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76-444: The Antarctic continental shelf is involved in global climate regulation and temperature stability through the overturning of water masses, where heat is circulated throughout the ocean. When ice forms, it results in brine rejection, where salt is expelled and dense water forms along the continental shelf. This cold and salty water is referred to Antarctic Bottom Water, which sinks to the deep ocean because of its high density. Furthermore,

152-489: A terrestrial gross primary production of 123±8 Gt carbon (NOT carbon dioxide) per year during 1998-2005 In areal terms, it was estimated that land production was approximately 426 g C m yr (excluding areas with permanent ice cover), while that for the oceans was 140 g C m yr . Another significant difference between the land and the oceans lies in their standing stocks - while accounting for almost half of total production, oceanic autotrophs only account for about 0.2% of

228-405: A living source of carbon or energy and are the producers in a food chain, such as plants on land or algae in water. Autotrophs can reduce carbon dioxide to make organic compounds for biosynthesis and as stored chemical fuel. Most autotrophs use water as the reducing agent , but some can use other hydrogen compounds such as hydrogen sulfide . The primary producers can convert the energy in

304-400: A measure of net photosynthesis (i.e. oxygen production via photosynthesis subtract oxygen consumption by respiration). Gross primary production is then obtained by adding oxygen consumption in the dark vessel to net oxygen production in the light vessel. The technique of using C incorporation (added as labelled Na 2 CO 3 ) to infer primary production is most commonly used today because it

380-490: A new indicator of sustainable development based precisely on the estimation of the human appropriation of NPP: he coined it "HANPP" (Human Appropriation of Net Primary Production) and introduced it at the inaugural conference of the European Society for Ecological Economics. HANPP has since been further developed and widely applied in research on ecological economics and in policy analysis for sustainability. HANPP represents

456-400: A number of comprehensive reviews of the field methods used to estimate NPP. Estimates of ecosystem respiration , the total carbon dioxide produced by the ecosystem, can also be made with gas flux measurements . The major unaccounted pool is belowground productivity, especially production and turnover of roots. Belowground components of NPP are difficult to measure. BNPP (below-ground NPP)

532-622: A portion of the ATP produced during photosynthesis or the oxidation of chemical compounds to reduce NADP to NADPH to form organic compounds. The term autotroph was coined by the German botanist Albert Bernhard Frank in 1892. It stems from the ancient Greek word τροφή ( trophḗ ), meaning "nourishment" or "food". The first autotrophic organisms likely evolved early in the Archean but proliferated across Earth's Great Oxidation Event with an increase to

608-506: A proxy of the human impact on nature and can be applied to different geographical and global scales. The extensive degree of human use of the Planet's resources, mostly via land use , results in various levels of impact on actual NPP (NPP act ). Although in some regions, such as the Nile valley, irrigation has resulted in a considerable increase in primary production, in most of the Planet, there

684-560: A reactor of the Chernobyl nuclear power plant . There are many different types of autotrophs in Earth's ecosystems. Lichens located in tundra climates are an exceptional example of a primary producer that, by mutualistic symbiosis, combines photosynthesis by algae (or additionally nitrogen fixation by cyanobacteria) with the protection of a decomposer fungus . As there are many examples of primary producers, two dominant types are coral and one of

760-542: A source of carbon , but are able to use light or inorganic compounds as a source of energy. Such organisms are mixotrophs . An organism that obtains carbon from organic compounds but obtains energy from light is called a photoheterotroph , while an organism that obtains carbon from organic compounds and energy from the oxidation of inorganic compounds is termed a chemolithoheterotroph . Evidence suggests that some fungi may also obtain energy from ionizing radiation : Such radiotrophic fungi were found growing inside

836-473: Is sunlight but a minute fraction of primary production is driven by lithotrophic organisms using the chemical energy of inorganic molecules. Regardless of its source, this energy is used to synthesize complex organic molecules from simpler inorganic compounds such as carbon dioxide (CO 2 ) and water (H 2 O). The following two equations are simplified representations of photosynthesis (top) and (one form of) chemosynthesis (bottom): In both cases,

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912-406: Is "consumed" in plants by the processes of photosynthesis (see above) and transpiration . The latter process (which is responsible for about 90% of water use) is driven by the evaporation of water from the leaves of plants. Transpiration allows plants to transport water and mineral nutrients from the soil to growth regions, and also cools the plant. Diffusion of water vapour out of a leaf,

988-400: Is a notable trend of NPP reduction due to land changes (ΔNPP LC ) of 9.6% across global land-mass. In addition to this, end consumption by people raises the total HANPP to 23.8% of potential vegetation (NPP 0 ). It is estimated that, in 2000, 34% of the Earth's ice-free land area (12% cropland ; 22% pasture ) was devoted to human agriculture. This disproportionate amount reduces

1064-867: Is almost always the desired variable, and estimation techniques involve various methods of estimating dry-weight biomass changes over time. Biomass estimates are often converted to an energy measure, such as kilocalories, by an empirically determined conversion factor. In terrestrial ecosystems, researchers generally measure net primary production (NPP). Although its definition is straightforward, field measurements used to estimate productivity vary according to investigator and biome. Field estimates rarely account for below ground productivity, herbivory, turnover, litterfall , volatile organic compounds , root exudates, and allocation to symbiotic microorganisms. Biomass based NPP estimates result in underestimation of NPP due to incomplete accounting of these components. However, many field measurements correlate well to NPP. There are

1140-681: Is assumed to measure NPP. In systems with persistent standing litter, live biomass is commonly reported. Measures of peak biomass are more reliable if the system is predominantly annuals. However, perennial measurements could be reliable if there were a synchronous phenology driven by a strong seasonal climate. These methods may underestimate ANPP in grasslands by as much as 2 ( temperate ) to 4 ( tropical ) fold. Repeated measures of standing live and dead biomass provide more accurate estimates of all grasslands, particularly those with large turnover, rapid decomposition, and interspecific variation in timing of peak biomass. Wetland productivity (marshes and fens)

1216-414: Is done by performing a Winkler titration . The other two vessels are incubated, one each in under light and darkened. After a fixed period of time, the experiment ends, and the oxygen concentration in both vessels is measured. As photosynthesis has not taken place in the dark vessel, it provides a measure of ecosystem respiration . The light vessel permits both photosynthesis and respiration, so provides

1292-491: Is exacerbated where summertime solar heating and reduced winds increases vertical stratification and leads to a strong thermocline , since this makes it more difficult for wind mixing to entrain deeper water. Consequently, between mixing events, primary production (and the resulting processes that leads to sinking particulate material) constantly acts to consume nutrients in the mixed layer, and in many regions this leads to nutrient exhaustion and decreased mixed layer production in

1368-423: Is logistically difficult to measure. Shallow water aquatic systems can also face this problem. Scale also greatly affects measurement techniques. The rate of carbon assimilation in plant tissues, organs, whole plants, or plankton samples can be quantified by biochemically based techniques , but these techniques are decidedly inappropriate for large scale terrestrial field situations. There, net primary production

1444-512: Is more life than expected living under the Antarctic Ice Sheet (AIS) and among the Antarctic continental shelf. In the Antarctic continental shelf, there are many invertebrate life-forms such as worms , mollusks , sea spiders , sea stars and sea cucumbers. Other animals like fish, jellyfish , and krill are also found in this ecosystem. Fossils suggest that life has existed under

1520-499: Is most often used as the unit of measurement. Note that a distinction is sometimes drawn between "production" and "productivity", with the former the quantity of material produced (g C m ), the latter the rate at which it is produced (g C m yr ), but these terms are more typically used interchangeably. On the land, almost all primary production is now performed by vascular plants , with a small fraction coming from algae and non-vascular plants such as mosses and liverworts . Before

1596-409: Is not an issue (though its salinity can be). Similarly, temperature, while affecting metabolic rates (see Q 10 ), ranges less widely in the ocean than on land because the heat capacity of seawater buffers temperature changes, and the formation of sea ice insulates it at lower temperatures. However, the availability of light, the source of energy for photosynthesis, and mineral nutrients ,

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1672-470: Is often estimated based on a ratio of ANPP:BNPP (above-ground NPP:below-ground NPP) rather than direct measurements. Gross primary production can be estimated from measurements of net ecosystem exchange (NEE) of carbon dioxide made by the eddy covariance technique . During night, this technique measures all components of ecosystem respiration. This respiration is scaled to day-time values and further subtracted from NEE. Most frequently, peak standing biomass

1748-531: Is performed by algae, with a small fraction contributed by vascular plants and other groups. Algae encompass a diverse range of organisms, ranging from single floating cells to attached seaweeds . They include photoautotrophs from a variety of groups. Eubacteria are important photosynthetizers in both oceanic and terrestrial ecosystems, and while some archaea are phototrophic , none are known to utilise oxygen-evolving photosynthesis. A number of eukaryotes are significant contributors to primary production in

1824-525: Is referred to as net primary production (NPP). Net primary production is the rate at which all the autotrophs in an ecosystem produce net useful chemical energy. Net primary production is available to be directed toward growth and reproduction of primary producers. As such it is available for consumption by herbivores. Both gross and net primary production are typically expressed in units of mass per unit area per unit time interval. In terrestrial ecosystems, mass of carbon per unit area per year (g C m yr )

1900-433: Is sensitive, and can be used in all ocean environments. As C is radioactive (via beta decay ), it is relatively straightforward to measure its incorporation in organic material using devices such as scintillation counters . Depending upon the incubation time chosen, net or gross primary production can be estimated. Gross primary production is best estimated using relatively short incubation times (1 hour or less), since

1976-436: Is shallower than the critical depth. Both the magnitude of wind mixing and the availability of light at the ocean's surface are affected across a range of space- and time-scales. The most characteristic of these is the seasonal cycle (caused by the consequences of the Earth's axial tilt ), although wind magnitudes additionally have strong spatial components . Consequently, primary production in temperate regions such as

2052-553: Is similarly measured. In Europe , annual mowing makes the annual biomass increment of wetlands evident. Methods used to measure forest productivity are more diverse than those of grasslands. Biomass increment based on stand specific allometry plus litterfall is considered a suitable although incomplete accounting of above-ground net primary production (ANPP). Field measurements used as a proxy for ANPP include annual litterfall, diameter or basal area increment ( DBH or BAI), and volume increment. In aquatic systems, primary production

2128-600: Is supported by phylogenetic evidence – the physiology and habitat of the last universal common ancestor (LUCA) is inferred to have also been a thermophilic anaerobe with a Wood-Ljungdahl pathway, its biochemistry was replete with FeS clusters and radical reaction mechanisms. It was dependent upon Fe, H 2 , and CO 2 . The high concentration of K present within the cytosol of most life forms suggests that early cellular life had Na /H antiporters or possibly symporters. Autotrophs possibly evolved into heterotrophs when they were at low H 2 partial pressures where

2204-522: Is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide . It principally occurs through the process of photosynthesis , which uses light as its source of energy, but it also occurs through chemosynthesis , which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Almost all life on Earth relies directly or indirectly on primary production. The organisms responsible for primary production are known as primary producers or autotrophs , and form

2280-422: Is typically measured using one of six main techniques: The technique developed by Gaarder and Gran uses variations in the concentration of oxygen under different experimental conditions to infer gross primary production. Typically, three identical transparent vessels are filled with sample water and stoppered . The first is analysed immediately and used to determine the initial oxygen concentration; usually this

2356-505: Is using the triple oxygen isotopes of sulfate . Together these records suggest large shifts in primary production throughout Earth's past with notable rises associated with Earth's Great Oxidation Event (approximately 2.4 to 2.0 billion years ago) and the Neoproterozoic (approximately 1.0 to 0.54 billion years ago). Human societies are part of the Earth's NPP cycle but disproportionately influence it. In 1996, Josep Garí designed

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2432-476: The North Atlantic is highly seasonal, varying with both incident light at the water's surface (reduced in winter) and the degree of mixing (increased in winter). In tropical regions, such as the gyres in the middle of the major basins , light may only vary slightly across the year, and mixing may only occur episodically, such as during large storms or hurricanes . Mixing also plays an important role in

2508-624: The biosphere is an important part of the carbon cycle , estimating it at the global scale is important in Earth system science . However, quantifying primary production at this scale is difficult because of the range of habitats on Earth, and because of the impact of weather events (availability of sunlight, water) on its variability. Using satellite -derived estimates of the Normalized Difference Vegetation Index (NDVI) for terrestrial habitats and sea-surface chlorophyll for

2584-590: The evolution of vascular plants, non-vascular plants likely played a more significant role. Primary production on land is a function of many factors, but principally local hydrology and temperature (the latter covaries to an extent with light, specifically photosynthetically active radiation (PAR), the source of energy for photosynthesis). While plants cover much of the Earth's surface, they are strongly curtailed wherever temperatures are too extreme or where necessary plant resources (principally water and PAR) are limiting, such as deserts or polar regions . Water

2660-415: The littoral zone and adjacent shallow waters, where they can attach to the underlying substrate but still be within the photic zone . There are exceptions, such as Sargassum , 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,

2736-545: The oxidation of inorganic chemical compounds, these organisms are called chemoautotrophs , and are frequently found in hydrothermal vents in the deep ocean. Primary producers are at the lowest trophic level , and are the reasons why Earth sustains life to this day. Most chemoautotrophs are lithotrophs , using inorganic electron donors such as hydrogen sulfide, hydrogen gas , elemental sulfur , ammonium and ferrous oxide as reducing agents and hydrogen sources for biosynthesis and chemical energy release. Autotrophs use

2812-401: The sun . Plants can only use a fraction (approximately 1%) of this energy for photosynthesis . The process of photosynthesis splits a water molecule (H 2 O), releasing oxygen (O 2 ) into the atmosphere, and reducing carbon dioxide (CO 2 ) to release the hydrogen atoms that fuel the metabolic process of primary production . Plants convert and store the energy of the photons into

2888-723: The AIS. When the flow of warm water from ocean circulation reaches the Antarctic continental shelf, it gets rapidly converted to the denser and colder water at the shelf, limiting the heat contact on the AIS. In this way, it limits the AIS ice melt. Due to its remote location, the Antarctic continental shelf is poorly mapped. A variety of methods have been used to map the bathymetry of the Antarctic continental shelf some including: seal dives, multi-beam echo sounder survey, and sea gliders . Tagged benthic feeding seals with satellite transmitters have been used as means to improve bathymetric surveyings. This data revealed some bathymetric features including

2964-463: The Antarctic continental shelf serves as a source for sedimentary iron, essential for primary productivity in phytoplankton , for the Southern Ocean. Although the Antarctic continental shelf was developed through the process of plate tectonics, there were other process acting upon it which resulted in its significant deepness in comparison to other continental shelves around the world. For one, it

3040-445: The advantage of providing estimates of respiration rates in the light without the need of incubations in the dark. Among them, the method of the triple oxygen isotopes and O 2 /Ar have the additional advantage of not needing incubations in closed containers and O 2 /Ar can even be measured continuously at sea using equilibrator inlet mass spectrometry (EIMS) or a membrane inlet mass spectrometry (MIMS). However, if results relevant to

3116-512: The animation, the boreal forests of Canada and Russia experience high productivity in June and July and then a slow decline through fall and winter. Year-round, tropical forests in South America, Africa, Southeast Asia, and Indonesia have high productivity, not surprising with the abundant sunlight, warmth, and rainfall. However, even in the tropics, there are variations in productivity over the course of

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3192-450: The base of the food chain . In terrestrial ecoregions , these are mainly plants , while in aquatic ecoregions algae predominate in this role. Ecologists distinguish primary production as either net or gross , the former accounting for losses to processes such as cellular respiration , the latter not. Primary production is the production of chemical energy in organic compounds by living organisms . The main source of this energy

3268-407: The biological systems of Earth would be unable to sustain themselves. Plants, along with other primary producers, produce the energy that other living beings consume, and the oxygen that they breathe. It is thought that the first organisms on Earth were primary producers located on the ocean floor. Autotrophs are fundamental to the food chains of all ecosystems in the world. They take energy from

3344-424: The building blocks for new growth, play crucial roles in regulating primary production in the ocean. 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. The sunlit zone of the ocean is called the photic zone (or euphotic zone). This is a relatively thin layer (10–100 m) near

3420-403: The carbon cycle are desired, it is probably better to rely on methods based on carbon (and not oxygen) isotopes. It is important to notice that the method based on carbon stable isotopes is not simply an adaptation of the classic C method, but an entirely different approach that does not suffer from the problem of lack of account of carbon recycling during photosynthesis. As primary production in

3496-480: The chemical bonds of simple sugars during photosynthesis. These plant sugars are polymerized for storage as long-chain carbohydrates , such as starch and cellulose; glucose is also used to make fats and proteins . When autotrophs are eaten by heterotrophs , i.e., consumers such as animals, the carbohydrates , fats , and proteins contained in them become energy sources for the heterotrophs . Proteins can be made using nitrates , sulfates , and phosphates in

3572-441: The deep canyons and troughs. Additionally, the bathymetry of the Antarctic continental shelf has been assessed using sea gliders where satellites and sensors are used to measure depth. Finally, another technology used as means of mapping is the multi-beam echo sounder survey. This sends out sound beams to measure seafloor depth by the intensity of the echo reflected back. Primary production In ecology , primary production

3648-473: The end point is a polymer of reduced carbohydrate , (CH 2 O) n , typically molecules such as glucose or other sugars . These relatively simple molecules may be then used to further synthesise more complicated molecules, including proteins , complex carbohydrates , lipids , and nucleic acids , or be respired to perform work . Consumption of primary producers by heterotrophic organisms, such as animals , then transfers these organic molecules (and

3724-492: The energy available to other species, having a marked impact on biodiversity , flows of carbon, water, and energy, and ecosystem services , . Scientists have questioned how large this fraction can be before these services break down. Reductions in NPP are also expected in the ocean as a result of ongoing climate change, potentially impacting marine ecosystems (~10% of global biodiversity) and goods and services (1-5% of global total) that

3800-510: The energy stored within them) up the food web , fueling all of the Earth 's living systems. Gross primary production (GPP) is the amount of chemical energy, typically expressed as carbon biomass , that primary producers create in a given length of time. Some fraction of this fixed energy is used by primary producers for cellular respiration and maintenance of existing tissues (i.e., "growth respiration" and " maintenance respiration "). The remaining fixed energy (i.e., mass of photosynthate)

3876-436: The environment in the form of sunlight or inorganic chemicals and use it to create fuel molecules such as carbohydrates. This mechanism is called primary production . Other organisms, called heterotrophs , take in autotrophs as food to carry out functions necessary for their life. Thus, heterotrophs – all animals , almost all fungi , as well as most bacteria and protozoa – depend on autotrophs, or primary producers , for

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3952-420: The experimental species used. Aside from those caused by the physiology of the experimental subject itself, potential losses due to the activity of consumers also need to be considered. This is particularly true in experiments making use of natural assemblages of microscopic autotrophs, where it is not possible to isolate them from their consumers. The methods based on stable isotopes and O 2 /Ar ratios have

4028-432: The first cellular lifeforms were not heterotrophs as they would rely upon autotrophs since organic substrates delivered from space were either too heterogeneous to support microbial growth or too reduced to be fermented. Instead, they consider that the first cells were autotrophs. These autotrophs might have been thermophilic and anaerobic chemolithoautotrophs that lived at deep sea alkaline hydrothermal vents. This view

4104-420: The focus. Gross production is almost always harder to measure than net, because of respiration, which is a continuous and ongoing process that consumes some of the products of primary production (i.e. sugars) before they can be accurately measured. Also, terrestrial ecosystems are generally more difficult because a substantial proportion of total productivity is shunted to below-ground organs and tissues, where it

4180-657: The force that drives transpiration, is regulated by structures known as stomata . These structures also regulate the diffusion of carbon dioxide from the atmosphere into the leaf, such that decreasing water loss (by partially closing stomata) also decreases carbon dioxide gain. Certain plants use alternative forms of photosynthesis, called Crassulacean acid metabolism (CAM) and C4 . These employ physiological and anatomical adaptations to increase water-use efficiency and allow increased primary production to take place under conditions that would normally limit carbon fixation by C3 plants (the majority of plant species). As shown in

4256-402: The ice shelf for a continuous 6000 years. However, marine biologists find this somewhat surprising because most of these animals eat phytoplankton, which are limited in the extreme conditions of the Antarctic continental shelf. The distance from the Antarctic continental shelf to the AIS ranges from tens to hundreds of kilometers. Nevertheless, it has been shown that there is an amplification in

4332-447: The impact made on the AIS given changes in the Antarctic continental shelf. For example, increasing AIS volume directly increases Antarctic continental shelf erosion. This is known as glacial erosion . Increased erosion of the continental shelf makes the AIS more sensitive to ocean forcing — the sum of forces that amplify the ocean's ability to affect climate and surface conditions. Inversely, the Antarctic continental shelf has an impact on

4408-662: The light ( phototroph and photoautotroph ) or the energy in inorganic chemical compounds ( chemotrophs or chemolithotrophs ) to build organic molecules , which is usually accumulated in the form of biomass and will be used as carbon and energy source by other organisms (e.g. heterotrophs and mixotrophs ). The photoautotrophs are the main primary producers, converting the energy of the light into chemical energy through photosynthesis , ultimately building organic molecules from carbon dioxide , an inorganic carbon source . Examples of chemolithotrophs are some archaea and bacteria (unicellular organisms) that produce biomass from

4484-437: The limitation of primary production by nutrients. Inorganic nutrients, such as nitrate , phosphate and silicic acid are necessary for phytoplankton to synthesise their cells and cellular machinery. Because of gravitational sinking of particulate material (such as plankton , dead or fecal material), nutrients are constantly lost from the photic zone, and are only replenished by mixing or upwelling of deeper water. This

4560-409: The loss of incorporated C (by respiration and organic material excretion / exudation) will be more limited. Net primary production is the fraction of gross production remaining after these loss processes have consumed some of the fixed carbon. Loss processes can range between 10 and 60% of incorporated C according to the incubation period, ambient environmental conditions (especially temperature) and

4636-498: The many types of brown algae, kelp. Gross primary production occurs by photosynthesis. This is the main way that primary producers get energy and make it available to other forms of life. Plants, many corals (by means of intracellular algae), some bacteria ( cyanobacteria ), and algae do this. During photosynthesis, primary producers receive energy from the sun and use it to produce sugar and oxygen. Without primary producers, organisms that are capable of producing energy on their own,

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4712-424: The ocean's surface where there is sufficient light for photosynthesis to occur. For practical purposes, the thickness of the photic zone is typically defined by the depth at which light reaches 1% of its surface value. Light is attenuated down the water column by its absorption or scattering by the water itself, and by dissolved or particulate material within it (including phytoplankton). Net photosynthesis in

4788-449: The ocean, including green algae , brown algae and red algae , and a diverse group of unicellular groups. Vascular plants are also represented in the ocean by groups such as the seagrasses . Unlike terrestrial ecosystems, the majority of primary production in the ocean is performed by free-living microscopic organisms called phytoplankton . Larger autotrophs, such as the seagrasses and macroalgae ( seaweeds ) are generally confined to

4864-490: The oceans is dust from the Earth's deserts , picked up and delivered by the wind as aeolian dust . In regions of the ocean that are distant from deserts or that are not reached by dust-carrying winds (for example, the Southern and North Pacific oceans), the lack of iron can severely limit the amount of primary production that can occur. These areas are sometimes known as HNLC (High-Nutrient, Low-Chlorophyll) regions, because

4940-453: The oceans provide. Autotroph An autotroph is an organism that can convert abiotic sources of energy into energy stored in organic compounds , which can be used by other organisms . Autotrophs produce complex organic compounds (such as carbohydrates , fats , and proteins ) using carbon from simple substances such as carbon dioxide, generally using energy from light or inorganic chemical reactions . Autotrophs do not need

5016-612: The oceans, it is estimated that the total (photoautotrophic) primary production for the Earth was 104.9 petagrams of carbon per year (Pg C yr ; equivalent to the non- SI Gt C yr ). Of this, 56.4 Pg C yr (53.8%), was the product of terrestrial organisms, while the remaining 48.5 Pg C yr , was accounted for by oceanic production. Scaling ecosystem-level GPP estimations based on eddy covariance measurements of net ecosystem exchange (see above) to regional and global values using spatial details of different predictor variables, such as climate variables and remotely sensed fAPAR or LAI led to

5092-402: The photic zone, to being much deeper than the photic zone. When it is much deeper than the photic zone, this results in phytoplankton spending too much time in the dark for net growth to occur. The maximum depth of the mixed layer in which net growth can occur is called the critical depth . As long as there are adequate nutrients available, net primary production occurs whenever the mixed layer

5168-400: The rate of oxygenic photosynthesis by cyanobacteria . Photoautotrophs evolved from heterotrophic bacteria by developing photosynthesis . The earliest photosynthetic bacteria used hydrogen sulphide . Due to the scarcity of hydrogen sulphide, some photosynthetic bacteria evolved to use water in photosynthesis, leading to cyanobacteria . Some organisms rely on organic compounds as

5244-485: The raw materials and fuel they need. Heterotrophs obtain energy by breaking down carbohydrates or oxidizing organic molecules (carbohydrates, fats, and proteins) obtained in food. Carnivorous organisms rely on autotrophs indirectly, as the nutrients obtained from their heterotrophic prey come from autotrophs they have consumed. Most ecosystems are supported by the autotrophic primary production of plants and cyanobacteria that capture photons initially released by

5320-432: The scarcity of iron both limits phytoplankton growth and leaves a surplus of other nutrients. Some scientists have suggested introducing iron to these areas as a means of increasing primary productivity and sequestering carbon dioxide from the atmosphere. The methods for measurement of primary production vary depending on whether gross vs net production is the desired measure, and whether terrestrial or aquatic systems are

5396-516: The soil. Aquatic algae are a significant contributor to food webs in tropical rivers and streams. This is displayed by net primary production, a fundamental ecological process that reflects the amount of carbon that is synthesized within an ecosystem. This carbon ultimately becomes available to consumers. Net primary production displays that the rates of in-stream primary production in tropical regions are at least an order of magnitude greater than in similar temperate systems. Researchers believe that

5472-520: The summer (even in the presence of abundant light). However, as long as the photic zone is deep enough, primary production may continue below the mixed layer where light-limited growth rates mean that nutrients are often more abundant. Another factor relatively recently discovered to play a significant role in oceanic primary production is the micronutrient iron . This is used as a cofactor in enzymes involved in processes such as nitrate reduction and nitrogen fixation . A major source of iron to

5548-425: The total biomass. Present day primary productivity can be estimated through a variety of methodologies including ship-board measurements, satellites and terrestrial observatories. Historical estimates have relied on biogeochemical models and geochemical proxies. One example is using barium , where barite concentrations in marine sediments rise in line with carbon export production at the surface. Another example

5624-432: The water column is determined by the interaction between the photic zone and the mixed layer . Turbulent mixing by wind energy at the ocean's surface homogenises the water column vertically until the turbulence dissipates (creating the aforementioned mixed layer). The deeper the mixed layer, the lower the average amount of light intercepted by phytoplankton within it. The mixed layer can vary from being shallower than

5700-476: The year. For example, the Amazon basin exhibits especially high productivity from roughly August through October - the period of the area's dry season. Because the trees have access to a plentiful supply of ground water that builds up in the rainy season, they grow better when the rainy skies clear and allow more sunlight to reach the forest. In a reversal of the pattern on land, in the oceans, almost all photosynthesis

5776-399: Was further shaped by thermal subsidence - put simply, the process by which the Earth's crust sinks. Additionally, the continental shelf was deepened by ice sheet loading where pressure from the ice mass causes the landmass to submerge. Its unusual bathymetry is also a result of long-term erosion caused by repeated glaciations from extreme climate changes over the past 34 million years. There

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