Earth's inner core is the innermost geologic layer of the planet Earth. It is primarily a solidball with a radius of about 1,230 km (760 mi), which is about 20% of Earth's radius or 70% of the Moon's radius.
There are no samples of the core accessible for direct measurement, as there are for Earth's mantle. The characteristics of the core have been deduced mostly from measurements of seismic waves and Earth's magnetic field. The inner core is believed to be composed of an iron–nickel alloy
with some other elements. The temperature at its surface is estimated
to be approximately 5,700 K (5,430 °C; 9,800 °F), about the temperature
at the surface of the Sun.
The inner core is solid at high temperature because of its high pressure, in accordance with the Simon-Glatzel equation.
Scientific history
Earth was discovered to have a solid inner core distinct from its molten Earth's outer core in 1936, by the Danish seismologist Inge Lehmann's study of seismograms from earthquakes in New Zealand, detected by sensitive seismographs
on the Earth's surface. She deduced that the seismic waves reflect off
the boundary of the inner core and inferred a radius of 1,400 km
(870 mi) for the inner core, not far from the currently accepted value
of 1,221 km (759 mi). In 1938, Beno Gutenberg and Charles Richter
analyzed a more extensive set of data and estimated the thickness of
the outer core as 1,950 km (1,210 mi) with a steep but continuous 300 km
(190 mi) thick transition to the inner core, implying a radius between
1,230 and 1,530 km (760 and 950 mi) for the inner core.
A few years later, in 1940, it was hypothesized that this inner core was made of solid iron. In 1952, Francis Birch published a detailed analysis of the available data and concluded that the inner core was probably crystalline iron.
The boundary between the inner and outer cores is sometimes called the "Lehmann discontinuity", although the name usually refers to another discontinuity. The name "Bullen" or "Lehmann-Bullen discontinuity", after Keith Edward Bullen, has been proposed, but its use seems to be rare. The rigidity of the inner core was confirmed in 1971.
Adam Dziewonski and James Freeman Gilbert established that measurements of normal modes of vibration of Earth caused by large earthquakes were consistent with a liquid outer core. In 2005, shear waves were detected passing through the inner core; these claims were initially controversial, but are now gaining acceptance.
Data sources
Seismic waves
Almost
all measurements that scientists have about the physical properties of
the inner core are the seismic waves that pass through it. Deep
earthquakes generate the most informative waves, 30 km or more below the
surface of the Earth (where the mantle is relatively more homogeneous)
and are recorded by seismographs as they reach the surface, all over the globe.
Seismic waves include "P" (primary or pressure) compressional waves that can travel through solid or liquid materials, and "S" (secondary or shear) shear waves that can only propagate through rigid elastic solids. The two waves have different velocities and are damped at different rates as they travel through the same material.
Of particular interest are the so-called "PKiKP" waves—pressure
waves (P) that start near the surface, cross the mantle-core boundary,
travel through the core (K), are reflected at the inner core boundary
(i), cross the liquid core (K) again, cross back into the mantle, and
are detected as pressure waves (P) at the surface. Also of interest are
the "PKIKP" waves, that travel through the inner core (I) instead of
being reflected at its surface (i). Those signals are easier to
interpret when the path from source to detector is close to a straight
line—namely, when the receiver is just above the source for the
reflected PKiKP waves, and antipodal to it for the transmitted PKIKP waves.
While S waves cannot reach or leave the inner core as such, P
waves can be converted into S waves, and vice versa, as they hit the
boundary between the inner and outer core at an oblique angle. The
"PKJKP" waves are similar to the PKIKP waves, but are converted into S
waves when they enter the inner core, travel through it as S waves (J),
and are converted again into P waves when they exit the inner core.
Thanks to this phenomenon, it is known that the inner core can propagate
S waves, and therefore must be solid.
Other sources
Other sources of information about the inner core include
the Earth's magnetic field.
While it seems to be generated mostly by fluid and electric currents in
the outer core, those currents are strongly affected by the presence of
the solid inner core and by the heat that flows out of it. (Although
made of iron, the core is not ferromagnetic, due to being above the Curie temperature.)
the Earth's mass, its gravitational field, and its angular inertia. These are all affected by the density and dimensions of the inner layers.
the natural oscillation frequencies and modes of the whole Earth oscillations, when large earthquakes make the planet "ring" like a bell. These oscillations also depend strongly on the inner layers' density, size, and shape.
Physical properties
Seismic wave velocity
The
velocity of the S waves in the core varies smoothly from about 3.7 km/s
at the center to about 3.5 km/s at the surface. That is considerably
less than the velocity of S waves in the lower crust (about 4.5 km/s)
and less than half the velocity in the deep mantle, just above the outer
core (about 7.3 km/s).
The velocity of the P-waves in the core also varies smoothly
through the inner core, from about 11.4 km/s at the center to about
11.1 km/s at the surface. Then the speed drops abruptly at the
inner-outer core boundary to about 10.4 km/s.
Size and shape
On the basis of the seismic data, the inner core is estimated to be about 1221 km in radius (2442 km in diameter), which is about 19% of the radius of the Earth and 70% of the radius of the Moon.
Its volume is about 7.6 billion cubic km (7.6 × 1018 m3), which is about 1⁄146 (0.69%) of the volume of the whole Earth.
Its shape is believed to be close to an oblate ellipsoid of revolution, like the surface of the Earth, only more spherical: the flatteningf is estimated to be between 1⁄400 and 1⁄416, meaning that the radius along the Earth's axis is estimated to be about
3 km shorter than the radius at the equator. In comparison, the
flattening of the Earth as a whole is close to 1⁄300, and the polar radius is 21 km shorter than the equatorial one.
Pressure and gravity
The
pressure in the Earth's inner core is slightly higher than it is at the
boundary between the outer and inner cores: It ranges from about 330 to
360 gigapascals (3,300,000 to 3,600,000 atm).
The acceleration of gravity at the surface of the inner core can be computed to be 4.3 m/s2; which is less than half the value at the surface of the Earth (9.8 m/s2).
Density and mass
The density of the inner core is believed to vary smoothly from about 13.0 kg/L (= g/cm3 = t/m3)
at the center to about 12.8 kg/L at the surface. As it happens with
other material properties, the density drops suddenly at that surface:
The liquid just above the inner core is believed to be significantly
less dense, at about 12.1 kg/L. For comparison, the average density in the upper 100 km of the Earth is about 3.4 kg/L.
That density implies a mass of about 1023 kg for the inner core, which is 1⁄60 (1.7%) of the mass of the whole Earth.
Temperature
The
temperature of the inner core can be estimated from the melting
temperature of impure iron at the pressure which iron is under at the
boundary of the inner core (about 330 GPa).
From these considerations, in 2002, D. Alfè and others estimated its
temperature as between 5,400 K (5,100 °C; 9,300 °F) and 5,700 K
(5,400 °C; 9,800 °F).
However, in 2013, S. Anzellini and others obtained experimentally a
substantially higher temperature for the melting point of iron,
6,230 ± 500 K (5,957 ± 500 °C; 10,754 ± 900 °F).
Iron can be solid at such high temperatures only because its
melting temperature increases dramatically at pressures of that
magnitude (see the Clausius–Clapeyron relation).
Magnetic field
In 2010, Bruce Buffett determined that the average magnetic field in the liquid outer core is about 2.5 milliteslas (25 gauss), which is about 40 times the maximum strength at the surface. He started from the known fact that the Moon and Sun cause tides in the liquid outer core, just as they do on the oceans on the surface. He observed that motion of the liquid through the local magnetic field creates electric currents, that dissipate energy as heat according to Ohm's law. This dissipation, in turn, damps the tidal motions and explains previously detected anomalies in Earth's nutation. From the magnitude of the latter effect he could calculate the magnetic field.
The field inside the inner core presumably has a similar strength.
While indirect, this measurement does not depend significantly on any
assumptions about the evolution of the Earth or the composition of the
core.
Viscosity
Although seismic waves propagate through the core as if it were solid, the measurements cannot distinguish a solid material from an extremely viscous
one. Some scientists have therefore considered whether there may be
slow convection in the inner core (as is believed to exist in the
mantle). That could be an explanation for the anisotropy detected in seismic studies. In 2009, B. Buffett estimated the viscosity of the inner core at 1018Pa·s, which is a sextillion times the viscosity of water, and more than a billion times that of pitch.
Composition
There
is still no direct evidence about the composition of the inner core.
However, based on the relative prevalence of various chemical elements
in the Solar System, the theory of planetary formation,
and constraints imposed or implied by the chemistry of the rest of the
Earth's volume, the inner core is believed to consist primarily of an iron–nickel alloy.
At the estimated pressures and temperatures of the core, it is
predicted that pure iron could be solid, but its density would exceed
the known density of the core by approximately 3%. That result implies
the presence of lighter elements in the core, such as silicon, oxygen, or sulfur, in addition to the probable presence of nickel. Recent estimates (2007) allow for up to 10% nickel and 2–3% of unidentified lighter elements.
According to computations by D. Alfè and others, the liquid outer
core contains 8–13% of oxygen, but as the iron crystallizes out to form
the inner core the oxygen is mostly left in the liquid.
Laboratory experiments and analysis of seismic wave velocities seem to indicate that the inner core consists specifically of ε-iron, a crystalline form of the metal with the hexagonal close-packed (HCP) structure. That structure can still admit the inclusion of small amounts of nickel and other elements.
Structure
Many scientists had initially expected that the inner core would be found to be homogeneous,
because that same process should have proceeded uniformly during its
entire formation. It was even suggested that Earth's inner core might be
a single crystal of iron.
Axis-aligned anisotropy
In
1983, G. Poupinet and others observed that the travel time of PKIKP
waves (P waves that travel through the inner core) was about 2 seconds
less for straight north–south paths than straight paths on the
equatorial plane.
Even taking into account the flattening of the Earth at the poles
(about 0.33% for the whole Earth, 0.25% for the inner core) and crust
and upper mantle heterogeneities, this difference implied that P waves (of a broad range of wavelengths) travel through the inner core about 1% faster in the north–south direction than along directions perpendicular to that.
This P wave speed anisotropy has been confirmed by later studies, including more seismic data and study of the free oscillations of the whole Earth. Some authors have claimed higher values for the difference, up to 4.8%; however, in 2017 Daniel Frost and Barbara Romanowicz confirmed that the value is between 0.5% and 1.5%.
Non-axial anisotropy
Some
authors have claimed that P wave speed is faster in directions that are
oblique or perpendicular to the N−S axis, at least in some regions of
the inner core.
However, these claims have been disputed by Frost and Romanowicz, who
instead claim that the direction of maximum speed is as close to the
Earth's rotation axis as can be determined.
Causes of anisotropy
Laboratory data and theoretical computations indicate that the propagation of pressure waves in the HCP
crystals of ε-iron are strongly anisotropic, too, with one "fast" axis
and two equally "slow" ones. A preference for the crystals in the core
to align in the north–south direction could account for the observed
seismic anomaly.
One phenomenon that could cause such partial alignment is slow
flow ("creep") inside the inner core, from the equator towards the poles
or vice versa. That flow would cause the crystals to partially reorient
themselves according to the direction of the flow. In 1996, S. Yoshida
and others proposed that such a flow could be caused by higher rate of
freezing at the equator than at polar latitudes. An equator-to-pole flow
then would set up in the inner core, tending to restore the isostatic equilibrium of its surface.
Others suggested that the required flow could be caused by slow thermal convection inside the inner core. T. Yukutake claimed in 1998 that such convective motions were unlikely.
However, B. Buffet in 2009 estimated the viscosity of the inner core
and found that such convection could have happened, especially when the
core was smaller.
On the other hand, M. Bergman in 1997 proposed that the
anisotropy was due to an observed tendency of iron crystals to grow
faster when their crystallographic axes are aligned with the direction
of the cooling heat flow. He, therefore, proposed that the heat flow out
of the inner core would be biased towards the radial direction.
In 1998, S. Karato proposed that changes in the magnetic field might also deform the inner core slowly over time.
Multiple layers
In
2002, M. Ishii and A. Dziewoński presented evidence that the solid
inner core contained an "innermost inner core" (IMIC) with somewhat
different properties than the shell around it. The nature of the
differences and radius of the IMIC are still unresolved as of 2019, with
proposals for the latter ranging from 300 km to 750 km.
A. Wang and X. Song proposed, in 2018, a three-layer model, with
an "inner inner core" (IIC) with about 500 km radius, an "outer inner
core" (OIC) layer about 600 km thick, and an isotropic shell 100 km
thick. In this model, the "faster P wave" direction would be parallel to
the Earth's axis in the OIC, but perpendicular to that axis in the IIC.
However, the conclusion has been disputed by claims that there need not
be sharp discontinuities in the inner core, only a gradual change of
properties with depth.
In 2023, a study reported new evidence "for an
anisotropically-distinctive innermost inner core" – a ~650-km thick
innermost ball – "and its transition to a weakly anisotropic outer
shell, which could be a fossilized record of a significant global event
from the past." They suggest that atoms in the IIC atoms are [packed]
slightly differently than its outer layer, causing seismic waves to pass
through the IIC at different speeds than through the surrounding core
(P-wave speeds ~4% slower at ~50° from the Earth’s rotation axis).
Lateral variation
In
1997, S. Tanaka and H. Hamaguchi claimed, on the basis of seismic data,
that the anisotropy of the inner core material, while oriented N−S, was
more pronounced in "eastern" hemisphere of the inner core (at about
110 °E longitude, roughly under Borneo) than in the "western" hemisphere (at about 70 °W, roughly under Colombia).
Alboussère and others proposed that this asymmetry could be due
to melting in the Eastern hemisphere and re-crystallization in the
Western one. C. Finlay conjectured that this process could explain the asymmetry in the Earth's magnetic field.
However, in 2017 Frost and Romanowicz disputed those earlier
inferences, claiming that the data shows only a weak anisotropy, with
the speed in the N−S direction being only 0.5% to 1.5% faster than in
equatorial directions, and no clear signs of E−W variation.
Other structure
Other
researchers claim that the properties of the inner core's surface vary
from place to place across distances as small as 1 km. This variation is
surprising since lateral temperature variations along the inner-core
boundary are known to be extremely small (this conclusion is confidently
constrained by magnetic field observations).
Growth
Schematic of the Earth's inner core and outer core motion and the magnetic field it generates.
The Earth's inner core is thought to be slowly growing as the liquid
outer core at the boundary with the inner core cools and solidifies due
to the gradual cooling of the Earth's interior (about 100 degrees
Celsius per billion years).
According to calculations by Alfé and others, as the iron
crystallizes onto the inner core, the liquid just above it becomes
enriched in oxygen, and therefore less dense than the rest of the outer
core. This process creates convection currents in the outer core, which
are thought to be the prime driver for the currents that create the
Earth's magnetic field.
The existence of the inner core also affects the dynamic motions
of liquid in the outer core, and thus may help fix the magnetic field.
Dynamics
Because the inner core is not rigidly connected to the Earth's solid mantle, the possibility that it rotates slightly more quickly or slowly than the rest of Earth has long been considered. In the 1990s, seismologists made various claims about detecting this kind of super-rotation
by observing changes in the characteristics of seismic waves passing
through the inner core over several decades, using the aforementioned
property that it transmits waves more quickly in some directions. In
1996, X. Song and P. Richards estimated this "super-rotation" of the
inner core relative to the mantle as about one degree per year.
In 2005, they and J. Zhang compared recordings of "seismic doublets"
(recordings by the same station of earthquakes occurring in the same
location on the opposite side of the Earth, years apart), and revised
that estimate to 0.3 to 0.5 degree per year. In 2023, it was reported that the core stopped spinning faster than the planet's
surface around 2009 and likely is now rotating slower than it. This is
not thought to have major effects and one cycle of the oscillation is
thought to be about seven decades, coinciding with several other
geophysical periodicities, "especially the length of day and magnetic
field".
In 1999, M. Greff-Lefftz and H. Legros noted that the gravitational fields of the Sun and Moon that are responsible for ocean tides also apply torques to the Earth, affecting its axis of rotation and a slowing down of its rotation rate.
Those torques are felt mainly by the crust and mantle, so that their
rotation axis and speed may differ from overall rotation of the fluid in
the outer core and the rotation of the inner core. The dynamics is
complicated because of the currents and magnetic fields in the inner
core. They find that the axis of the inner core wobbles (nutates)
slightly with a period of about 1 day. With some assumptions on the
evolution of the Earth, they conclude that the fluid motions in the
outer core would have entered resonance
with the tidal forces at several times in the past (3.0, 1.8, and
0.3 billion years ago). During those epochs, which lasted
200–300 million years each, the extra heat generated by stronger fluid
motions might have stopped the growth of the inner core.
Age
Theories about the age of the core are part of theories of the history of Earth.
It is widely believed that the Earth's solid inner core formed out of
an initially completely liquid core as the Earth cooled. However, the
time when this process started is unknown.
Age estimates in billion years from different studies and methods
T = thermodynamic modeling P = paleomagnetism analysis (R) = with radioactive elements (N) = without them
Date
Authors
Age
Method
2001
Labrosse et al.
1±0.5
T(N)
2003
Labrosse
~2
T(R)
2011
Smirnov et al.
2–3.5
P
2014
Driscoll and Bercovici
0.65
T
2015
Labrosse
< 0.7
T
2015
Biggin et al.
1–1.5
P
2016
Ohta et al.
< 0.7
T
2016
Konôpková et al.
< 4.2
T
2019
Bono et al.
0.5
P
Two main approaches have been used to infer the age of the inner core: thermodynamic modeling of the cooling of the Earth, and analysis of paleomagnetic evidence. The estimates yielded by these methods vary from 0.5 to 2 billion years old.
Thermodynamic evidence
Heat flow of the inner Earth, according to S.T. Dye and R. Arevalo.
One of the ways to estimate the age of the inner core is by modeling
the cooling of the Earth, constrained by a minimum value for the heat flux at the core–mantle boundary (CMB). That estimate is based on the prevailing theory that the Earth's magnetic field is primarily triggered by convection
currents in the liquid part of the core, and the fact that a minimum
heat flux is required to sustain those currents. The heat flux at the
CMB at present time can be reliably estimated because it is related to
the measured heat flux at Earth's surface and to the measured rate of mantle convection.
In 2001, S. Labrosse and others, assuming that there were no radioactive elements
in the core, gave an estimate of 1±0.5 billion years for the age of the
inner core — considerably less than the estimated age of the Earth and
of its liquid core (about 4.5 billion years)
In 2003, the same group concluded that, if the core contained a
reasonable amount of radioactive elements, the inner core's age could be
a few hundred million years older.
In 2012, theoretical computations by M. Pozzo and others indicated that the electrical conductivity
of iron and other hypothetical core materials, at the high pressures
and temperatures expected there, were two or three times higher than
assumed in previous research. These predictions were confirmed in 2013 by measurements by Gomi and others. The higher values for electrical conductivity led to increased estimates of the thermal conductivity, to 90 W/m·K; which, in turn, lowered estimates of its age to less than 700 million years old.
However, in 2016 Konôpková and others directly measured the
thermal conductivity of solid iron at inner core conditions, and
obtained a much lower value, 18–44 W/m·K. With those values, they
obtained an upper bound of 4.2 billion years for the age of the inner
core, compatible with the paleomagnetic evidence.
In 2014, Driscoll and Bercovici published a thermal history of the Earth that avoided the so-called mantle thermal catastrophe and new core paradox by invoking 3 TW of radiogenic heating by the decay of 40 K
in the core. Such high abundances of K in the core are not supported by
experimental partitioning studies, so such a thermal history remains
highly debatable.
Paleomagnetic evidence
Another way to estimate the age of the Earth is to analyze changes in the magnetic field of Earth
during its history, as trapped in rocks that formed at various times
(the "paleomagnetic record"). The presence or absence of the solid inner
core could result in different dynamic processes in the core that could
lead to noticeable changes in the magnetic field.
In 2011, Smirnov and others published an analysis of the paleomagnetism in a large sample of rocks that formed in the Neoarchean (2.8–2.5 billion years ago) and the Proterozoic (2.5–0.541 billion). They found that the geomagnetic field was closer to that of a magnetic dipole
during the Neoarchean than after it. They interpreted that change as
evidence that the dynamo effect was more deeply seated in the core
during that epoch, whereas in the later time currents closer to the
core-mantle boundary grew in importance. They further speculate that the
change may have been due to growth of the solid inner core between
3.5–2.0 billion years ago.
In 2015, Biggin and others published the analysis of an extensive and carefully selected set of Precambrian
samples and observed a prominent increase in the Earth's magnetic field
strength and variance around 1.0–1.5 billion years ago. This change had
not been noticed before due to the lack of sufficient robust
measurements. They speculated that the change could be due to the birth
of Earth's solid inner core. From their age estimate they derived a
rather modest value for the thermal conductivity of the outer core, that
allowed for simpler models of the Earth's thermal evolution.
In 2016, P. Driscoll published a numerical evolving dynamo model that made a detailed prediction of the paleomagnetic field evolution over 0.0–2.0 Ga. The evolving dynamo
model was driven by time-variable boundary conditions produced by the
thermal history solution in Driscoll and Bercovici (2014). The evolving dynamo
model predicted a strong-field dynamo prior to 1.7 Ga that is
multipolar, a strong-field dynamo from 1.0–1.7 Ga that is predominantly
dipolar, a weak-field dynamo from 0.6–1.0 Ga that is a non-axial dipole,
and a strong-field dynamo after inner core nucleation from 0.0–0.6 Ga
that is predominantly dipolar.
An analysis of rock samples from the Ediacaran
epoch (formed about 565 million years ago), published by Bono and
others in 2019, revealed unusually low intensity and two distinct
directions for the geomagnetic field during that time that provides
support for the predictions by Driscoll (2016). Considering other
evidence of high frequency of magnetic field reversals
around that time, they speculate that those anomalies could be due to
the onset of formation of the inner core, which would then be 0.5
billion years old. A News and Views by P. Driscoll summarizes the state of the field following the Bono results. New paleomagnetic data from the Cambrian appear to support this hypothesis.
The GEBCO Gazetteer of Undersea Feature Names indicates that the feature is situated at 11°22.4′N142°35.5′E and has an approximated maximum depth of 10,920 ± 10 m (35,827 ± 33 ft) below sea level. A subsequent study revised the value to 10,935 ± 6 m (35,876 ± 20 ft) at a 95% confidence interval.
However, both the precise geographic location and depth remain
ambiguous, with contemporary measurements ranging from 10,903 to
11,009 m (35,771 to 36,119 ft).
Sonar mapping of the Challenger Deep by the DSSV Pressure Drop employing a Kongsberg SIMRAD EM124 multibeam echosounder system (26 April – 4 May 2019)
The Challenger Deep is a relatively small slot-shaped depression in the bottom of a considerably larger crescent-shaped oceanic trench, which itself is an unusually deep feature in the ocean floor. The Challenger Deep consists of three basins, each 6 to 10 km (3.7 to 6.2 mi)
long, 2 km (1.2 mi) wide, and over 10,850 m (35,597 ft) in depth,
oriented in echelon from west to east, separated by mounds between the
basins 200 to 300 m (660 to 980 ft) higher. The three basins feature
extends about 48 km (30 mi) west to east if measured at the 10,650 m
(34,941 ft) isobath.
Both the western and eastern basins have recorded depths (by sonar
bathymetry) in excess of 10,920 m (35,827 ft), while the center basin is
slightly less deep. The closest land to the Challenger Deep is Fais Island (one of the outer islands of Yap), 287 km (178 mi) southwest, and Guam, 304 km (189 mi) to the northeast.
Detailed sonar mapping of the western, center and eastern basins in June 2020 by the DSSV Pressure Drop combined with manned descents revealed that they undulate with slopes and piles of rocks above a bed of pelagic ooze.
This conforms with the description of Challenger Deep as consisting of
an elongated seabed section with distinct sub-basins or sediment-filled
pools.
Surveys and bathymetry
Over many years, the search for, and investigation of, the location
of the maximum depth of the world's oceans has involved many different
vessels, and continues into the twenty-first century.
The accuracy of determining geographical location, and the
beamwidth of (multibeam) echosounder systems, limits the horizontal and
vertical bathymetric sensor resolution
that hydrographers can obtain from onsite data. This is especially
important when sounding in deep water, as the resulting footprint of an
acoustic pulse gets large once it reaches a distant sea floor. Further,
sonar operation is affected by variations in sound speed, particularly in the vertical plane. The speed is determined by the water's bulk modulus, mass, and density. The bulk modulus is affected by temperature, pressure, and dissolved impurities (usually salinity).
1875 – HMS Challenger
In 1875, during her transit from the Admiralty Islands in the Bismarck Archipelago to Yokohama in Japan, the three-masted sailing corvette HMS Challengerattempted to make landfall at Spanish Marianas (now Guam), but was set to the west by "baffling winds" preventing her crew from "visiting either the Carolines or the Ladrones." Their altered path took them over the undersea canyon which later became known as the Challenger Deep. Depth soundings were taken by Baillie-weighted marked rope, and geographical locations were determined by celestial navigation
(to an estimated accuracy of two nautical miles). One of their samples
was taken within fifteen miles of the deepest spot in all of Earth's
oceans. On 23 March 1875, at sample station number #225, HMS Challenger recorded the bottom at 4,475 fathoms (26,850 ft; 8,184 m) deep, (the deepest sounding of her three-plus-year eastward circumnavigation of the Earth) at 11°24′N143°16′E – and confirmed it with a second sounding at the same location. The serendipitous discovery of Earth's deepest depression by history's first major scientific expedition devoted entirely to the emerging science of oceanography, was incredibly good fortune, and especially notable when compared to the Earth's third deepest site (the Sirena Deep only 150 nautical miles east of the Challenger Deep), which would remain undiscovered for another 122 years.
Seventy-five years later, the 1,140-ton British survey vessel HMS Challenger II, on her three-year westward circumnavigation of Earth, investigated the extreme depths southwest of Guam reported in 1875 by her predecessor, HMS Challenger. On her southbound track from Japan to New Zealand (May–July 1951), Challenger II conducted a survey of the Marianas Trench between Guam and Ulithi atoll, using seismic-sized bomb-soundings and recorded a maximum depth of 5,663 fathoms (33,978 ft; 10,356 m). The depth was beyond Challenger II'secho sounder
capability to verify, so they resorted to using a taut wire with
"140 lbs of scrap iron", and documented a depth of 5,899 fathoms
(35,394 ft; 10,788 m). The Senior Scientist aboard Challenger II, Thomas Gaskell, recalled:
[I]t
took from ten past five in the evening until twenty to seven, that is
an hour and a half, for the iron weight to fall to the sea-bottom. It
was almost dark by the time the weight struck, but great excitement
greeted the reading.
In New Zealand, the Challenger II
team gained the assistance of the Royal New Zealand Dockyard, "who
managed to boost the echo sounder to record at the greatest depths". They returned to the "Marianas Deep" (sic)
in October 1951. Using their newly improved echo sounder, they ran
survey lines at right angles to the axis of the trench and discovered "a
considerable area of a depth greater than 5,900 fathoms (35,400 ft;
10,790 m)" – later identified as the Challenger Deep's western basin. The greatest depth recorded was 5,940 fathoms (35,640 ft; 10,863 m), at 11°19′N142°15′E. Navigational accuracy of several hundred meters was attained by celestial navigation and LORAN-A. As Gaskell explained, the measurement
was not more than 50 miles from the spot where the nineteenth-century Challenger found her deepest depth [...] and it may be thought fitting that a ship with the name Challenger should put the seal on the work of that great pioneering expedition of oceanography.
The term "Challenger Deep" came into use after this 1951–52 Challenger
circumnavigation, and commemorates both British ships of that name
involved with the discovery of the deepest basin of the world's oceans.
Research vessel Vityaz in Kaliningrad "Museum of world ocean"
1957–1958 – RV Vityaz
In August 1957, the Soviet 3,248-ton Vernadsky Institute of Geochemistry research vessel Vityaz recorded a maximum depth of 11,034 ± 50 m (36,201 ± 164 ft) at 11°20.9′N142°11.5′E
in the western basin of the Challenger Deep during a brief transit of
the area on Cruise #25. She returned in 1958, Cruise #27, to conduct a
detailed single beam bathymetry survey involving over a dozen transects
of the Deep, with an extensive examination of the western basin and a
quick peek into the eastern basin. Fisher records a total of three Vityaz sounding locations on Fig.2 "Trenches" (1963), one within yards of the 142°11.5' E location, and a third at 11°20.0′N142°07′E, all with 11,034 ± 50 m (36,201 ± 164 ft) depth. The depths were considered statistical outliers, and a depth greater than 11,000 m has never been proven. Taira reports that if Vityaz's depth was corrected with the same methodology used by the Japanese RV Hakuho Maru expedition of December 1992, it would be presented as 10,983 ± 50 m (36,033 ± 164 ft),
as opposed to modern depths from multibeam echosounder systems greater
than 10,900 metres (35,800 ft) with the NOAA accepted maximum of
10,995 ± 10 m (36,073 ± 33 ft) in the western basin.
1959 – RV Stranger
The
first definitive verification of both the depth and location of the
Challenger Deep (western basin) was determined by Dr. R. L. Fisher from
the Scripps Institution of Oceanography, aboard the 325-ton research vessel Stranger. Using explosive soundings, they recorded 10,850 ± 20 m (35,597 ± 66 ft) at/near 11°18′N142°14′E in July 1959. Stranger used celestial and LORAN-C for navigation.LORAN-C navigation provided geographical accuracy of 460 m (1,509 ft) or better. According to another source RV Stranger using bomb-sounding surveyed a maximum depth of 10,915 ± 10 m (35,810 ± 33 ft) at 11°20.0′N142°11.8′E. Discrepancies between the geographical location (lat/long) of Stranger's deepest depths and those from earlier expeditions (Challenger II 1951; Vityaz 1957 and 1958) "are probably due to uncertainties in fixing the ships' positions". Stranger's
north-south zig-zag survey passed well to the east of the eastern basin
southbound, and well to the west of the eastern basin northbound, thus
failed to discover the eastern basin of the Challenger Deep.
The maximum depth measured near longitude 142°30'E was 10,760 ± 20 m
(35,302 ± 66 ft), about 10 km west of the eastern basin's deepest point.
This was an important gap in information, as the eastern basin was
later reported as deeper than the other two basins.
Stranger crossed the center basin twice, measuring a maximum
depth of 10,830 ± 20 m (35,531 ± 66 ft) in the vicinity of 142°22'E. At
the western end of the central basin (approximately 142°18'E), they
recorded a depth of 10,805 ± 20 m (35,449 ± 66 ft).
The western basin received four transects by Stranger, recording depths of 10,830 ± 20 m (35,531 ± 66 ft) toward the central basin, near where Trieste dived in 1960 (vicinity 11°18.5′N142°15.5′E, and where Challenger II, in 1950, recorded 10,863 ± 35 m (35,640 ± 115 ft). At the far western end of the western basin (about 142°11'E), the Stranger recorded 10,850 ± 20 m (35,597 ± 66 ft), some 6 km south of the location where Vityaz recorded 11,034 ± 50 m (36,201 ± 164 ft) in 1957–1958. Fisher stated: "differences in the Vitiaz [sic] and Stranger–Challenger II depths can be attributed to the [sound] velocity correction function used".
After investigating the Challenger Deep, Stranger proceeded to the Philippine Trench
and transected the trench over twenty times in August 1959, finding a
maximum depth of 10,030 ± 10 m (32,907 ± 33 ft), and thus established
that the Challenger Deep was about 800 metres (2,600 ft) deeper than the
Philippine Trench. The 1959 Stranger surveys of the Challenger Deep and of the Philippine Trench informed the U.S. Navy as to the appropriate site for Trieste's record dive in 1960.
1962 – RV Spencer F. Baird
The Proa Expedition, Leg 2, returned Fisher to the Challenger Deep on 12–13 April 1962 aboard the Scripps research vessel Spencer F. Baird (formerly the steel-hulled US Army large tug LT-581)
and employed a Precision Depth Recorder (PDR) to verify the extreme
depths previously reported. They recorded a maximum depth of 10,915
metres (35,810 ft) (location not available).
Additionally, at location "H-4" in the Challenger Deep, the expedition
cast three taut-wire soundings: on 12 April, the first cast was to 5,078
fathoms (corrected for wire angle) 9,287 metres (30,469 ft) at 11°23′N142°19.5′E
in the central basin (Up until 1965, US research vessels recorded
soundings in fathoms). The second cast, also on 12 April, was to 5,000+ fathoms at 11°20.5′N142°22.5′E
in the central basin. On 13 April, the final cast recorded 5,297
fathoms (corrected for wire angle) 9,687 metres (31,781 ft) at 11°17.5′N142°11′E (the western basin).
They were chased off by a hurricane after only two days on-site. Once
again, Fisher entirely missed the eastern basin of the Challenger Deep,
which later proved to contain the deepest depths.
1975–1980 – RV Thomas Washington
The Scripps Institution of Oceanography deployed the 1,490-ton Navy-owned, civilian-crewed research vessel Thomas Washington (AGOR-10) to the Mariana Trench on several expeditions from 1975 to 1986. The first of these was the Eurydice Expedition, Leg 8 which brought Fisher back to the Challenger Deep's western basin from 28–31 March 1975. Thomas Washington established geodetic positioning by (SATNAV) with Autolog Gyro and EM Log. Bathymetrics
were by a 12 kHz Precision Depth Recorder (PDR) with a single 60° beam.
They mapped one, "possibly two", axial basins with a depth of
10,915 ± 20 m (35,810 ± 66 ft).
Five dredges were hauled 27–31 March, all into or slightly north of the
deepest depths of the western basin. Fisher noted that this survey of
the Challenger Deep (western basin) had "provided nothing to support and
much to refute recent claims of depths there greater than 10,915 ± 20 m
(35,810 ± 66 ft)."
While Fisher missed the eastern basin of the Challenger Deep (for the
third time), he did report a deep depression about 150 nautical miles
east of the western basin. The 25 March dredge haul at 12°03.72′N142°33.42′E encountered 10,015 metres (32,858 ft), which pre-shadowed by 22 years the discovery of HMRG Deep/Sirena Deep in 1997. The deepest waters of the HMRG Deep/Sirena Deep at 10,714 ± 20 m (35,151 ± 66 ft) are centered at/near 12°03.94′N142°34.866′E, approximately 2.65 km from Fisher's 25 March 1975 10,015 metres (32,858 ft) dredge haul.
On Scripps Institution of Oceanography's INDOPAC Expedition Leg 3, the chief scientist, Dr. Joseph L. Reid, and oceanographer Arnold W. Mantyla made a hydrocast of a free vehicle (a special-purpose benthic lander
(or "baited camera") for measurements of water temperature and
salinity) on 27 May 1976 into the western basin of the Challenger Deep,
"Station 21", at 11°19.9′N142°10.8′E at about 10,840 metres (35,560 ft) depth. On INDOPAC Expedition Leg 9, under chief scientist A. Aristides Yayanos, Thomas Washington
spent nine days from 13–21 January 1977 conducting an extensive and
detailed investigation of the Challenger Deep, mainly with biological
objectives.
"Echo soundings were carried out primarily with a 3.5 kHz single-beam
system, with a 12 kHz echosounder operated in addition some of the time"
(the 12 kHz system was activated for testing on 16 January). A benthic lander was put into the western basin (11°19.7′N142°09.3′E)
on 13 January, bottoming at 10,663 metres (34,984 ft) and recovered 50
hours later in damaged condition. Quickly repaired, it was again put
down on the 15th to 10,559 metres (34,642 ft) depth at 11°23.3′N142°13.8′E. It was recovered on the 17th with excellent photography of amphipods (shrimp) from the Challenger Deep's western basin. The benthic lander was put down for the third and last time on the 17th, at 11°20.1′N142°25.2′E,
in the central basin at a depth of 10,285 metres (33,743 ft). The
benthic lander was not recovered and may remain on the bottom in the
vicinity of 11°20.1′N142°25.2′E.
Free traps and pressure-retaining traps were put down at eight
locations from 13 to 19 January into the western basin, at depths
ranging from 7,353 to 10,715 metres (24,124–35,154 ft). Both the free
traps and the pressure-retaining traps brought up good sample amphipods
for study. While the ship briefly visited the area of the eastern basin,
the expedition did not recognize it as potentially the deepest of the
three Challenger Deep basins.
Thomas Washington returned briefly to the Challenger Deep on 17–19 October 1978 during Mariana Expedition Leg 5 under chief scientist James W. Hawkins.
The ship tracked to the south and west of the eastern basin, and
recorded depths between 5,093 and 7,182 metres (16,709–23,563 ft).
Another miss. On Mariana Expedition Leg 8, under chief scientist Yayanos, Thomas Washington
was again involved, from 12–21 December 1978, with an intensive
biological study of the western and central basins of the Challenger
Deep.
Fourteen traps and pressure-retaining traps were put down to depths
ranging from 10,455 to 10,927 metres (34,301–35,850 ft); the greatest
depth was at 11°20.0′N142°11.8′E.
All of the 10,900-plus m recordings were in the western basin. The
10,455 metres (34,301 ft) depth was furthest east at 142°26.4' E (in the
central basin), about 17 km west of the eastern basin. Again, focused
efforts on the known areas of extreme depths (the western and central
basins) were so tight that the eastern basin again was missed by this
expedition.
From 20 to 30 November 1980, Thomas Washington was on site at the western basin of the Challenger Deep, as part of Rama Expedition Leg 7, again with chief-scientist Dr. A. A. Yayanos. Yayanos directed Thomas Washington
in arguably the most extensive and wide-ranging of all single-beam
bathymetric examinations of the Challenger Deep ever undertaken, with
dozens of transits of the western basin, and ranging far into the backarc
of the Challenger Deep (northward), with significant excursions into
the Pacific Plate (southward) and along the trench axis to the east.
They hauled eight dredges in the western basin to depths ranging from
10,015 to 10,900 metres (32,858–35,761 ft), and between hauls, cast
thirteen free vertical traps. The dredging and traps were for biological
investigation of the bottom. In the first successful retrieval of a
live animal from the Challenger Deep, on 21 November 1980 in the western
basin at 11°18.7′N142°11.6′E, Yayanos recovered a live amphipod from about 10,900 meters depth with a pressurized trap.
Once again, other than a brief look into the eastern basin, all
bathymetric and biological investigations were into the western basin.
1976–1977 – RV Kana Keoki
Pacific plate subduction at the Challenger Deep
On Leg 3 of the Hawaii Institute of Geophysics' (HIG) expedition 76010303, the 156-foot (48 m) research vessel Kana Keoki departed Guam primarily for a seismic investigation of the Challenger Deep area, under chief scientist Donald M. Hussong. The ship was equipped with air guns (for seismic reflection soundings deep into the Earth's mantle), magnetometer, gravimeter,
3.5 kHz and 12 kHz sonar transducers, and precision depth recorders.
They ran the Deep from east to west, collecting single beam bathymetry,
magnetic and gravity measurements, and employed the air guns along the
trench axis, and well into the backarc and forearc, from 13 to 15 March 1976. Thence they proceeded south to the Ontong Java Plateau. All three deep basins of the Challenger Deep were covered, but Kana Keoki recorded a maximum depth of 7,800 m (25,591 ft). Seismic information developed from this survey was instrumental in gaining an understanding of the subduction of the Pacific Plate under the Philippine Sea Plate. In 1977, Kana Keoki returned to the Challenger Deep area for wider coverage of the forearc and backarc.
1984 – SV Takuyo
The Hydrographic Department, Maritime Safety Agency, Japan (JHOD) deployed the newly commissioned 2,600-ton survey vessel Takuyo (HL 02) to the Challenger Deep 17–19 February 1984. Takuyo was the first Japanese ship to be equipped with the new narrowbeam SeaBeammulti-beam sonar echosounder, and was the first survey ship
with multi-beam capability to survey the Challenger Deep. The system
was so new that JHOD had to develop their own software for drawing
bathymetric charts based on the SeaBeam digital data. In just three days, they tracked 500 miles of sounding lines, and covered about 140 km2 of the Challenger Deep with multibeam ensonification. Under chief scientist Hideo Nishida, they used CTD temperature and salinity data from the top 4,500 metres (14,764 ft) of the water column to correct depth measurements, and later conferred with Scripps Institution of Oceanography (including Fisher), and other GEBCO experts to confirm their depth correction methodology. They employed a combination of NAVSAT, LORAN-C and OMEGA
systems for geodetic positioning with accuracy better than 400 metres
(1,300 ft). The deepest location recorded was 10,920 ± 10 m
(35,827 ± 33 ft) at 11°22.4′N142°35.5′E; for the first time documenting the eastern basin as the deepest of the three en echelon pools. In 1993, GEBCO recognized the 10,920 ± 10 m (35,827 ± 33 ft) report as the deepest depth of the world's oceans. Technological advances such as improved multi-beam sonar would be the driving force in uncovering the mysteries of the Challenger Deep into the future.
1986 – RV Thomas Washington
The Scripps research vessel Thomas Washington's returned to the Challenger Deep in 1986 during the Papatua Expedition, Leg 8,
mounting one of the first commercial multi-beam echosounders capable of
reaching into the deepest trenches, i.e. the 16-beam Seabeam "Classic".
This allowed chief scientist Yayanos an opportunity to transit the
Challenger Deep with the most modern depth-sounding equipment available.
During the pre-midnight hours of 21 April 1986, the multibeam
echosounder produced a map of the Challenger Deep bottom with a swath
of about 5–7 miles wide. The maximum depth recorded was 10,804 metres
(35,446 ft) (location of depth is not available). Yayanos noted: "The
lasting impression from this cruise comes from the thoughts of the
revolutionary things that Seabeam data can do for deep biology."
1988 – RV Moana Wave
On 22 August 1988, the U.S. Navy-owned 1,000-ton research vessel Moana Wave (AGOR-22), operated by the Hawaii Institute of Geophysics (HIG), University of Hawaii, under the direction of chief scientist Robert C. Thunell from the University of South Carolina,
transited northwesterly across the central basin of the Challenger
Deep, conducting a single-beam bathymetry track by their 3.5 kHz narrow
(30-degs) beam echosounder with a Precision Depth Recorder. In addition
to sonar bathymetry, they took 44 gravity cores and 21 box cores
of bottom sediments. The deepest echosoundings recorded were 10,656 to
10,916 metres (34,961–35,814 ft), with the greatest depth at 11°22′N
142°25′E in the central basin. This was the first indication that all three basins contained depths in excess of 10,900 metres (35,800 ft).
The RV Hakuhō Maru
1992 – RV Hakuhō Maru
The 3,987-ton Japanese research vessel Hakuhō Maru, an Ocean Research Institute – University of Tokyo sponsored ship, on cruise KH-92-5 cast three Sea-Bird SBE-9 ultra-deep CTD
(conductivity-temperature-depth) profilers in a transverse line across
the Challenger Deep on 1 December 1992. The center CTD was located at 11°22.78′N142°34.95′E,
in the eastern basin, at 10,989 metres (36,053 ft) by the SeaBeam depth
recorder and 10,884 metres (35,709 ft) by the CTD. The other two CTDs
were cast 19.9 km to the north and 16.1 km to the south. Hakuhō Maru
was equipped with a narrow beam SeaBeam 500 multi-beam echosounder for
depth determination, and had an Auto-Nav system with inputs from NAVSAT/NNSS, GPS, Doppler Log, EM log and track display, with a geodetic positioning accuracy approaching 100 metres (330 ft). When conducting CTD operations in the Challenger deep, they used the SeaBeam as a single beam depth recorder. At 11°22.6′N142°35.0′E the corrected depth was 10,989 metres (36,053 ft), and at 11°22.0′N142°34.0′E the depth was 10,927 metres (35,850 ft); both in the eastern basin. This may demonstrate that the basins might not be flat sedimentary pools but rather undulate with a difference of 50 metres (160 ft) or more. Taira revealed, "We considered that a trough deeper that Vitiaz's
record by 5 metres (16 ft) was detected. There is a possibility that a
depth exceeding 11,000 metres (36,089 ft) with a horizontal scale less
than the beam width of measurements exists in the Challenger Deep.
Since each SeaBeam 2.7-degree beam width sonar ping expands to cover a
circular area about 500 metres (1,640 ft) in diameter at 11,000 metres
(36,089 ft) depth, dips in the bottom that are less than that size would
be difficult to detect from a sonar-emitting platform seven miles
above.
RV Yokosuka was used as the support ship for ROV Kaikō.
1996 – RV Yokosuka
For most of 1995 and into 1996, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) employed the 4,439-ton Research Vessel Yokosuka to conduct the testing and workup of the 11,000-meter remotely-operated vehicle (ROV) Kaikō, and the 6,500 meter ROV Shinkai. It was not until February 1996, during Yokosuka's cruise Y96-06, that Kaikō
was ready for its first full depth dives. On this cruise, JAMSTEC
established an area of the Challenger Deep (11°10'N to 11°30'N, by
141°50'E to 143°00'E – which later was recognized as containing three
separate pools/basins en echelon, each with depths in excess of 10,900 m
(35,761 ft)) toward which JAMSTEC expeditions would concentrate their
investigations for the next two decades.
The Yokosuka employed a 151-beam SeaBeam 2112 12 kHz multibeam
echosounder, allowing search swaths 12–15 km in width at 11,000 metres
(36,089 ft) depth. The depth accuracy of Yokosuka's
Seabeam was about 0.1% of water depth (i.e. ± 110 metres (361 ft) for
11,000 metres (36,089 ft) depth). The ship's dual GPS systems attained
geodetic positioning within double digit meter (100 metres (328 ft) or
better) accuracy.
1998, 1999 and 2002 – RV Kairei
Cruise KR98-01 sent JAMSTEC's two-year-old 4,517-ton Deep Sea Research Vessel RV Kairei
south for a quick but thorough depth survey of the Challenger Deep,
11–13 January 1998, under chief scientist Kantaro Fujioka. Tracking
largely along the trench axis of 070–250° they made five 80-km
bathymetric survey tracks, spaced about 15 km apart, overlapping their
SeaBeam 2112-004 (which now allowed sub-bottom profiling penetrating as
much as 75 m below the bottom) while gaining gravity and magnetic data
covering the entire Challenger Deep: western, central, and eastern
basins.
The Deep Sea Research Vessel RV Kairei was also used as the support ship for the ROV Kaikō.
Kairei returned in May 1998, cruise KR98-05, with ROV Kaikō,
under the direction of chief scientist Jun Hashimoto with both
geophysical and biological goals. Their bathymetric survey from 14–26
May was the most intensive and thorough depth and seismic survey of the
Challenger Deep performed to date. Each evening, Kaikō deployed
for about four hours of bottom time for biological-related sampling,
plus about seven hours of vertical transit time. When Kaikō was onboard for servicing, Kairei conducted bathymetric surveys and observations. Kairei gridded a survey area about 130 km N–S by 110 km E–W. Kaikō
made six dives (#71–75) all to the same location, (11°20.8' N,
142°12.35' E), near the 10,900 metres (35,800 ft) bottom contour line in
the western basin.
The regional bathymetric map made from the data obtained in 1998
shows that the greatest depths in the eastern, central, and western
depressions are 10,922 ± 74 m (35,833 ± 243 ft), 10,898 ± 62 m
(35,755 ± 203 ft), and 10,908 ± 36 m (35,787 ± 118 ft), respectively,
making the eastern depression the deepest of the three.
In 1999, Kairei revisited the Challenger Deep during
cruise KR99-06. The results of the 1998–1999 surveys include the first
recognition that the Challenger Deep consists of three "right-stepping
en echelon individual basins bounded by the 10,500 metres (34,400 ft)
depth contour line. The size of [each of] the deeps are almost
identical, 14–20 km long, 4 km wide". They concluded with the proposal
"that these three individual elongated deeps constitute the 'Challenger
Deep', and [we] identify them as the East, Central and West Deep. The
deepest depth we obtained during the swath mapping is 10,938 metres
(35,886 ft) in the West Deep (11°20.34' N, 142°13.20 E)."
The depth was "obtained during swath mapping ... confirmed in both N–S
and E-W swaths." Speed of sound corrections were from XBT to 1,800
metres (5,900 ft), and CTD below 1,800 metres (5,900 ft).
The cross track survey of the 1999 Kairei cruise shows
that the greatest depths in the eastern, central, and western
depressions are 10,920 ± 10 m (35,827 ± 33 ft), 10,894 ± 14 m
(35,741 ± 46 ft), and 10,907 ± 13 m (35,784 ± 43 ft), respectively,
which supports the results of the previous survey.
In 2002 Kairei revisited the Challenger Deep 16–25 October
2002, as cruise KR02-13 (a cooperative Japan-US-South Korea research
program) with chief scientist Jun Hashimoto in charge; again with
Kazuyoshi Hirata managing the ROV Kaikō team. On this survey, the
size of each of the three basins was refined to 6–10 km long by about
2 km wide and in excess of 10,850 m (35,597 ft) deep. In marked contrast
to the Kairei surveys of 1998 and 1999, the detailed survey in
2002 determined that the deepest point in the Challenger Deep is located
in the eastern basin around 11°22.260′N142°35.589′E,
with a depth of 10,920 ± 5 m (35,827 ± 16 ft), located about 290 m
(950 ft) southeast of the deepest site determined by the survey vessel Takuyo
in 1984. The 2002 surveys of both the western and eastern basins were
tight, with especially meticulous cross-gridding of the eastern basin
with ten parallel tracks N–S and E–W less than 250 meters apart. On the
morning of 17 October, ROV Kaikō dive #272 began and recovered
over 33 hours later, with the ROV working at the bottom of the western
basin for 26 hours (vicinity of 11°20.148' N, 142°11.774 E at 10,893 m
(35,738 ft)). Five Kaikō dives followed on a daily basis into the
same area to service benthic landers and other scientific equipment,
with dive #277 recovered on 25 October. Traps brought up large numbers
of amphipods (sea fleas), and cameras recorded holothurians (sea cucumbers), White polychaetes (bristle worms), tube worms, and other biological species. During its 1998, 1999 surveys, Kairei was equipped with a GPS satellite-based radionavigation system. The United States government lifted the GPS selective availability in 2000, so during its 2002 survey, Kairei had access to non-degraded GPS positional services and achieved single-digit meter accuracy in geodetic positioning.
2001 – RV Melville
The RV Melville was operated by the Scripps Institution of Oceanography.
The 2.516-ton research vessel Melville,
at the time operated by the Scripps Institution of Oceanography, took
the Cook Expedition, Leg 6 with chief scientist Patricia Fryer of the
University of Hawaii from Guam on 10 February 2001 to the Challenger
Deep for a survey titled "Subduction Factory Studies in the Southern
Mariana", including HMR-1 sonar mapping, magnetics, gravity
measurements, and dredging in the Mariana arc region.They covered all three basins, then tracked 120-nautical-mile-long
(222.2 km) lines of bathymetry East-West, stepping northward from the
Challenger Deep in 12 km (7.5 mi) sidesteps, covering more than 90 nmi
(166.7 km) north into the backarc with overlapping swaths from their
SeaBeam 2000 12 kHz multi-beam echosounder and MR1 towed system. They
also gathered magnetic and gravity information, but no seismic data. Their primary survey instrument was the MR1 towed sonar, a shallow-towed 11/12 kHz bathymetric sidescan sonar
developed and operated by the Hawaii Mapping Research Group (HMRG), a
research and operational group within University of Hawaii's School of
Ocean and Earth Science and Technology (SOEST) and the Hawaii Institute
of Geophysics and Planetology (HIGP). The MR1 is full-ocean-depth
capable, providing both bathymetry and sidescan data.
Leg 7 of the Cook Expedition continued the MR-1 survey of the
Mariana Trench backarc from 4 March to 12 April 2001 under chief
scientist Sherman Bloomer of Oregon State University.
2009 – RV Kilo Moana
The RV Kilo Moana was used as the support ship of the HROV Nereus.
In May/June 2009, the US Navy-owned 3,064-ton twin-hulled research vessel Kilo Moana (T-AGOR 26) was sent to the Challenger Deep area to conduct research. Kilo Moana
is civilian-crewed and operated by SOEST. It is equipped with two
multibeam echosounders with sub-bottom profiler add-ons (the 191-beam
12 kHz Kongsberg Simrad EM120 with SBP-1200, capable of accuracies of 0.2–0.5% of water depth across the entire swath), gravimeter, and magnetometer.
The EM-120 uses 1 by 1 degree sonar-emissions at the sea surface. Each 1
degree beam width sonar ping expands to cover a circular area about 192
metres (630 ft) in diameter at 11,000 metres (36,089 ft) depth. Whilst
mapping the Challenger Deep the sonar equipment indicated a maximum
depth of 10,971 m (35,994 ft) at an undisclosed position. Navigation equipment includes the Applanix POS MV320 V4, rated at accuracies of 0.5–2 m. RV Kilo Moana was also used as the support ship of the hybrid remotely operated underwater vehicle (HROV) Nereus
that dived three times to the Challenger Deep bottom during the
May/June 2009 cruise and did not confirm the sonar established maximum
depth by its support ship.
2009 – RV Yokosuka
Cruise YK09-08 brought the JAMSTEC 4,429-ton research vessel Yokosuka back to the Mariana Trough and to the Challenger Deep June–July 2009. Their mission was a two-part program: surveying three hydrothermal vent
sites in the southern Mariana Trough backarc basin near 12°57'N,
143°37'E about 130 nmi northeast of the central basin of the Challenger
Deep, using the autonomous underwater vehicle Urashima. AUV Urashima
dives #90–94, were to a maximum depth of 3500 meters, and were
successful in surveying all three sites with a Reson SEABAT7125AUV
multibeam echosounder for bathymetry, and multiple water testers to
detect and map trace elements spewed into the water from hydrothermal
vents, white smokers, and hot spots. Kyoko OKINO from the Ocean Research
Institute, University of Tokyo, was principal investigator for this aspect of the cruise.
The second goal of the cruise was to deploy a new "10K free fall camera system" called Ashura,
to sample sediments and biologics at the bottom of the Challenger Deep.
The principal investigator at the Challenger Deep was Taishi Tsubouchi
of JAMSTEC. The lander Ashura made two descents: on the first, 6 July 2009, Ashura bottomed at 11°22.3130′N142°25.9412′E at 10,867 metres (35,653 ft). The second descent (on 10 July 2009) was to 11°22.1136′N142°25.8547′E at 10,897 metres (35,751 ft). The 270 kg Ashura
was equipped with multiple baited traps, a HTDV video camera, and
devices to recover sediment, water, and biological samples (mostly
amphipods at the bait, and bacteria and fungus from the sediment and
water samples).
2010 – USNS Sumner
On 7 October 2010, further sonar mapping of the Challenger Deep area was conducted by the US Center for Coastal & Ocean Mapping/Joint Hydrographic Center (CCOM/JHC) aboard the 4.762-ton Sumner. The results were reported in December 2011 at the annual American Geophysical Union
fall meeting. Using a Kongsberg Maritime EM 122 multi-beam echosounder
system coupled to positioning equipment that can determine latitude and
longitude up to 50 cm (20 in) accuracy, from thousands of individual
soundings around the deepest part the CCOM/JHC team preliminary
determined that the Challenger Deep has a maximum depth of 10,994 m
(36,070 ft) at 11.326344°N 142.187248°E, with an estimated vertical uncertainty of ±40 m (131 ft) at two standard deviations (i.e. ≈ 95.4%) confidence level. A secondary deep with a depth of 10,951 m (35,928 ft) was located at approximately 23.75 nmi (44.0 km) to the east at 11.369639°N 142.588582°E in the eastern basin of the Challenger Deep.
2010 – RV Yokosuka
JAMSTEC returned Yokosuka
to the Challenger Deep with cruise YK10-16, 21–28 November 2010. The
chief scientist of this joint Japanese-Danish expedition was Hiroshi
Kitazato of the Institute of Biogeosciences, JAMSTEC. The cruise was
titled "Biogeosciences at the Challenger Deep: relict organisms and
their relations to biogeochemical cycles". The Japanese teams made five
deployments of their 11,000-meter camera system (three to 6,000 meters –
two into the central basin of the Challenger Deep) which returned with
15 sediment cores, video records and 140 scavenging amphipod specimens.
The Danish Ultra Deep Lander System was employed by Ronnie Glud et al on
four casts, two into the central basin of the Challenger Deep and two
to 6,000 m some 34 nmi west of the central basin. The deepest depth
recorded was on 28 November 2010 – camera cast CS5 – 11°21.9810′N142°25.8680′E}, at a corrected depth of 10,889.6 metres (35,727 ft) (the central basin).
2013 – RV Yokosuka
With JAMSTEC Cruises YK13-09 and YK13-12, Yokosuka
hosted chief scientist Hidetaka Nomaki for a trip to New Zealand waters
(YK13-09), with the return cruise identified as YK13-12. The project
name was QUELLE2013; and the cruise title was: "In situ experimental
& sampling study to understand abyssal biodiversity and
biogeochemical cycles". They spent one day on the return trip at the
Challenger Deep to obtain DNA/RNA on the large amphipods inhabiting the
Deep (Hirondellea gigas). Hideki Kobayashi (Biogeos, JAMSTEC) and
the team deployed a benthic lander on 23 November 2013 with eleven
baited traps (three bald, five covered by insulating materials, and
three automatically sealed after nine hours) into the central basin of
the Challenger Deep at 11°21.9082′N142°25.7606′E, depth 10,896 metres (35,748 ft). After an eight-hour, 46-minute stay at the bottom, they recovered some 90 individual Hirondellea gigas.
RV Kairei is used as the support ship for deep-diving ROVs.
2014 – RV Kairei
JAMSTEC deployed Kairei
to the Challenger Deep again 11–17 January 2014, under the leadership
of chief scientist Takuro Nunora. The cruise identifier was KR14-01,
titled: "Trench biosphere
expedition for the Challenger Deep, Mariana Trench". The expedition
sampled at six stations transecting the central basin, with only two
deployments of the "11-K camera system" lander for sediment cores and
water samples to "Station C" at the deepest depth, i.e. 11°22.19429′N142°25.7574′E,
at 10,903 metres (35,771 ft). The other stations were investigated with
the "Multi-core" lander, both to the backarc northward, and to the
Pacific Plate southward. The 11,000-meter capable crawler-driven ROV ABIMSO
was sent to 7,646 m depth about 20 nmi due north of the central basin
(ABISMO dive #21) specifically to identify possible hydrothermal
activity on the north slope of the Challenger Deep, as suggested by
findings from Kairei cruise KR08-05 in 2008. AMISMO's
dives #20 and #22 were to 7,900 meters about 15 nmi north of the
deepest waters of the central basin. Italian researchers under the
leadership of Laura Carugati from the Polytechnic University of Marche, Italy (UNIVPM) were investigating the dynamics in virus/prokaryotes interactions in the Mariana Trench.
2014 – RV Falkor
From 16–19 December 2014, the Schmidt Ocean Institute's 2,024-ton research vessel Falkor,
under chief scientist Douglas Bartlett from the Scripps Institution of
Oceanography, deployed four different untethered instruments into the
Challenger Deep for seven total releases. Four landers were deployed on
16 December into the central basin: the baited video-equipped lander Leggo for biologics; the lander ARI to 11°21.5809′N142°27.2969′E for water chemistry; and the probes Deep Sound 3 and Deep Sound 2. Both Deep Sound probes recorded acoustics floating at 9,000 metres (29,528 ft) depth, until Deep Sound 3 imploded at the depth of 8,620 metres (28,281 ft) (about 2,200 metres (7,218 ft) above the bottom) at 11°21.99′N142°27.2484′E. The Deep Sound 2 recorded the implosion of Deep Sound 3, providing a unique recording of an implosion within the Challenger Deep depression. In addition to the loss of the Deep Sound 3 by implosion, the lander ARI failed to respond upon receiving its instruction to drop weights, and was never recovered. On 16/17 December, Leggo was returned to the central basin baited for amphipods. On the 17th, RV Falkor relocated 17 nms eastward to the eastern basin, where they again deployed both the Leggo (baited and with its full camera load), and the Deep Sound 2. Deep Sound 2
was programmed to drop to 9,000 metres (29,528 ft) and remain at that
depth during its recording of sounds within the trench. On 19 December Leggo landed at 11°22.11216′N142°35.250996′E
at a uncorrected depth of 11,168 metres (36,640 ft) according to its
pressure sensor readings. This reading was corrected to 10,929 metres
(35,856 ft) depth. Leggo returned with good photography of amphipods feeding on the lander's mackerel bait and with sample amphipods. Falknor departed the Challenger Deep on 19 December en route the Marianas Trench Marine National Monument to the Sirena Deep. RV Falkor
had both a Kongsberg EM302 and EM710 multibeam echosounder for
bathymetry, and an Oceaneering C-Nav 3050 global navigation satellite
system receiver, capable of calculating geodetic positioning with an
accuracy better than 5 cm (2.0 in) horizontally and 15 cm (5.9 in)
vertically.
2015 – USCGC Sequoia
US Coast Guard Cutter Sequoia (WLB 215)
From 10 to 13 July 2015, the Guam-based 1,930-ton US Coast Guard Cutter Sequoia (WLB 215) hosted a team of researchers, under chief scientist Robert P. Dziak, from the NOAA Pacific Marine Environmental Laboratory (PMEL), the University of Washington, and Oregon State University, in deploying PMEL's "Full-Ocean Depth Mooring", a 45-meter-long moored deep-ocean hydrophone and pressure sensor array
into the western basin of the Challenger Deep. A 6-hour descent into
the western basin anchored the array at 10,854.7 ± 8.9 m
(35,613 ± 29 ft) of water depth, at 11°20.127′N142°12.0233′E, about 1 km northeast of Sumner's deepest depth, recorded in 2010.
After 16 weeks, the moored array was recovered on 2–4 November 2015.
"Observed sound sources included earthquake signals (T phases), baleen
and odontocete cetacean vocalizations, ship propeller sounds, airguns,
active sonar and the passing of a Category 4 typhoon." The science team
described their results as "the first multiday, broadband record of
ambient sound at Challenger Deep, as well as only the fifth direct depth
measurement".
2016 – RV Xiangyanghong 09
The 3,536-ton research vessel Xiangyanghong 09
deployed on Leg II of the 37th China Cruise Dayang (DY37II) sponsored
by the National Deep Sea Center, Qingdao and the Institute of Deep-Sea
Science and Engineering, Chinese Academy of Sciences
(Sanya, Hainan), to the Challenger Deep western basin area (11°22' N,
142°25' E) 4 June – 12 July 2016. As the mother ship for China's manned
deep submersible Jiaolong,
the expedition carried out an exploration of the Challenger Deep to
investigate the geological, biological, and chemical characteristics of
the hadal zone.
The diving area for this leg was on the southern slope of the
Challenger Deep, at depths from about 6,300 to 8,300 metres (20,669 to
27,231 ft). The submersible completed nine piloted dives on the northern
backarc and south area (Pacific plate) of the Challenger Deep to depths from 5,500 to 6,700 metres (18,045 to 21,982 ft). During the cruise, Jiaolong regularly deployed gas-tight samplers to collect water near the sea bottom. In a test of navigational proficiency, Jiaolong used an Ultra-Short Base Line (USBL) positioning system at a depth more than 6,600 metres (21,654 ft) to retrieve sampling bottles.
2016 – RV Tansuo 01
From 22 June to 12 August 2016 (cruises 2016S1 and 2016S2), the Chinese Academy of Sciences' 6,250-ton submersible support ship Tansuo 1
(meaning: to explore) on her maiden voyage deployed to the Challenger
Deep from her home port of Sanya, Hainan Island. On 12 July 2016, the
ROV Haidou-1 dived to a depth of 10,767 metres (35,325 ft) in the
Challenger Deep area. They also cast a free-drop lander, 9,000 metres
(29,528 ft) rated free-drop ocean-floor seismic instruments (deployed to
7,731 metres (25,364 ft)), obtained sediment core samples, and
collected over 2000 biological samples from depths ranging from 5,000 to
10,000 metres (16,404–32,808 ft). The Tansuo 01 operated along the 142°30.00' longitude line, about 30 nmi east of the earlier DY37II cruise survey (see Xiangyanghong 09 above).
In November 2016 sonar mapping of the Challenger Deep area was conducted by the Royal Netherlands Institute for Sea Research (NIOZ)/GEOMAR Helmholtz Centre for Ocean Research Kiel aboard the 8,554-ton Deep Ocean Research Vessel Sonne.
The results were reported in 2017. Using a Kongsberg Maritime EM 122
multi-beam echosounder system coupled to positioning equipment that can
determine latitude and longitude the team determined that the Challenger
Deep has a maximum depth of 10,925 m (35,843 ft) at 11°19.945′N142°12.123′E (11.332417°N 142.20205°E),
with an estimated vertical uncertainty of ±12 m (39 ft) at one standard
deviation (≈ 68.3%) confidence level. The analysis of the sonar survey
offered a 100 by 100 metres (328 ft × 328 ft) grid resolution at bottom
depth, so small dips in the bottom that are less than that size would be
difficult to detect from the 0.5 by 1 degree sonar-emissions at the sea
surface. Each 0.5-degree beam width sonar ping expands to cover a
circular area about 96 metres (315 ft) in diameter at 11,000 metres
(36,089 ft) depth.
The horizontal position of the grid point has an uncertainty of ±50 to
100 m (164 to 328 ft), depending on along-track or across-track
direction. This depth (59 m (194 ft)) and position (about 410 m
(1,345 ft) to the northeast) measurements differ significantly from the
deepest point determined by the Gardner et al. (2014) study.
The observed depth discrepancy with the 2010 sonar mapping and Gardner
et al 2014 study are related to the application of differing sound
velocity profiles, which are essential for accurate depth determination.
Sonne used CTD casts about 1.6 km west of the deepest sounding to near the bottom of the Challenger Deep that were used for sound velocity profile
calibration and optimization. Likewise, the impact of using different
projections, datum and ellipsoids during data acquisition can cause
positional discrepancies between surveys.
2016 – RV Shyian 3
In December 2016, the CAS 3,300-ton research vessel Shiyan 3
deployed 33 broadband seismometers onto both the backarc northwest of
the Challenger Deep, and onto the near southern Pacific Plate to the
southeast, at depths of up to 8,137 m (26,696 ft). This cruise was part
of a $12 million Chinese-U.S. initiative, led by co-leader Jian Lin of
the Woods Hole Oceanographic Institution; a 5-year effort (2017–2021) to image in fine detail the rock layers in and around the Challenger Deep.
2016 – RV Zhang Jian
The newly launched 4,800-ton research vessel (and mothership for the Rainbow Fish series of deep submersibles), the Zhang Jian departed Shanghai on 3 December. Their cruise was to test three new deep-sea landers, one uncrewed search submersible and the new Rainbow Fish
11,000-meter manned deep submersible, all capable of diving to 10,000
meters. From 25 to 27 December, three deep-sea landing devices descended
into the trench. The first Rainbow Fish lander took photographs, the
second took sediment samples, and the third took biological samples. All
three landers reached over 10,000 meters, and the third device brought
back 103 amphipods. Cui Weicheng, director of Hadal Life Science
Research Center at Shanghai Ocean University,
led the team of scientists to carry out research at the Challenger Deep
in the Mariana Trench. The ship is part of China's national marine
research fleet but is owned by a Shanghai marine technology company.
2017 – RV Tansuo-1
CAS' Institute of Deep-sea Science and Engineering sponsored Tansuo-1's
return to the Challenger Deep 20 January – 5 February 2017 (cruise
TS03) with baited traps for the capture of fish and other macrobiology
near the Challenger and Sirena Deeps. On 29 January they recovered
photography and samples of a new species of snailfish from the Northern
slope of the Challenger Deep at 7,581 metres (24,872 ft), newly
designated Pseudoliparis swirei. They also placed four or more CTD casts into the central and eastern basins of the Challenger Deep, as part of the World Ocean Circulation Experiment (WOCE).
2017 – RV Shinyo Maru
Tokyo University of Marine Science and Technology dispatched the research vessel Shinyo Maru
to the Mariana Trench from 20 January to 5 February 2017 with baited
traps for the capture of fish and other macrobiology near the Challenger
and Sirena Deeps. On 29 January they recovered photography and samples
of a new species of snailfish from the Northern slope of the Challenger
Deep at 7,581 metres (24,872 ft), which has been newly designated Pseudoliparis swirei.
2017 – RV Kexue 3
Water
samples were collected at Challenger Deep from 11 layers of the Mariana
Trench in March 2017. Seawater samples from 4 to 4,000 m were collected
by Niskin bottles mounted to a Seabird SBE25 CTDs; whereas water
samples at depths from 6,050 m to 8,320 m were collected by a
self-designed acoustic-controlled full ocean depth water samplers. In
this study, scientists studied the RNA of pico- and nano-plankton from
the surface to the hadal zone.
2017 – RV Kairei
JAMSTEC deployed Kairei to the Challenger Deep in May 2017 for the express purpose of testing the new full-ocean depth ROV UROV11K
(Underwater ROV 11,000-meter-capable), as cruise KR 17-08C, under chief
scientist Takashi Murashima. The cruise title was: "Sea trial of a full
depth ROV UROV11K system in the Mariana Trench". UROV11K carried a new 4K High Definition
video camera system, and new sensors to monitor the hydrogen-sulfide,
methane, oxygen, and hydrogen content of the water. Unfortunately, on UROV11K's ascent from 10,899 metres (35,758 ft) (at about 11°22.30'N 142°35.8 E, in the eastern
basin) on 14 May 2017, the ROV's buoyancy failed at 5,320 metres
(17,454 ft) depth, and all efforts to retrieve the ROV were
unsuccessful. The rate of descent and drift is not available, but the
ROV bottomed to the east of the deepest waters of the eastern basin as
revealed by the ship's maneuvering on 14 May. Murashima then directed
the Kairei to a location about 35 nmi east of the eastern basin of the
Challenger Deep to test a new "Compact Hadal Lander" which made three
descents to depths from 7,498 to 8,178 m for testing the Sony 4K camera
and for photography of fish and other macro-biologics.
2018 – RV Shen Kuo
On its maiden voyage, the 2,150-ton twin-hulled scientific research vessel Shen Kuo (also Shengkuo, Shen Ko, or Shen Quo),
departed Shanghai on 25 November 2018 and returned on 8 January 2019.
They operated in the Mariana Trench area, and on 13 December tested a
system of underwater navigation at a depth exceeding 10,000 metres,
during a field trial of the Tsaihungyuy (ultra-short baseline)
system. Project leader Tsui Veichen stated that, with the Tsaihungyuy
equipment at depth, it was possible to obtain a signal and determine
exact geolocations. The research team from Shanghai Ocean University and Westlake University was led by Cui Weicheng, director of Shanghai Ocean University's Hadal Science and Technology Research Center (HSRC).
The equipment to be tested included a piloted submersible (not full
ocean depth – depth achieved not available) and two deep-sea landers,
all capable of diving to depths of 10,000 meters, as well as an ROV that
can go to 4,500 meters. They took photographs and obtained samples from
the trench, including water, sediment, macro-organisms and
micro-organisms. Cui says, "If we can take photos of fish more than
8,145 meters under water, ... we will break the current world record. We
will test our new equipment including the landing devices. They are
second generation. The first generation could only take samples in one
spot per dive, but this new second generation can take samples at
different depths in one dive. We also tested the ultra short baseline
acoustic positioning system on the manned submersible, the future of
underwater navigation."
2019 – RV Sally Ride
General Oceanographic RV Sally Ride
In November 2019, as cruise SR1916, a NIOZ team led by chief scientist Hans van Haren, with Scripps technicians, deployed to the Challenger Deep aboard the 2,641-ton research vessel Sally Ride,
to recover a mooring line from the western basin of the Challenger
Deep. The 7 km (4.3 mi) long mooring line in the Challenger Deep
consisted of top-floatation positioned around 4 km (2.5 mi) depth, two
sections of Dyneema neutrally buoyant 6 mm (0.2 in) line, two Benthos
acoustic releases and two sections of self-contained instrumentation to
measure and store current, salinity and temperature. Around the 6 km
(3.7 mi) depth position two current meters were mounted below a 200 m
(656 ft) long array of 100 high-resolution temperature sensors. In the
lower position starting 600 m (1,969 ft) above the sea floor 295
specially designed high-resolution temperature sensors were mounted, the
lowest of which was 8 m (26 ft) above the trench floor. The mooring
line was deployed and left by the NIOZ team during the November 2016 RV Sonne expedition with the intention to be recovered in late 2018 by Sonne. The acoustic commanded release mechanism near the bottom of the Challenger Deep failed at the 2018 attempt. RV Sally Ride was made available exclusively for a final attempt to retrieve the mooring line before the release mechanism batteries expired. Sally Ride arrived at the Challenger Deep on 2 November. This time a 'deep release unit' lowered by one of Sally Ride's
winch-cables to around 1,000 m depth pinged release commands and
managed to contact the near-bottom releases. After being submerged for
nearly three years, mechanical problems occurred in 15 of the 395
temperature sensors. The first results indicate the occurrence of internal waves in the Challenger Deep.
Study of the depth and location of the Challenger Deep
Since May 2000, with the help of non-degraded signal satellite navigation,
civilian surface vessels equipped with professional dual-frequency
capable satellite navigation equipment can measure and establish their
geodetic position with an accuracy in the order of meters to tens of
meters whilst the western, central and eastern basins are kilometers
apart.
GEBCO 2019 bathymetry of the Challenger Deep and Sirena Deep. (a)
Mariana Trench multibeam bathymetry data gridded at 75 m acquired
on-board the DSSV Pressure Drop overtop the GEBCO 2019 source grid (as
shown in Figure 1) and the complete GEBCO 2019 grid with hillshade. EM
124 black contours at 500 m intervals, GEBCO 2019 grey contours at 1,000
m intervals. The white circle indicates the deepest point and
submersible dive location, the white triangle indicates the submersible
dive location from Sirena Deep, the red spot was the deepest point
derived by van Haren et al., (2017). (b) Challenger Deep. (c) Sirena Deep. Bathymetric cross sections A'–A” and B'–B” over Challenger Deep and Sirena Deep displayed in (d) and (e), respectively.
In 2014, a study was conducted regarding the determination of the
depth and location of the Challenger Deep based on data collected
previous to and during the 2010 sonar mapping of the Mariana Trench with
a Kongsberg Maritime EM 122 multibeam echosounder system aboard USNS Sumner.
This study by James. V. Gardner et al. of the Center for Coastal &
Ocean Mapping-Joint Hydrographic Center (CCOM/JHC), Chase Ocean
Engineering Laboratory of the University of New Hampshire splits the
measurement attempt history into three main groups: early single-beam
echo sounders (1950s–1970s), early multibeam echo sounders (1980s – 21st
century), and modern (i.e., post-GPS, high-resolution) multibeam echo
sounders. Taking uncertainties in depth measurements and position
estimation into account, the raw data of the 2010 bathymetry of the
Challenger Deep vicinity consisting of 2,051,371 soundings from eight
survey lines was analyzed. The study concludes that with the best of
2010 multibeam echosounder technologies after the analysis a depth
uncertainty of ±25 m (82 ft) (95% confidence level) on 9 degrees of
freedom and a positional uncertainty of ±20 to 25 m (66 to 82 ft) (2drms) remain and the location of the deepest depth recorded in the 2010 mapping is 10,984 m (36,037 ft) at 11.329903°N 142.199305°E.
The depth measurement uncertainty is a composite of measured
uncertainties in the spatial variations in sound-speed through the water
volume, the ray-tracing and bottom-detection algorithms of the
multibeam system, the accuracies and calibration of the motion sensor
and navigation systems, estimates of spherical spreading, attenuation
throughout the water volume, and so forth.
Both the RV Sonne expedition in 2016, and the RV Sally Ride
expedition in 2019 expressed strong reservations concerning the depth
corrections applied by the Gardner et al. study of 2014, and serious
doubt concerning the accuracy of the deepest depth calculated by Gardner
(in the western basin), of 10,984 m (36,037 ft) after analysis
of their multibeam data on a 100 m (328 ft) grid. Dr. Hans van Haren,
chief scientist on the RV Sally Ride cruise SR1916, indicated
that Gardner's calculations were 69 m (226 ft) too deep due to the
"sound velocity profiling by Gardner et al. (2014)."
In 2018-2019, the deepest points of each ocean were mapped using a
full-ocean depth Kongsberg EM 124 multibeam echosounder aboard DSSV Pressure Drop.
In 2021, a data paper was published by Cassandra Bongiovanni, Heather
A. Stewart and Alan J. Jamieson regarding the gathered data donated to
GEBCO. The deepest depth recorded in the 2019 Challenger Deep sonar
mapping was 10,924 m (35,840 ft) ±15 m (49 ft) at 11.369°N 142.587°E
in the eastern basin. This depth closely agrees with the deepest point
(10,925 m (35,843 ft) ±12 m (39 ft)) determined by the Van Haren et al.
sonar bathymetry. The geodetic position of the deepest depth according
to the Van Haren et al. significantly differs (about 42 km (26 mi) to
the west) with the 2021 paper. After post-processing the initial depth
estimates by application of a full-ocean depth sound velocity profile
Bongiovanni et al. report an (almost) as deep point at 11.331°N 142.205°E
in the western basin that geodetically differs about 350 m (1,150 ft)
with the deepest point position determined by Van Haren et al. (11.332417°N 142.20205°E
in the western basin). After analysis of their multibeam data on a 75 m
(246 ft) grid, the Bongiovanni et al. 2021 paper states the
technological accuracy does not currently exist on low-frequency
ship-mounted sonars required to determine which location was truly the
deepest, nor does it currently exist on deep-sea pressure sensors.
In 2021, a study by Samuel F. Greenaway, Kathryn D. Sullivan,
Samuel H. Umfress, Alice B. Beittel and Karl D. Wagner was published
presenting a revised estimate of the maximum depth of the Challenger
Deep based on a series of submersible dives conducted in June 2020.
These depth estimates are derived from acoustic echo sounding profiles
referenced to in-situ direct pressure measurements and corrected for
observed oceanographic properties of the water-column, atmospheric
pressure, gravity and gravity-gradient anomalies, and water-level
effects. The study concludes according to their calculations the deepest
observed seafloor depth was 10,935 m (35,876 ft) ±6 m (20 ft) below
mean sea level at a 95% confidence level at 11°22.3′N142°35.3′E
in the eastern basin. For this estimate, the error term is dominated by
the uncertainty of the employed pressure sensor, but Greenaway et al.
show that the gravity correction is also substantial. The Greenaway et
al. study compares its results with other recent acoustic and
pressure-based measurements for the Challenger Deep and concludes the
deepest depth in the western basin is very nearly as deep as the eastern
basin. The disagreement between the maximum depth estimates and their
geodetic positions between post-2000 published depths however exceed the
accompanying margins of uncertainty, raising questions regarding the
measurements or the reported uncertainties.
Another 2021 paper by Scott Loranger, David Barclay and Michael
Buckingham, besides a December 2014 implosion shock wave based depth
estimate of 10,983 m (36,033 ft), which is among the deepest estimated
depths, also treatises the differences between various maximum depth
estimates and their geodetic positions.
Direct measurements
The
2010 maximal sonar mapping depths reported by Gardner et.al. in 2014
and Greenaway et al. study in 2021 have not been confirmed by direct
descent (pressure gauge/manometer) measurements at full-ocean depth. Expeditions have reported direct measured maximal depths in a narrow range.
For the western basin deepest depths were reported as 10,913 m (35,804 ft) by Trieste in 1960 and 10,923 m (35,837 ft) ±4 m (13 ft) by DSV Limiting Factor in June 2020.
For the central basin the greatest reported depth is 10,915 m (35,810 ft) ±4 m (13 ft) by DSV Limiting Factor in June 2020.
For the eastern basin deepest depths were reported as 10,911 m (35,797 ft) by Kaikō ROV in 1995, 10,902 m (35,768 ft) by ROV Nereus in 2009, 10,908 m (35,787 ft) by Deepsea Challenger in 2012, 10,929 m (35,856 ft) by benthic lander "Leggo" in May 2019, and 10,925 m (35,843 ft) ±4 m (13 ft) by DSV Limiting Factor in May 2019.
Descents
Manned descents
Bathyscaphe Trieste.
The spherical crew cabin is attached to the underside of a tank filled
with gasoline (which is incompressible), which serves as a float giving
the craft buoyancy.Lt. Don Walsh, USN (bottom) and Jacques Piccard (center) in the Trieste
On 23 January 1960, the Swiss-designed Trieste, originally built in Italy and acquired by the U.S. Navy, supported by the USS Wandank (ATF 204) and escorted by the USS Lewis (DE 535), descended to the ocean floor in the trench piloted by Jacques Piccard (who co-designed the submersible along with his father, Auguste Piccard) and USN Lieutenant Don Walsh.
Their crew compartment was inside a spherical pressure vessel –
measuring 2.16 metres in diameter suspended beneath a buoyancy tank 18.4
metres in length – which was a heavy-duty replacement (of the Italian original) built by Krupp Steel Works of Essen, Germany. The steel
walls were 12.7 cm (5.0 in) thick and designed to withstand pressure of
up to 1250 kilograms per square centimetre (17800 psi; 1210 atm;
123 MPa).
Their descent took almost five hours and the two men spent barely twenty
minutes on the ocean floor before undertaking the
three-hour-and-fifteen-minute ascent. Their early departure from the ocean floor was due to their concern over a crack in the outer window caused by the temperature differences during their descent.
Trieste dived at/near 11°18.5′N142°15.5′E, bottoming at 10,911 metres (35,797 ft) ±7 m (23 ft) into the Challenger Deep's western basin, as measured by an onboard manometer. Another source states the measured depth at the bottom was measured with a manometer at 10,913 m (35,804 ft) ±5 m (16 ft).
Navigation of the support ships was by celestial and LORAN-C with an accuracy of 460 metres (1,510 ft) or less. Fisher noted that the Trieste's reported depth "agrees well with the sonic sounding."
On 26 March 2012 (local time), Canadian film director James Cameron made a solo descent in the DSVDeepsea Challenger to the bottom of the Challenger Deep. At approximately 05:15 ChST on 26 March (19:15 UTC on 25 March), the descent began.
At 07:52 ChST (21:52 UTC), Deepsea Challenger arrived at the bottom. The descent lasted 2 hours and 36 minutes and the recorded depth was 10,908 metres (35,787 ft) when Deepsea Challenger touched down.
Cameron had planned to spend about six hours near the ocean floor
exploring but decided to start the ascent to the surface after only 2
hours and 34 minutes.
The time on the bottom was shortened because a hydraulic fluid leak in
the lines controlling the manipulator arm obscured the visibility out of
the only viewing port. It also caused the loss of the submersible's
starboard thrusters. At around 12:00 ChST (02:00 UTC on 26 March), the Deepsea Challenger website says the sub resurfaced after a 90-minute ascent, although Paul Allen's tweets indicate the ascent took only about 67 minutes.
During a post-dive press conference Cameron said: "I landed on a very
soft, almost gelatinous flat plain. Once I got my bearings, I drove
across it for quite a distance ... and finally worked my way up the
slope." The whole time, Cameron said, he didn't see any fish, or any
living creatures more than an inch (2.54 cm) long: "The only free
swimmers I saw were small amphipods" – shrimplike bottom-feeders.
2019 – Five Deeps Expedition / DSV Limiting Factor
DSSV Pressure Drop and DSV Limiting Factor at its sternThe landers Skaff and Closp are prepared for a deployment during the Five Deeps Expedition.
The Five Deeps Expedition's objective was to thoroughly map and visit
the deepest points of all five of the world's oceans by the end of
September 2019. On 28 April 2019, explorer Victor Vescovo descended to the "Eastern Pool" of the Challenger Deep in the Deep-Submergence Vehicle Limiting Factor (a Triton 36000/2 model submersible). Between 28 April and 4 May 2019, the Limiting Factor
completed four dives to the bottom of Challenger Deep. The fourth dive
descended to the slightly less deep "Central Pool" of the Challenger
Deep (crew: Patrick Lahey, Pilot; John Ramsay, Sub Designer). The Five
Deeps Expedition estimated maximum depths of 10,927 m (35,850 ft) ±8 m
(26 ft) and 10,928 m (35,853 ft) ±10.5 m (34 ft) at (11.3693°N 142.5889°E) by direct CTD pressure measurements and a survey of the operating area by the support ship, the Deep Submersible Support Vessel DSSV Pressure Drop,
with a Kongsberg SIMRAD EM124 multibeam echosounder system. The CTD
measured pressure at 10,928 m (35,853 ft) of seawater depth was
1,126.79 bar (112.679 MPa; 16,342.7 psi).Due to a technical problem the (uncrewed) ultra-deep-sea lander Skaff used by the Five Deeps Expedition stayed on the bottom for two and half days before it was salvaged by the Limiting Factor (crew: Patrick Lahey, Pilot; Jonathan Struwe, DNV GL Specialist) from an estimated depth of 10,927 m (35,850 ft).
The gathered data was published with the caveat that it was subject to
further analysis and could possibly be revised in the future. The data
will be donated to the GEBCO Seabed 2030 initiative. Later in 2019, following a review of bathymetric data, and multiple sensor recordings taken by the DSV Limiting Factor and the ultra-deep-sea landers Closp, Flere and Skaff, the Five Deeps Expedition revised the maximum depth to 10,925 m (35,843 ft) ±4 m (13 ft).
2020 – Ring of Fire Expedition / DSV Limiting Factor
Caladan Oceanic's "Ring of Fire" expedition in the Pacific included
six manned descents and twenty-five lander deployments into all three
basins of the Challenger Deep all piloted by Victor Vescovo and further topographical and marine life survey of the entire Challenger Deep. The expedition craft used are the Deep Submersible Support Vessel DSSV Pressure Drop, Deep-Submergence Vehicle DSV Limiting Factor and the ultra-deep-sea landers Closp, Flere and Skaff.
During the first manned dive on 7 June 2020 Victor Vescovo and former US astronaut (and former NOAA Administrator) Kathryn D. Sullivan descended to the "Eastern Pool" of the Challenger Deep in the Deep-Submergence Vehicle Limiting Factor.
On 12 June 2020, Victor Vescovo and mountaineer and explorer Vanessa O'Brien
descended to the "Eastern Pool" of the Challenger Deep spending three
hours mapping the bottom. O'Brien said her dive scanned about a mile of
desolate bottom terrain, finding that the surface is not flat, as once
was thought, but sloping by about 18 ft (5.5 m) per mile, subject to verification.
On 14 June 2020, Victor Vescovo and John Rost descended to the "Eastern
Pool" of the Challenger Deep in the Deep-Submergence Vehicle Limiting Factor spending four hours at depth and transiting the bottom for nearly 2 miles.
On 20 June 2020, Victor Vescovo and Kelly Walsh descended to the
"Western Pool" of the Challenger Deep in the Deep-Submergence Vehicle Limiting Factor spending four hours at the bottom. They reached a maximum depth of 10,923 m (35,837 ft). Kelly Walsh is the son of the Trieste's captain Don Walsh who descended there in 1960 with Jacques Piccard.
On 21 June 2020, Victor Vescovo and Woods Hole Oceanographic Institution
researcher Ying-Tsong Lin descended to the "Central Pool" of the
Challenger Deep in the Deep-Submergence Vehicle Limiting Factor. They reached a maximum depth of 10,915 m (35,810 ft) ±4 m (13 ft).
On 26 June 2020 Victor Vescovo and Jim Wigginton descended to the "Eastern Pool" of the Challenger Deep in the Deep-Submergence Vehicle Limiting Factor.
Fendouzhe (奋斗者, Striver) is a manned Chinese
deep-sea submersible developed by the China Ship Scientific Research
Center (CSSRC). Between 10 October and 28 November, 2020, it carried out
thirteen dives in the Mariana Trench as part of a test programme. Of
these, eight led to depths of more than 10,000 m (32,808 ft). On 10
November 2020, the bottom of the Challenger Deep was reached by Fendouzhe
with three Chinese scientists (Zhāng Wěi 张伟 [pilot], Zhào Yáng 赵洋, and
Wáng Zhìqiáng 王治强) onboard whilst live-streaming the descent to a
reported depth of 10,909 m (35,791 ft). This makes the Fendouzhe the fourth manned submersible vehicle achieving a successful descent. The pressure hull of Fendouzhe, made from a newly developed titanium alloy, offers space for three people in addition to technical equipment. Fendouzhe is equipped with cameras made by the Norwegian manufacturer Imenco.
According to Ye Cong 叶聪, the chief designer of the submersible, China's
goals for the dive aren't just scientific investigation but also the
future use of deep-sea seabed resources.
2021 – Ring of Fire 2 Expedition / DSV Limiting Factor
On 28 February 2021 Caladan Oceanic's "Ring of Fire 2" expedition
arrived over the Challenger Deep and conducted manned descents and
lander deployments into the Challenger Deep. At the start the (uncrewed) ultra-deep-sea lander Skaff
was deployed to collect water column data by CTD for the expedition.
The effects of the Pacific subducting plate crashing into the Philippine
Plate was among the things researched onsite.
On 1 March 2021, the first manned descent to the eastern pool was made
by Victor Vescovo and Richard Garriott. Garriott became the 17th person to descend to the bottom.
On 2 March 2021, a descent to the eastern pool was made by Victor Vescovo and Michael Dubno.On 5 March a descent to the eastern pool was made by Victor Vescovo and Hamish Harding. They traversed the bottom of Challenger Deep.
On 11 March 2021 a descent to the Western Pool was made by Victor Vescovo and marine botanist Nicole Yamase.
On 13 April 2021 a descent was made by deep water submersible operations expert Rob McCallum and Tim Macdonald who piloted the dive.
A 2021 descent with a Japanese citizen is planned.
All manned descents were conducted in the Deep-Submergence Vehicle DSV Limiting Factor.
2022 - Ring of Fire 3 Expedition / DSV Limiting Factor
Dawn Wright and Victor Vescovo aboard DSV Limiting Factor during their July 2022 dive into the Western Pool
Southern wall of the Western Pool
In July 2022 for the fourth consecutive year, Caladan Oceanic's deep submergence system, consisting of the deep submersible DSV Limiting Factor supported by the mother ship DSSV Pressure Drop, returned to the Challenger Deep for dives into the Challenger Deep.
In early July 2022, Victor Vescovo was joined by Aaron Newman as a mission specialist for a dive into the Central pool. On 5 July 2022, Tim Macdonald as pilot and Jim Kitchen as mission specialist for a dive into the Eastern pool. On 8 July 2022 Victor Vescovo was joined by Dylan Taylor as mission specialist for a dive into the Eastern pool.
Victor Vescovo (for his 15th dive into the Challenger Deep) was joined by geographer and oceanographer Dawn Wright as mission specialist on the 12 July 2022 dive to 10,919 m (35,823 ft) in the Western Pool.
Wright operated the world's first sidescan sonar to ever operate at
full-ocean depth to capture detailed imagery along short transects of
the southern wall of the Western Pool.
The remotely operated vehicle (ROV) Kaikō made many uncrewed descents to the Mariana Trench from its support ship RV Yokosuka during two expeditions in 1996 and 1998.
From 29 February to 4 March the ROV Kaiko made three dives into the central basin, Kaiko #21 – Kaiko #23, . Depths ranged from 10,898 metres (35,755 ft) at 11°22.536′N142°26.418′E, to 10,896 metres (35,748 ft) at 11°22.59′N142°25.848′E; dives #22 & #23 to the north, and dive #21 northeast of the deepest waters of the central basin. During the 1996 measurements the temperature (water temperature increases at great depth due to adiabatic compression), salinity
and water pressure at the sampling station was 2.6 °C (36.7 °F), 34.7‰
and 1,113 bar (111.3 MPa; 16,140 psi), respectively at 10,897 m
(35,751 ft) depth. The Japanese robotic deep-sea probe Kaikō broke the depth record for uncrewed probes when it reached close to the surveyed bottom of the Challenger Deep. Created by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC),
it was one of the few uncrewed deep-sea probes in operation that could
dive deeper than 6,000 metres (20,000 ft). The manometer measured depth
of 10,911.4 m (35,799 ft) ±3 m (10 ft) at 11°22.39′N142°35.54′E for the Challenger Deep is believed to be the most accurate measurement taken up to then.
Another source states the greatest depth measured by Kaikō in 1996 was 10,898 m (35,755 ft) at 11°22.10′N142°25.85′E and 10,907 m (35,784 ft) at 11°22.95′N142°12.42′E in 1998.
The ROV Kaiko was the first vehicle to visit to the bottom of the Challenger Deep since the bathyscaph Trieste's dive in 1960, and the first success in sampling the trench bottom sediment/mud, from which Kaiko obtained over 360 samples. Approximately 3,000 different microbes were identified in the samples.
Kaikō was lost at sea off Shikoku Island during Typhoon Chan-Hom on 29 May 2003.
From 2 May to 5 June 2009, the RV Kilo Moana hosted the Woods Hole Oceanographic Institution (WHOI) hybrid remotely operated vehicle (HROV) Nereus team for the first operational test of the Nereus in its 3-ton tethered ROV mode. The Nereus team was headed by the Expedition Leader Andy Bowen of WHOI, Louis Whitcomb of Johns Hopkins University,
and Dana Yoerger, also of WHOI. The expedition had co-chief scientists:
biologist Tim Shank of WHOI, and geologist Patricia Fryer of the
University of Hawaii, to head the science team exploiting the ship's bathymetry and organizing the science experiments deployed by the Nereus. From Nereus dive #007ROV to 880 m (2,887 ft) just south of Guam, to dive #010ROV into the Nero Deep at 9,050 m (29,692 ft), the testing gradually increased depths and complexities of activities at the bottom.
Dive #011ROV, on 31 May 2009, saw the Nereus piloted on a 27.8-hour underwater mission, with about ten hours transversing the eastern
basin of the Challenger Deep – from the south wall, northwest to the
north wall – streaming live video and data back to its mothership. A
maximum depth of 10,902 m (35,768 ft) was registered at 11°22.10′N142°35.48′E. The RV Kilo Moana then relocated to the western
basin, where a 19.3-hour underwater dive found a maximum depth of
10,899 m (35,758 ft) on dive #012ROV, and on dive #014ROV in the same
area (11°19.59 N, 142°12.99 E) encountered a maximum depth of 10,176 m
(33,386 ft). The Nereus was successful in recovering both sediment and rock samples from the eastern and the western
basins with its manipulator arm for further scientific analysis. The
HROV's final dive was about 80 nmi (148.2 km) to the north of the
Challenger Deep, in the backarc, where they dived 2,963 m (9,721 ft) at the TOTO Caldera (12°42.00 N, 143°31.5 E). Nereus thus became the first vehicle to reach the Mariana Trench since 1998 and the deepest-diving vehicle then in operation. Project manager and developer Andy Bowen heralded the achievement as "the start of a new era in ocean exploration". Nereus, unlike Kaikō, did not need to be powered or controlled by a cable connected to a ship on the ocean surface.
The HROV Nereus was lost on 10 May 2014 while conducting a dive at 9,900 metres (32,500 ft) in depth in the Kermadec Trench.
In June 2008, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) deployed the research vessel Kairei to the area of Guam for cruise KR08-05 Leg 1 and Leg 2.
On 1–3 June 2008, during Leg 1, the Japanese robotic deep-sea probe ABISMO
(Automatic Bottom Inspection and Sampling Mobile) on dives 11–13 almost
reached the bottom about 150 km (93 mi) east of the Challenger Deep:
"Unfortunately, we were unable to dive to the sea floor because the
legacy primary cable of the Kaiko system was a little bit short. The 2-m
long gravity core sampler was dropped in free fall, and sediment
samples of 1.6m length were obtained. Twelve bottles of water samples
were also obtained at various depths..." ABISMO's dive #14 was into the
TOTO caldera (12°42.7777 N, 143°32.4055 E), about 60 nmi northeast of
the deepest waters of the central basin of the Challenger Deep, where they obtained videos of the hydrothermal plume. Upon successful testing to 10,000 m (32,808 ft), JAMSTEC' ROV ABISMO
became, briefly, the only full-ocean-depth rated ROV in existence. On
31 May 2009, the ABISMO was joined by the Woods Hole Oceanographic
Institution's HROV Nereus as the only two operational full ocean depth capable remotely operated vehicles in existence. During the ROV ABISMO's deepest sea trails dive its manometer measured a depth of 10,257 m (33,652 ft) ±3 m (10 ft) in "Area 1" (vicinity of 12°43' N, 143°33' E).
Leg 2, under chief scientist Takashi Murashima, operated at the
Challenger Deep 8–9 June 2008, testing JAMSTEC's new full ocean depth
"Free Fall Mooring System," i.e. a lander. The lander was successfully tested twice to 10,895 m (35,745 ft) depth, taking video images and sediment samplings at 11°22.14′N142°25.76′E, in the central basin of the Challenger Deep.
2016 – Haidou-1
On 23 May 2016, the Chinese submersible Haidou-1
dived to a depth of 10,767 m (35,325 ft) at an undisclosed position in
the Mariana Trench, making China the third country after Japan (ROV Kaikō), and the US (HROV Nereus), to deploy a full-ocean-depth ROV. This autonomous and remotely operated vehicle has a design depth of 11,000 m (36,089 ft).
2020 – Vityaz-D
On 8 May 2020, the Russian submersible Vityaz-D dived to a depth of 10,028 m (32,900 ft) at an undisclosed position in the Mariana Trench.
Lifeforms
The summary report of the HMS Challenger expedition lists unicellular life forms from the two dredged samples taken when the Challenger Deep was first discovered. These (Nassellaria and Spumellaria) were reported in the Report on Radiolaria (1887) written by Ernst Haeckel.
On their 1960 descent, the crew of the Trieste noted that the floor consisted of diatomaceous ooze and reported observing "some type of flatfish" lying on the seabed.
And as we were settling this final fathom, I saw a wonderful thing. Lying on the bottom just beneath us was some type of flatfish, resembling a sole,
about 1 foot [30 cm] long and 6 inches [15 cm] across. Even as I saw
him, his two round eyes on top of his head spied us – a monster of
steel – invading his silent realm. Eyes? Why should he have eyes? Merely
to see phosphorescence? The floodlight that bathed him was the first
real light ever to enter this hadal realm. Here, in an instant, was the
answer that biologists had asked for the decades. Could life exist in
the greatest depths of the ocean? It could! And not only that, here
apparently, was a true, bony teleost fish, not a primitive ray or elasmobranch.
Yes, a highly evolved vertebrate, in time's arrow very close to man
himself. Slowly, extremely slowly, this flatfish swam away. Moving along
the bottom, partly in the ooze and partly in the water, he disappeared
into his night. Slowly too – perhaps everything is slow at the bottom of
the sea – Walsh and I shook hands.
Many marine biologists are now skeptical of this supposed sighting,
and it is suggested that the creature may instead have been a sea cucumber. The video camera on board the Kaiko probe spotted a sea cucumber, a scale worm and a shrimp at the bottom.At the bottom of the Challenger Deep, the Nereus probe spotted one polychaete worm (a multi-legged predator) about an inch long.
An analysis of the sediment samples collected by Kaiko found large numbers of simple organisms at 10,900 m (35,800 ft). While similar lifeforms have been known to exist in shallower ocean trenches (> 7,000 m) and on the abyssal plain, the lifeforms discovered in the Challenger Deep possibly represent distinct from those in shallower ecosystems.
Most of the organisms collected were simple, soft-shelled foraminifera (432 species according to National Geographic), with four of the others representing species of the complex, multi-chambered genera Leptohalysis and Reophax. Eighty-five per cent of the specimens were organic, soft-shelled allogromiids, which is unusual compared to samples of sediment-dwelling organisms from other deep-sea environments, where the percentage of organic-walled foraminifera
ranges from 5% to 20%. As small organisms with hard, calcareous shells
have trouble growing at extreme depths because of the high solubility of
calcium carbonate
in the pressurized water, scientists theorize that the preponderance of
soft-shelled organisms in the Challenger Deep may have resulted from
the typical biosphere
present when the Challenger Deep was shallower than it is now. Over the
course of six to nine million years, as the Challenger Deep grew to its
present depth, many of the species present in the sediment died out or
were unable to adapt to the increasing water pressure and changing
environment.
On 17 March 2013, researchers reported data that suggested piezophilic microorganisms thrive in the Challenger Deep.
Other researchers reported related studies that microbes thrive inside
rocks up to 579 m (1,900 ft) below the sea floor under 2,591 m
(8,500 ft) of ocean off the coast of the northwestern United States.
According to one of the researchers, "You can find microbes
everywhere – they're extremely adaptable to conditions, and survive
wherever they are."
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