![Pelagiczone](https://upload.wikimedia.org/wikipedia/commons/b/bc/Pelagiczone.svg)
The bathypelagic zone or bathyal zone (from Greek βαθύς (bathýs), deep) is the part of the
open ocean
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...
that extends from a depth of below the
ocean surface
The ocean (also the sea or the world ocean) is the body of Saline water, salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Water distribution on Earth, Earth's water. An ocean can also refer to any of the ...
. It lies between the
mesopelagic
The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins ...
above, and the
abyssopelagic
The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. "Abyss" derives from the Greek word , meaning bottomless. At depths of , this zone remains in perpetual darkness. It covers 83% of the total area of the ocean ...
below. The bathypelagic is known as the midnight zone because of the lack of sunlight; this feature does not allow for
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
-driven
primary production
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...
, preventing growth of
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
or
aquatic plant
Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...
s. Although larger by volume than the
photic zone, our knowledge of the bathypelagic zone remains limited by our ability to explore the deep ocean.
Physical characteristics
![Oceanic_basin](https://upload.wikimedia.org/wikipedia/commons/1/13/Oceanic_basin.svg)
The bathypelagic zone is characterized by a nearly constant temperature of approximately and a salinity range of 33-35 g/kg. This region has little to no light, because sunlight does not reach this deep in the ocean and
bioluminescence
Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some b ...
is limited.
The
hydrostatic pressure
Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...
in this zone ranges 100-400 atmospheres (atm), due to the increase of 1 atm for every 10 m depth. It is believed that these conditions have been consistent for the past 8000 years.
This ocean depth spans from the edge of the
continental shelf
A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...
down to the top of the
abyssal zone
The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. "Abyss" derives from the Greek word , meaning bottomless. At depths of , this zone remains in perpetual darkness. It covers 83% of the total area of the ocean a ...
, and along
continental slope
A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margin ...
depths.
The bathymetry of the bathypelagic zone consists of limited areas where the seafloor is in this depth range along the deepest parts of the
continental margin
A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margin ...
s, as well as
seamount
A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abru ...
s, and
mid-ocean ridge
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diverge ...
s.
The continental slopes are mostly made up of accumulated sediment, while seamounts and mid-ocean ridges contain large areas of hard substrate that provide habitats for bathypelagic fishes and benthic invertebrates.
Although currents at these depths are very slow, the topography of seamounts interrupts the
currents
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
and creates
eddies
In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid is in a turbulent flow regime. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object. Fluid beh ...
that retain plankton in the seamount region, thus increasing fauna nearby as well
Hydrothermal vent
A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...
s are also a common feature in some areas of the bathypelagic zone and are primarily formed from the spreading of Earth’s
tectonic plates
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...
at
mid-ocean ridge
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diverge ...
s. As the bathypelagic region lacks light, these vents play an important role in global ocean chemical processes, thus supporting unique ecosystems that have adapted to utilize chemicals as energy, via
chemoautotrophy
A Chemotroph is an organism that obtains energy by the oxidation of electron donors in their environments. These molecules can be organic (chemoorganotrophs) or inorganic (chemolithotrophs). The chemotroph designation is in contrast to phototrop ...
, instead of sunlight, to sustain themselves.
In addition,
hydrothermal vent
A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...
s facilitate precipitation of minerals on the seafloor,
making them regions of interest for
deep-sea mining.
Biogeochemistry
![Champagne_vent_white_smokers](https://upload.wikimedia.org/wikipedia/commons/a/aa/Champagne_vent_white_smokers.jpg)
Many of the biogeochemical processes in the bathypelagic region are dependent upon the input of
organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
from the overlying
epipelagic
The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...
and
mesopelagic
The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins ...
zones. This organic material, sometimes called
marine snow
In the deep ocean, marine snow (also known as "ocean dandruff") is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to ...
, sinks in the water column or is transported within downward
convected water masses such as the
Thermohaline Circulation
Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective ''thermohaline'' derives from '' thermo-'' referring to temper ...
.
Hydrothermal vent
A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...
s also deliver heat and chemicals such as
sulfide
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...
and
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
. These chemicals can be utilized to sustain metabolism by organisms in the region.
Our understanding of these biogeochemical processes has historically been limited due to the difficulty and cost of collecting samples from these ocean depths. Other technological challenges, such as measuring microbial activity under the pressure conditions experienced in the bathypelagic zone, have also restricted our knowledge of the region. Although scientific advancements have increased our understanding over the past several decades, many aspects remain a mystery.
One of the major areas of current research is focused on understanding carbon
remineralization
In biogeochemistry, remineralisation (or remineralization) refers to the breakdown or transformation of organic matter (those molecules derived from a biological source) into its simplest Inorganic compound, inorganic forms. These transformations ...
rates in the region. Prior studies have struggled to quantify the rates at which
prokaryote
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
s in this region remineralize
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
because previously developed techniques may not be adequate for this region, and indicate remineralization rates much higher than expected. Further work is needed to explore this question, and may require revisions to our understanding of the
global carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major component ...
.
Particulate organic matter
Organic material from
primary production
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...
in the
epipelagic zone
The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...
, and to a far lesser extent, organic inputs from terrestrial sources, make up a majority of the
Particulate Organic Matter
Particulate organic matter (POM) is a fraction of total organic matter operationally defined as that which does not pass through a filter pore size that typically ranges in size from 0.053 to 2 millimeters.
Particulate organic carbon (POC) is ...
(POM) in the ocean. POM is delivered to the bathypelagic zone via sinking
copepod
Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...
fecal pellets and dead organisms; these parcels of organic matter fall through the water column and deliver organic
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
,
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, and
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
, to organisms that live below the photic zone. These parcels are sometimes referred to as
marine snow
In the deep ocean, marine snow (also known as "ocean dandruff") is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to ...
or ocean dandruff. This is also the dominant delivery mechanism of food to organisms in the bathypelagic zone because there is no sunlight for
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
, with chemoautotrophy playin a more minor role as far as we know.
As POM sinks through the water column, it is consumed by organisms which deplete it of nutrients. The size and density of these particles affect their likelihood of reaching organisms in the bathypelagic zone. Smaller parcels of POM often become aggregated together as they fall, which quickens their descent and prohibits their consumption by other organisms, increasing their likelihood of reaching lower depths.
The density of these particles may be increased in some regions where minerals associated with some forms of phytoplankton, such as
biogenic silica
Biogenic silica (bSi), also referred to as opal, biogenic opal, or amorphous opaline silica, forms one of the most widespread biogenic minerals. For example, microscopic particles of silica called phytoliths can be found in grasses and other plant ...
and
calcium carbonate “ballast” resulting in more rapid transport to deeper depth.
Carbon
A majority of organic carbon is produced in the
epipelagic zone
The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...
, with a small portion transported deeper into the ocean interior. This process, known as the
biological pump
The biological pump (or ocean carbon biological pump or marine biological carbon pump) is the ocean's biologically driven sequestration of carbon from the atmosphere and land runoff to the ocean interior and seafloor sediments.Sigman DM & GH ...
, plays a large role in the
sequestration of carbon from the atmosphere into the ocean. Organic carbon is primarily exported to the bathypelagic zone in the form of
particulate organic carbon
Particulate organic matter (POM) is a fraction of total organic matter operationally defined as that which does not pass through a filter pore size that typically ranges in size from 0.053 to 2 millimeters.
Particulate organic carbon (POC) is ...
(POC) and
dissolved organic carbon
Dissolved organic carbon (DOC) is the fraction of organic carbon operationally defined as that which can pass through a filter with a pore size typically between 0.22 and 0.7 micrometers. The fraction remaining on the filter is called particu ...
(DOC).
POC is the largest component of
organic carbon
Total organic carbon (TOC) is the amount of carbon found in an organic compound and is often used as a non-specific indicator of water quality or cleanliness of pharmaceutical manufacturing equipment. TOC may also refer to the amount of organic c ...
delivered to the bathypelagic zone; it primarily takes the form of fecal pellets and dead organisms that sink out of the surface waters and fall toward the ocean floor. Regions with higher primary productivity where particles are able to sink quickly, such as equatorial upwelling zones and the
Arabian Sea
The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel ...
, have the greatest amount of POC delivery to the bathypelagic zone.
The vertical mixing of DOC-rich surface waters is also a process that delivers carbon to the bathypelagic zone, however, it constitutes a substantially smaller portion of overall transport than POC delivery.
DOC transport occurs most readily in regions with high rates of ventilation or ocean turnover, such as the interior of
gyres or deep water formation sites along the
thermohaline circulation
Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective ''thermohaline'' derives from '' thermo-'' referring to temper ...
.
Calcium carbonate dissolution
The region in the water column at which calcite
dissolution
Dissolution may refer to:
Arts and entertainment Books
* ''Dissolution'' (''Forgotten Realms'' novel), a 2002 fantasy novel by Richard Lee Byers
* ''Dissolution'' (Sansom novel), a 2003 historical novel by C. J. Sansom Music
* Dissolution, in mu ...
begins to occur rapidly, known as the
lysocline
The lysocline is the depth in the ocean dependent upon the carbonate compensation depth (CCD), usually around 3.5 km, below which the rate of dissolution of calcite increases dramatically because of a pressure effect. While the lysocline is the u ...
, is typically located near the base bathypelagic zone at approximately 3,500 m depth, but varies among ocean basins. The lysocline lies below the saturation depth (the transition to
undersaturated
Undersaturation is a state of a solution that contains less of a dissolved material than could be dissolved by that quantity of solvent under normal circumstances. It can also refer to a vapor of a compound that has a lower (partial) pressure than ...
conditions with respect to
calcium carbonate) and above the
carbonate compensation depth
Carbonate compensation depth (CCD) is the depth in the oceans below which the rate of supply of calcite ( calcium carbonate) lags behind the rate of solvation, such that no calcite is preserved. Shells of animals therefore dissolve and carbonate ...
(below which there is no calcium carbonate preservation). In a supersaturated environment, the
tests
Test(s), testing, or TEST may refer to:
* Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities
Arts and entertainment
* ''Test'' (2013 film), an American film
* ''Test'' (2014 film), ...
of calcite-forming organisms are preserved as they sink toward the sea floor, resulting in sediments with relatively high amounts of CaCO
3. However, as depth and pressure increase and temperature decreases, the solubility of calcium carbonate also increases, which results in more dissolution and less net transport to the deeper, underlying seafloor. As a result of this rapid change in dissolution rates, sediments in the bathypelagic region vary widely in CaCO
3 content and burial.
Ecology
The ecology of the bathypelagic ecosystem is constrained by its lack of sunlight and
primary producers
An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...
, with limited production of microbial biomass via autotrophy. The
trophic network
A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one ...
s in this region rely on
particulate organic matter
Particulate organic matter (POM) is a fraction of total organic matter operationally defined as that which does not pass through a filter pore size that typically ranges in size from 0.053 to 2 millimeters.
Particulate organic carbon (POC) is ...
(POM) that sinks from the
epipelagic
The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...
and
mesopelagic
The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins ...
water, and oxygen inputs from the
thermohaline circulation
Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective ''thermohaline'' derives from '' thermo-'' referring to temper ...
. Despite these limitations, this open-ocean ecosystem is home to
microbial organisms,
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
, and
nekton
Nekton or necton (from the ) refers to the actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms ...
.
Microbial ecology
![RT8-4](https://upload.wikimedia.org/wikipedia/commons/4/46/RT8-4.jpg)
A comprehensive understanding of the inputs driving the microbial ecology in the bathypelagic zone is lacking due to limited observational data, but has been improving with advancements in deep-sea technology. A majority of our knowledge of ocean
microbial activity comes from studies of the shallower regions of the ocean because it is easier to access, and it was previously assumed that deeper water did not have suitable physical conditions for diverse microbial communities. The bathypelagic zone receives inputs of organic material and
POM from the surface ocean on the order of 1-3.6 Pg C/year.
Prokaryote
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
biomass in the bathypelagic is dependent and thus correlated with the amount of sinking
POM and
organic carbon
Total organic carbon (TOC) is the amount of carbon found in an organic compound and is often used as a non-specific indicator of water quality or cleanliness of pharmaceutical manufacturing equipment. TOC may also refer to the amount of organic c ...
availability. These essential organic carbon inputs for microbes typically decrease with depth as they are utilized while sinking to the bathypelagic.
Microbial production varies over six orders of magnitude based on resource availability in a given area.
Prokaryote abundance can range from 0.03-2.3x105 cells ml
−1, and have population
turnover time
The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a lake, a human body). The residence time of a set of parcels is quantified in terms of the frequency distribution ...
s that can range from 0.1–30 years.
Archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
make up a larger portion of the total prokaryote cell abundance, and different groups have different growth needs, with some archaea groups for example utilizing
amino acid groups more readily than others. Some archaea like
Crenarchaeota have Crenarchaeota 16S rRNA and archaeal amoA gene abundances correlated to
dissolved inorganic carbon (DIC) fixation. The utilization of
DIC is thought to be fueled by the oxidation of
ammonium
The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...
and is one form of chemoautotrophy. Based on regional variation and differences in prokaryote abundance,
heterotroph
A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
ic prokaryote production, and
particulate organic carbon (POC) inputs to the bathypelagic zone.
Research to quantify bacterial-consuming grazers, like
heterotroph
A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
ic
eukaryote
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
s, has been limited by difficulties in sampling. Oftentimes organisms do not survive being brought to the surface due to experiencing drastic pressure changes in a short amount of time. Work is underway to quantify cell abundance and biomass, but due to poor survival, it is difficult to get accurate counts. In more recent years there has been an effort to categorize the diversity of the eukaryotic assemblages in the bathypelagic zone using methods to assess the genetic compositions of microbial communities based on supergroups, which is a way to classify organisms that have common ancestry. Some important groups of bacterial grazers include
Rhizaria
The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many foramini ...
,
Alveolata,
Fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
,
Stramenopile
Stramenopile is a clade of organisms distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular surface, and in some they have be ...
s,
Amoebozoa
Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported classi ...
, and
Excavata
Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in 2002 as a formal taxon. It contains a variety of free- ...
(listed from most to least abundant), with the remaining composition classified as uncertain or other.
Virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's 1 ...
es influence biogeochemical cycling through the role they play in
marine food web
Compared to terrestrial environments, marine environments have biomass pyramids which are inverted at the base. In particular, the biomass of consumers (copepods, krill, shrimp, forage fish) is larger than the biomass of primary producers. This ...
s. Their overall abundance can be up to two orders of magnitude lower than the
mesopelagic zone
The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins ...
, however, there is often high viral abundance found around deep-sea
hydrothermal vent
A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...
s. The magnitude of their impacts on biological systems is demonstrated by the varying range of viral-to-prokaryote abundance ratios ranging from 1-223, this indicates that there are the same amount or more viruses than prokaryotes.
Fauna
Fish ecology
Despite the lack of light, vision plays a role in life within the bathypelagic with
bioluminescence
Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some b ...
a trait among both
nekton
Nekton or necton (from the ) refers to the actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms ...
ic and
plankton
Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...
ic organisms. In contrast to organisms in the water column organisms,
benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
organisms in this region tend to have limited to no
bioluminescence
Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some b ...
. The bathypelagic zone contains
shark
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimo ...
s,
squid
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
,
octopus
An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...
es, and many species of fish, including deep-water
anglerfish
The anglerfish are fish of the teleost order Lophiiformes (). They are bony fish named for their characteristic mode of predation, in which a modified luminescent fin ray (the esca or illicium) acts as a lure for other fish. The luminescence ...
,
gulper eel
The saccopharyngiformes are a derived lineage of unusual eels within the order Anguilliformes, and includes families Cyematidae, Monognathidae, Eurypharyngidae, Saccopharyngidae, and the proposed family Neocyematidae. Most of the fish in this gro ...
,
amphipods
Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...
, and
dragonfish. The fish are characterized by weak muscles, soft skin, and slimy bodies. The adaptations of some of the fish that live there include small eyes and transparent skin. However, this zone is difficult for fish to live in since food is scarce; resulting in species evolving slow metabolic rates in order to conserve energy.
Occasionally, large sources of organic matter from decaying organisms, such as
whale fall
A whale fall occurs when the carcass of a whale has fallen onto the ocean floor at a depth greater than , in the bathyal or abyssal zones. On the sea floor, these carcasses can create complex localized ecosystems that supply sustenance to deep-s ...
s, create a brief burst of activity by attracting organisms from different bathypelagic communities.
Diel vertical migration
Some bathypelagic species undergo
vertical migration, which differs from the
diel vertical migration
Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The word ''diel'' comes from the Latin ''dies'' day, and means a 24-h ...
of mesopelagic species in that it is not driven by sunlight. Instead, the migration of bathypelagic organisms is driven by other factors, most of which remain unknown. Some research suggests the movement of species within the overlying
pelagic
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...
region could prompt individual bathypelagic species to migrate, such as
Sthenoteuthis sp., a species of
squid
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
.
In this particular example,
Sthenoteuthis sp. appears to migrate individually over the course of ~4–5 hours towards the surface and then form into groups.
While in most regions
migration patterns can be driven by
predation
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
, in this particular region, the migration patterns are not believed to result solely from predator-prey relations. Instead, these relations are
commensalistic, with the species who remain in the bathypelagic benefitting from the
POM mixing caused by the upward movement of another species.
In addition, the vertical migrating species' timing bathypelagic appears linked to the
lunar cycle
Concerning the lunar month of ~29.53 days as viewed from Earth, the lunar phase or Moon phase is the shape of the Moon's directly sunlit portion, which can be expressed quantitatively using areas or angles, or described qualitatively using the t ...
. However, the exact indicators causing this timing are still unknown.
Research and exploration
![ROV_JASON_AT42-22](https://upload.wikimedia.org/wikipedia/commons/0/01/ROV_JASON_AT42-22.jpg)
This region is understudied due to a lack of data/observations and difficulty of access (i.e. cost, remote locations, extreme pressure).
Historically in oceanography, continental margins were the most sampled and researched due to their relatively easy access.
However, more recently locations further offshore and at greater depths, such as
ocean ridges and
seamount
A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abru ...
s, are being increasingly studied due to advances in technology and laboratory methods, as well as collaboration with industry.
The first discovery of communities subsisting off of the chemical energy in hydrothermal vents was aboard an expedition in 1977 led by
Jack Corliss
John B. ("Jack") Corliss is a scientist who has worked in the fields of geology, oceanography, and the origins of life.
Corliss is a University of California, San Diego Alumnus, receiving his PhD from Scripps Institution of Oceanography in the ...
, an oceanographer from
Oregon State University
Oregon State University (OSU) is a public land-grant, research university in Corvallis, Oregon. OSU offers more than 200 undergraduate-degree programs along with a variety of graduate and doctoral degrees. It has the 10th largest engineering co ...
. More recent advancements include
remotely operated vehicles (ROVs),
autonomous underwater vehicle
An autonomous underwater vehicle (AUV) is a robot that travels underwater without requiring input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification that includes ...
s (AUVs), and independent gliders and floats.
Specific technologies and research projects
* SERPENT Project
* Ocean Twilight Zone (OTZ) Project
* DEEP SEARCH Project
* DEEPEND Project
*
AUV Sentry
*
ROV Jason
* Hybrid
ROV Nereus
In Greek mythology, Nereus ( ; ) was the eldest son of Pontus (the Sea) and Gaia (the Earth), with Pontus himself being a son of Gaia. Nereus and Doris became the parents of 50 daughters (the Nereids) and a son ( Nerites), with whom Nereus liv ...
*
AUV Autosub Long Range
Climate change
The oceans act as a buffer for
anthropogenic climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
due to their ability to take up atmospheric CO
2 and absorb heat from the atmosphere. However, the ocean’s ability to do so will be negatively affected as atmospheric CO
2 concentrations continue to rise and global temperatures continue to warm. This will lead to changes such as
deoxygenation
Deoxygenation is a chemical reaction involving the removal of oxygen atoms from a molecule. The term also refers to the removal of molecular oxygen (O2) from gases and solvents, a step in air-free technique and gas purifiers. As applied to orga ...
,
ocean acidification
Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
, temperature increase, and
carbon sequestration
Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land ...
decrease, among other physical and chemical alterations. These perturbations may have significant impacts on the organisms that dwell in the bathypelagic region and the properties that deliver organic carbon to the deep sea.
Carbon storage
The bathypelagic zone currently acts as a significant
reservoir
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including contro ...
for carbon because of its sheer volume and the century to millennial timescales these waters are isolated from the atmosphere, this ocean zone plays an important role in moderating the effects of anthropogenic climate change.
The burial of
particulate organic carbon (POC) in the underlying sediments via the
biological carbon pump
The biological pump (or ocean carbon biological pump or marine biological carbon pump) is the ocean's biologically driven sequestration of carbon from the atmosphere and land runoff to the ocean interior and seafloor sediments.Sigman DM & GH ...
, and the
solubility pump
In oceanic biogeochemistry, the solubility pump is a physico-chemical process that transports carbon as dissolved inorganic carbon (DIC) from the ocean's surface to its interior.
Overview
The solubility pump is driven by the coincidence of two ...
of
dissolved inorganic carbon (DIC) into the ocean interior via the
thermohaline conveyor are key processes for removing excess atmospheric carbon. However, as atmospheric CO
2 concentrations and global temperatures continue to rise, the efficiency at which the bathypelagic will store and bury the influx of carbon will most likely decrease. While some regions may experience an increase in POC input, such as Arctic regions where increased periods of minimal sea ice coverage will increase the downward flux of carbon from the surface oceans, overall, there will likely be less carbon sequestered to the bathypelagic region.
References
{{Reflist
External links
Woods Hole Oceanographic Institution - Midnight Zone
Oceanography