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{{aquatic layer topics}}
The '''photic zone'''
== Photosynthesis in photic zone ==
In the photic zone, the photosynthesis rate exceeds the respiration rate. This is due to the abundant [[solar energy]] which is used as an energy source for photosynthesis by [[primary producers]] such as phytoplankton. These [[phytoplankton]] grow extremely quickly because of sunlight's heavy influence, enabling it to be produced at a fast rate. In fact, ninety five percent of photosynthesis in the ocean occurs in the photic zone. Therefore, if we go deeper, beyond the photic zone, such as into the [[compensation point]], there is little to no phytoplankton, because of insufficient sunlight.<ref>{{Cite book|title=Evolution of primary producers in the sea|date=2007|publisher=Elsevier Academic Press|others=
== Life in the photic zone ==
[[File:Light penetration zones in the water column.png|thumb|upright=1.1|left| Zones of the water column as defined by the amount of light penetration. The mesopelagic is sometimes referred to as the ''dysphotic zone''.]]▼
[[File:Pelagiczone.svg|thumb|upright=0.74|right| Layers of the pelagic zone]]
▲[[File:Light penetration zones in the water column.png|thumb|upright=1.1|left| Zones of the water column as defined by the amount of light penetration. The mesopelagic is sometimes referred to as the ''dysphotic zone''.]]
Ninety percent of [[marine life]] lives in the photic zone, which is approximately two hundred meters deep. This includes phytoplankton (plants), including [[dinoflagellate]]s, [[diatom]]s, [[cyanobacteria]], [[coccolithophore]]s, and [[cryptomonad]]s. It also includes [[zooplankton]], the consumers in the photic zone. There are [[Carnivore|carnivorous]] meat eaters and [[herbivorous]] plant eaters. Next, [[copepod]]s are the small [[crustacean]]s distributed everywhere in the photic zone. Finally, there are [[nekton]] (animals that can propel themselves, like fish, squids, and crabs), which are the largest and the most obvious animals in the photic zone, but their quantity is the smallest among all the groups.<ref>{{Cite web|url=https://sciencing.com/trophic-levels-coral-reefs-5523723.html|title=Trophic Levels of Coral Reefs|website=Sciencing|access-date=2019-11-22}}</ref>▼
▲Ninety percent of [[marine life]] lives in the photic zone, which is approximately two hundred meters deep. This includes phytoplankton (plants), including [[dinoflagellate]]s, [[diatom]]s, [[cyanobacteria]], [[coccolithophore]]s, and [[cryptomonad]]s. It also includes [[zooplankton]], the consumers in the photic zone. There are [[Carnivore|carnivorous]] meat eaters and [[herbivorous]] plant eaters. Next, [[copepod]]s are the small [[crustacean]]s distributed everywhere in the photic zone. Finally, there are [[nekton]] (animals that can propel themselves, like fish, squids, and crabs), which are the largest and the most obvious animals in the photic zone, but their quantity is the smallest among all the groups.<ref>{{Cite web|url=https://sciencing.com/trophic-levels-coral-reefs-5523723.html|title=Trophic Levels of Coral Reefs|website=Sciencing|access-date=2019-11-22}}</ref> Phytoplankton are microscopic plants living suspended in the water column that have little or no means of motility. They are primary producers that use solar energy as a food source.{{cn|date=January 2024}}
Detritivores and scavengers are rare in the photic zone. Microbial decomposition of dead organisms begins here and continues once the bodies sink to the aphotic zone where they form the most important source of nutrients for deep sea organisms.<ref>{{Cite web |title=Photic Zone - an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/earth-and-planetary-sciences/photic-zone |access-date=2023-11-27 |website=www.sciencedirect.com}}</ref> The depth of the photic zone depends on the transparency of the water. If the water is very clear, the photic zone can become very deep. If it is very murky, it can be only fifty feet (fifteen meters) deep.
== Nutrients uptake in the photic zone ==▼
Due to biological uptake, the photic zone has relatively low levels of nutrient concentrations. As a result, phytoplankton doesn't receive enough nutrients when there is high water-column stability.<ref>{{Cite book|chapter=Photic zone|work=SpringerReference|publisher=Springer-Verlag|doi=10.1007/springerreference_4643|title=Springer ''Reference''|year=2011}}</ref> The [[spatial distribution]] of organisms can be controlled by a number of factors. Physical factors include: temperature, hydrostatic pressure, turbulent mixing such as the upward [[Turbulence|turbulent flux]] of inorganic nitrogen across the nutricline.<ref>{{Cite journal|last1=Longhurst|first1=Alan R.|last2=Glen Harrison|first2=W.|date=June 1988|title=Vertical nitrogen flux from the oceanic photic zone by diel migrant zooplankton and nekton|journal=Deep Sea Research Part A. Oceanographic Research Papers|volume=35|issue=6|pages=881–889|doi=10.1016/0198-0149(88)90065-9|bibcode=1988DSRA...35..881L|issn=0198-0149}}</ref> Chemical factors include oxygen and trace elements. Biological factors include grazing and migrations.<ref>{{Cite journal|last1=Gundersen|first1=K.|last2=Mountain|first2=C. W.|last3=Taylor|first3=Diane|last4=Ohye|first4=R.|last5=Shen|first5=J.|date=July 1972|journal=Limnology and Oceanography|volume=17|issue=4|pages=524–532|doi=10.4319/lo.1972.17.4.0524|issn=0024-3590|title=Some Chemical and Microbiological Observations in the Pacific Ocean off the Hawaiian Islands1|bibcode=1972LimOc..17..524G|doi-access=free}}</ref> Upwelling carries nutrients from the deep waters into the photic zone, strengthening phytoplankton growth. The remixing and upwelling eventually bring nutrient-rich wastes back into the photic zone. The [[Ekman transport]] additionally brings more nutrients to the photic zone. Nutrient pulse frequency affects the phytoplankton competition. Photosynthesis produces more of it. Being the first link in the food chain, what happens to phytoplankton creates a rippling effect for other species. Besides phytoplankton, many other animals also live in this zone and utilize these nutrients. The majority of ocean life occurs in the photic zone, the smallest ocean zone by water volume. The photic zone, although small, has a large impact on those who reside in it.▼
Animals within the photic zone use the cycle of light and dark as an important environmental signal, migration is directly linked to this fact, fishes use the concept of dusk and dawn when its time to migrate, the photic zone resembles this concept providing a sense of time. These animals can be herrings and sardines and other fishes that consistently live within the photic zone.<ref>{{Cite web |title=Photic Zone - an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/earth-and-planetary-sciences/photic-zone |access-date=2023-12-01 |website=www.sciencedirect.com}}</ref>
▲Due to biological uptake, the photic zone has relatively low levels of nutrient concentrations. As a result, phytoplankton doesn't receive enough nutrients when there is high water-column stability.<ref>{{
== Photic zone depth ==
[[File:Light Penetration Spectrum in Water 01.png|thumb|Depth of light penetration ]]
The depth is, by definition, where radiation is degraded down to 1% of its surface strength.<ref>{{Cite journal|last1=Lee|first1=ZhongPing|last2=Weidemann|first2=Alan|last3=Kindle|first3=John|last4=Arnone|first4=Robert|last5=Carder|first5=Kendall L.|last6=Davis|first6=Curtiss|date=2007|title=Euphotic zone depth: Its derivation and implication to ocean-color remote sensing|journal=Journal of Geophysical Research: Oceans|volume=112|issue=C3|pages=C03009|doi=10.1029/2006JC003802|bibcode=2007JGRC..112.3009L|issn=2156-2202|url=https://scholarcommons.usf.edu/msc_facpub/11|doi-access=free}}</ref> Accordingly, its thickness depends on the extent of light [[attenuation]] in the water column. As incoming light at the surface can vary widely, this says little about the net growth of phytoplankton. Typical euphotic depths vary from only a few centimetres in highly [[turbidity|turbid]] [[eutrophic]] lakes, to around 200 meters in the open [[ocean]]. It also varies with seasonal changes in turbidity, which can be strongly driven by [[phytoplankton]] concentrations, such that the depth of the photic zone often decreases as [[primary production]] increases. Moreover, the [[respiration rate]] is actually greater than the photosynthesis rate. The reason why phytoplankton production is so important is because it plays a prominent role when interwoven with other [[food web]]s.
==Light attenuation==
[[File:Linear visible spectrum.svg|thumb|upright=2| {{center|Phytoplankton growth is affected by the colour spectrum of light,<br />and in the process called [[photosynthesis]] absorb light<br />in the blue and red range through [[photosynthetic pigment]]s}}]]
[[File:NOAA Deep Light diagram3.jpg|thumb|upright=1.1|
Most of the solar energy reaching the Earth is in the range of visible light, with wavelengths between about 400-700 nm. Each colour of visible light has a unique wavelength, and together they make up white light. The shortest wavelengths are on the violet and ultraviolet end of the spectrum, while the longest wavelengths are at the red and infrared end. In between, the colours of the visible spectrum comprise the familiar “ROYGBIV”; red, orange, yellow, green, blue, indigo, and violet.<ref name=Webb2019>Webb, Paul (2019) [https://rwu.pressbooks.pub/webboceanography/chapter/6-5-light/ ''Introduction to Oceanography''], chapter 6.5 Light, Rebus Community, Roger Williams University, open textbook. [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>
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In addition to overall attenuation, the oceans absorb the different wavelengths of light at different rates. The wavelengths at the extreme ends of the visible spectrum are attenuated faster than those wavelengths in the middle. Longer wavelengths are absorbed first; red is absorbed in the upper 10 metres, orange by about 40 metres, and yellow disappears before 100 metres. Shorter wavelengths penetrate further, with blue and green light reaching the deepest depths.<ref name=Webb2019 />
[[File:Cycling of marine phytoplankton.png|thumb|upright=1.5|Cycling of marine phytoplankton]]
This is why things appear blue underwater. How colours are perceived by the eye depends on the wavelengths of light that are received by the eye. An object appears red to the eye because it reflects red light and absorbs other colours. So the only colour reaching the eye is red. Blue is the only colour of light available at depth underwater, so it is the only colour that can be reflected back to the eye, and everything has a blue tinge under water. A red object at depth will not appear red to us because there is no red light available to reflect off of the object. Objects in water will only appear as their real colours near the surface where all wavelengths of light are still available, or if the other wavelengths of light are provided artificially, such as by illuminating the object with a dive light.<ref name=Webb2019 />
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The ocean can be divided into depth layers depending on the amount of light penetration, as discussed in [[pelagic zone]]. The upper 200 metres is referred to as the photic or euphotic zone. This represents the region where enough light can penetrate to support photosynthesis, and it corresponds to the epipelagic zone. From 200 to 1000 metres lies the dysphotic zone, or the twilight zone (corresponding with the mesopelagic zone). There is still some light at these depths, but not enough to support photosynthesis. Below 1000 metres is the aphotic (or midnight) zone, where no light penetrates. This region includes the majority of the ocean volume, which exists in complete darkness.<ref name=Webb2019 />
== Paleoclimatology ==
[[File:Triceratium morlandii var. morlandii.jpg|thumb| {{center|Intricate silicate (glass) shell, 32-40 million years old, of a [[diatom]] microfossil}}]]
{{further|diatoms|microfossils}}
[[Phytoplankton]] are [[unicellular]] [[Marine microorganisms|microorganisms]] which form the base of the [[ocean food chain]]s. They are dominated by [[diatom]]s, which grow silicate shells called [[frustule]]s. When diatoms die their shells can settle on the [[seafloor]] and become [[microfossil]]s. Over time, these microfossils become buried as [[opal]] deposits in the [[marine sediment]]. [[Paleoclimatology]] is the study of past climates. [[Proxy data]] is used in order to relate elements collected in modern-day sedimentary samples to climatic and oceanic conditions in the past. [[Paleoclimate proxies]] refer to preserved or fossilized physical markers which serve as substitutes for direct meteorological or ocean measurements.<ref>{{Cite web|title=What Are "Proxy" Data? {{!}} National Centers for Environmental Information (NCEI) formerly known as National Climatic Data Center (NCDC)|url=https://www.ncdc.noaa.gov/news/what-are-proxy-data|access-date=2020-10-20|website=www.ncdc.noaa.gov}}</ref> An example of proxies is the use of [[diatom]] [[marine isotope stage|isotope records]] of [[δ13C]], [[δ18O]], [[Isotopes of silicon|δ30Si]] (δ13C<sub>diatom</sub>, δ18O<sub>diatom</sub>, and δ30Si<sub>diatom</sub>). In 2015, Swann and Snelling used these isotope records to document historic changes in the photic zone conditions of the north-west [[Pacific Ocean]], including nutrient supply and the efficiency of the soft-tissue [[biological pump]], from the modern day back to [[Marine Isotope Stage 5#Marine Isotope Stage (MIS) 5e|marine isotope stage 5e]], which coincides with the [[Eemian|last interglacial period]]. Peaks in opal productivity in the marine isotope stage are associated with the breakdown of the regional [[Halocline|halocline stratification]] and increased nutrient supply to the photic zone.<ref name=Swann2015>{{cite journal | last1=Swann | first1=G. E. A. | last2=Snelling | first2=A. M. | title=Photic zone changes in the north-west Pacific Ocean from MIS 4–5e | journal=Climate of the Past | publisher=Copernicus GmbH | volume=11 | issue=1 | date=2015-01-06 | issn=1814-9332 | doi=10.5194/cp-11-15-2015 | pages=15–25| bibcode=2015CliPa..11...15S | doi-access=free }} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 International License].</ref>
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{{clear}}
The initial development of the halocline and [[Stratification (water)|stratified water column]] has been attributed to the onset of major [[Würm glaciation|Northern Hemisphere glaciation]] at 2.73 Ma, which increased the flux of freshwater to the region, via increased monsoonal rainfall and/or glacial meltwater, and [[sea surface
== Phytoplankton side notes. ==
[[File:Dimethyl sulfide structure.svg|thumb|Dimethyl sulfide structure]]
Phytoplankton are restricted to the photo zone only. As its growth is completely dependent upon photosynthesis. This results in the 50–100 m water level inside the ocean. Growth can also come from land factors, for example minerals that are dissolved from rocks, mineral nutrients from generations of plants and animals ,that made its way into the photic zone.<ref name = "Accumulation">{{Cite web |title=Accumulation |url=https://www.dnr.louisiana.gov/assets/TAD/education/BGBB/3/accumulation.html#:~:text=Planktonic%20aquatic%20organisms%20such%20as,is%20totally%20dependent%20upon%20photosynthesis. |access-date=2023-12-01 |website=www.dnr.louisiana.gov}}</ref>
[[File:Phytopla.jpg|thumb|upright|Drawn image of a phytoplankton ]]An increase in the amount of phytoplankton also creates an increase in zooplankton, the zooplankton feeds on the phytoplankton as they are at the bottom of the food chain.<ref name = "Accumulation" />
== Dimethylsulfide ==
Dimethylsulfide loss within the photic zone is controlled by microbial uptake and photochemical degradation. But what exactly is dimethylsulfide and why is it important? This compound (see the photo) helps regulate sulfur cycle and ecology within the ocean. Marine bacteria, algae, coral and most other organisms within the ocean release this, constituting a range of gene families.
However this compound can be toxic to humans if swallowed, absorbed through the skin and inhaled. Proteins within plants and animals depend on this compound. Making it a significant part of ecology, it's good to know that it lives in the photic zone as well. [https://www.sciencedirect.com/topics/earth-and-planetary-sciences/photic-zone]
==See also==
* [[Mesophotic coral reef]]▼
* [[Electromagnetic absorption by water]]
* [[Epipelagic fish]]
▲* [[Mesophotic coral reef]]
==References==
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