Mesopelagic zone: Difference between revisions

Content deleted Content added

Inline

Revision as of 21:27, 26 November 2018

The mesopelagic (Greek μέσον, middle) (also known as the middle pelagic or twilight zone) is the part of the pelagic zone that begins at the depth where 1% of incident light at the water surface. It lies between the photic epipelagic above and the aphotic bathypelagic below, where there is no light at all. The depth of this zone is approximately 200 to 1000 meters (~660 to 3300 feet) below the ocean surface.^[1] It hosts a diverse biological community that includes bristlemouths, blobfish, bioluminescent jellyfish, giant squid, and a myriad of other unique organisms adapted to live in a low-light environment.^[2] It has long captivated the imagination of scientist, artists and writers; deep sea creatures are prominent in popular culture, particularly as horror movie villains.^[3]

Physical conditions

The mesopelagic zone includes the region of sharp changes in temperature, salinity and density called the thermocline, halocline, and pycnocline.^[4] The temperature varies from over 20 °C (68 °F) at the top to around 4 °C (39 °F) at the boundary with the bathyal zone. The variation in salinity is smaller typically between 34.5 and 35 psu. The density range is 1023 to 1027 g/kg of seawater. These changes in temperature, salinity, and density induce stratification which create ocean layers that affect gradients and mixing of nutrients and dissolved gasses. The Sound Fixing and Ranging channel (SOFAR) is located at the base of the mesopelagic zone at about 600-1200m.^[5] Sound travels the slowest in this channel due to the salinity and temperature variations. It is a wave-guided zone where sound waves reflect within the layer and propagate long distances.^[6] Mode water is a water mass that is typically defined by its vertically mixed properties.^[6] It often forms as deep mixed layers at the depth of the thermocline. ^[6] The mode water in the mesopelagic has residency times on decadal or century scales.^[6] The longer overturning times contrast with the daily and shorter scales that a variety of animals move vertically through the zone and sinking of various debris.

The region was initially discovered by American researchers during World War II in 1942 during anti-submarine research with sonar. Sonar at the time could not penetrate below this depth due to the large number of creatures obstructing sound waves.^[7]

Biogeochemistry

Carbon

The mesopelagic zone plays a key role in the ocean's biological pump, which contributes to the oceanic carbon cycle. In the biological pump, organic carbon is produced in the surface euphotic zone where light promotes photosynthesis, and a fraction of this production is exported out of the surface mixed layer and into the mesopelagic zone. One pathway for carbon export from the euphotic layer is through sinking of particles, which can be accelerated through repackaging of organic matter in zooplankton fecal pellets, ballasted particles, and aggregates.

In the mesopelagic zone, the biological pump is key to carbon cycling, as this zone is largely dominated by remineralization of particulate organic carbon (POC). When a fraction of POC is exported from the euphotic zone, an estimated 90% of that POC is respired in the mesopelagic zone.^[8] This is due to the microbial organisms that respire organic matter and remineralize the nutrients, while mesopelagic fish also package organic matter into quick-sinking parcels for deeper export.^[9]

Another key process occurring in this zone is the diel vertical migration of certain species, which move between the euphotic zone and mesopelagic zone and actively transport particulate organic matter to the deep.^[8] In one study in the Equatorial Pacific, myctophids in the mesopelagic zone were estimated to actively transport 15-28% of the passive POC sinking to the deep,^[10] while a study near the Canary Islands estimated 53% of vertical carbon flux was due to active transport from a combination of zooplankton and micronekton.^[11] When primary productivity is high, the contribution of active transport by vertical migration has been estimated to be comparable to sinking particle export.^[8]

Particle Packaging and sinking

Mean particle sinking rates are 10 to 100 m/day. ^[12] Sinking rates have been measured in the project VERTIGO (Vertical Transport in the Global Ocean) using neutrally buoyant sediment traps.^[13] The variability in sinking rates is due to differences in ballast, water temperature, food web structure and the types of phyto- and zooplankton in different areas of the ocean. ^[13] If the material sinks faster, then it gets respired less by bacteria, transporting more carbon from the surface layer to the deep ocean. Larger fecal pellets sink faster due to gravity. More viscous waters could slow the sinking rate of particles. ^[13]

Oxygen

Dissolved oxygen is a requirement for aerobic respiration, and while the surface ocean is usually oxygen-rich due to atmospheric gas exchange, the mesopelagic zone is not in contact with the atmosphere and is controlled by other processes. Organic matter is exported to the mesopelagic zone from the overlying euphotic layer, while the minimal light in the mesopelagic zone limits photosynthesis. This results in oxygen consumption through respiration of most of the sinking organic matter, depleting oxygen and often creating an oxygen minimum zone (OMZ). The mesopelagic OMZ is particularly severe in the eastern tropical Pacific Ocean and tropical Indian Ocean due to poor ventilation.^[8] Oxygen concentrations are occasionally depleted to suboxic concentrations due to remineralization, which can make aerobic respiration difficult for organisms.^[8] In these anoxic regions, chemosynthesis is more likely to occur in which CO₂ and reduced compounds such as sulfide or ammonia are taken up to form organic carbon, contributing to the carbon reservoir in the mesopelagic.^[14] This pathway of carbon fixation has been estimated to be comparable in rate to the contribution by heterotrophic production. ^[15]

Nitrogen

The mesopelagic zone, an area of significant respiration and remineralization of particles, is generally nutrient-rich. This is in contrast to the overlying euphotic zone, which is usually nutrient-limited. Areas of low oxygen such as OMZ’s are a key area of denitrification by prokaryotes, where nitrate is converted into nitrogen gas, a loss to the ocean reservoir of nitrogen.^[8] At the suboxic interface that occurs at the edge of the OMZ, nitrite and ammonium can be coupled to produce nitrogen gas through anammox, removing nitrogen from the biologically available pool.

Biology

Although some light penetrates the mesopelagic zone, it is insufficient for photosynthesis. This is a very efficient ecosystem with many organisms recycling the organic matter descending from the epipelagic zone.^[16] The general types of life forms found are daytime-visiting herbivores, detritivores feeding on dead organisms and fecal pellets, and carnivores feeding on those detritivores.^[17] Phytoplankton do not inhabit the mesopelagic layer, due to lack of light.^[3] The biological community of the mesopelagic zone has adapted to a low-light, low-nutrient environment.^[17]

Virus and microbial ecology

Very little is known about the microbial community of the mesopelagic zone because it is a difficult area to study, but recent work has used DNA from seawater samples.^[18] Recent research highlights the importance of viruses and microbes role in recycling organic matter from the surface ocean, known as the biological pump.^[18]^[19]

These many microbes can get their energy from different pathways.^[20] Some are autotrophs, heterotrophs, and a 2006 study even discovered chemoautotrophs^[20]. This Archaea crenarchaeon Candidatus can oxidize ammonia as their food source without oxygen.^[20] They could be a major impact on the nitrogen and carbon cycles. One study estimates these nitrite-oxidizing bacteria, which are only 5% of the microbial population, can annually capture 1.1 Gt of carbon.^[18]

Overall, biomass and diversity typically decline exponentially with depth in the mesopelagic zone.^[21] The community composition changes at different depths in the mesopelagic as different organisms are evolved for different light conditions.^[21] Microbial biomass in the mesopelagic is greater at higher latitudes, decreasing towards the tropics, likely linked to the productivity levels in the surface waters.^[21] Viruses are very abundant in the mesopelagic, around 10¹⁰ - 10¹² every cubic meter and are fairly uniform throughout the mesopelagic zone.^[21]

Zooplankton ecology

Helmet jellyfish, *Periphylla periphylla*

The mesopelagic zone hosts a diverse zooplankton community. Many inhabitants of the mesopelagic zone move between the epipelagic zone during the night, and retreat to the mesopelagic zone during the day, a process known as diel vertical migration.^[21] These migrators can avoid predation during the day and feed at night, while their predators migrate up at night to follow the prey. This is such a massive migration that sonar operators in World War II would regularly misinterpret the signal returned by this thick layer of plankton as a false sea floor.^[22]

Gelatinous organisms are thought to play an important role in the ecology of the mesopelagic and are common predators.^[23] One study found that the helmet jellyfish Periphylla periphylla exhibit social behavior and can find each other at depth and form groups.^[23] Scientists speculate this could be a feeding strategy to allow a group to hunt together.^[23]

Mesopelagic zooplankton have unique adaptations for the low light. Bioluminescence is very common, which is used for a variety of functions like communication, prey attraction and mating.^[21] Many jellyfish are bioluminescent.^[23] Other organisms, like shrimp, have highly developed eyes to pick up the limited available light.^[17] Light organs, common in krill and shrimp, are another adaptation.^[17] Some octopus and krill even have tubular eyes that look upwards.^[22]

Most life processes, like growth rates and reproductive rates, are slower in the mesopelagic.^[17] Metabolic activity has been shown to decrease with depth and with temperature in colder-water environments.^[24] For example, the mesopelagic shrimp-like mysid, Gnathophausia ingens, lives for 6.4 to 8 years, while benthic shrimp only live for 2 years.^[17]

Fish ecology

Mesopelagic fish have a global distribution, except for the Arctic Ocean.^[25] Overall, this zone is home to a significant portion of the world's total fish biomass; one study estimated mesopelagic fish could be 95% of the total fish biomass.^[26] Another estimate puts mesopelagic fish biomass at 1 billion tons. ^[27] Because it is difficult to sample this area with nets, mesopelagic fish numbers are often estimated by usingechosounders and finding the 'deep scattering layer' through the backscatter received from these acoustic sounders.^[16] It could be the largest fishery in the world and there is active development for this zone to become a commercial fishery.^[25]

There are thirty families of mesopelagic fish^[28]. The dominant fish in the mesopelagic zone are lanternfish (Myctophidae.)^[27] They have prominent photophores along their ventral side. The Myctophid group includes 245 species distributed among 33 different genera.^[27] The Gonostomatidae, or bristlemouth, are also common mesopelagic fish. The bristlemouth could be the Earth's most abundant vertebrate, numbering in the hundreds of trillions to quadrillions.^[29] However, some areas have shown declining abundance, like in Southern California over a long-term study dating back to the 1970s.^[30] Cold water species were especially vulnerable to decline.^[30]

Many organisms are black, because these colors appear black due to light penetration. Many fish also have rows of photophores, which are small light-producing organs, mirrors on their sides angled to reflect the surrounding ocean and protect the fish, or countershading, with light colors on ventral side and dark colors on the dorsal side.^[17]

Food is often limited and patchy, leading to dietary adaptions. Many fish have sensitive eyes, huge jaws and small bodies, reducing the effort put into building muscles.^[17] Adaptations include jaws that can unhinge, elastic throats, and massive, long teeth. Other predators develop bioluminescent lures, like the angler fish, that can attract prey.^[17] Many fish also respond to chemical cues.^[17]

Human Impacts

Pollution

Marine Debris

Marine debris, specifically in the plastic form, have been found in every ocean basin and have a wide range of impacts on the marine world^[31] One of the most critical issues is ingestion of plastic debris, specifically microplastics.^[32] Mesopelagic species migrate to the surface waters to feast on their main prey species, Zooplankton, who are mixed with microplastics in the surface waters. Additionally, research has shown that even Zooplankton are consuming the microplastics themselves.^[33] These fish play a key role in energy dynamics, meaning they provide food to a number of predators including birds, fish and marine mammals. The concentration of these plastics has the potential to increase, meaning more economically important species could be contaminated as well.^[34] Concentration of plastic debris in mesopelagic populations can vary depending on geographical location and the concentration of marine debris located there. In 2018, approximately 73% of over 200 fish sampled in the North Atlantic had consumed plastic.^[35]

Bioaccumulation

The process of bioaccumulation (a buildup of a certain substance in the adipose tissue) and biomagnification (the process in which the concentration of the substance grows higher as you rise through the food chain) are growing issues in the mesopelagic zone.^[36] Mercury in fish, which can be traced back to a combination of anthropological factors (such as coal mining) in addition to natural factors. Mercury is a particularly important bioaccumulation contaminant, as it’s concentration in the mesopelagic zone is increasing faster than in surface waters.^[37] Inorganic mercury occurs in anthropogenic atmospheric emissions as it’s gaseous elemental form, which can be oxidized and then deposited in the ocean.^[38] Once there, the oxidized form can be converted to methylmercury, which is its organic form.^[38] Research suggests that current levels anthropogenic emissions will not equilibrate between the atmosphere and ocean for a period of decades to centuries^[39], which means we can expect current mercury concentrations in the ocean to keep rising. Mercury is a potent neurotoxin, and poses health risks to not only the mesopelagic species that consume it. Many of the mesopelagic species, such as myctophids, make their diurnal migration to the surface waters where they are consumed by pelagic fish, birds and mammals.^[40]

Fishing

Historically, there have been few examples of efforts to commercialize the mesopelagic zone, due to low economic value, technical feasibility and environmental impacts^[41]. While the biomass may be abundant, fish species here generally smaller in size and slower to reproduce.^[42] Fishing with large trawl nets poses threats to a high percentage of bycatch as well as poses potential impacts to the carbon cycling process^[41]. Additionally, getting to the mesopelagic requires fairly long journeys offshore.^[43] In 1977, a Soviet fishery opened but closed less than 20 years later due to low commercial profits, while a South African purse seine fishery closed in the mid-1980's due to processing difficulties from the high oil content of fish^[44]. As the biomass in the mesopelagic is so abundant, there has been an increase in interest to whether or not these populations could be of economic use in areas other than direct human consumption. For example, it has been suggested that the high abundance of fish in this zone could potentially satisfy a demand for fishmeal and nutraceuticals.^[41]

With a growing population, the demand for fishmeal in support of a growing aquaculture industry is high. There is a potential for economically viable harvest, for example, 5 billion tons of mesopelagic biomass could result in the production of circa 1.25 billion tons of food for human consumption^[45]. Additionally, the demand for nutraceuticals is also rapidly growing, stemming from the consumption of Omega-3 Fatty Acids in addition to the aquaculture industry requiring a specific marine oil for feed material.^[41] Lanternfish are of much interest to the aquaculture market, as they are especially high in fatty acids.^[46]

Climate Change

The mesopelagic region plays an important role in the Global Carbon Cycle, as it is the area where most of the organic matter that is travelling down the water column is respired. Mesopelagic species acquire carbon during their migration to feed in surface waters, and transport that carbon into the deep sea when they die. It is estimated that the mesopelagic cycles between 5 and 12 billion tons of carbon dioxide from the atmosphere per year, and until recently, this estimate was not included in many climate models. ^[47] It is difficult to quantify the effects of climate change on the mesopelagic zone as a whole, as climate change does not have uniform impacts geographically. Research suggests that in warming waters, as long as there are adequate nutrients and food for fish, then mesopelagic biomass could actually be higher due to increases in trophic efficiency and temperature driven metabolism.^[48] However, because warming will not be uniform throughout the global mesopelagic zone, it is predicted that some areas may actually decrease in fish production, while others increase. ^[48] Also, with warming waters there is a higher likelihood of increased stratification^[47]. This increase reduces the input of nutrients to the euphotic zone through an increase in nutrient limitation, and can lead to decreases in both net primary production and sinking particulate matter^[47]. Additional research suggests shifts in the geographical range of many species could also occur with warming, with many of them shifting away from the equator^[49]. The combination of these factors could potentially mean that as global ocean basins continue to warm, there could be areas in the mesopelagic that increase in biodiversity and species richness, especially moving farther from the equator^[49].

Research and Exploration

There is a dearth of knowledge about the mesopelagic zone so researchers have begun to develop new technology to explore and sample this area. The Woods Hole Oceanographic Institution (WHOI), NASA, and the Norwegian Institute of Marine Research are all working on projects to gain a better understanding of this zone in the ocean and its influence on the global carbon cycle. Traditional sampling nets have proved to be inadequate due to scaring off creatures from the pressure wave formed by the towed net and from the light produced by the bioluminescent species caught in the net. Mesopelagic activity was first investigated by use of sonar. However, there are many challenges with acoustic survey methods and previous research has estimated errors in measured amounts of biomass of up to three orders of magnitude. ^[50] This is due to inaccurate incorporation of depth, species size distribution, and acoustic properties of the species. Norway’s Institute of Marine Research has launched a research vessel named Dr. Fridtjof Nansen to investigate mesopelagic activity using sonar with their focus being on the sustainability of fishing operations. To overcome the challenges faced with acoustic sampling, WHOI is developing robots (Deep-See, Mesobot, and Snowclops) that are capable of studying this zone more precisely.

Discovery and Detection

The deep scattering layer often characterizes the mesopelagic due to the high amount of biomass that exists in the region.^[48] Acoustic sound sent into the ocean bounces off particles and organisms in the water column and return a strong signal. The region was initially discovered by American researchers during World War II in 1942 during anti-submarine research with sonar. Sonar at the time could not penetrate below this depth due to the large number of creatures obstructing sound waves.^[47] It is uncommon to detect deep scattering layers below 1000m. Until recently, sonar has been the predominate method for studying the mesopelagic.^[48]

The Malaspina Circumnavigation Expedition was a spanish led scientific quest to gain a better understanding of the state of the ocean in 2011 and the diversity in the deep oceans.^[51] The data collected, particularly through sonar observations showed that the biomass estimation in the mesopelagic was lower than previously thought.^[52]

Deep-See

WHOI is currently working on a project to characterize and document the mesopelagic ecosystem. They have developed a device named Deep-See weighing approximately 700 kg, which is designed to be towed behind a research vessel^[47]. The Deep-See is capable of reaching depths up to 2000 m and can estimate the amount of biomass and biodiversity in this mesopelagic ecosystem. Deep-See is equipped with cameras, sonars, sensors, water sample collection devices, and a real-time data transmission system^[53].

Mesobot

WHOI is collaborating with the Monterey Bay Aquarium Research Institute (MBARI), Stanford University, and the University of Texas Rio Grande Valley to develop a small autonomous robot, Mesobot, weighing approximately 75 kg.^[47]^[54] Mesobot is equipped with high-definition cameras to track and record mesopelagic species on their daily migration over extended periods of time. The robot's thrusters were designed so that they do not disturb the life in the mesopelagic that it is observing.^[47] Traditional sample collection devices fail to preserve organisms captured in the mesopelagic due to the large pressure change associated with surfacing. The mesobot also has a unique sampling mechanism that is capable of keeping the organisms alive during their ascent. The first sea trial of this device is expected to be in 2019.

Snowclops

Another mesopelagic robot developed by WHOI is the Snowclops. This device descends down the water column and measures the amount of marine snow at various depths. These tiny particles are a food source for other organisms so it is important to monitor the different levels of marine snow to characterize the carbon exchange between the surface ocean and the mesopelagic.

Old material:

Ecology

Although some light penetrates the mesopelagic zone, it is insufficient for photosynthesis. The general types of life forms found are daytime visiting herbivores, detritivores feeding on dead organisms and fecal pellets, and carnivores feeding on the former types.^[55] Algae do not reside inside the mesopelagic layer, due to lack of light.^[7]

Examples of animals in the mesopelagic zone are bristlemouth, swordfish, squid, wolf eels, cuttlefish and other semi-deepsea creatures. The bristlemouth is the Earth's most abundant vertebrate, numbering in the hundreds of trillions to quadrillions.^[56] The small amount of sunlight is sufficient for animals, such as the chain catshark, to be fluorescent.

A 2015 study found that the zone's biomass is up to 10 times greater than earlier estimates, totaling 10 billion tons and representing some 90 percent of the planet’s fish biomass, some 100 times that of the annual seafood catch and 200 times that of the world’s 24 billion chickens.^[57] Commercial fisherman have found the biomass viable for fish farming meal, oil and silage.^[57] In 2002, the UN Food and Agriculture Organization discussed in a report that the mesopelagic zone has biomass viable for fish-meal and fish-oil industry.^[7]

Climate change

The quantity of mesopelagic life is large enough to play a significant role in global carbon cycling. As the fish participate in the food chain, they acquire carbon rendered from carbon dioxide absorbed by surface waters. Upon death, they transport that carbon into the sea bottom or back upon coastal shores. As of 2015 the revised estimates of mesopelagic life had yet to be incorporated into climate models. Per year, it is estimated to cycle between 5 billion and 12 billion tonnes of CO2 from the atmosphere through the ocean region.^[7]

References

^ del Giorgio, Paul A.; Duarte, Carlos M. (28 November 2002). "Respiration in the open ocean". Nature. 420 (6914): 379–384. doi:10.1038/nature01165.
^ "The mesopelagic: Cinderella of the oceans". The Economist. Retrieved 2018-11-06.
^ Hackett, Jon; Harrington, Seán, eds. (2018-02-02). Beasts of the Deep. John Libbey Publishing. ISBN 9780861969395.
^ del Giorgio, Paul A.; Duarte, Carlos M. (28 November 2002). "Respiration in the open ocean". Nature. 420 (6914): 379–384. doi:10.1038/nature01165.
^ "NOAA Ocean Explorer: Sounds in the Sea 2001: diagram of how sound travels underwater". oceanexplorer.noaa.gov. Retrieved 2018-11-18.
^ ^a ^b ^c ^d L., Talley, Lynne D. Emery, William J. Pickard, George (2012). Descriptive physical oceanography : an introduction. Academic Press. ISBN 9780750645522. OCLC 842833260.{{cite book}}: CS1 maint: multiple names: authors list (link)
^ ^a ^b ^c ^d "The mesopelagic: Cinderella of the oceans". The Economist. Retrieved 2017-04-23.
^ ^a ^b ^c ^d ^e ^f Robinson, Carol; Steinberg, Deborah K.; Anderson, Thomas R.; Arístegui, Javier; Carlson, Craig A.; Frost, Jessica R.; Ghiglione, Jean-François; Hernández-León, Santiago; Jackson, George A.; Koppelmann, Rolf; Quéguiner, Bernard; Ragueneau, Olivier; Rassoulzadegan, Fereidoun; Robison, Bruce H.; Tamburini, Christian; Tanaka, Tsuneo; Wishner, Karen F.; Zhang, Jing (August 2010). "Mesopelagic zone ecology and biogeochemistry – a synthesis". Deep Sea Research Part II: Topical Studies in Oceanography. 57 (16): 1504–1518. doi:10.1016/j.dsr2.2010.02.018.
^ Davison, P.C.; Checkley, D.M.; Koslow, J.A.; Barlow, J. (September 2013). "Carbon export mediated by mesopelagic fishes in the northeast Pacific Ocean". Progress in Oceanography. 116: 14–30. doi:10.1016/j.pocean.2013.05.013.
^ Hidaka, Kiyotaka; Kawaguchi, Kouichi; Murakami, Masahiro; Takahashi, Mio. "Downward transport of organic carbon by diel migratory micronekton in the western equatorial Pacific:". Deep Sea Research Part I: Oceanographic Research Papers. 48 (8): 1923–1939. doi:10.1016/s0967-0637(01)00003-6. ISSN 0967-0637.
^ Ariza, A.; Garijo, J.C.; Landeira, J.M.; Bordes, F.; Hernández-León, S. "Migrant biomass and respiratory carbon flux by zooplankton and micronekton in the subtropical northeast Atlantic Ocean (Canary Islands)". Progress in Oceanography. 134: 330–342. doi:10.1016/j.pocean.2015.03.003. ISSN 0079-6611.
^ Fowler, Scott W; Knauer, George A. "Role of large particles in the transport of elements and organic compounds through the oceanic water column". Progress in Oceanography. 16 (3): 147–194. doi:10.1016/0079-6611(86)90032-7. ISSN 0079-6611.
^ ^a ^b ^c Buesseler, Ken O.; Lamborg, Carl H.; Boyd, Philip W.; Lam, Phoebe J.; Trull, Thomas W.; Bidigare, Robert R.; Bishop, James K. B.; Casciotti, Karen L.; Dehairs, Frank (2007-04-27). "Revisiting Carbon Flux Through the Ocean's Twilight Zone". Science. 316 (5824): 567–570. doi:10.1126/science.1137959. ISSN 0036-8075. PMID 17463282.
^ Sanders, Richard J.; Henson, Stephanie A.; Martin, Adrian P.; Anderson, Tom R.; Bernardello, Raffaele; Enderlein, Peter; Fielding, Sophie; Giering, Sarah L. C.; Hartmann, Manuela (2016). "Controls over Ocean Mesopelagic Interior Carbon Storage (COMICS): Fieldwork, Synthesis, and Modeling Efforts". Frontiers in Marine Science. 3. doi:10.3389/fmars.2016.00136. ISSN 2296-7745.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ Reinthaler, Thomas; van Aken, Hendrik M.; Herndl, Gerhard J. "Major contribution of autotrophy to microbial carbon cycling in the deep North Atlantic's interior". Deep Sea Research Part II: Topical Studies in Oceanography. 57 (16): 1572–1580. doi:10.1016/j.dsr2.2010.02.023. ISSN 0967-0645.
^ ^a ^b Hays, Graeme C. (2003). "A review of the adaptive significance and ecosystem consequences of zooplankton diel vertical migrations". Hydrobiologia. 503 (1–3): 163–170. doi:10.1023/b:hydr.0000008476.23617.b0. ISSN 0018-8158.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j Miller, Charles B. (2004). Biological Oceanography. Oxford, UK: Blackwell Publishing. pp. 232–245. ISBN 0-632-05536-7.
^ ^a ^b ^c Sciences, Bigelow Laboratory for Ocean. "Dark Ocean Bacteria Discovered to Play Large Role in Carbon Capture - Bigelow Laboratory for Ocean Sciences". www.bigelow.org. Retrieved 2018-11-26.
^ Reinthaler, Thomas; van Aken, Hendrik M.; Herndl, Gerhard J. "Major contribution of autotrophy to microbial carbon cycling in the deep North Atlantic's interior". Deep Sea Research Part II: Topical Studies in Oceanography. 57 (16): 1572–1580. doi:10.1016/j.dsr2.2010.02.023. ISSN 0967-0645.
^ ^a ^b ^c Ingalls, Anitra E.; Shah, Sunita R.; Hansman, Roberta L.; Aluwihare, Lihini I.; Santos, Guaciara M.; Druffel, Ellen R. M.; Pearson, Ann (2006-04-25). "Quantifying archaeal community autotrophy in the mesopelagic ocean using natural radiocarbon". Proceedings of the National Academy of Sciences. 103 (17): 6442–6447. doi:10.1073/pnas.0510157103. ISSN 0027-8424. PMC 1564200. PMID 16614070.{{cite journal}}: CS1 maint: PMC format (link)
^ ^a ^b ^c ^d ^e ^f Robinson, Carol; Steinberg, Deborah K.; Anderson, Thomas R.; Arístegui, Javier; Carlson, Craig A.; Frost, Jessica R.; Ghiglione, Jean-François; Hernández-León, Santiago; Jackson, George A.; Koppelmann, Rolf; Quéguiner, Bernard; Ragueneau, Olivier; Rassoulzadegan, Fereidoun; Robison, Bruce H.; Tamburini, Christian; Tanaka, Tsuneo; Wishner, Karen F.; Zhang, Jing (August 2010). "Mesopelagic zone ecology and biogeochemistry – a synthesis". Deep Sea Research Part II: Topical Studies in Oceanography. 57 (16): 1504–1518. doi:10.1016/j.dsr2.2010.02.018.
^ ^a ^b Taonga, New Zealand Ministry for Culture and Heritage Te Manatu. "2. – Deep-sea creatures – Te Ara Encyclopedia of New Zealand". Retrieved 2018-11-26.
^ ^a ^b ^c ^d Kaartvedt, Stein; Ugland, Karl I.; Klevjer, Thor A.; Røstad, Anders; Titelman, Josefin; Solberg, Ingrid (2015-06-11). "Social behaviour in mesopelagic jellyfish". Scientific Reports. 5 (1). doi:10.1038/srep11310. ISSN 2045-2322.
^ Frost, Jessica R.; Denda, Anneke; Fox, Clive J.; Jacoby, Charles A.; Koppelmann, Rolf; Nielsen, Morten Holtegaard; Youngbluth, Marsh J. (2011-10-12). "Distribution and trophic links of gelatinous zooplankton on Dogger Bank, North Sea". Marine Biology. 159 (2): 239–253. doi:10.1007/s00227-011-1803-7. ISSN 0025-3162.
^ ^a ^b Davison, Peter C.; Koslow, J. Anthony; Kloser, Rudy J. (2015-02-19). "Acoustic biomass estimation of mesopelagic fish: backscattering from individuals, populations, and communities". ICES Journal of Marine Science. 72 (5): 1413–1424. doi:10.1093/icesjms/fsv023. ISSN 1095-9289.
^ "Ninety-five per cent of world's fish hide in mesopelagic zone". Retrieved 2018-11-26.
^ ^a ^b ^c John, St; A, Michael; Borja, Angel; Chust, Guillem; Heath, Michael; Grigorov, Ivo; Mariani, Patrizio; Martin, Adrian P.; Santos, Ricardo S. (2016). "A Dark Hole in Our Understanding of Marine Ecosystems and Their Services: Perspectives from the Mesopelagic Community". Frontiers in Marine Science. 3. doi:10.3389/fmars.2016.00031. ISSN 2296-7745.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ Encylopedia [i.e. Encyclopedia] of Ocean Sciences : Marine biology. Steele, John H. (2nd ed ed.). London: Academic Press. 2009. ISBN 9780123757241. OCLC 501069621. {{cite book}}: |edition= has extra text (help)CS1 maint: others (link)
^ "An Ocean Mystery in the Trillions". Retrieved 2018-11-16.
^ ^a ^b Koslow, J. Anthony; Miller, Eric F.; McGowan, John A. (2015-10-28). "Dramatic declines in coastal and oceanic fish communities off California". Marine Ecology Progress Series. 538: 221–227. doi:10.3354/meps11444. ISSN 0171-8630.
^ Cózar, Andrés; Echevarría, Fidel; González-Gordillo, J. Ignacio; Irigoien, Xabier; Úbeda, Bárbara; Hernández-León, Santiago; Palma, Álvaro T.; Navarro, Sandra; García-de-Lomas, Juan (2014-07-15). "Plastic debris in the open ocean". Proceedings of the National Academy of Sciences. 111 (28): 10239–10244. doi:10.1073/pnas.1314705111. ISSN 0027-8424. PMID 24982135.
^ "Microplastics as contaminants in the marine environment: A review". Marine Pollution Bulletin. 62 (12): 2588–2597. 2011-12-01. doi:10.1016/j.marpolbul.2011.09.025. ISSN 0025-326X.
^ Cole, Matthew; Lindeque, Pennie; Fileman, Elaine; Halsband, Claudia; Goodhead, Rhys; Moger, Julian; Galloway, Tamara S. (2013-06-06). "Microplastic Ingestion by Zooplankton". Environmental Science & Technology. 47 (12): 6646–6655. doi:10.1021/es400663f. ISSN 0013-936X.
^ Davison, Peter; Asch, Rebecca G. (2011-06-27). "Plastic ingestion by mesopelagic fishes in the North Pacific Subtropical Gyre". Marine Ecology Progress Series. 432: 173–180. doi:10.3354/meps09142. ISSN 0171-8630.
^ Wieczorek, Alina M.; Morrison, Liam; Croot, Peter L.; Allcock, A. Louise; MacLoughlin, Eoin; Savard, Olivier; Brownlow, Hannah; Doyle, Thomas K. (2018). "Frequency of Microplastics in Mesopelagic Fishes from the Northwest Atlantic". Frontiers in Marine Science. 5. doi:10.3389/fmars.2018.00039. ISSN 2296-7745.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ Monteiro, L.R.; Costa, V.; Furness, R.W.; Santos, R.S. (1997). "Mercury concentrations in prey fish indicate enhanced bioaccumulation in mesopelagic environments". Oceanographic Literature Review. 5 (44). ISSN 0967-0653.
^ Peterson, Sarah H.; Ackerman, Joshua T.; Costa, Daniel P. (2015-07-07). "Marine foraging ecology influences mercury bioaccumulation in deep-diving northern elephant seals". Proc. R. Soc. B. 282 (1810): 20150710. doi:10.1098/rspb.2015.0710. ISSN 0962-8452. PMC 4590481. PMID 26085591.{{cite journal}}: CS1 maint: PMC format (link)
^ ^a ^b Blum, Joel D.; Popp, Brian N.; Drazen, Jeffrey C.; Anela Choy, C.; Johnson, Marcus W. (2013-08-25). "Methylmercury production below the mixed layer in the North Pacific Ocean". Nature Geoscience. 6 (10): 879–884. doi:10.1038/ngeo1918. ISSN 1752-0894.
^ Sunderland, Elsie M.; Mason, Robert P. "Human impacts on open ocean mercury concentrations". Global Biogeochemical Cycles. 21 (4): n/a–n/a. doi:10.1029/2006gb002876. ISSN 0886-6236.
^ Neff, J. M. (2002-04-16). Bioaccumulation in Marine Organisms: Effect of Contaminants from Oil Well Produced Water. Elsevier. ISBN 9780080527840.
^ ^a ^b ^c ^d John, St; A, Michael; Borja, Angel; Chust, Guillem; Heath, Michael; Grigorov, Ivo; Mariani, Patrizio; Martin, Adrian P.; Santos, Ricardo S. (2016). "A Dark Hole in Our Understanding of Marine Ecosystems and Their Services: Perspectives from the Mesopelagic Community". Frontiers in Marine Science. 3. doi:10.3389/fmars.2016.00031. ISSN 2296-7745.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ John, St; A, Michael; Borja, Angel; Chust, Guillem; Heath, Michael; Grigorov, Ivo; Mariani, Patrizio; Martin, Adrian P.; Santos, Ricardo S. (2016). "A Dark Hole in Our Understanding of Marine Ecosystems and Their Services: Perspectives from the Mesopelagic Community". Frontiers in Marine Science. 3. doi:10.3389/fmars.2016.00031. ISSN 2296-7745.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ "The Ocean's 'Twilight Zone' Faces Fishing Threat". Oceans. Retrieved 2018-11-07.
^ Prellezo, Raúl. "Exploring the economic viability of a mesopelagic fishery in the Bay of Biscay". ICES Journal of Marine Science. doi:10.1093/icesjms/fsy001.
^ Naylor, Rosamond L.; Hardy, Ronald W.; Bureau, Dominique P.; Chiu, Alice; Elliott, Matthew; Farrell, Anthony P.; Forster, Ian; Gatlin, Delbert M.; Goldburg, Rebecca J. (2009-09-08). "Feeding aquaculture in an era of finite resources". Proceedings of the National Academy of Sciences. 106 (36): 15103–15110. doi:10.1073/pnas.0905235106. ISSN 0027-8424. PMC 2741212. PMID 19805247. {{cite journal}}: |last3= has generic name (help)CS1 maint: PMC format (link)
^ Koizumi, Kyoko; Hiratsuka, Seiichi; Saito, Hiroaki (2014). "Lipid and Fatty Acids of Three Edible Myctophids, Diaphus watasei, Diaphus suborbitalis, and Benthosema pterotum: High Levels of Icosapentaenoic and Docosahexaenoic Acids". Journal of Oleo Science. 63 (5): 461–470. doi:10.5650/jos.ess13224. ISSN 1345-8957.
^ ^a ^b ^c ^d ^e ^f ^g "The mesopelagic: Cinderella of the oceans". The Economist. Retrieved 2018-11-06.
^ ^a ^b ^c ^d Proud, Roland; Cox, Martin J.; Brierley, Andrew S. "Biogeography of the Global Ocean's Mesopelagic Zone". Current Biology. 27 (1): 113–119. doi:10.1016/j.cub.2016.11.003. ISSN 0960-9822.
^ ^a ^b Costello, Mark J.; Breyer, Sean. "Ocean Depths: The Mesopelagic and Implications for Global Warming". Current Biology. 27 (1): R36–R38. doi:10.1016/j.cub.2016.11.042. ISSN 0960-9822. {{cite journal}}: no-break space character in |title= at position 51 (help)
^ Davison, Peter C.; Koslow, J. Anthony; Kloser, Rudy J. (2015-02-19). "Acoustic biomass estimation of mesopelagic fish: backscattering from individuals, populations, and communities". ICES Journal of Marine Science. 72 (5): 1413–1424. doi:10.1093/icesjms/fsv023. ISSN 1095-9289.
^ Duarte, Carlos M. (2015-01-28). "Seafaring in the 21St Century: The Malaspina 2010 Circumnavigation Expedition". Limnology and Oceanography Bulletin. 24 (1): 11–14. doi:10.1002/lob.10008. ISSN 1539-607X.
^ Irigoien, Xabier; Klevjer, T. A.; Røstad, A.; Martinez, U.; Boyra, G.; Acuña, J. L.; Bode, A.; Echevarria, F.; Gonzalez-Gordillo, J. I. (2014-02-07). "Large mesopelagic fishes biomass and trophic efficiency in the open ocean". Nature Communications. 5 (1). doi:10.1038/ncomms4271. ISSN 2041-1723.
^ "What lives in the ocean's twilight zone? New technologies might finally tell us". Science | AAAS. 2018-08-22. Retrieved 2018-11-16.
^ "Mesobot". Woods Hole Oceanographic Institution. Retrieved 2018-11-16.
^ Hogan, Michael C. "Mesopelagic zone". The Encyclopedia or Earth. Retrieved 17 September 2013.
^ Broad, William J. (June 29, 2015). "An Ocean Mystery in the Trillions". The New York Times. Retrieved August 2015. {{cite news}}: Check date values in: |accessdate= (help)
^ ^a ^b BROAD, WILLIAM J. (June 29, 2015). "Dark Region of Ocean May Shed Light on Climate Change and Other Issues". New York Times. Retrieved 2017-04-23. {{cite news}}: Cite has empty unknown parameter: |dead-url= (help)

@@ Line 1: / Line 1: @@
+[[File:FMIB_35304_Luminous_Fish_of_the_Deep_Sea.jpeg|link=https://en.wikipedia.org/wiki/File:FMIB_35304_Luminous_Fish_of_the_Deep_Sea.jpeg|thumb|Illustration by [[Charles Frederick Holder]] of various bioluminescent fish that live in the mesopelagic zone.]]
-{{short description|The part of the pelagic zone between the photic epipelagic above and the aphotic bathypelagic below}}
+[[Image:Pelagiczone.svg|thumb|200px|left|Pelagic zones]]{{Aquatic layer topics}}The '''mesopelagic''' ([[Greek language|Greek]] μέσον, middle) (also known as the ''middle pelagic'' or ''twilight zone'') is the part of the [[pelagic zone]] that begins at the depth where 1% of incident light at the water surface.  It lies between the [[Photic zone|photic]] [[epipelagic]] above and the [[Aphotic zone|aphotic]] [[bathypelagic]] below, where there is no [[light]] at all. The depth of this zone is approximately 200 to 1000 meters (~660 to 3300 feet) below the [[Sea level|ocean surface]].<ref name=":162">{{cite journal|last1=del Giorgio|first1=Paul A.|last2=Duarte|first2=Carlos M.|date=28 November 2002|title=Respiration in the open ocean|journal=Nature|volume=420|issue=6914|pages=379–384|doi=10.1038/nature01165}}</ref>  It hosts a diverse biological community that includes [[Gonostomatidae|bristlemouths]], [[blobfish]], bioluminescent [[jellyfish]], [[giant squid]], and a myriad of other unique organisms adapted to live in a low-light environment.<ref name=":13">{{Cite news|url=https://www.economist.com/science-and-technology/2017/04/15/the-mesopelagic-cinderella-of-the-oceans|title=The mesopelagic: Cinderella of the oceans|work=The Economist|access-date=2018-11-06|language=en}}</ref>  It has long captivated the imagination of scientist, artists and writers; deep sea creatures are prominent in popular culture, particularly as horror movie villains.<ref>{{Cite book|url=http://dx.doi.org/10.2307/j.ctt20krz85|title=Beasts of the Deep|date=2018-02-02|publisher=John Libbey Publishing|isbn=9780861969395|editor-last=Hackett|editor-first=Jon|editor-last2=Harrington|editor-first2=Seán}}</ref>
-{{Aquatic layer topics}}
-[[Image:Pelagiczone.svg|thumb|200px|left|Pelagic zones]]
-The '''mesopelagic''' ([[Greek language|Greek]] μέσον, middle) (also known as the ''middle pelagic'' or ''twilight zone'') is that part of the [[pelagic zone]] that extends from a depth of 200 to 1000 meters (~660 to 3300 feet)<ref>{{cite book|title=Essentials of Oceanography|year=2010|publisher=Prentice Hall|pages=363–366|author=Trujillo, Alan P.|edition=10th|author2=Thurman, Harold V.}}</ref> below the [[Sea level|ocean surface]]. It lies between the [[photic zone|photic]] [[epipelagic]] above and the [[aphotic zone|aphotic]] [[bathypelagic]] below, where there is no [[light]] at all.
 ==Physical conditions==
+The mesopelagic zone includes the region of sharp changes in temperature, salinity and density called the [[thermocline]], [[halocline]], and [[Pycnocline|pycnocline.]]<ref name=":16">{{cite journal|last1=del Giorgio|first1=Paul A.|last2=Duarte|first2=Carlos M.|date=28 November 2002|title=Respiration in the open ocean|journal=Nature|volume=420|issue=6914|pages=379–384|doi=10.1038/nature01165}}</ref> The temperature varies from over 20 °C (68 °F) at the top to around 4 °C (39 °F) at the boundary with the [[bathyal zone]]. The variation in salinity is smaller typically between 34.5 and 35 psu. The density range is 1023 to 1027 g/kg of seawater. These changes in temperature, salinity, and density induce stratification which create ocean layers that affect gradients and mixing of nutrients and dissolved gasses. The [[SOFAR channel|Sound Fixing and Ranging channel (SOFAR)]] is located at the base of the mesopelagic zone at about 600-1200m.<ref>{{Cite web|url=https://oceanexplorer.noaa.gov/explorations/sound01/background/acoustics/media/sofar.html|title=NOAA Ocean Explorer: Sounds in the Sea 2001: diagram of how sound travels underwater|website=oceanexplorer.noaa.gov|access-date=2018-11-18}}</ref> Sound travels the slowest in this channel due to the salinity and temperature variations. It is a wave-guided zone where sound waves reflect within the layer and propagate long distances.<ref name=":17">{{Cite book|url=http://worldcat.org/oclc/842833260|title=Descriptive physical oceanography : an introduction|last=L.|first=Talley, Lynne D. Emery, William J. Pickard, George|date=2012|publisher=Academic Press|isbn=9780750645522|oclc=842833260}}</ref> [[Mode water]] is a water mass that is typically defined by its vertically mixed properties.<ref name=":17" /> It often forms as deep mixed layers at the depth of the thermocline. <ref name=":17" /> The mode water in the mesopelagic has [[Water cycle#Residence times|residency time]]<nowiki/>s on decadal or century scales.<ref name=":17" /> The longer overturning times contrast with the daily and shorter scales that a variety of animals move vertically through the zone and sinking of various debris.
-Although the temperature varies less at any one height than the epipelagic, the mesopelagic is the location of the [[thermocline]], and in warmer regions of the world, the temperature varies from over 20&nbsp;°C (68&nbsp;°F) at the top to around 4&nbsp;°C (39&nbsp;°F) at the boundary with the [[bathyal zone]]. Water generally moves slowly in the mesopelagic with a [[Water cycle#Residence times|residency time]] of about a century,<ref name="auto">{{cite web|last=Hogan|first=Michael C.|title=Mesopelagic zone|url=http://www.eoearth.org/view/article/154574/|publisher=The Encyclopedia or Earth|accessdate=17 September 2013}}</ref> though a variety of animals move vertically through the zone on a daily basis and various debris sink down in relatively short time frames.
 The region was initially discovered by American researchers during [[World War II]] in 1942 during [[Anti-submarine warfare|anti-submarine]] research with [[sonar]]. Sonar at the time could not penetrate below this depth due to the large number of creatures obstructing sound waves.<ref name=":1" />
+== Biogeochemistry ==
+=== Carbon ===
+The mesopelagic zone plays a key role in the ocean's biological pump, which contributes to the [[oceanic carbon cycle]]. In the biological pump, organic carbon is produced in the surface [[euphotic zone]] where light promotes photosynthesis, and a fraction of this production is exported out of the surface mixed layer and into the mesopelagic zone. One pathway for carbon export from the euphotic layer is through sinking of particles, which can be accelerated through repackaging of organic matter in zooplankton fecal pellets, ballasted particles, and aggregates.
+In the mesopelagic zone, the [[biological pump]] is key to carbon cycling, as this zone is largely dominated by [[Remineralisation|remineralization]] of particulate organic carbon (POC).  When a fraction of POC is exported from the euphotic zone, an estimated 90% of that POC is respired in the mesopelagic zone.<ref name="Robinson">{{cite journal|last1=Robinson|first1=Carol|last2=Steinberg|first2=Deborah K.|last3=Anderson|first3=Thomas R.|last4=Arístegui|first4=Javier|last5=Carlson|first5=Craig A.|last6=Frost|first6=Jessica R.|last7=Ghiglione|first7=Jean-François|last8=Hernández-León|first8=Santiago|last9=Jackson|first9=George A.|date=August 2010|title=Mesopelagic zone ecology and biogeochemistry – a synthesis|journal=Deep Sea Research Part II: Topical Studies in Oceanography|volume=57|issue=16|pages=1504–1518|doi=10.1016/j.dsr2.2010.02.018|last10=Koppelmann|first10=Rolf|last11=Quéguiner|first11=Bernard|last12=Ragueneau|first12=Olivier|last13=Rassoulzadegan|first13=Fereidoun|last14=Robison|first14=Bruce H.|last15=Tamburini|first15=Christian|last16=Tanaka|first16=Tsuneo|last17=Wishner|first17=Karen F.|last18=Zhang|first18=Jing}}</ref> This is due to the microbial organisms that respire organic matter and remineralize the nutrients, while mesopelagic fish also package organic matter into quick-sinking parcels for deeper export.<ref>{{cite journal|last1=Davison|first1=P.C.|last2=Checkley|first2=D.M.|last3=Koslow|first3=J.A.|last4=Barlow|first4=J.|date=September 2013|title=Carbon export mediated by mesopelagic fishes in the northeast Pacific Ocean|journal=Progress in Oceanography|volume=116|pages=14–30|doi=10.1016/j.pocean.2013.05.013}}</ref>
+Another key process occurring in this zone is the [[diel vertical migration]] of certain species, which move between the euphotic zone and mesopelagic zone and actively transport particulate organic matter to the deep.<ref name="Robinson" />  In one study in the Equatorial Pacific, myctophids in the mesopelagic zone were estimated to actively transport 15-28% of the passive POC sinking to the deep,<ref>{{Cite journal|last=Hidaka|first=Kiyotaka|last2=Kawaguchi|first2=Kouichi|last3=Murakami|first3=Masahiro|last4=Takahashi|first4=Mio|title=Downward transport of organic carbon by diel migratory micronekton in the western equatorial Pacific:|url=https://linkinghub.elsevier.com/retrieve/pii/S0967063701000036|journal=Deep Sea Research Part I: Oceanographic Research Papers|volume=48|issue=8|pages=1923–1939|doi=10.1016/s0967-0637(01)00003-6|issn=0967-0637|via=}}</ref> while a study near the Canary Islands estimated 53% of vertical carbon flux was due to active transport from a combination of zooplankton and micronekton.<ref>{{Cite journal|last=Ariza|first=A.|last2=Garijo|first2=J.C.|last3=Landeira|first3=J.M.|last4=Bordes|first4=F.|last5=Hernández-León|first5=S.|title=Migrant biomass and respiratory carbon flux by zooplankton and micronekton in the subtropical northeast Atlantic Ocean (Canary Islands)|url=https://doi.org/10.1016/j.pocean.2015.03.003|journal=Progress in Oceanography|volume=134|pages=330–342|doi=10.1016/j.pocean.2015.03.003|issn=0079-6611|via=}}</ref> When primary productivity is high, the contribution of active transport by vertical migration has been estimated to be comparable to sinking particle export.<ref name="Robinson" />
+==== Particle Packaging and sinking ====
+Mean particle sinking rates are 10 to 100 m/day. <ref>{{Cite journal|last=Fowler|first=Scott W|last2=Knauer|first2=George A|title=Role of large particles in the transport of elements and organic compounds through the oceanic water column|url=https://linkinghub.elsevier.com/retrieve/pii/0079661186900327|journal=Progress in Oceanography|volume=16|issue=3|pages=147–194|doi=10.1016/0079-6611(86)90032-7|issn=0079-6611|via=}}</ref> Sinking rates have been measured in the project VERTIGO (Vertical Transport in the Global Ocean) using neutrally buoyant sediment traps.<ref name=":15">{{Cite journal|last=Buesseler|first=Ken O.|last2=Lamborg|first2=Carl H.|last3=Boyd|first3=Philip W.|last4=Lam|first4=Phoebe J.|last5=Trull|first5=Thomas W.|last6=Bidigare|first6=Robert R.|last7=Bishop|first7=James K. B.|last8=Casciotti|first8=Karen L.|last9=Dehairs|first9=Frank|date=2007-04-27|title=Revisiting Carbon Flux Through the Ocean's Twilight Zone|url=http://science.sciencemag.org/content/316/5824/567|journal=Science|language=en|volume=316|issue=5824|pages=567–570|doi=10.1126/science.1137959|issn=0036-8075|pmid=17463282}}</ref> The variability in sinking rates is due to differences in ballast, water temperature, food web structure and the types of phyto- and zooplankton in different areas of the ocean. <ref name=":15" /> If the material sinks faster, then it gets respired less by bacteria, transporting more carbon from the surface layer to the deep ocean. Larger fecal pellets sink faster due to gravity. More viscous waters could slow the sinking rate of particles. <ref name=":15" />
+=== Oxygen ===
+Dissolved oxygen is a requirement for aerobic respiration, and while the surface ocean is usually oxygen-rich due to atmospheric gas exchange, the mesopelagic zone is not in contact with the atmosphere and is controlled by other processes. Organic matter is exported to the mesopelagic zone from the overlying euphotic layer, while the minimal light in the mesopelagic zone limits photosynthesis. This results in oxygen consumption through respiration of most of the sinking organic matter, depleting oxygen and often creating an [[oxygen minimum zone]] (OMZ). The mesopelagic OMZ is particularly severe in the eastern tropical Pacific Ocean and tropical Indian Ocean due to poor ventilation.<ref name="Robinson" /> Oxygen concentrations are occasionally depleted to suboxic concentrations due to remineralization, which can make aerobic respiration difficult for organisms.<ref name="Robinson" /> In these anoxic regions, chemosynthesis is more likely to occur in which CO<sub>2</sub> and reduced compounds such as sulfide or ammonia are taken up to form organic carbon, contributing to the carbon reservoir in the mesopelagic.<ref>{{Cite journal|last=Sanders|first=Richard J.|last2=Henson|first2=Stephanie A.|last3=Martin|first3=Adrian P.|last4=Anderson|first4=Tom R.|last5=Bernardello|first5=Raffaele|last6=Enderlein|first6=Peter|last7=Fielding|first7=Sophie|last8=Giering|first8=Sarah L. C.|last9=Hartmann|first9=Manuela|date=2016|title=Controls over Ocean Mesopelagic Interior Carbon Storage (COMICS): Fieldwork, Synthesis, and Modeling Efforts|url=https://www.frontiersin.org/articles/10.3389/fmars.2016.00136/full|journal=Frontiers in Marine Science|language=English|volume=3|doi=10.3389/fmars.2016.00136|issn=2296-7745}}</ref> This pathway of carbon fixation has been estimated to be comparable in rate to the contribution by heterotrophic production. <ref name=":02">{{Cite journal|last=Reinthaler|first=Thomas|last2=van Aken|first2=Hendrik M.|last3=Herndl|first3=Gerhard J.|title=Major contribution of autotrophy to microbial carbon cycling in the deep North Atlantic’s interior|url=https://linkinghub.elsevier.com/retrieve/pii/S0967064510000895|journal=Deep Sea Research Part II: Topical Studies in Oceanography|volume=57|issue=16|pages=1572–1580|doi=10.1016/j.dsr2.2010.02.023|issn=0967-0645|via=}}</ref>
+=== Nitrogen ===
+The mesopelagic zone, an area of significant respiration and [[Remineralisation|remineralization]] of particles, is generally nutrient-rich. This is in contrast to the overlying euphotic zone, which is usually nutrient-limited. Areas of low oxygen such as OMZ’s are a key area of [[denitrification]] by prokaryotes, where nitrate is converted into nitrogen gas, a loss to the ocean reservoir of nitrogen.<ref name="Robinson" /> At the suboxic interface that occurs at the edge of the OMZ, nitrite and ammonium can be coupled to produce nitrogen gas through [[anammox]], removing nitrogen from the biologically available pool.
+== Biology ==
+Although some light penetrates the mesopelagic zone, it is insufficient for [[photosynthesis]].  This is a very efficient ecosystem with many organisms recycling the organic matter descending from the [[Pelagic zone|epipelagic zone]].<ref name=":5">{{Cite journal|last=Hays|first=Graeme C.|date=2003|title=A review of the adaptive significance and ecosystem consequences of zooplankton diel vertical migrations|url=https://doi.org/10.1023/B:HYDR.0000008476.23617.b0|journal=Hydrobiologia|language=en|volume=503|issue=1-3|pages=163–170|doi=10.1023/b:hydr.0000008476.23617.b0|issn=0018-8158|via=}}</ref>  The general types of life forms found are daytime-visiting [[Herbivore|herbivores]], [[Detritivore|detritivores]] feeding on dead organisms and fecal pellets, and [[Carnivore|carnivores]] feeding on those detritivores[[Mesopelagic zone#cite note-auto-2|.]]<ref name=":2">{{Cite book|title=Biological Oceanography|last=Miller|first=Charles B.|publisher=Blackwell Publishing|year=2004|isbn=0-632-05536-7|location=Oxford, UK|pages=232-245}}</ref>  [[Phytoplankton]] do not inhabit the mesopelagic layer, due to lack of light.[[Mesopelagic zone#cite note-:1-3|<sup>[3]</sup>]]  The biological community of the mesopelagic zone has adapted to a low-light, low-nutrient environment.<ref name=":2" />
+=== Virus and microbial ecology ===
+Very little is known about the microbial community of the mesopelagic zone because it is a difficult area to study, but recent work has used DNA from seawater samples.<ref name=":6">{{Cite web|url=https://www.bigelow.org/news/articles/2017-11-27-2.html|title=Dark Ocean Bacteria Discovered to Play Large Role in Carbon Capture - Bigelow Laboratory for Ocean Sciences|last=Sciences|first=Bigelow Laboratory for Ocean|website=www.bigelow.org|access-date=2018-11-26}}</ref>  Recent research highlights the importance of [[Virus|viruses]] and [[Microorganism|microbes]] role in recycling organic matter from the surface ocean, known as the [[biological pump]].<ref name=":6" /><ref name=":03">{{Cite journal|last=Reinthaler|first=Thomas|last2=van Aken|first2=Hendrik M.|last3=Herndl|first3=Gerhard J.|title=Major contribution of autotrophy to microbial carbon cycling in the deep North Atlantic’s interior|url=https://linkinghub.elsevier.com/retrieve/pii/S0967064510000895|journal=Deep Sea Research Part II: Topical Studies in Oceanography|volume=57|issue=16|pages=1572–1580|doi=10.1016/j.dsr2.2010.02.023|issn=0967-0645|via=}}</ref>
+These many microbes can get their energy from different pathways.<ref name=":14">{{Cite journal|last=Ingalls|first=Anitra E.|last2=Shah|first2=Sunita R.|last3=Hansman|first3=Roberta L.|last4=Aluwihare|first4=Lihini I.|last5=Santos|first5=Guaciara M.|last6=Druffel|first6=Ellen R. M.|last7=Pearson|first7=Ann|date=2006-04-25|title=Quantifying archaeal community autotrophy in the mesopelagic ocean using natural radiocarbon|url=http://www.pnas.org/content/103/17/6442|journal=Proceedings of the National Academy of Sciences|language=en|volume=103|issue=17|pages=6442–6447|doi=10.1073/pnas.0510157103|issn=0027-8424|pmc=PMC1564200|pmid=16614070}}</ref>  Some are [[Autotroph|autotrophs]], [[Heterotroph|heterotrophs]], and a 2006 study even discovered [[Chemotroph|chemoautotrophs]]<ref name=":14" />.  This Archaea crenarchaeon ''Candidatus'' can oxidize ammonia as their food source without oxygen.<ref name=":14" />  They could be a major impact on the nitrogen and carbon cycles.  One study estimates these nitrite-oxidizing bacteria, which are only 5% of the microbial population, can annually capture 1.1 Gt of carbon.<ref name=":6" />
+Overall, [[Biomass (ecology)|biomass]] and [[Biodiversity|diversity]] typically decline exponentially with depth in the mesopelagic zone.<ref name="Robinson2">{{cite journal|last1=Robinson|first1=Carol|last2=Steinberg|first2=Deborah K.|last3=Anderson|first3=Thomas R.|last4=Arístegui|first4=Javier|last5=Carlson|first5=Craig A.|last6=Frost|first6=Jessica R.|last7=Ghiglione|first7=Jean-François|last8=Hernández-León|first8=Santiago|last9=Jackson|first9=George A.|date=August 2010|title=Mesopelagic zone ecology and biogeochemistry – a synthesis|journal=Deep Sea Research Part II: Topical Studies in Oceanography|volume=57|issue=16|pages=1504–1518|doi=10.1016/j.dsr2.2010.02.018|last10=Koppelmann|first10=Rolf|last11=Quéguiner|first11=Bernard|last12=Ragueneau|first12=Olivier|last13=Rassoulzadegan|first13=Fereidoun|last14=Robison|first14=Bruce H.|last15=Tamburini|first15=Christian|last16=Tanaka|first16=Tsuneo|last17=Wishner|first17=Karen F.|last18=Zhang|first18=Jing}}</ref>   The community composition changes at different depths in the mesopelagic as different organisms are evolved for different light conditions.<ref name="Robinson2" />  Microbial biomass in the mesopelagic is greater at higher latitudes, decreasing towards the tropics, likely linked to the productivity levels in the surface waters.<ref name="Robinson2" />  Viruses are very abundant in the mesopelagic, around 10<sup>10</sup> - 10<sup>12</sup> every cubic meter and are fairly uniform throughout the mesopelagic zone.<ref name="Robinson2" />
+=== Zooplankton ecology ===
+[[File:Periphylla_periphylla00.jpg|link=https://en.wikipedia.org/wiki/File:Periphylla_periphylla00.jpg|thumb|Helmet jellyfish, ''[[Helmet jellyfish|Periphylla periphylla]]'']]
+The mesopelagic zone hosts a diverse zooplankton community.  Many inhabitants of the mesopelagic zone  move between the epipelagic zone during the night, and retreat to the mesopelagic zone during the day, a process known as [[diel vertical migration]].<ref name="Robinson2" />  These migrators can avoid predation during the day and feed at night, while their predators migrate up at night to follow the prey.  This is such a massive migration that sonar operators in World War II would regularly misinterpret the signal returned by this thick layer of plankton as a false sea floor.<ref name=":18">{{Cite news|url=https://teara.govt.nz/en/deep-sea-creatures/page-2|title=2.  – Deep-sea creatures – Te Ara Encyclopedia of New Zealand|last=Taonga|first=New Zealand Ministry for Culture and Heritage Te Manatu|access-date=2018-11-26|language=en}}</ref>
+Gelatinous organisms are thought to play an important role in the ecology of the mesopelagic and are common predators.<ref name=":19">{{Cite journal|last=Kaartvedt|first=Stein|last2=Ugland|first2=Karl I.|last3=Klevjer|first3=Thor A.|last4=Røstad|first4=Anders|last5=Titelman|first5=Josefin|last6=Solberg|first6=Ingrid|date=2015-06-11|title=Social behaviour in mesopelagic jellyfish|url=https://www.nature.com/articles/srep11310|journal=Scientific Reports|language=En|volume=5|issue=1|doi=10.1038/srep11310|issn=2045-2322}}</ref>  One study found that the helmet jellyfish ''[[Helmet jellyfish|Periphylla periphylla]]'' exhibit social behavior and can find each other at depth and form groups.<ref name=":19" />  Scientists speculate this could be a feeding strategy to allow a group to hunt together.<ref name=":19" />
+Mesopelagic zooplankton have unique adaptations for the low light.  [[Bioluminescence]] is  very common, which is used for a variety of functions like  communication, prey attraction and mating.<ref name="Robinson2" />  Many jellyfish are bioluminescent.<ref name=":19" />  Other organisms, like shrimp, have highly developed eyes to pick up the limited available light.<ref name=":2" />  Light organs, common in krill and shrimp, are another adaptation.<ref name=":2" />  Some octopus and krill even have tubular eyes that look upwards.<ref name=":18" />
+[[File:FMIB_46273_Gnathophausia_millemoesii,_one_of_the_deep-sea_mysidacea.jpeg|link=https://en.wikipedia.org/wiki/File:FMIB_46273_Gnathophausia_millemoesii,_one_of_the_deep-sea_mysidacea.jpeg|thumb|Deep sea mysid, ''Gnauthophausia spp.'']]
+Most life processes, like growth rates and reproductive rates, are slower in the mesopelagic.<ref name=":2" />  Metabolic activity has been shown to decrease with depth and with temperature in colder-water environments.<ref>{{Cite journal|last=Frost|first=Jessica R.|last2=Denda|first2=Anneke|last3=Fox|first3=Clive J.|last4=Jacoby|first4=Charles A.|last5=Koppelmann|first5=Rolf|last6=Nielsen|first6=Morten Holtegaard|last7=Youngbluth|first7=Marsh J.|date=2011-10-12|title=Distribution and trophic links of gelatinous zooplankton on Dogger Bank, North Sea|url=http://dx.doi.org/10.1007/s00227-011-1803-7|journal=Marine Biology|volume=159|issue=2|pages=239–253|doi=10.1007/s00227-011-1803-7|issn=0025-3162}}</ref>  For example, the mesopelagic shrimp-like [[Mysida|mysid]], ''Gnathophausia ingens'', lives for 6.4 to 8 years, while benthic shrimp only live for 2 years.<ref name=":2" />
+=== Fish ecology ===
+Mesopelagic fish have a global distribution, except for the Arctic Ocean.<ref name=":4">{{Cite journal|last=Davison|first=Peter C.|last2=Koslow|first2=J. Anthony|last3=Kloser|first3=Rudy J.|date=2015-02-19|title=Acoustic biomass estimation of mesopelagic fish: backscattering from individuals, populations, and communities|url=https://doi.org/10.1093/icesjms/fsv023|journal=ICES Journal of Marine Science|language=en|volume=72|issue=5|pages=1413–1424|doi=10.1093/icesjms/fsv023|issn=1095-9289}}</ref>  Overall, this zone is home to a significant portion of the world's total fish biomass; one study estimated mesopelagic fish could be 95% of the total fish biomass.<ref>{{Cite news|url=https://phys.org/news/2014-03-ninety-five-cent-world-fish-mesopelagic.html|title=Ninety-five per cent of world's fish hide in mesopelagic zone|access-date=2018-11-26}}</ref>  Another estimate puts mesopelagic fish biomass at 1 billion tons. <ref name=":3">{{Cite journal|last=John|first=St|last2=A|first2=Michael|last3=Borja|first3=Angel|last4=Chust|first4=Guillem|last5=Heath|first5=Michael|last6=Grigorov|first6=Ivo|last7=Mariani|first7=Patrizio|last8=Martin|first8=Adrian P.|last9=Santos|first9=Ricardo S.|date=2016|title=A Dark Hole in Our Understanding of Marine Ecosystems and Their Services: Perspectives from the Mesopelagic Community|url=https://www.frontiersin.org/articles/10.3389/fmars.2016.00031/full|journal=Frontiers in Marine Science|language=English|volume=3|doi=10.3389/fmars.2016.00031|issn=2296-7745}}</ref>  Because it is difficult to sample this area with nets, mesopelagic fish numbers are often estimated by using[[Echo sounding|echosounders]] and finding the 'deep scattering layer' through the backscatter received from these acoustic sounders.<ref name=":5" />  It could be the largest fishery in the world and there is active development for this zone to become a commercial fishery.<ref name=":4" />
+[[File:Lanternfish_by_NOAA.jpg|link=https://en.wikipedia.org/wiki/File:Lanternfish_by_NOAA.jpg|thumb|Myctophids (lanternfish)]]
+There are thirty families of mesopelagic fish<ref>{{Cite book|url=https://www.worldcat.org/oclc/501069621|title=Encylopedia [i.e. Encyclopedia] of Ocean Sciences : Marine biology|date=2009|publisher=Academic Press|others=Steele, John H.|isbn=9780123757241|edition=2nd ed|location=London|oclc=501069621}}</ref>. The dominant fish in the mesopelagic zone are [[lanternfish]] (Myctophidae.)<ref name=":3" /> They have prominent [[Photophore|photophores]] along their ventral side. The Myctophid group includes 245 species distributed among 33 different genera.<ref name=":3" /> The Gonostomatidae, or bristlemouth, are also common mesopelagic fish.  The bristlemouth could be the Earth's most abundant [[vertebrate]], numbering in the hundreds of trillions to quadrillions.<ref>{{Cite news|url=https://www.nytimes.com/2015/06/30/science/bristlemouth-ocean-deep-sea-cyclothone.html|title=An Ocean Mystery in the Trillions|access-date=2018-11-16|language=en}}</ref>   However, some areas have shown declining abundance, like in Southern California over a long-term study dating back to the 1970s.<ref name=":132">{{Cite journal|last=Koslow|first=J. Anthony|last2=Miller|first2=Eric F.|last3=McGowan|first3=John A.|date=2015-10-28|title=Dramatic declines in coastal and oceanic fish communities off California|url=https://www.int-res.com/abstracts/meps/v538/p221-227/|journal=Marine Ecology Progress Series|language=en|volume=538|pages=221–227|doi=10.3354/meps11444|issn=0171-8630}}</ref>  Cold water species were especially vulnerable to decline.<ref name=":132" />
+Many organisms are black, because these colors appear black due to light penetration.  Many fish also have rows of [[Photophore|photophores]], which are small light-producing organs, mirrors on their sides angled to reflect the surrounding ocean and protect the fish, or [[countershading]], with light colors on ventral side and dark colors on the dorsal side.<ref name=":2" />
+Food is often limited and patchy, leading to dietary adaptions.  Many fish have sensitive eyes, huge jaws and small bodies, reducing the effort put into building muscles.<ref name=":2" />  Adaptations include jaws that can unhinge, elastic throats, and massive, long teeth.  Other predators develop [[Bioluminescence|bioluminescent]] lures, like the angler fish, that can attract prey.<ref name=":2" />  Many fish also respond to chemical cues.<ref name=":2" />
+== Human Impacts ==
+=== Pollution ===
+==== ''Marine Debris'' ====
+[[File:Pre-production_plastic_pellets_(7656726070).jpg|link=https://en.wikipedia.org/wiki/File:Pre-production_plastic_pellets_(7656726070).jpg|thumb|Plastic pellets are a common form of marine debris]]
+[[Marine debris|Marine debris,]] specifically in the plastic form, have been found in every [[Oceanic basin|ocean basin]] and have a wide range of impacts on the marine world<ref>{{Cite journal|last=Cózar|first=Andrés|last2=Echevarría|first2=Fidel|last3=González-Gordillo|first3=J. Ignacio|last4=Irigoien|first4=Xabier|last5=Úbeda|first5=Bárbara|last6=Hernández-León|first6=Santiago|last7=Palma|first7=Álvaro T.|last8=Navarro|first8=Sandra|last9=García-de-Lomas|first9=Juan|date=2014-07-15|title=Plastic debris in the open ocean|url=http://www.pnas.org/content/111/28/10239|journal=Proceedings of the National Academy of Sciences|language=en|volume=111|issue=28|pages=10239–10244|doi=10.1073/pnas.1314705111|issn=0027-8424|pmid=24982135}}</ref> One of the most critical issues is ingestion of plastic debris, specifically [[microplastics]].<ref>{{Cite journal|date=2011-12-01|title=Microplastics as contaminants in the marine environment: A review|url=https://www.sciencedirect.com/science/article/pii/S0025326X11005133|journal=Marine Pollution Bulletin|language=en|volume=62|issue=12|pages=2588–2597|doi=10.1016/j.marpolbul.2011.09.025|issn=0025-326X}}</ref> Mesopelagic species migrate to the surface waters to feast on their main prey species, [[Zooplankton]], who are mixed with microplastics in the surface waters. Additionally, research has shown that even Zooplankton are consuming the microplastics themselves.<ref>{{Cite journal|last=Cole|first=Matthew|last2=Lindeque|first2=Pennie|last3=Fileman|first3=Elaine|last4=Halsband|first4=Claudia|last5=Goodhead|first5=Rhys|last6=Moger|first6=Julian|last7=Galloway|first7=Tamara S.|date=2013-06-06|title=Microplastic Ingestion by Zooplankton|url=https://pubs.acs.org/doi/abs/10.1021/es400663f|journal=Environmental Science & Technology|language=EN|volume=47|issue=12|pages=6646–6655|doi=10.1021/es400663f|issn=0013-936X}}</ref> These fish play a key role in energy dynamics, meaning they provide food to a number of predators including birds, fish and marine mammals. The concentration of these plastics has the potential to increase, meaning more economically important species could be contaminated as well.<ref>{{Cite journal|last=Davison|first=Peter|last2=Asch|first2=Rebecca G.|date=2011-06-27|title=Plastic ingestion by mesopelagic fishes in the North Pacific Subtropical Gyre|url=https://www.int-res.com/abstracts/meps/v432/p173-180/|journal=Marine Ecology Progress Series|language=en|volume=432|pages=173–180|doi=10.3354/meps09142|issn=0171-8630}}</ref> Concentration of plastic debris in mesopelagic populations can vary depending on geographical location and the concentration of marine debris located there. In 2018, approximately 73% of over 200 fish sampled in the North Atlantic had consumed plastic.<ref>{{Cite journal|last=Wieczorek|first=Alina M.|last2=Morrison|first2=Liam|last3=Croot|first3=Peter L.|last4=Allcock|first4=A. Louise|last5=MacLoughlin|first5=Eoin|last6=Savard|first6=Olivier|last7=Brownlow|first7=Hannah|last8=Doyle|first8=Thomas K.|date=2018|title=Frequency of Microplastics in Mesopelagic Fishes from the Northwest Atlantic|url=https://www.frontiersin.org/articles/10.3389/fmars.2018.00039/full|journal=Frontiers in Marine Science|language=English|volume=5|doi=10.3389/fmars.2018.00039|issn=2296-7745}}</ref>
+==== ''Bioaccumulation'' ====
+The process of [[bioaccumulation]] (a buildup of a certain substance in the [[adipose tissue]]) and [[biomagnification]] (the process in which the concentration of  the substance grows higher as you rise through the food chain) are growing issues in the mesopelagic zone.<ref>{{Cite journal|last=Monteiro|first=L.R.|last2=Costa|first2=V.|last3=Furness|first3=R.W.|last4=Santos|first4=R.S.|date=1997|title=Mercury concentrations in prey fish indicate enhanced bioaccumulation in mesopelagic environments|url=https://www.infona.pl/resource/bwmeta1.element.elsevier-dfdd42b1-2413-30be-a003-e1f70f0dba99|journal=Oceanographic Literature Review|language=English|volume=5|issue=44|issn=0967-0653}}</ref> [[Mercury in fish]], which can be traced back to a combination of anthropological factors (such as coal mining) in addition to natural factors. Mercury is a particularly important bioaccumulation contaminant, as it’s concentration in the mesopelagic zone is increasing faster than in surface waters.<ref>{{Cite journal|last=Peterson|first=Sarah H.|last2=Ackerman|first2=Joshua T.|last3=Costa|first3=Daniel P.|date=2015-07-07|title=Marine foraging ecology influences mercury bioaccumulation in deep-diving northern elephant seals|url=http://rspb.royalsocietypublishing.org/content/282/1810/20150710|journal=Proc. R. Soc. B|language=en|volume=282|issue=1810|pages=20150710|doi=10.1098/rspb.2015.0710|issn=0962-8452|pmc=PMC4590481|pmid=26085591}}</ref> Inorganic mercury occurs in anthropogenic atmospheric emissions as it’s gaseous elemental form, which can be oxidized and then deposited in the ocean.<ref name=":7">{{Cite journal|last=Blum|first=Joel D.|last2=Popp|first2=Brian N.|last3=Drazen|first3=Jeffrey C.|last4=Anela Choy|first4=C.|last5=Johnson|first5=Marcus W.|date=2013-08-25|title=Methylmercury production below the mixed layer in the North Pacific Ocean|url=http://www.nature.com/articles/ngeo1918|journal=Nature Geoscience|language=En|volume=6|issue=10|pages=879–884|doi=10.1038/ngeo1918|issn=1752-0894}}</ref> Once there, the oxidized form can be converted to [[Methylmercury|methylmercury,]] which is its organic form.<ref name=":7" /> Research suggests that current levels anthropogenic emissions will not equilibrate between the atmosphere and ocean for a period of decades to centuries<ref>{{Cite journal|last=Sunderland|first=Elsie M.|last2=Mason|first2=Robert P.|title=Human impacts on open ocean mercury concentrations|url=https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2006GB002876|journal=Global Biogeochemical Cycles|language=en|volume=21|issue=4|pages=n/a–n/a|doi=10.1029/2006gb002876|issn=0886-6236|via=}}</ref>, which means we can expect current mercury concentrations in the ocean to keep rising. Mercury is a potent [[neurotoxin]], and poses health risks to not only the mesopelagic species that consume it. Many of the mesopelagic species, such as [[Myctophids|myctophids,]] make their [[Diurnality|diurnal]] migration to the surface waters where they are consumed by pelagic fish, birds and mammals.<ref>{{Cite book|url=https://books.google.com/books?id=ABIQ_FGKOZcC&pg=PA121&lpg=PA121&dq=bioaccumulation+in+the+mesopelagic+zone&source=bl&ots=v2gPjI6Q00&sig=4rs-jcg9MMDxVUGXWmqqqsViWhM&hl=en&sa=X&ved=2ahUKEwj_x_vfs8DeAhV1HzQIHV64Br04ChDoATACegQICBAB#v=onepage&q=bioaccumulation%20in%20the%20mesopelagic%20zone&f=false|title=Bioaccumulation in Marine Organisms: Effect of Contaminants from Oil Well Produced Water|last=Neff|first=J. M.|date=2002-04-16|publisher=Elsevier|isbn=9780080527840|language=en}}</ref>
+=== Fishing ===
+[[File:Fishmeal_powder.jpg|link=https://en.wikipedia.org/wiki/File:Fishmeal_powder.jpg|thumb|Fishmeal Powder]]
+Historically, there have been few examples of efforts to commercialize the mesopelagic zone, due to low economic value, technical feasibility and environmental impacts<ref name=":8">{{Cite journal|last=John|first=St|last2=A|first2=Michael|last3=Borja|first3=Angel|last4=Chust|first4=Guillem|last5=Heath|first5=Michael|last6=Grigorov|first6=Ivo|last7=Mariani|first7=Patrizio|last8=Martin|first8=Adrian P.|last9=Santos|first9=Ricardo S.|date=2016|title=A Dark Hole in Our Understanding of Marine Ecosystems and Their Services: Perspectives from the Mesopelagic Community|url=https://www.frontiersin.org/articles/10.3389/fmars.2016.00031/full|journal=Frontiers in Marine Science|language=English|volume=3|doi=10.3389/fmars.2016.00031|issn=2296-7745}}</ref>. While the biomass may be abundant, fish species here generally smaller in size and slower to reproduce.<ref name=":33">{{Cite journal|last=John|first=St|last2=A|first2=Michael|last3=Borja|first3=Angel|last4=Chust|first4=Guillem|last5=Heath|first5=Michael|last6=Grigorov|first6=Ivo|last7=Mariani|first7=Patrizio|last8=Martin|first8=Adrian P.|last9=Santos|first9=Ricardo S.|date=2016|title=A Dark Hole in Our Understanding of Marine Ecosystems and Their Services: Perspectives from the Mesopelagic Community|url=https://www.frontiersin.org/articles/10.3389/fmars.2016.00031/full|journal=Frontiers in Marine Science|language=English|volume=3|doi=10.3389/fmars.2016.00031|issn=2296-7745}}</ref> Fishing with large trawl nets poses threats to a high percentage of [[bycatch]] as well as poses potential impacts to the carbon cycling process<ref name=":8" />. Additionally, getting to the mesopelagic requires fairly long journeys offshore.<ref name=":9">{{Cite news|url=https://www.newsdeeply.com/oceans/articles/2018/02/26/the-oceans-twilight-zone-faces-fishing-threat|title=The Ocean’s ‘Twilight Zone’ Faces Fishing Threat|work=Oceans|access-date=2018-11-07|language=en}}</ref> In 1977, a Soviet [[fishery]] opened but closed less than 20 years later due to low commercial profits, while a South African purse seine fishery closed in the mid-1980's due to processing difficulties from the high oil content of fish<ref>{{Cite journal|last=Prellezo|first=Raúl|title=Exploring the economic viability of a mesopelagic fishery in the Bay of Biscay|url=https://academic.oup.com/icesjms/advance-article/doi/10.1093/icesjms/fsy001/4823616|journal=ICES Journal of Marine Science|language=en|doi=10.1093/icesjms/fsy001}}</ref>.  As the [[Biomass (ecology)|biomass]] in the mesopelagic is so abundant, there has been an increase in interest to whether or not these populations could be of economic use in areas other than direct human consumption. For example, it has been suggested that the high abundance of fish in this zone could potentially satisfy a demand for fishmeal and [[Nutraceutical|nutraceuticals]].<ref name=":8" />
+With a growing population, the demand for fishmeal in support of a growing aquaculture industry is high. There is a potential for economically viable harvest, for example, 5 billion tons of mesopelagic biomass could result in the production of circa 1.25 billion tons of food for human consumption<ref>{{Cite journal|last=Naylor|first=Rosamond L.|last2=Hardy|first2=Ronald W.|last3=Bureau|first3=Dominique P.|last4=Chiu|first4=Alice|last5=Elliott|first5=Matthew|last6=Farrell|first6=Anthony P.|last7=Forster|first7=Ian|last8=Gatlin|first8=Delbert M.|last9=Goldburg|first9=Rebecca J.|date=2009-09-08|title=Feeding aquaculture in an era of finite resources|url=http://www.pnas.org/content/106/36/15103|journal=Proceedings of the National Academy of Sciences|language=en|volume=106|issue=36|pages=15103–15110|doi=10.1073/pnas.0905235106|issn=0027-8424|pmc=PMC2741212|pmid=19805247}}</ref>. Additionally, the demand for nutraceuticals is also rapidly growing, stemming from the consumption of  [[Omega-3 fatty acid|Omega-3]] Fatty Acids in addition to the aquaculture industry requiring a specific marine oil for feed material.<ref name=":8" /> [[Lanternfish]] are of much interest to the aquaculture market, as they are especially high in fatty acids.<ref>{{Cite journal|last=Koizumi|first=Kyoko|last2=Hiratsuka|first2=Seiichi|last3=Saito|first3=Hiroaki|date=2014|title=Lipid and Fatty Acids of Three Edible Myctophids, Diaphus watasei, Diaphus suborbitalis, and Benthosema pterotum: High Levels of Icosapentaenoic and Docosahexaenoic Acids|url=http://dx.doi.org/10.5650/jos.ess13224|journal=Journal of Oleo Science|volume=63|issue=5|pages=461–470|doi=10.5650/jos.ess13224|issn=1345-8957}}</ref>
+=== Climate Change ===
+The mesopelagic region plays an important role in the [[Carbon cycle|Global Carbon Cycle]], as it is the area where most of the [[organic matter]] that is travelling down the [[water column]] is respired. Mesopelagic species acquire carbon during their migration to feed in surface waters, and transport that carbon into the deep sea when they die. It is estimated that the mesopelagic cycles between 5 and 12 billion tons of carbon dioxide from the atmosphere per year, and until recently, this estimate was not included in many climate models. <ref name=":12">{{Cite news|url=https://www.economist.com/science-and-technology/2017/04/15/the-mesopelagic-cinderella-of-the-oceans|title=The mesopelagic: Cinderella of the oceans|work=The Economist|access-date=2018-11-06|language=en}}</ref> It is difficult to quantify the effects of climate change on the mesopelagic zone as a whole, as climate change does not have uniform impacts geographically. Research suggests that in warming waters, as long as there are adequate nutrients and food for fish, then mesopelagic biomass could actually be higher due to increases in trophic efficiency and temperature driven [[metabolism]].<ref name=":10">{{Cite journal|last=Proud|first=Roland|last2=Cox|first2=Martin J.|last3=Brierley|first3=Andrew S.|title=Biogeography of the Global Ocean’s Mesopelagic Zone|url=https://doi.org/10.1016/j.cub.2016.11.003|journal=Current Biology|volume=27|issue=1|pages=113–119|doi=10.1016/j.cub.2016.11.003|issn=0960-9822|via=}}</ref> However, because warming will not be uniform throughout the global mesopelagic zone, it is predicted that some areas may actually decrease in fish production, while others increase. <ref name=":10" /> Also, with warming waters there is a higher likelihood of increased [[Stratification (water)|stratification]]<ref name=":12" />. This increase reduces the input of nutrients to the [[euphotic zone]] through an increase in nutrient limitation, and can lead to decreases in both net primary production and sinking particulate matter<ref name=":12" />. Additional research suggests shifts in the geographical range of many species could also occur with warming, with many of them shifting away from the equator<ref name=":11">{{Cite journal|last=Costello|first=Mark J.|last2=Breyer|first2=Sean|title=Ocean Depths: The Mesopelagic and Implications for Global Warming|url=https://doi.org/10.1016/j.cub.2016.11.042|journal=Current Biology|volume=27|issue=1|pages=R36–R38|doi=10.1016/j.cub.2016.11.042|issn=0960-9822|via=}}</ref>. The combination of these factors could potentially mean that as global ocean basins continue to warm, there could be areas in the mesopelagic that increase in [[biodiversity]] and species richness, especially moving farther from the equator<ref name=":11" />.
+== Research and Exploration ==
+There is a dearth of knowledge about the mesopelagic zone so researchers have begun to develop new technology to explore and sample this area. The [[Woods Hole Oceanographic Institution]] (WHOI), [[NASA|NASA,]] and the [[Norwegian Institute of Marine Research]] are all working on projects to gain a better understanding of this zone in the ocean and its influence on the global carbon cycle. Traditional sampling nets have proved to be inadequate due to scaring off creatures from the pressure wave formed by the towed net and from the light produced by the [[Bioluminescence|bioluminescent]] species caught in the net. Mesopelagic activity was first investigated by use of sonar. However, there are many challenges with acoustic survey methods and previous research has estimated errors in measured amounts of biomass of up to three orders of magnitude. <ref name=":43">{{Cite journal|last=Davison|first=Peter C.|last2=Koslow|first2=J. Anthony|last3=Kloser|first3=Rudy J.|date=2015-02-19|title=Acoustic biomass estimation of mesopelagic fish: backscattering from individuals, populations, and communities|url=https://doi.org/10.1093/icesjms/fsv023|journal=ICES Journal of Marine Science|language=en|volume=72|issue=5|pages=1413–1424|doi=10.1093/icesjms/fsv023|issn=1095-9289}}</ref> This is due to inaccurate incorporation of depth, species size distribution, and acoustic properties of the species. Norway’s Institute of Marine Research has launched a research vessel named Dr. Fridtjof Nansen to investigate mesopelagic activity using sonar with their focus being on the sustainability of fishing operations. To overcome the challenges faced with acoustic sampling, WHOI is developing robots (Deep-See, Mesobot, and Snowclops) that are capable of studying this zone more precisely.
+=== Discovery and Detection ===
+The [[deep scattering layer]] often characterizes the mesopelagic due to the high amount of biomass that exists in the region.<ref name=":10" /> Acoustic sound sent into the ocean bounces off particles and organisms in the water column and return a strong signal. The region was initially discovered by American researchers during [[World War II]] in 1942 during [[Anti-submarine warfare|anti-submarine]] research with [[sonar]]. Sonar at the time could not penetrate below this depth due to the large number of creatures obstructing sound waves.<ref name=":12" /> It is uncommon to detect deep scattering layers below 1000m. Until recently, sonar has been the predominate method for studying the mesopelagic.<ref name=":10" />
+The [[Malaspina Expedition 2010|Malaspina Circumnavigation Expedition]] was a spanish led scientific quest to gain a better understanding of the state of the ocean in 2011 and the diversity in the deep oceans.<ref>{{Cite journal|last=Duarte|first=Carlos M.|date=2015-01-28|title=Seafaring in the 21St Century: The Malaspina 2010 Circumnavigation Expedition|url=https://doi.org/10.1002/lob.10008|journal=Limnology and Oceanography Bulletin|language=en|volume=24|issue=1|pages=11–14|doi=10.1002/lob.10008|issn=1539-607X}}</ref> The data collected, particularly through sonar observations showed that the biomass estimation in the mesopelagic was lower than previously thought.<ref>{{Cite journal|last=Irigoien|first=Xabier|last2=Klevjer|first2=T. A.|last3=Røstad|first3=A.|last4=Martinez|first4=U.|last5=Boyra|first5=G.|last6=Acuña|first6=J. L.|last7=Bode|first7=A.|last8=Echevarria|first8=F.|last9=Gonzalez-Gordillo|first9=J. I.|date=2014-02-07|title=Large mesopelagic fishes biomass and trophic efficiency in the open ocean|url=https://www.nature.com/articles/ncomms4271|journal=Nature Communications|language=En|volume=5|issue=1|doi=10.1038/ncomms4271|issn=2041-1723}}</ref>
+=== Deep-See ===
+WHOI is currently working on a project to characterize and document the mesopelagic ecosystem. They have developed a device named Deep-See weighing approximately 700 kg, which is designed to be towed behind a research vessel<ref name=":12" />. The Deep-See is capable of reaching depths up to 2000 m and can estimate the amount of biomass and biodiversity in this mesopelagic ecosystem. Deep-See is equipped with cameras, sonars, sensors, water sample collection devices, and a real-time data transmission system<ref>{{Cite news|url=http://www.sciencemag.org/news/2018/08/what-lives-ocean-s-twilight-zone-new-technologies-might-finally-tell-us|title=What lives in the ocean’s twilight zone? New technologies might finally tell us|date=2018-08-22|work=Science {{!}} AAAS|access-date=2018-11-16|language=en}}</ref>.
+=== Mesobot ===
+WHOI is collaborating with the [[Monterey Bay Aquarium Research Institute]] (MBARI), Stanford University, and the University of Texas Rio Grande Valley to develop a small autonomous robot, Mesobot, weighing approximately 75 kg.<ref name=":12" /><ref>{{Cite web|url=http://www.whoi.edu/main/mesobot|title=Mesobot|website=Woods Hole Oceanographic Institution|language=en|access-date=2018-11-16}}</ref> Mesobot is equipped with high-definition cameras to track and record mesopelagic species on their daily migration over extended periods of time. The robot's thrusters were designed so that they do not disturb the life in the mesopelagic that it is observing.<ref name=":12" /> Traditional sample collection devices fail to preserve organisms captured in the mesopelagic due to the large pressure change associated with surfacing. The mesobot also has a unique sampling mechanism that is capable of keeping the organisms alive during their ascent. The first sea trial of this device is expected to be in 2019.
+=== Snowclops ===
+Another mesopelagic robot developed by WHOI is the Snowclops. This device descends down the water column and measures the amount of [[marine snow]] at various depths. These tiny particles are a food source for other organisms so it is important to monitor the different levels of marine snow to characterize the carbon exchange between the surface ocean and the mesopelagic.
+Old material:
 ==Ecology==
-Although some light penetrates the mesopelagic zone, it is insufficient for [[photosynthesis]]. The general types of life forms found are daytime visiting [[herbivore]]s, [[detritivore]]s feeding on dead organisms and fecal pellets, and [[carnivore]]s feeding on the former types.<ref name="auto"/> [[Algae]] do not reside inside the mesopelagic layer, due to lack of light.<ref name=":1">{{Cite web|url=https://www.economist.com/news/science-and-technology/21720618-one-least-understood-parts-sea-also-one-most-important|title=The mesopelagic: Cinderella of the oceans|website=The Economist|access-date=2017-04-23}}</ref>
+Although some light penetrates the mesopelagic zone, it is insufficient for [[photosynthesis]]. The general types of life forms found are daytime visiting [[herbivore]]s, [[detritivore]]s feeding on dead organisms and fecal pellets, and [[carnivore]]s feeding on the former types.<ref name="auto">{{cite web|url=http://www.eoearth.org/view/article/154574/|title=Mesopelagic zone|last=Hogan|first=Michael C.|publisher=The Encyclopedia or Earth|accessdate=17 September 2013}}</ref> [[Algae]] do not reside inside the mesopelagic layer, due to lack of light.<ref name=":1">{{Cite web|url=https://www.economist.com/news/science-and-technology/21720618-one-least-understood-parts-sea-also-one-most-important|title=The mesopelagic: Cinderella of the oceans|website=The Economist|access-date=2017-04-23}}</ref>
 Examples of animals in the mesopelagic zone are [[bristlemouth]], [[swordfish]], [[squid]], [[wolf eel]]s, [[cuttlefish]] and other semi-deepsea creatures. The bristlemouth is the Earth's most abundant [[vertebrate]], numbering in the hundreds of trillions to quadrillions.<ref>{{cite news|last=Broad |first=William J. |url=https://www.nytimes.com/2015/06/30/science/bristlemouth-ocean-deep-sea-cyclothone.html |title=An Ocean Mystery in the Trillions |publisher=[[The New York Times]] |date=June 29, 2015 |accessdate=August 2015}}
@@ Line 27: / Line 110: @@
 ==See also==
-* [[Mesopelagic fish]]
+**[[Mesopelagic fish]]
+*
+*
 {{physical oceanography|expanded=other}}

v t e Physical oceanography
Waves	Airy wave theory Ballantine scale Benjamin–Feir instability Boussinesq approximation Breaking wave Clapotis Cnoidal wave Cross sea Dispersion Edge wave Equatorial waves Fetch Gravity wave Green's law Infragravity wave Internal wave Iribarren number Kelvin wave Kinematic wave Longshore drift Luke's variational principle Mild-slope equation Radiation stress Rogue wave Rossby wave Rossby-gravity waves Sea state Seiche Significant wave height Soliton Stokes boundary layer Stokes drift Stokes wave Swell Trochoidal wave Tsunami megatsunami Undertow Ursell number Wave action Wave base Wave height Wave nonlinearity Wave power Wave radar Wave setup Wave shoaling Wave turbulence Wave–current interaction Waves and shallow water one-dimensional Saint-Venant equations shallow water equations Wind setup Wind wave model
Circulation	Atmospheric circulation Baroclinity Boundary current Coriolis force Coriolis–Stokes force Craik–Leibovich vortex force Downwelling Eddy Ekman layer Ekman spiral Ekman transport El Niño–Southern Oscillation General circulation model Geochemical Ocean Sections Study Geostrophic current Global Ocean Data Analysis Project Gulf Stream Halothermal circulation Humboldt Current Hydrothermal circulation Langmuir circulation Longshore drift Loop Current Modular Ocean Model Ocean current Ocean dynamics Ocean dynamical thermostat Ocean gyre Overflow Princeton ocean model Rip current Subsurface currents Sverdrup balance Thermohaline circulation shutdown Upwelling Wind generated current Whirlpool World Ocean Circulation Experiment
Tides	Amphidromic point Earth tide Head of tide Internal tide Lunitidal interval Perigean spring tide Rip tide Rule of twelfths Slack tide Tidal bore Tidal force Tidal power Tidal race Tidal range Tidal resonance Tide gauge Tideline Theory of tides
Landforms	Abyssal fan Abyssal plain Atoll Bathymetric chart Carbonate platform Coastal geography Cold seep Continental margin Continental rise Continental shelf Contourite Guyot Hydrography Knoll Ocean bank Oceanic basin Oceanic plateau Oceanic trench Passive margin Seabed Seamount Submarine canyon Submarine volcano
Plate tectonics	Convergent boundary Divergent boundary Fracture zone Hydrothermal vent Marine geology Mid-ocean ridge Mohorovičić discontinuity Vine–Matthews–Morley hypothesis Oceanic crust Outer trench swell Ridge push Seafloor spreading Slab pull Slab suction Slab window Subduction Transform fault Volcanic arc
Ocean zones	Benthic Deep ocean water Deep sea Littoral Mesopelagic Oceanic Pelagic Photic Surf Swash
Sea level	Deep-ocean Assessment and Reporting of Tsunamis Future sea level Global Sea Level Observing System North West Shelf Operational Oceanographic System Sea-level curve Sea level rise Sea level drop World Geodetic System
Acoustics	Deep scattering layer Hydroacoustics Ocean acoustic tomography Sofar bomb SOFAR channel Underwater acoustics
Satellites	Jason-1 Jason-2 (Ocean Surface Topography Mission) Jason-3
Related	Acidification Argo Benthic lander Color of water DSV Alvin Marginal sea Marine energy Marine pollution Mooring National Oceanographic Data Center Ocean Explorations Observations Reanalysis Ocean surface topography Ocean temperature Ocean thermal energy conversion Oceanography Outline of oceanography Pelagic sediment Sea surface microlayer Sea surface temperature Seawater Science On a Sphere Stratification Thermocline Underwater glider Water column World Ocean Atlas
Oceans portal Category Commons