A
ABYSSAL PLAINS
David Voelker
MARUM-Center for Marine Environmental Sciences,
University of Bremen, Bremen, Germany
Abyssal plains are flat areas of the ocean floor in a water
depth between 3,500 and 5,000 with a gradient well below
0.1
. They occupy around 28 % of the global seafloor. The
thickness of the sediment cover seldom exceeds 1,000 m,
and the sediments consist of fine-grained erosional detritus and biogenic particles. The first global map of seafloor
physiography, published by Heezen and Tharp in 1977,
illustrated that the bottom of the ocean is bordered by continental margins of variable width and hosts large submarine mountain chains, the mid-ocean ridges. It also
illustrated that between the continental margins and
mid-ocean ridges, there exist vast flat and almost featureless regions, the so-called abyssal plains (Figure 1). The
global seafloor map has been refined in recent years
(e.g., by Smith and Sandwell, 1995; Becker et al., 2009),
in a way that has allowed to perform quantitative analyses
of the global distribution of specific seafloor features
(Harris et al., 2014).
Bathymetry
Earth is a sphere with an equatorial radius of 6,378 km
and a surface area of ~5.1 Â 10
14 m
2
. Roughly 71 % or
~3.58 Â 10
14 m
2 of that surface is covered by oceans.
The largest part of the ocean floor is at a depth between
3,500 and 5,000 m (with a mean ocean depth of
3,795 m), in the depth range of abyssal plains. Exceptions
from this rule are (1) continental margins and epeiric seas,
(2) mid-ocean ridges, (3) seamounts and basaltic plateaus
that are shallower, as well as (4) submarine trenches at
subduction zones that are deeper. These areas are exceptional because plate collision forces govern the shape of
the seafloor (at subduction zone trenches), because they
form a transition between continental and oceanic crust
(continental margins) or because of atypical structure of
the ocean crust (basaltic plateaus and seamounts).
Mid-ocean ridges stand out as the crust that is formed at
these plate boundaries is young and hot. Cooling of the
plate leads to crustal subsidence to abyssal depth within
~12 Ma.
Apart from those areas, the seafloor is relatively monotonous in its depth and also very flat. Those regions that
typically stretch from the foot of the continental slopes
to the mid-ocean ridges have been classified as a specific
physiographic entity and termed abyssal plains. The word
abyss comes from the Greek word abyssos “bottomless
(pool)” indicating the enormous lightless depths, whereas
plain refers to the morphological notion of vast monotonously flat areas. Strictly speaking, the term is a kind of
contradiction because a plain cannot be bottomless, but
it is meant in the same way as its correspondent “deepsea plain.”
The depth distribution of the world oceans is shown in
Figure 2 in the form of a hypsometric curve. The curve
shows a bimodal distribution with one peak between
0 and 500 m and another broader peak between 3,500
and 6,000 m. This distribution reflects the double nature
of the seafloor: around the continents, large areas of the
seafloor are actually drowned parts of the continents with
a crustal structure that is similar to the crust underlying the
continents. The deeper part of the ocean is in contrast
underlain by oceanic crust that is formed at mid-ocean
ridges in a similar composition on global scale.
The lifespan of a portion of oceanic crust from its creation
at a spreading center to its destruction at a subduction
zone ranges seldom exceeds 120 Ma (Müller et al., 2008).
J. Harff et al. (eds.), Encyclopedia of Marine Geosciences, DOI 10.1007/978-94-007-6238-1,
© Springer Science+Business Media Dordrecht 2016
ABYSSAL PLAINS
David Voelker
MARUM-Center for Marine Environmental Sciences,
University of Bremen, Bremen, Germany
Abyssal plains are flat areas of the ocean floor in a water
depth between 3,500 and 5,000 with a gradient well below
0.1
. They occupy around 28 % of the global seafloor. The
thickness of the sediment cover seldom exceeds 1,000 m,
and the sediments consist of fine-grained erosional detritus and biogenic particles. The first global map of seafloor
physiography, published by Heezen and Tharp in 1977,
illustrated that the bottom of the ocean is bordered by continental margins of variable width and hosts large submarine mountain chains, the mid-ocean ridges. It also
illustrated that between the continental margins and
mid-ocean ridges, there exist vast flat and almost featureless regions, the so-called abyssal plains (Figure 1). The
global seafloor map has been refined in recent years
(e.g., by Smith and Sandwell, 1995; Becker et al., 2009),
in a way that has allowed to perform quantitative analyses
of the global distribution of specific seafloor features
(Harris et al., 2014).
Bathymetry
Earth is a sphere with an equatorial radius of 6,378 km
and a surface area of ~5.1 Â 10
14 m
2
. Roughly 71 % or
~3.58 Â 10
14 m
2 of that surface is covered by oceans.
The largest part of the ocean floor is at a depth between
3,500 and 5,000 m (with a mean ocean depth of
3,795 m), in the depth range of abyssal plains. Exceptions
from this rule are (1) continental margins and epeiric seas,
(2) mid-ocean ridges, (3) seamounts and basaltic plateaus
that are shallower, as well as (4) submarine trenches at
subduction zones that are deeper. These areas are exceptional because plate collision forces govern the shape of
the seafloor (at subduction zone trenches), because they
form a transition between continental and oceanic crust
(continental margins) or because of atypical structure of
the ocean crust (basaltic plateaus and seamounts).
Mid-ocean ridges stand out as the crust that is formed at
these plate boundaries is young and hot. Cooling of the
plate leads to crustal subsidence to abyssal depth within
~12 Ma.
Apart from those areas, the seafloor is relatively monotonous in its depth and also very flat. Those regions that
typically stretch from the foot of the continental slopes
to the mid-ocean ridges have been classified as a specific
physiographic entity and termed abyssal plains. The word
abyss comes from the Greek word abyssos “bottomless
(pool)” indicating the enormous lightless depths, whereas
plain refers to the morphological notion of vast monotonously flat areas. Strictly speaking, the term is a kind of
contradiction because a plain cannot be bottomless, but
it is meant in the same way as its correspondent “deepsea plain.”
The depth distribution of the world oceans is shown in
Figure 2 in the form of a hypsometric curve. The curve
shows a bimodal distribution with one peak between
0 and 500 m and another broader peak between 3,500
and 6,000 m. This distribution reflects the double nature
of the seafloor: around the continents, large areas of the
seafloor are actually drowned parts of the continents with
a crustal structure that is similar to the crust underlying the
continents. The deeper part of the ocean is in contrast
underlain by oceanic crust that is formed at mid-ocean
ridges in a similar composition on global scale.
The lifespan of a portion of oceanic crust from its creation
at a spreading center to its destruction at a subduction
zone ranges seldom exceeds 120 Ma (Müller et al., 2008).
J. Harff et al. (eds.), Encyclopedia of Marine Geosciences, DOI 10.1007/978-94-007-6238-1,
© Springer Science+Business Media Dordrecht 2016