Marine primary production is the chemical synthesis in the ocean oforganic compounds from atmospheric or dissolvedcarbon dioxide. It principally occurs through the process ofphotosynthesis, which uses light as its source of energy, but it also occurs throughchemosynthesis, which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Almost alllife on Earth relies directly or indirectly onprimary production. The organisms responsible for primary production are calledprimary producers orautotrophs.
Most marine primary production is generated by a diverse collection ofmarine microorganisms calledalgae andcyanobacteria. Together these form the principal primary producers at the base of theocean food chain and produce half of the world's oxygen. Marine primary producers underpin almost all marine animal life by generating nearly all of the oxygen and food marine animals need to exist. Some marine primary producers are alsoecosystem engineers which change the environment and providehabitats for other marine life.
Primary production in the ocean can be contrasted with primary production on land. Globally the ocean and the land each produce about the same amount of primary production, but in the ocean primary production comes mainly from cyanobacteria and algae, while on land it comes mainly fromvascular plants.
Marine algae includes the largely invisible and oftenunicellularmicroalgae, which together withcyanobacteria form the oceanphytoplankton, as well as the larger, more visible and complexmulticellularmacroalgae commonly calledseaweed. Seaweeds are found along coastal areas, living on the floor ofcontinental shelves and washed up inintertidal zones. Some seaweeds drift with plankton in the sunlit surface waters (epipelagic zone) of the open ocean. Back in theSilurian, some phytoplankton evolved intored,brown andgreen algae. These algae then invaded the land and started evolving into theland plants we know today. Later in theCretaceous some of these land plants returned to the sea asmangroves andseagrasses. These are found along coasts inintertidal regions and in the brackish water ofestuaries. In addition, some seagrasses, like seaweeds, can be found at depths up to 50 metres on both soft and hard bottoms of the continental shelf.
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The rate of marine primary production is controlled primarily bylight availability, nutrient supply, andtemperature.[2] In the sunlit surface layer of the ocean,photosynthesis byphytoplankton is generally limited by nutrient concentrations rather than light,[3] while in deeper waters, low irradiance restricts production.Nitrogen,phosphorus, and in some regions,iron are the key limiting nutrients.[4] Productivity is highest in coastalupwelling zones and high-latitude spring blooms,[5] where nutrient availability is abundant, and lowest in subtropicalgyres, which are characterized by strong stratification and low nutrient availability.[6]
Marine primary production is measured asgross primary production (GPP), the total carbon fixed byphotosynthesis, or asnet primary production (NPP), which subtracts the carbon respired byprimary producers themselves.[7] Estimates are made using in-situ bottle incubations, satellite ocean-color observations, and globalbiogeochemical models. Current analyses suggest that marine NPP averages about 45–55 gigatons of carbon per year,[8] accounting for nearly half of Earth's total primary production.[9] This production fluctuates across regions and time scales, influenced by phenomena such as theEl Niño–Southern Oscillation, monsoons, and long-term shifts in ocean circulation.[10][11][12]
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Primary producers are theautotroph organisms that make their own food instead of eating other organisms. This means primary producers become the starting point in thefood chain forheterotroph organisms that do eat other organisms. Some marine primary producers are specialised bacteria and archaea which arechemotrophs, making their own food by gathering aroundhydrothermal vents andcold seeps and usingchemosynthesis. However, most marineprimary production comes from organisms which usephotosynthesis on the carbon dioxide dissolved in the water. This process uses energy from sunlight to convert water andcarbon dioxide[15]: 186–187 into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells.[15]: 1242 Marine primary producers are important because they underpin almost all marine animal life by generating most of theoxygen and food that provide other organisms with the chemical energy they need to exist.
The principal marine primary producers arecyanobacteria,algae and marine plants. Theoxygen released as a by-product of photosynthesis is needed bynearly all living things to carry outcellular respiration. In addition, primary producers are influential in the globalcarbon andwater cycles. They stabilize coastal areas and can provide habitats for marine animals. The termdivision has been traditionally used instead ofphylum when discussing primary producers, although theInternational Code of Nomenclature for algae, fungi, and plants now accepts the terms as equivalent.[16]
In a reversal of the pattern on land, in the oceans, almost all photosynthesis is performed by algae andcyanobacteria, with a small fraction contributed byvascular plants and other groups. Algae encompass a diverse range of organisms, ranging from single floating cells to attachedseaweeds. They include photoautotrophs from a variety of groups.Eubacteria are important photosynthetizers in both oceanic and terrestrial ecosystems, and while somearchaea arephototrophic, none are known to utilise oxygen-evolvingphotosynthesis.[17] A number ofeukaryotes are significant contributors to primary production in the ocean, includinggreen algae,brown algae andred algae, and a diverse group of unicellular groups. Vascular plants are also represented in the ocean by groups such as theseagrasses.
Unlike terrestrial ecosystems, the majority of primary production in the ocean is performed by free-livingmicroscopic organisms calledphytoplankton. It has been estimated that half of the world's oxygen is produced by phytoplankton.[18][19] Larger autotrophs, such as the seagrasses and macroalgae (seaweeds) are generally confined to thelittoral zone and adjacent shallow waters, where they canattach to the underlying substrate but still be within thephotic zone. There are exceptions, such asSargassum, but the vast majority of free-floating production takes place within microscopic organisms.
The factors limiting primary production in the ocean are also very different from those on land. The availability of water, obviously, is not an issue (though itssalinity can be). Similarly, temperature, while affectingmetabolic rates (seeQ10), ranges less widely in the ocean than on land because theheat capacity of seawater buffers temperature changes, and the formation ofsea iceinsulates it at lower temperatures. However, the availability of light, the source of energy for photosynthesis, and mineralnutrients, the building blocks for new growth, play crucial roles in regulating primary production in the ocean.[20] Available Earth System Models suggest that ongoing ocean bio-geochemical changes could trigger reductions in ocean NPP between 3% and 10% of current values depending on the emissions scenario.[21]
In 2020 researchers reported that measurements over the last two decades of primary production in theArctic Ocean show an increase of nearly 60% due to higher concentrations ofphytoplankton. They hypothesize new nutrients are flowing in from other oceans and suggest this means the Arctic Ocean may be able to supporthigher trophic level production and additionalcarbon fixation in the future.[22][23]
Cyanobacteria are a phylum (division) of bacteria, ranging from unicellular tofilamentous and includingcolonial species, whichfix inorganic carbon into organic carbon compounds. They are found almost everywhere on earth: in damp soil, in both freshwater and marine environments, and even on Antarctic rocks.[30] In particular, some species occur as drifting cells floating in the ocean, and as such were amongst the first of thephytoplankton. These bacteria function like algae in that they can process nitrogen from the atmosphere when none is in the ocean.
The first primary producers that used photosynthesis were oceaniccyanobacteria about 2.3 billion years ago.[31][32] The release of molecularoxygen bycyanobacteria as a by-product of photosynthesis induced global changes in the Earth's environment. Because oxygen was toxic to most life on Earth at the time, this led to the near-extinction ofoxygen-intolerant organisms, adramatic change which redirected the evolution of the major animal and plant species.[33]
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The tiny marine cyanobacteriumProchlorococcus, discovered in 1986, forms today part of the base of the oceanfood chain and accounts for more than half the photosynthesis of the open ocean[34] and an estimated 20% of the oxygen in the Earth's atmosphere.[35] It is possibly the most plentiful genus on Earth: a single millilitre of surface seawater may contain 100,000 cells or more.[36]
Originally, biologists thoughtcyanobacteria was algae, and referred to it as "blue-green algae". The more recent view is that cyanobacteria are bacteria, and hence are not even in the sameKingdom as algae. Most authorities exclude allprokaryotes, and hence cyanobacteria from the definition of algae.[37][38]
Biological pigments are any coloured material in plant or animal cells. All biological pigments selectivelyabsorb certain wavelengths of light whilereflecting others.[39][40] The primary function of pigments in plants isphotosynthesis, which uses the green pigmentchlorophyll and several colourful pigments that absorb as much light energy as possible.Chlorophyll is the primary pigment in plants; it is achlorin that absorbs yellow and blue wavelengths of light while reflectinggreen. It is the presence and relative abundance of chlorophyll that gives plants their green colour.Green algae and plants possess two forms of this pigment: chlorophylla and chlorophyllb.Kelps,diatoms, and other photosyntheticheterokonts contain chlorophyllc instead ofb, while red algae possess only chlorophylla. All chlorophylls serve as the primary means plants use to intercept light in order to fuel photosynthesis.
Chloroplasts (from the Greekchloros for green, andplastes for "the one who forms"[42]) areorganelles that conductphotosynthesis, where the photosynthetic pigmentchlorophyll captures theenergy fromsunlight, converts it, and stores it in the energy-storage molecules while freeingoxygen from water inplant andalgal cells. They then use the stored energy to make organic molecules fromcarbon dioxide in a process known as theCalvin cycle.
A chloroplast is a type of organelle known as aplastid, characterized byits two membranes and a high concentration ofchlorophyll. They are highly dynamic—they circulate and are moved around within plant cells, and occasionallypinch in two to reproduce. Their behavior is strongly influenced by environmental factors like light colour and intensity. Chloroplasts, likemitochondria, contain their ownDNA, which is thought to be inherited from their ancestor—a photosyntheticcyanobacterium that wasengulfed by an earlyeukaryotic cell.[43] Chloroplasts cannot be made by the plant cell and must be inherited by each daughter cell during cell division.
Most chloroplasts can probably be traced back to a singleendosymbiotic event, when a cyanobacterium was engulfed by the eukaryote. Despite this, chloroplasts can be found in an extremely wide set of organisms, some not even directly related to each other—a consequence of manysecondary and eventertiary endosymbiotic events.
Phototrophic metabolism relies on one of three energy-converting pigments:chlorophyll,bacteriochlorophyll, andretinal. Retinal is thechromophore found inrhodopsins. The significance of chlorophyll in converting light energy has been written about for decades, but phototrophy based on retinal pigments is just beginning to be studied.[46]
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In 2000 a team of microbiologists led byEdward DeLong made a crucial discovery in the understanding of the marine carbon and energy cycles. They discovered a gene in several species of bacteria[48][49] responsible for production of the proteinrhodopsin, previously unheard of in bacteria. These proteins found in the cell membranes are capable of converting light energy to biochemical energy due to a change in configuration of the rhodopsin molecule as sunlight strikes it, causing the pumping of aproton from inside out and a subsequent inflow that generates the energy.[50] The archaeal-like rhodopsins have subsequently been found among different taxa, protists as well as in bacteria and archaea, though they are rare in complexmulticellular organisms.[48][51][52]
Research in 2019 shows these "sun-snatching bacteria" are more widespread than previously thought and could change how oceans are affected by global warming. "The findings break from the traditional interpretation of marine ecology found in textbooks, which states that nearly all sunlight in the ocean is captured by chlorophyll in algae. Instead, rhodopsin-equipped bacteria function like hybrid cars, powered by organic matter when available—as most bacteria are—and by sunlight when nutrients are scarce."[53][46]
There is anastrobiological conjecture called thePurple Earth hypothesis which surmises that original life forms on Earth were retinal-based rather than chlorophyll-based, which would have made the Earth appear purple instead of green.[54][55]
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Algae is an informal term for a widespread and diverse collection of photosyntheticeukaryotic organisms which are not necessarily closely related and are thuspolyphyletic. Unlike higher plants, algae lack roots, stems, or leaves.
Marine algae have traditionally been placed in groups such as:green algae,red algae,brown algae,diatoms,coccolithophores anddinoflagellates.
Green algae live most of their lives as single cells or are filamentous, while others formcolonies made up from long chains of cells, or are highly differentiated macroscopic seaweeds. They form an informal group containing about 8,000 recognized species.[57]
Modernred algae are mostlymulticellular with differentiated cells and include many notableseaweeds.[58][59] Ascoralline algae, they play an important role in the ecology of coral reefs. They form a (disputed) phylum containing about 7,000 recognized species.[58]
Brown algae are mostlymulticellular and include many seaweeds, includingkelp. They form aclass containing about 2,000 recognized species.[60]
Altogether, about 45 percent of theprimary production in the oceans is contributed bydiatoms.[61]
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![They are a major algae group generating about 20% of world oxygen production.[62]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aDiatoms_through_the_microscope.jpg)
![Diatoms have glass like cell walls called frustules which are made of silica.[63]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aDiatom_algae_Amphora_sp.jpg)
![Diatoms linked in a colonial chain[64]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aPhytoplankton_in_the_form_of_a_diatom_chain.jpg)
Coccolithophores are almost exclusively marine and are found in large numbers throughout thesunlight zone of theocean. They havecalcium carbonate plates (or scales) of uncertain function calledcoccoliths, which are importantmicrofossils. Coccolithophores are of interest to those studying globalclimate change because asocean acidity increases, their coccoliths may become even more important as acarbon sink.[65] The most abundant species of coccolithophore,Emiliania huxleyi is an ubiquitous component of the plankton base inmarine food webs.[66] Management strategies are being employed to prevent eutrophication-related coccolithophore blooms, as these blooms lead to a decrease in nutrient flow to lower levels of the ocean.[67]
![Karenia brevis produces red tides highly toxic to humans.[68]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aKarenia_brevis.jpg)
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Traditionally thephylogeny of microorganisms, such as the algal groups discussed above, was inferred and theirtaxonomy established based on studies ofmorphology. However developments inmolecular phylogenetics have allowed the evolutionary relationship of species to be established by analyzing theirDNA andprotein sequences.[69] Many taxa, including the algal groups discussed above, are in the process of being reclassified or redefined using molecular phylogenetics. Recent developments inmolecular sequencing have allowed for the recovery ofgenomes directly from environmental samples and avoiding the need for culturing. This has led for example, to a rapid expansion in knowledge of the abundance and diversity ofmarine microorganisms. Molecular techniques such as genome-resolvedmetagenomics andsingle cell genomics are being used in combination withhigh throughput techniques.
Between 2009 and 2013, theTara Oceans expedition traversed the world oceans collecting plankton and analysing them with contemporary molecular techniques. They found a huge range of previously unknown photosynthetic and mixotrophic algae.[70] Among their findings were thediplonemids. These organisms are generally colourless and oblong in shape, typically about 20 μm long and with two flagella.[71] Evidence fromDNA barcoding suggests diplonemids may be among the most abundant and most species-rich of all marine eukaryote groups.[72][73]
Algae can be classified by size asmicroalgae ormacroalgae.
Microalgae are the microscopic types of algae, not visible to the naked eye. They are mostlyunicellular species which exist as individuals or in chains or groups, though some aremulticellular. Microalgae are important components of themarine protists, as well as themarine phytoplankton. They are verydiverse. It has been estimated there are 200,000–800,000 species of which about 50,000 species have been described.[74] Depending on the species, their sizes range from a few micrometers (μm) to a few hundred micrometers. They are specially adapted to an environment dominated by viscous forces.
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Macroalgae are the larger,multicellular and more visible types of algae, commonly calledseaweeds. Seaweeds usually grow in shallow coastal waters where they are anchored to the seafloor by aholdfast. Seaweed that becomes adrift can wash up on beaches.Kelp is a large brown seaweed that forms large underwaterforests covering about 25% of the world coastlines.[75] They are among the most productive and dynamic ecosystems on Earth.[76] SomeSargassum seaweeds are planktonic (free-floating) and form floating drifts.[77]: 246–255 Like microalgae, macroalgae (seaweeds) are technicallymarine protists since they are not true plants.
![This unicellular bubble algae lives in tidal zones. It can have a 4 cm (1.6 in) diameter.[78]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aVentricaria_ventricosa.JPG)
The diagram on the right shows an evolutionary scenario for the conquest of land by streptophytes.[79]Streptophyte algae include allgreen algae, and are the only photosyntheticeukaryotes from which the macroscopic land flora evolved(red lines). That said, throughout the course of evolution, algae from various other lineages have colonized land(yellow lines)—but also streptophyte algae have continuously and independently made the wet to dry transition (convergence of red and yellow). Throughout history, numerous lineages have become extinct(X labels). Terrestrial algae of various taxonomic affiliations dwell on rock surfaces and form biologicalsoil crusts. From the diversity of theparaphyletic streptophyte algae, however, did an organism whose descendants eventually conquered land on a global scale emerge: a likely branched filamentous—or evenparenchymatous—organism that formedrhizoidal structures and experienced desiccation from time to time. From this "hypothetical hydro-terrestrial alga", the lineages ofZygnematophyceae andembryophytes (land plants) arose.[79] In its infancy, the trajectory leading to the embryophytes was represented by the—now extinct—earliest land plants.[81]
The earliest land plants probably interacted with beneficialsubstratemicrobiota that aided them in obtaining nutrients from their substrate. Furthermore, the earliest land plants had to successfully overcome a barrage of terrestrial stressors (including ultraviolet light and photosynthetically activeirradiance, drought, drastic temperature shifts, etc.). They succeeded because they had the right set of traits—a mix of adaptations that were selected for in their hydro-terrestrial algal ancestors, exaptations, and the potential for co-option of a fortuitous set of genes and pathways.[79] During the course of evolution, some members of the populations of the earliest land plants gained traits that are adaptive in terrestrial environments (such as some form of water conductance,stomata-like structures, embryos, etc.); eventually, the "hypotheticallast common ancestor of land plants" emerged. From this ancestor, the extantbryophytes andtracheophytes evolved. While the exact trait repertoire of the hypothetical last common ancestor of land plants is uncertain, it will certainly have entailed properties ofvascular andnon-vascular plants. What is also certain is that the last common ancestor of land plants had traits of algal ancestry.[79]
Back in theSilurian, some phytoplankton evolved intored,brown andgreen algae. Green algae then invaded the land and started evolving into theland plants we know today. Later, in theCretaceous, some of these land plants returned to the sea asmangroves andseagrasses.[82]
Plant life can flourish in the brackish waters ofestuaries, wheremangroves orcordgrass orbeach grass might grow.Flowering plants grow in sandy shallows in the form ofseagrass meadows,[83]mangroves line the coast in tropical and subtropical regions[84] andsalt-tolerant plants thrive in regularly inundatedsalt marshes.[85] All of these habitats are able to sequester large quantities of carbon and support abiodiverse range of larger and smaller animal life.[86] Marine plants can be found inintertidal zones and shallow waters, such asseagrasses likeeelgrass andturtle grass,Thalassia. These plants have adapted to the high salinity of the ocean environment.
Light is only able to penetrate the top 200 metres (660 ft) so this is the only part of the sea where plants can grow.[87] The surface layers are often deficient in biologically active nitrogen compounds. The marinenitrogen cycle consists of complex microbial transformations which include thefixation of nitrogen, its assimilation,nitrification,anammox and denitrification.[88] Some of these processes take place in deep water so that where there is an upwelling of cold waters, and also near estuaries where land-sourced nutrients are present, plant growth is higher. This means that the most productive areas, rich in plankton and therefore also in fish, are mainly coastal.[89]: 160–163
Mangroves provide important nursery habitats for marine life, acting as hiding and foraging places for larval and juvenile forms of larger fish and invertebrates. Based on satellite data, the total world area of mangrove forests was estimated in 2010 as 134,257 square kilometres (51,837 sq mi).[90][91]
Like mangroves, seagrasses provide important nursery habitats for larval and juvenile forms of larger fish and invertebrates. The total world area of seagrass meadows is more difficult to determine than mangrove forests, but was conservatively estimated in 2003 as 177,000 square kilometres (68,000 sq mi).[92]
![Sea dragons camouflaged to look like floating seaweed live in kelp forests and seagrass meadows[93]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aLeafy_Sea_Dragon_SA.jpg)
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Thestoichiometry (measurement of chemicalreactants andproducts) of primary production in the surface ocean plays a crucial role in thecycling of elements in the global ocean. The ratio between the elementscarbon (C),nitrogen (N), andphosphorus (P) in exported organic matter expressed in terms of the C:N:P ratio helps determine how muchatmospheric carbon issequestered in the deep ocean with respect to the availability oflimiting nutrients.[94] On geologic timescales, the N:P ratio reflects the relative availability ofnitrate with respect tophosphate, both of which are externally supplied from the atmosphere vianitrogen fixation and/or continents via river supply and lost bydenitrification and burial.[95][96][97][98] On shorter timescales, the average stoichiometry of exported bulkparticulate organic matter reflects the elemental stoichiometry ofphytoplankton,[99][100][101] with additional influences from biological diversity and secondary processing of organic matter byzooplankton andheterotrophic bacteria. In the face of global change, understanding and quantifying the mechanisms that lead to variability in C:N:P ratios are crucial in order to have an accurate projection of future climate change.[94]
A key unresolved question is what determines C:N:P of individual phytoplankton. Phytoplankton grows in theupper light-lit layer of the ocean, where the amount of inorganic nutrients, light, and temperature vary spatially and temporally.[94] Laboratory studies show that these fluctuations trigger responses at the cellular level, whereby cells modify resource allocation in order to adapt optimally to their ambient environment.[102] For example, phytoplankton may alter resource allocation between the P-rich biosynthetic apparatus, N-rich light-harvesting apparatus, and C-rich energy storage reserves.[103] Under a typical future warming scenario, the global ocean is expected to undergo changes in nutrient availability, temperature, andirradiance.[104] These changes are likely to have profound effects on the physiology of phytoplankton,[105][106] and observations show that competitive phytoplankton species can acclimate and adapt to changes in temperature, irradiance, and nutrients on decadal timescales.[107] Numerous laboratory and field experiments have been conducted that study the relationship between the C:N:P ratio of phytoplankton and environmental drivers. It is, however, challenging to synthesize those studies and generalize the response of phytoplankton C:N:P to changes in environmental drivers.[94] Individual studies employ different sets ofstatistical analyses to characterize the effects of the environmental driver(s) on elemental ratios, ranging from a simplet test to more complex mixed models, which makes interstudy comparisons challenging. In addition, since environmentally induced trait changes are driven by a combination ofplasticity (acclimation), adaptation, and life history,[108][109] stoichiometric responses of phytoplankton can be variable even amongst closely related species.[94]
Meta-analysis/systematic review is a powerful statistical framework for synthesizing and integrating research results obtained from independent studies and for uncovering general trends.[110] The seminal synthesis by Geider and La Roche in 2002,[111] as well as the more recent work by Persson et al. in 2010,[112] has shown that C:P and N:P could vary by up to a factor of 20 between nutrient-replete and nutrient-limited cells. These studies have also shown that the C:N ratio can be modestly plastic due to nutrient limitation. A meta-analysis study by Hillebrand et al. in 2013 highlighted the importance of growth rate in determining elemental stoichiometry and showed that both C:P and N:P ratios decrease with the increasing growth rate.[113] In 2015, Yvon-Durocher et al. investigated the role of temperature in modulating C:N:P.[114] Although their dataset was limited to studies conducted prior to 1996, they have shown a statistically significant relationship between C:P and temperature increase. MacIntyre et al. (2002)[115] and Thrane et al. (2016)[116] have shown that irradiance plays an important role in controlling optimal cellular C:N and N:P ratios. Most recently, Moreno and Martiny (2018) provided a comprehensive summary of how environmental conditions regulate cellular stoichiometry from a physiological perspective.[103][94]
The elemental stoichiometry of marine phytoplankton plays a critical role in global biogeochemical cycles through its impact on nutrient cycling, secondary production, and carbon export. Although extensive laboratory experiments have been carried out over the years to assess the influence of different environmental drivers on the elemental composition of phytoplankton, a comprehensive quantitative assessment of the processes is still lacking. Here, the responses of P:C and N:C ratios of marine phytoplankton have been synthesized to five major drivers (inorganic phosphorus, inorganic nitrogen, inorganic iron, irradiance, and temperature) by a meta-analysis of experimental data across 366 experiments from 104 journal articles. These results show that the response of these ratios to changes in macronutrients is consistent across all the studies, where the increase in nutrient availability is positively related to changes in P:C and N:C ratios. The results show that eukaryotic phytoplankton are more sensitive to the changes in macronutrients compared to prokaryotes, possibly due to their larger cell size and their abilities to regulate their gene expression patterns quickly. The effect of irradiance was significant and constant across all studies, where an increase in irradiance decreased both P:C and N:C. The P:C ratio decreased significantly with warming, but the response to temperature changes was mixed depending on the culture growth mode and the growth phase at the time of harvest. Along with other oceanographic conditions of the subtropical gyres (e.g., low macronutrient availability), the elevated temperature may explain why P:C is consistently low in subtropical oceans. Iron addition did not systematically change either P:C or N:C.[94]
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This article incorporates text from this source, which is in thepublic domain.The deep chlorophyll maximum (DCM) occurs at the contact where there is adequate light for photosynthesis and yet significant nutrient supply from below.
Modified text was copied from this source, which is available under aCreative Commons Attribution 4.0 International License. Modified text was copied from this source, which is available under aCreative Commons Attribution 4.0 International License. Modified text was copied from this source, which is available under aCreative Commons Attribution 4.0 International License. Modified text was copied from this source, which is available under aCreative Commons Attribution 4.0 International License. Modified text was copied from this source, which is available under aCreative Commons Attribution 4.0 International License. Modified text was copied from this source, which is available under aCreative Commons Attribution 4.0 International License.
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