multibeam echosounder data. Likewise, for all the other oceanic trenches, the depth and exact location in the respective oceanic trench is currently undetermined (Stewart and Jamieson, 2019); thus both acquisition of high-density and high-resolution bathymetric data as well as sound velocity measurements and conductivity-temperature-depth profiler (CTD) casts are crucial for better characterizing oceanic trench geomorphologies. 5 What controls the depth of seafloor at an oceanic trench? ...
This chapter overviews global and local features of oceanic trenches. Most oceanic trenches are associated with plate subduction boundary systems; they form due to the downward bending of an oceanic plate entering a subduction system. Their total length is 47,900 km, longer than Earth's circumference. There are 27 hadal trenches with their deepest points situated in the hadal zone (water depths < − 6 km). Most of these are located along erosive plate subduction margins. The hadal trenches occupy 33% of the entire hadal seafloor and accommodate more than 90% of the global seafloor with water depths of <− 7 km. The depths of oceanic trenches are explained systematically by the present-day oceanic crustal age, sediment thickness, and isostatic correction. Recent high-resolution bathymetric surveys have revealed that the seafloors within oceanic trenches do not always show V-shaped structures with very steep landward and seaward slopes. Several trenches locally accommodate flat floors with small isolated depositional basins along the trench axis. For example, the Japan Trench has several tens of small trench-fill basins with their largest area of ~ 30 km². Further detailed surveys are necessary to better understand the geomorphology of deep trench floors worldwide – the least studied places on the Earth's surface.
... GEBCO data presents the updated and comprehensive topographic data of the Earth, regularly updated and publicly available: GEBCO is widely used in geoscience [8][9][10][11][12][13][14][15][16]. The geophysical gravity grid ( Fig. 4b) was taken from the available data developed based on satellite derived geophysical observations from the CryoSat-2 and Jason-1 sources [17]. ...
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This paper describes a scripting cartographic techniques that automatically generate maps from open source spatial data using syntax of General Mapping Tools (GMT) and R. A case study present mapping East Africa with a focus on Malawi. In this study, two different approaches of scripting cartography using R programming language and GMT were studied for geophysical analysis aimed to visualize a series of eight new maps in Malawi: topography based on the GEBCO data, seismicity, geomo-rphometric modeling based on SRTM-90 m (slope, aspect, hillshade and elevation) and geophysical fields: geoid based on EGM-2008 and free-air Faye's gravity based on satellite derived gravity data from CryoSat-2 and Jason-1. In contrast to previous maps of Malawi, a scripting approach was introduced as a console-based cartographic mapping developed for plotting a series of thematic maps based on the high-resolution data. The maps demonstrate correlations between the topography and tectonic faults (Malawi Rift Zone) and earthquakes in the Malawi Lake and extent of landforms. The results demonstrate strong correspondence between the topography and geophysical fields (geoid and gravity): negative values of geoid (-15 to-20) are notable over the Malawi (Nyasa) Lake which corresponds with local topographic depressions. Free-air gravity fields reach the lowest values (-50 to-100) over the Malawi Lake. Local heights in gravity are compared with topographic mountain ranges in the NW and SW of the country on the borders with Zambia and Mozambique. The location of earthquakes vary with the majority located in the north. The geomorphological landforms demonstrate variability in slope steepness and aspect orientation shown on histogram. The techniques of scripts can be used to automatically map spatial data using raster datasets for geophysical visualization, and this paper demonstrated this through a variety of map from the presented thematic series of geophysical maps of Malawi. Full scripts used for mapping are available on the author's public GitHub repository with provided link to her open access codes.
... Over the last 2 decades, multibeam echosounders (MBES) have become a mainstream tool for acoustic remote sensing of the seabed (Brown et al., 2011;Menandro and Bastos, 2020). MBES are now widely used for hydrographic purposes and applied research on the continental shelf (Innangi et al., 2015;Rocha et al., 2020) and deep sea (Sen et al., 2016;Picard et al., 2018;Stewart and Jamieson, 2019). In addition to measuring bathymetry, acoustic backscatter can be recorded from the MBES signal. ...
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Improvements to acoustic seafloor mapping systems have motivated novel marine geological and benthic biological research. Multibeam echosounders (MBES) have become a mainstream tool for acoustic remote sensing of the seabed. Recently, “multispectral” MBES backscatter, which is acquired at multiple operating frequencies, has been developed to characterize the seabed in greater detail, yet methods for the use of these data are still being explored. Here, we evaluate the potential for seabed discrimination using multispectral backscatter data within a multi-method framework. We present a novel MBES dataset acquired using four operating frequencies (170, 280, 400, and 700 kHz) near the Doce River mouth, situated on the eastern Brazilian continental shelf. Image-based and angular range analysis methods were applied to characterize the multifrequency response of the seabed. The large amount of information resulting from these methods complicates a manual seabed segmentation solution. The data were therefore summarized using a combination of dimensionality reduction and density-based clustering, enabling hierarchical spatial classification of the seabed with sparse ground-truth. This approach provided an effective solution to synthesizing these data spatially to identify two distinct acoustic seabed classes, with four subclasses within one of the broader classes, which corresponded closely with seafloor sediment samples collected at the site. The multispectral backscatter data also provided information in likely, unknown, sub-surface substrate differences at this site. The study demonstrates that the adoption of a multi-method framework combining image-based and angular range analysis methods with multispectral MBES data can offer significant advantages for seafloor characterization and mapping.
... These studies indicated that the South Sandwich Islands combine benthic faunal elements of the Antarctic and sub-Antarctic faunas and there also seemed to be a boundary for distributions of some species within the island arc (Arntz et al., 2004b, Hogg et al., 2016. Knowledge for the deep bathyal, abyssal and hadal depth is based on the Russian deep-sea investigations in the middle of the last century (Malyutina, 2004 and references therein), the Antarctic benthic Deep-Sea Biodiversity Project ANDEEP II expedition in 2002 (Brandt et al., 2004(Brandt et al., , 2007 and, more recently, the Five Deeps Expedition to the hadal part of the South Sandwich Trench (Stewart and Jamieson, 2019;Jamieson et al., 2021 this issue), as well as from the Biogeography of Deep-Water Chemosynthetic Ecosystems in the Southern Ocean (ChEsSO) expeditions, which investigated hydrothermal active habitats specifically (e.g. Rogers et al., 2012;Linse et al., 2019). ...
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The Sandwich Plate is known as one of the tectonically most active regions in the Southern Ocean and Antarctica, characterised by a subsurface chain of active volcanic islands (the South Sandwich Arc), submarine volcanic features, an earthquake rich area along the South Sandwich Trench and hydrothermal vents on segments of the East Scotia Ridge. In 2013 and 2019 we investigated eight potential hydrothermally active sites in the forearc, island arc and back arc of the Sandwich Plate from shallow (60 m) to abyssal (3886 m) depths. All Protector Seamounts sites, Protector Shoal, Quest Caldera, and an unnamed submarine volcano, showed thermal anomalies, as did the East Scotia Ridge segment E5 back arc site. At Quest Caldera, chimney structures, bacterial mats and mineral precipitates were observed in a depression on the caldera rim. The investigated forearc sites showed hydroacoustic, but not temperature anomalies. None of the sites showed evidence of megafauna associated with hydrothermal venting or hydrocarbon seep sites, but did have evidence of both unexpectedly dense and sparse communities of Southern Ocean taxa in the vicinities of the anomalies. Overall, our investigations showed that the benthic habitats and communities of the Sandwich Plate are still barely known.
... The ocean covers 71% of the planet's surface, and in turn is the habitat of the vast majority (97%) of living organisms (González et al. 2012;Toro et al. 2018). Due to its expanse, exploration has been complicated for humanity (Stewart and Jamieson 2019). For the most part, deep-sea mineral extraction has not been widely implemented due to several engineering challenges, such as (1) the distant location with respect to the coast; (2) it is not possible to predict climate changes in the long term; and (3) the high-pressure environment complicates the survival of any component of engineering systems (Sharma 2017). ...
Global warming is the biggest problem that humanity is facing. Most climate scientists agree on how human intervention has affected the atmospheric change in the past two centuries, leading to a rise in global temperature by 1 °C. This is mainly due to the high production of CO2 by the energy sector, which is why it is necessary to promote accelerated growth in the renewable energy market. However, there is a shortage of critical materials in the Earth's crust, wherein China (the largest producer) has a monopolistic position in the rare earth market. This situation restricts the growth of the cleaner energies market and, in turn, generates significant political conflicts between the world's great powers. The vast mineral wealth that is available in the seabed might provide several critical metals, highlighting a large concentration of rare earth, which makes deep-sea mining a great alternative to satisfy the demand for these resources. However, the environmental damage in the marine ecosystem due to large submarine mining is still unknown, leaving us a critical question: Is large submarine mining a viable solution to the problems of market and environmental issues?
The deep sea (>200 m) is the world’s least explored and largest biome, covering ~65% of the earth’s surface, it is increasingly subject to anthropogenic disturbance from fishing. The offshore Greenland halibut (Reinhardtius hippoglossoides) fishery, west Greenland, employs demersal trawl gear at depths of 800-1,400 m. Recent Marine Stewardship Council (MSC) certification of this fishery highlighted the paucity of knowledge of benthic habitats and trawling impacts. This interdisciplinary thesis employs a benthic video sled to investigate deep-sea habitats and trawling impacts and conducts a critical analysis of the fishery’s governance, with reference to the role of the MSC certification. The results provide new insights into this poorly known region of the Northwest Atlantic, including identifying four candidate vulnerable marine ecosystems (VMEs). Imagery obtained demonstrates that chronic trawling has had extensive impacts on the seafloor, which are significantly associated with the benthic communities observed. Further, trawling effort is shown to have a significant negative association with the abundance of some VME indicator taxa. The governance case study finds an effective system of state-led governance, supported by scientific, certification and industry actors. Outcomes directly attributable to engagement with the MSC certification include the introduction of a management plan and new benthic research programmes. However, questions are raised about the MSC certification, providing case study examples of existing criticisms. Assessments are weak with respect to benthic habitats and overreliant on the definitive, expert judgement of Conformity Assessment Bodies (CABs), whose independence is questioned. The assurance offered by the MSC certification in terms of the sustainability of trawling impacts on benthic ecosystems is found to seriously lack credibility. Findings are of direct relevance to the management of deep-sea fisheries in Greenland and elsewhere. Widely applicable critical insights into deep-sea fishery governance are presented, including into the role of eco-labels as a market-mechanism to promote sustainable fishery management.
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Ocean and coastal ecosystems support life on Earth and many aspects of human well-being. Covering two-thirds of the planet, the ocean hosts vast biodiversity and modulates the global climate system by regulating cycles of heat, water, and elements including carbon. Marine systems are central to many cultures, and they also provide food, minerals, energy and employment to people. Since previous assessments, new laboratory studies, field observations and process studies, a wider range of model simulations, Indigenous Knowledge, and local knowledge provide increasing evidence on the impacts of climate change on ocean and coastal systems, how human communities
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High resolution remotely sensed bathymetric data is rapidly increasing in volume, but analyzing this data requires a mastery of a complex toolchain of disparate software, including computing derived measurements of the environment. Bathymetric gradients play a fundamental role in energy transport through the seascape. Benthic Terrain Modeler (BTM) uses bathymetric data to enable simple characterization of benthic biotic communities and geologic types, and produces a collection of key geomorphological variables known to affect marine ecosystems and processes. BTM has received continual improvements since its 2008 release; here we describe the tools and morphometrics BTM can produce, the research context which this enables, and we conclude with an example application using data from a protected reef in St. Croix, US Virgin Islands.
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Despite many of years of mapping effort, only a small fraction of the world ocean’s seafloor has been sampled for depth, greatly limiting our ability to explore and understand critical ocean and seafloor processes. Recognizing this poor state of our knowledge of ocean depths and the critical role such knowledge plays in understanding and maintaining our planet, GEBCO and the Nippon Foundation have joined forces to establish the Nippon Foundation GEBCO Seabed 2030 Project, an international effort with the objective of facilitating the complete mapping of the world ocean by 2030. The Seabed 2030 Project will establish globally distributed regional data assembly and coordination centers (RDACCs) that will identify existing data from their assigned regions that are not currently in publicly available databases and seek to make these data available. They will develop protocols for data collection (including resolution goals) and common software and other tools to assemble and attribute appropriate metadata as they assimilate regional grids using standardized techniques. A Global Data Assembly and Coordination Center (GDACC) will integrate the regional grids into a global grid and distribute to users world-wide. The GDACC will also act as the central focal point for the coordination of common data standards and processing tools as well as the outreach coordinator for Seabed 2030 efforts. The GDACC and RDACCs will collaborate with existing data centers and bathymetric compilation efforts. Finally, the Nippon Foundation GEBCO Seabed 2030 Project will encourage and help coordinate and track new survey efforts and facilitate the development of new and innovative technologies that can increase the efficiency of seafloor mapping and thus make the ambitious goals of Seabed 2030 more likely to be achieved.
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The hadal zone largely comprises a series of subduction trenches that do not form part of the continental shelf-slope rise to abyssal plain continuum. Instead they form geographically isolated clusters of deep-sea (6000-11,000 m water depth) environments. There is a growing realization in hadal science that ecological patterns and processes are not driven solely by responses to hydrostatic pressure, with comparable levels of habitat heterogeneity as observed in other marine biozones. Furthermore, this heterogeneity can be expressed at multiple scales from inter-trench levels (degrees of geographical isolation, and biochemical province), to intra-trench levels (variation between trench flanks and axis), topographical features within the trench interior (se-dimentary basins, ridges, escarpments, 'deeps', seamounts) to the substrate of the trench floor (seabed-sediment composition, mass movement deposits, bedrock outcrop). Using best available bathymetry data combined with the largest lander-derived imaging dataset that spans the full depth range of three hadal trenches (including adjacent slopes); the Mariana, Kermadec and New Hebrides trenches, the topographic variability, fine-scale habitat heterogeneity and distribution of seabed sediments of these three trenches have been assessed for the first time. As well as serving as the first descriptive study of habitat heterogeneity at hadal depths, this study also provides guidance for future hadal sampling campaigns taking into account geographic isolation, total trench particulate organic matter flux, maximum water depth and area.
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Historical Note: Trigonometrical Survey of India and Naming of Peak XV as Mt. Everest
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In the year 1988, a new topographical map 1:50,000 of the Mount Everest region was published by the National Geographic Society. The full map content was derived from aerial images of scale 1:35,000, acquired in a 1984 photogrammetric flight. This highly acclaimed topographical map, produced with Swiss photogrammetric and cartographic know-how, serves until nowadays as an important work of reference. We took the analogue data (images, contours), converted them into digital form through scanning, and produced a texture-mapped 3D computer model. With a DTM of 10 m grid-size and natural texture pixel-size of 1 m this model is currently the best dataset available for an area of 25 by 25 km2 around the summit of Mount Everest.This paper reports about the production procedure of the model and shows some high-resolution photorealistic visualization results. The dataset has been used in the meantime by cartographers and animation experts for the production of new map-related visualization products and is much sought after by scientists of various disciplines.
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Geomorphometry, the science of quantitative terrain characterization, has traditionally focused on the investigation of terrestrial landscapes. However, the dramatic increase in the availability of digital bathymetric data and the increasing ease by which geomorphometry can be investigated using geographic information systems (GISs) and spatial analysis software has prompted interest in employing geomorphometric techniques to investigate the marine environment. Over the last decade or so, a multitude of geomorphometric techniques (e.g. terrain attributes, feature extraction, automated classification) have been applied to characterize seabed terrain from the coastal zone to the deep sea. Geomorphometric techniques are, however, not as varied, nor as extensively applied, in marine as they are in terrestrial environments. This is at least partly due to difficulties associated with capturing, classifying, and validating terrain characteristics underwater. There is, nevertheless, much common ground between terrestrial and marine geomorphometry applications and it is important that, in developing marine geomorphometry, we learn from experiences in terrestrial studies. However, not all terrestrial solutions can be adopted by marine geomorphometric studies since the dynamic, four-dimensional (4-D) nature of the marine environment causes its own issues throughout the geomorphometry workflow. For instance, issues with underwater positioning, variations in sound velocity in the water column affecting acoustic-based mapping, and our inability to directly observe and measure depth and morphological features on the seafloor are all issues specific to the application of geomorphometry in the marine environment. Such issues fuel the need for a dedicated scientific effort in marine geomorphometry. This review aims to highlight the relatively recent growth of marine geomorphometry as a distinct discipline, and offers the first comprehensive overview of marine geomorphometry to date. We address all the five main steps of geomorphometry, from data collection to the application of terrain attributes and features. We focus on how these steps are relevant to marine geomorphometry and also highlight differences and similarities from terrestrial geomorphometry. We conclude with recommendations and reflections on the future of marine geomorphometry. To ensure that geomorphometry is used and developed to its full potential, there is a need to increase awareness of (1) marine geomorphometry amongst scientists already engaged in terrestrial geomorphometry, and of (2) geomorphometry as a science amongst marine scientists with a wide range of backgrounds and experiences.
The hadal zone (6000–~ 11,000 m deep) arguably represents the last great frontier in marine science. Although scientific endeavour in these deepest ecosystems has been slow relative to other more accessible environments, progress is steadily being made, particularly in the last 10 years. This paper details the latest developments in technology and sampling effort at full ocean depth, scientific literature, representation in international conferences and symposia, the recent acquisition of large ecological data sets, conservation, the potential for biodiscovery and describes some key strategic sampling approaches to ensure recent progress is sustained effectively. The timing of this article is indeed to reflect on recent sampling efforts and resulting publications to provide perspectives on where the scientific community is with regards to hadal science and where it might lead in the immediate future.
Reliable very deep shipborne SBE 911plus Conductivity Temperature Depth (CTD) data to within 60m from the bottom and Kongsberg EM122 0.5° × 1° multibeam echosounder data are collected in the Challenger Deep, Mariana Trench. A new position and depth are given for the deepest point in the world's ocean. The data provide insight into the interplay between topography and internal waves in the ocean that lead to mixing of the lowermost water masses on Earth. Below 5000m, the vertical density stratification is weak, with a minimum buoyancy frequency N = 1.0 ± 0.6 cpd, cycles per day, between 6500 and 8500m. In that depth range, the average turbulence is coarsely estimated from Thorpe-overturning scales, with limited statistics to be ten times higher than the mean values of dissipation rate εT = 3 ± 2 × 10⁻¹¹ m² s⁻³ and eddy diffusivity KzT = 2 ± 1.5 × 10⁻⁴ m² s⁻¹ estimated for the depth range between 10,300 and 10,850m, where N = 2.5 ± 0.6 cpd. Inertial and meridionally directed tidal inertio-gravity waves can propagate between the differently stratified layers. These waves are suggested to be responsible for the observed turbulence. The turbulence values are similar to those recently estimated from CTD and moored observations in the Puerto Rico Trench. Yet, in contrast to the Puerto Rico Trench, seafloor morphology in the Mariana Trench shows up to 500m-high fault scarps on the incoming tectonic plate and a very narrow trench, suggesting that seafloor topography does not play a crucial role for mixing.
The South Sandwich Islands and associated seamounts constitute the volcanic arc of an active subduction system situated in the South Atlantic. We introduce a map of the bathymetry and geological setting of the South Sandwich Islands and the associated East Scotia Ridge back-arc spreading centre that consists of two sides: side 1, a regional overview of the volcanic arc, trench and back-arc, and side 2, detailed maps of the individual islands. Side 1 displays the bathymetry at scale 1:750 000 of the intra-oceanic, largely submarine South Sandwich arc, the back-arc system and other tectonic boundaries of the subduction system. Satellite images of the islands on side 2 are at scales of 1:50 000 and 1:25 000 with contours and main volcanological features indicated. These maps are the first detailed topological and bathymetric maps of the area. The islands are entirely volcanic in origin, and most have been volcanically or fumarolically active in historic times. Many of the islands are ice-covered, and the map forms a baseline for future glaciological changes caused by volcanic activities and climate change. The back-arc spreading centre consists of nine segments, most of which have rift-like morphologies.