99-430: Particulate organic matter (POM) is a fraction of total organic matter operationally defined as that which does not pass through a filter pore size that typically ranges in size from 0.053 millimeters (53 μm) to 2 millimeters. Particulate organic carbon (POC) is a closely related term often used interchangeably with POM. POC refers specifically to the mass of carbon in the particulate organic material, while POM refers to
198-449: A conservative estimate (excluding release from decaying tissues) suggesting that macroalgae release between 1-39% of their gross primary production, while seagrasses release less than 5% as DOC of their gross primary production. The released DOC has been shown to be rich in carbohydrates, with rates depending on temperature and light availability. Globally the macrophyte communities have been suggested to produce ~160 Tg C yr of DOC, which
297-434: A continued diffusive flux and suggests that sediments are a major DOC source releasing 350 Tg C yr , which is comparable to the input of DOC from rivers. This estimate is based on calculated diffusive fluxes and does not include resuspension events which also releases DOC and therefore the estimate could be conservative. Also, some studies have shown that geothermal systems and petroleum seepage contribute with pre-aged DOC to
396-654: A crucial role in regulating global marine biogeochemical cycles and events, from the Great Oxidation Event in Earth's early history to the sequestration of atmospheric carbon dioxide in the deep ocean. Understanding the distribution, characteristics, dynamics, and changes over time of particulate matter in the ocean is hence fundamental in understanding and predicting the marine ecosystem, from food web dynamics to global biogeochemical cycles. Optical particle measurements are emerging as an important technique for understanding
495-539: A diameter of >5 μm have been shown to sink at rates up to several 10 s meters per day, though this is only possible owing to the heavy ballast of a silica frustule . Both size and density affect particle sinking velocity; for example, for sinking velocities that follow Stokes' Law , doubling the size of the particle increases the sinking speed by a factor of 4. However, the highly porous nature of many marine particles means that they do not obey Stokes' Law because small changes in particle density (i.e., compactness) can have
594-424: A filter with a pore size typically between 0.22 and 0.7 micrometers . The fraction remaining on the filter is called particulate organic carbon (POC). Dissolved organic matter (DOM) is a closely related term often used interchangeably with DOC. While DOC refers specifically to the mass of carbon in the dissolved organic material, DOM refers to the total mass of the dissolved organic matter. So DOM also includes
693-457: A high proportion of biodegradable dissolved organic carbon (BDOC) in first order streams compared to higher order streams. In the absence of extensive wetlands , bogs , or swamps , baseflow concentrations of DOC in undisturbed watersheds generally range from approximately 1 to 20 mg/L carbon. Carbon concentrations considerably vary across ecosystems. For example, the Everglades may be near
792-471: A large impact on their sinking velocities. Large sinking particles are typically of two types: (1) aggregates formed from a number of primary particles, including phytoplankton, bacteria, fecal pellets , live protozoa and zooplankton and debris, and (2) zooplankton fecal pellets , which can dominate particle flux events and sink at velocities exceeding 1,000 m d. Knowing the size, abundance, structure and composition (e.g. carbon content) of settling particles
891-536: A large pool. The dilution hypothesis has found support in recent experimental and theoretical studies. DOM is found in low concentrations in nature for direct analysis with NMR or MS . Moreover, DOM samples often contain high concentrations of inorganic salts that are incompatible with such techniques. Therefore, it is necessary a concentration and isolation step of the sample. The most used isolation techniques are ultrafiltration , reverse osmosis , and solid-phase extraction . Among them solid-phase extraction
990-462: A mix of these. They range in size from a few micrometers to several centimeters, with particles of a diameter of >0.5 mm being referred to as marine snow . In general, particles in a fluid are thought to sink once their densities are higher than the ambient fluid, i.e., when excess densities are larger than zero. Larger individual phytoplankton cells can thus contribute to sedimentary fluxes. For example, large diatom cells and diatom chains with
1089-447: A self-cleaning strainer instead of a basket strainer or a simplex strainer due to limitations of simple filtration systems. The self-cleaning strainers or filters are more efficient and provide an automatic filtration solution. Sieving is a simple technique for separating particles of different sizes. A sieve such as used for sifting flour has very small holes. Coarse particles are separated or broken up by grinding against one another and
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#17330858177841188-453: A wooden sieve might be made from wood or wicker . Use of wood to avoid contamination is important when the sieve is used for sampling. Henry Stephens, in his Book of the Farm , advised that the withes of a wooden riddle or sieve be made from fir or willow with American elm being best. The rims would be made of fir, oak or, especially, beech . A sieve analysis (or gradation test)
1287-549: Is a form of sieve used to separate suspended solids from a liquid by filtration . Some industrial strainers available are simplex basket strainers , duplex basket strainers , T-strainers and Y-strainers . Simple basket strainers are used to protect valuable or sensitive equipment in systems that are meant to be shut down temporarily. Some commonly used strainers are bell mouth strainers , foot valve strainers , basket strainers. Most processing industries (mainly pharmaceutical, coatings and liquid food industries) will opt for
1386-531: Is a major component of the Earth's carbon cycling . DOC is a basic nutrient, supporting growth of microorganisms and plays an important role in the global carbon cycle through the microbial loop . In some organisms (stages) that do not feed in the traditional sense, dissolved matter may be the only external food source. Moreover, DOC is an indicator of organic loadings in streams, as well as supporting terrestrial processing (e.g., within soil, forests, and wetlands) of organic matter. Dissolved organic carbon has
1485-399: Is a practice or procedure used (commonly used in civil engineering or sedimentology ) to assess the particle size distribution (also called gradation) of a granular material. Sieve sizes used in combinations of four to eight sieves. Dissolved organic matter Dissolved organic carbon ( DOC ) is the fraction of organic carbon operationally defined as that which can pass through
1584-437: Is a tool used for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet material. The word sift derives from sieve . In cooking, a sifter is used to separate and break up clumps in dry ingredients such as flour , as well as to aerate and combine them. A strainer (see Colander ), meanwhile,
1683-482: Is an operational classification. Many researchers use the term "dissolved" for compounds that pass through a 0.45 μm filter, but 0.22 μm filters have also been used to remove higher colloidal concentrations. A practical definition of dissolved typically used in marine chemistry is all substances that pass through a GF/F filter, which has a nominal pore size of approximately 0.7 μm (Whatman glass microfiber filter, 0.6–0.8 μm particle retention ). The recommended procedure
1782-404: Is approximately half the annual global river DOC input (250 Tg C yr ). Marine sediments represent the main sites of OM degradation and burial in the ocean, hosting microbes in densities up to 1000 times higher than found in the water column . The DOC concentrations in sediments are often an order of magnitude higher than in the overlying water column. This concentration difference results in
1881-420: Is approximately the same as the annual global input of riverine DOC (250 Tg C yr ; ), while others suggest that direct photodegradation exceeds the riverine DOC inputs. DOC is conceptually divided into labile DOC, which is rapidly taken up by heterotrophic microbes, and the recalcitrant DOC reservoir, which has accumulated in the ocean (following a definition by Hansell). As a consequence of its recalcitrance,
1980-438: Is decomposes, particulate organic matter provides much of the energy required by soil organisms as well as providing a steady release of nutrients into the soil environment. The decomposition of POM provides energy and nutrients. Nutrients not taken up by soil organisms may be available for plant uptake. The amount of nutrients released ( mineralized ) during decomposition depends on the biological and chemical characteristics of
2079-484: Is degraded in the dark ocean can impact atmospheric CO 2 concentration. Therefore, a central focus of marine organic geochemistry studies is to improve the understanding of POC distribution, composition, and cycling. The last few decades have seen improvements in analytical techniques that have greatly expanded what can be measured, both in terms of organic compound structural diversity and isotopic composition, and complementary molecular omics studies . As illustrated in
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#17330858177842178-588: Is discussed further in the next section. Humus : is usually the largest proportion of organic matter in soil, contributing 45 to 75%. Typically it adheres to soil minerals, and plays an important role structuring soil. Humus is the end product of soil organism activity, is chemically complex, and does not have recognisable characteristics of its origin. Humus is of very small unit size and has large surface area in relation to its weight. It holds nutrients, has high water holding capacity and significant cation exchange capacity , buffers pH change and can hold cations. Humus
2277-608: Is enhanced under high light and low nutrient levels, and thus should increase relatively from eutrophic to oligotrophic areas, probably as a mechanism for dissipating cellular energy. Phytoplankton can also produce DOC by autolysis during physiological stress situations e.g., nutrient limitation. Other studies have demonstrated DOC production in association with meso- and macro-zooplankton feeding on phytoplankton and bacteria. Zooplankton-mediated release of DOC occurs through sloppy feeding , excretion and defecation which can be important energy sources for microbes. Such DOC production
2376-477: Is evenly spread throughout the water column and consists of high molecular weight and structurally complex compounds that are difficult for marine organisms to use such as the lignin , pollen , or humic acids . As a result, the observed vertical distribution consists of high concentrations of labile DOC in the upper water column and low concentrations at depth. In addition to vertical distributions, horizontal distributions have been modeled and sampled as well. In
2475-446: Is frequently used as an indicator to measure soil quality . In poorly-managed soils, particularly on sloped ground, erosion and transport of soil sediment rich in POM can contaminate water bodies. Because POM provides a source of energy and nutrients, rapid build-up of organic matter in water can result in eutrophication . Suspended organic materials can also serve as a potential vector for
2574-503: Is hence impracticable. Along with dissolved organic matter , POM drives the lower aquatic food web by providing energy in the form of carbohydrates, sugars, and other polymers that can be degraded. POM in water bodies is derived from terrestrial inputs (e.g. soil organic matter, leaf litterfall), submerged or floating aquatic vegetation, or autochthonous production of algae (living or detrital). Each source of POM has its own chemical composition that affects its lability, or accessibility to
2673-431: Is important as these characteristics impose fundamental constraints on the biogeochemical cycling of carbon. For example, changes in climate are expected to facilitate a shift in species composition in a manner that alters the elemental composition of particulate matter, cell size and the trajectory of carbon through the food web , influencing the proportion of biomass exported to depth. As such, any climate-induced change in
2772-495: Is its key component comprising about 58% by weight. Simple assessment of total organic matter is obtained by measuring organic carbon in soil. Living organisms (including roots) contribute about 15% of the total organic matter in soil. These are critical to operation of the soil carbon cycle . What follows refers to the remaining 85% of the soil organic matter - the non-living component. As shown below, non-living organic matter in soils can be grouped into four distinct categories on
2871-473: Is largest during periods with high food concentration and dominance of large zooplankton species. Bacteria are often viewed as the main consumers of DOC, but they can also produce DOC during cell division and viral lysis . The biochemical components of bacteria are largely the same as other organisms, but some compounds from the cell wall are unique and are used to trace bacterial derived DOC (e.g., peptidoglycan ). These compounds are widely distributed in
2970-500: Is mainly produced in the near-surface layers during primary production and zooplankton grazing processes. Other sources of marine DOC are dissolution from particles, terrestrial and hydrothermal vent input, and microbial production . Prokaryotes (bacteria and archaea) contribute to the DOC pool via release of capsular material, exopolymers , and hydrolytic enzymes , as well as via mortality (e.g. viral shunt ). Prokaryotes are also
3069-864: Is observed due to high fresh water flux and sediments. Since the time scales of horizontal motion along the ocean bottom are in the thousands of years, the refractory dissolved organic carbon is slowly consumed on its way from the North Atlantic and reaches a minimum in the North Pacific. Dissolved organic matter is a heterogeneous pool of thousands, likely millions, of organic compounds. These compounds differ not only in composition and concentration (from pM to μM), but also originate from various organisms (phytoplankton, zooplankton, and bacteria) and environments (terrestrial vegetation and soils, coastal fringe ecosystems) and may have been produced recently or thousands of years ago. Moreover, even organic compounds deriving from
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3168-511: Is quite slow to decompose and exists in soil for decades. Resistant organic matter: has a high carbon content and includes charcoal, charred plant materials, graphite and coal. Turnover times are long and estimated in hundreds of years. It is not biologically active but contributes positively to soil structural properties, including water holding capacity, cation exchange capacity and thermal properties. Particulate organic matter (POM) includes steadily decomposing plant litter and animal faeces, and
3267-547: Is readily decomposable, serving many soil functions and providing terrestrial material to water bodies. It is a source of food for both soil organisms and aquatic organisms and provides nutrients for plants. In water bodies, POM can contribute substantially to turbidity, limiting photic depth which can suppress primary productivity. POM also enhances soil structure leading to increased water infiltration , aeration and resistance to erosion . Soil management practices, such as tillage and compost / manure application, alter
3366-507: Is relatively recalcitrant in anoxic marine sediments. This example shows bioavailability varies as a function of the ecosystem's properties. Accordingly, even normally ancient and recalcitrant compounds, such as petroleum, carboxyl-rich alicyclic molecules, can be degraded in the appropriate environmental setting. Dissolved organic matter (DOM) is one of the most active and mobile carbon pools and has an important role in global carbon cycling. In addition, dissolved organic carbon (DOC) affects
3465-408: Is sometimes called suspended organic matter, macroorganic matter, or coarse fraction organic matter. When land samples are isolated by sieving or filtration, this fraction includes partially decomposed detritus and plant material, pollen , and other materials. When sieving to determine POM content, consistency is crucial because isolated size fractions will depend on the force of agitation. POM
3564-597: Is subjected to microbial decomposition, resulting in a reduction in size and molecular weight. Novel molecules are synthesized by soil microbes , and some of these metabolites enter the DOC reservoir in groundwater. Aquatic carbon occurs in different forms. Firstly, a division is made between organic and inorganic carbon. Organic carbon is a mixture of organic compounds originating from detritus or primary producers. It can be divided into POC ( particulate organic carbon ; particles > 0.45 μm) and DOC (dissolved organic carbon; particles < 0.45 μm). DOC usually makes up 90% of
3663-538: Is the HTCO technique, which calls for filtration through pre-combusted glass fiber filters, typically the GF/F classification. Dissolved organic matter can be classified as labile or as recalcitrant, depending on its reactivity. Recalcitrant DOC is also called refractory DOC, and these terms seem to be used interchangeably in the context of DOC. Depending on the origin and composition of DOC, its behavior and cycling are different;
3762-407: Is the organic matter which dissolves in soil water. It comprises the relatively simple organic compounds (e.g. organic acids, sugars and amino acids) which easily decompose. It has a turnover time of less than 12 months. Exudates from plant roots (mucilages and gums) are included here. Particulate organic matter (POM): is the organic matter that retains evidence of its original cellular structure, and
3861-399: The euphotic zone , and regenerated production from nutrient recycling in the surface waters. The total new production in the ocean roughly equates to the sinking flux of particulate organic matter to the deep ocean, about 4 × 10 tons of carbon annually. Sinking oceanic particles encompass a wide range of shape, porosity, ballast and other characteristics. The model shown in the diagram at
3960-425: The DOC chemical composition, by removing humic compounds and reducing molecular size, transforming DOC to particulate organic flocs which can sediment and/or be consumed by grazers and filter feeders , but it also stimulates the bacterial degradation of the flocculated DOC. The impacts of flocculation on the removal of DOC from coastal waters are highly variable with some studies suggesting it can remove up to 30% of
4059-551: The DOC pool, while others find much lower values (3–6%; ). Such differences could be explained by seasonal and system differences in the DOC chemical composition, pH, metallic cation concentration, microbial reactivity, and ionic strength. The colored fraction of DOC (CDOM) absorbs light in the blue and UV-light range and therefore influences plankton productivity both negatively by absorbing light, that otherwise would be available for photosynthesis, and positively by protecting plankton organisms from harmful UV-light. However, as
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4158-592: The DOM pool under consideration. The surprising resistance of high concentrations of DOC to microbial degradation has been addressed by several hypotheses. The prevalent notion is that the recalcitrant fraction of DOC has certain chemical properties, which prevent decomposition by microbes ("intrinsic stability hypothesis"). An alternative or additional explanation is given by the "dilution hypothesis", that all compounds are labile, but exist in concentrations individually too low to sustain microbial populations but collectively form
4257-409: The POM content of soil and water. Particulate organic carbon (POC) is operationally defined as all combustible, non- carbonate carbon that can be collected on a filter . The oceanographic community has historically used a variety of filters and pore sizes, most commonly 0.7, 0.8, or 1.0 μm glass or quartz fiber filters. The biomass of living zooplankton is intentionally excluded from POC through
4356-581: The POM, such as the C:N ratio . In addition to nutrient release, decomposers colonizing POM play a role in improving soil structure. Fungal mycelium entangle soil particles and release sticky, cement-like, polysaccharides into the soil; ultimately forming soil aggregates Soil POM content is affected by organic inputs and the activity of soil decomposers. The addition of organic materials, such as manure or crop residues , typically results in an increase in POM. Alternatively, repeated tillage or soil disturbance increases
4455-525: The accumulated DOC reaches average radiocarbon ages between 1,000 and 4,000 years in surface waters, and between 3,000 and 6,000 years in the deep ocean, indicating that it persists through several deep ocean mixing cycles between 300 and 1,400 years each. Behind these average radiocarbon ages, a large spectrum of ages is hidden. Follett et al. showed DOC comprises a fraction of modern radiocarbon age, as well as DOC reaching radiocarbon ages of up to 12,000 years. More precise measurement techniques developed in
4554-459: The atmosphere and deposition in aquatic environments (e.g., volatile organic carbon and pollens), and also thousands of synthetic human-made organic chemicals that can be measured in the ocean at trace concentrations. Dissolved organic carbon (DOC) represents one of the Earth's major carbon pools. It contains a similar amount of carbon as the atmosphere and exceeds the amount of carbon bound in marine biomass by more than two-hundred times. DOC
4653-587: The atmosphere. Organic carbon is produced by organisms and is released during and after their life; e.g., in rivers, 1–20% of the total amount of DOC is produced by macrophytes. Carbon can enter the system from the catchment and is transported to the oceans by rivers and streams. There is also exchange with carbon in the sediments, e.g., burial of organic carbon, which is important for carbon sequestration in aquatic habitats. Aquatic systems are very important in global carbon sequestration; e.g., when different European ecosystems are compared, inland aquatic systems form
4752-552: The attenuation of the sinking flux with depth. The range of recorded sinking velocities of particles in the oceans spans from negative (particles float toward the surface) to several km per day (as with salp fecal pellets) When considering the sinking velocity of an individual particle, a first approximation can be obtained from Stokes' law (originally derived for spherical, non-porous particles and laminar flow) combined with White's approximation, which suggest that sinking velocity increases linearly with excess density (the difference from
4851-445: The bacterial transformation of labile DOC, which reshapes its composition. Due to the continuous production and degradation in natural systems, the DOC pool contains a spectrum of reactive compounds each with their own reactivity, that have been divided into fractions from labile to recalcitrant, depending on the turnover times, as shown in the following table... This wide range in turnover or degradation times has been linked with
4950-472: The basis of size, behaviour and persistence. These categories are arranged in order of decreasing ability to decompose. Each of them contribute to soil health in different ways. relatively simple molecules from decomposing materials (< 0.45 microns) litter of plant and herbivore origin (< 2 mm) detritus (2 mm – 54 micron) amorphous colloidal particles (< 53 microns) charcoals and related compounds Dissolved organic matter (DOM):
5049-532: The biological carbon pump, hence ocean carbon storage, is partly determined by the amount of organic matter exported and the rate at which it is remineralized (i.e., the rate with which sinking organic matter is reworked and respired in the mesopelagic zone region. Especially particle size and composition are important parameters determining how fast a particle sinks, how much material it contains, and which organisms can find and utilize it. Sinking particles can be phytoplankton, zooplankton, detritus, fecal pellets, or
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#17330858177845148-434: The body of water is known as allochthonous DOC and typically comes from soils or terrestrial plants . When water originates from land areas with a high proportion of organic soils, these components can drain into rivers and lakes as DOC. The marine DOC pool is important for the functioning of marine ecosystems because they are at the interface between the chemical and the biological worlds. DOC fuels marine food webs , and
5247-430: The chemical composition, structure and molecular size, but degradation also depends on the environmental conditions (e.g., nutrients), prokaryote diversity, redox state, iron availability, mineral-particle associations, temperature, sun-light exposure, biological production of recalcitrant compounds, and the effect of priming or dilution of individual molecules. For example, lignin can be degraded in aerobic soils but
5346-407: The collection of biogeochemical processes associated with the production, sinking, and remineralization of organic carbon in the ocean. In brief, photosynthesis by microorganisms in the upper tens of meters of the water column fix inorganic carbon (any of the chemical species of dissolved carbon dioxide) into biomass . When this biomass sinks to the deep ocean, a portion of it fuels the metabolism of
5445-531: The consumer community. As such, the compositional changes that occur during degradation are more complex than the simple removal of more labile components and resultant accumulation of remaining, less labile compounds. Dissolved organic matter recalcitrance (i.e., its overall reactivity toward degradation and/or utilization) is therefore an emergent property. The perception of DOM recalcitrance changes during organic matter degradation and in conjunction with any other process that removes or adds organic compounds to
5544-528: The contrary. Photochemical reactions are particularly important in coastal waters which receive high loads of terrestrial derived CDOM, with an estimated ~20–30% of terrestrial DOC being rapidly photodegraded and consumed. Global estimates also suggests that in marine systems photodegradation of DOC produces ~180 Tg C yr of inorganic carbon, with an additional 100 Tg C yr of DOC made more available to microbial degradation. Another attempt at global ocean estimates also suggest that photodegradation (210 Tg C yr )
5643-590: The decomposition of organic material, most carbon is lost as CO 2 to the atmosphere by microbial oxidation. Soil type and landscape slope, leaching , and runoff are also important processes associated to DOM losses in the soil. In well-drained soils, leached DOC can reach the water table and release nutrients and pollutants that can contaminate groundwater , whereas runoff transports DOM and xenobiotics to other areas, rivers, and lakes. Precipitation and surface water leaches dissolved organic carbon (DOC) from vegetation and plant litter and percolates through
5742-551: The deep ocean basins , but consistent global estimates of the overall input are currently lacking. Globally, groundwaters account for an unknown part of the freshwater DOC flux to the oceans. The DOC in groundwater is a mixture of terrestrial, infiltrated marine, and in situ microbially produced material. This flux of DOC to coastal waters could be important, as concentrations in groundwater are generally higher than in coastal seawater, but reliable global estimates are also currently lacking. The main processes that remove DOC from
5841-463: The deep ocean, where some of it (~0.2–0.5 Gt C) is sequestered for several millennia. The biological carbon pump is hence of similar magnitude to current carbon emissions from fossil fuels (~10 Gt C year−1). Any changes in its magnitude caused by a warming world may have direct implications for both deep-sea organisms and atmospheric carbon dioxide concentrations. The magnitude and efficiency (amount of carbon sequestered relative to primary production) of
5940-443: The detritus from the activity of microorganisms. Most of it continually undergoes decomposition by microorganisms (when conditions are sufficiently moist) and usually has a turnover time of less than 10 years. Less active parts may take 15 to 100 years to turnover. Where it is still at the soil surface and relatively fresh, particulate organic matter intercepts the energy of raindrops and protects physical soil surfaces from damage. As it
6039-427: The diagram on the right, the sinking POC is moving downward followed by a chemical plume. The plain white arrows represent the carbon flow. Panel (a) represents the classical view of a non-bioluminescent particle. The length of the plume is identified by the scale on the side. Panel (b) represents the case of a glowing particle in the bioluminescence shunt hypothesis. Bioluminescent bacteria are represented aggregated onto
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#17330858177846138-455: The diagram, phytoplankton fix carbon dioxide in the euphotic zone using solar energy and produce POC. POC formed in the euphotic zone is processed by marine microorganisms (microbes), zooplankton and their consumers into organic aggregates ( marine snow ), which is then exported to the mesopelagic (200–1000 m depth) and bathypelagic zones by sinking and vertical migration by zooplankton and fish. The biological carbon pump describes
6237-445: The food web. Algal-derived POM is thought to be most labile, but there is growing evidence that terrestrially-derived POM can supplement the diets of micro-organisms such as zooplankton when primary productivity is limited. The dynamics of the particulate organic carbon (POC) pool in the ocean are central to the marine carbon cycle . POC is the link between surface primary production, the deep ocean, and sediments. The rate at which POC
6336-770: The impact of UV damage and ability to repair is extremely variable, there is no consensus on how UV-light changes might impact overall plankton communities. The CDOM absorption of light initiates a complex range of photochemical processes, which can impact nutrient, trace metal and DOC chemical composition, and promote DOC degradation. Photodegradation involves the transformation of CDOM into smaller and less colored molecules (e.g., organic acids), or into inorganic carbon (CO, CO 2 ), and nutrient salts (NH 4 , HPO 4 ). Therefore, it generally means that photodegradation transforms recalcitrant into labile DOC molecules that can be rapidly used by prokaryotes for biomass production and respiration. However, it can also increase CDOM through
6435-840: The increase in excess density. On the other hand, the addition of ballasting mineral particles to marine particle populations frequently leads to smaller more densely packed aggregates that sink slower because of their smaller size. Mucous-rich particles have been shown to float despite relatively large sizes, whereas oil- or plastic-containing aggregates have been shown to sink rapidly despite the presence of substances with an excess density smaller than seawater. In natural environments, particles are formed through different mechanisms, by different organisms, and under varying environmental conditions that affect aggregation (e.g., salinity, pH, minerals), ballasting (e.g., dust deposition, sediment load; van der Jagt et al., 2018) and sinking behaviour (e.g., viscosity;). A universal conversion of size-to-sinking velocity
6534-401: The labile fraction of DOC decomposes rapidly through microbially or photochemically mediated processes, whereas refractory DOC is resistant to degradation and can persist in the ocean for millennia. In the coastal ocean, organic matter from terrestrial plant litter or soils appears to be more refractory and thus often behaves conservatively. In addition, refractory DOC is produced in the ocean by
6633-491: The last two decades, but the quantitative translation of these immense datasets into biogeochemical properties remains a challenge. In particular, advances are needed to enable the optimal translation of imaged objects into carbon content and sinking velocities. In addition, different devices often measure different optical properties, leading to difficulties in comparing results. Marine primary production can be divided into new production from allochthonous nutrient inputs to
6732-544: The late 1990s have allowed for a good understanding of how dissolved organic carbon is distributed in marine environments both vertically and across the surface. It is now understood that dissolved organic carbon in the ocean spans a range from very labile to very recalcitrant (refractory). The labile dissolved organic carbon is mainly produced by marine organisms and is consumed in the surface ocean, and consists of sugars, proteins, and other compounds that are easily used by marine bacteria . Recalcitrant dissolved organic carbon
6831-596: The main decomposers of DOC, although for some of the most recalcitrant forms of DOC very slow abiotic degradation in hydrothermal systems or possibly sorption to sinking particles may be the main removal mechanism. Mechanistic knowledge about DOC-microbe-interactions is crucial to understand the cycling and distribution of this active carbon reservoir. Phytoplankton produces DOC by extracellular release commonly accounting between 5 and 30% of their total primary production, although this varies from species to species. Nonetheless, this release of extracellular DOC
6930-438: The major sinks of DOC. Thermal degradation of DOC has been found at high-temperature hydrothermal ridge-flanks, where outflow DOC concentrations are lower than in the inflow. While the global impact of these processes has not been investigated, current data suggest it is a minor DOC sink. Abiotic DOC flocculation is often observed during rapid (minutes) shifts in salinity when fresh and marine waters mix. Flocculation changes
7029-408: The mass of other elements present in the organic material, such as nitrogen, oxygen and hydrogen. DOC is a component of DOM and there is typically about twice as much DOM as DOC. Many statements that can be made about DOC apply equally to DOM, and vice versa . DOC is abundant in marine and freshwater systems and is one of the greatest cycled reservoirs of organic matter on Earth, accounting for
7128-434: The ocean carbon cycle, including contributions to estimates of their downward flux, which sequesters carbon dioxide in the deep sea. Optical instruments can be used from ships or installed on autonomous platforms, delivering much greater spatial and temporal coverage of particles in the mesopelagic zone of the ocean than traditional techniques, such as sediment traps . Technologies to image particles have advanced greatly over
7227-431: The ocean water column are: (1) Thermal degradation in e.g., submarine hydrothermal systems ; (2) bubble coagulation and abiotic flocculation into microparticles or sorption to particles; (3) abiotic degradation via photochemical reactions ; and (4) biotic degradation by heterotrophic marine prokaryotes . It has been suggested that the combined effects of photochemical and microbial degradation represent
7326-613: The ocean, suggesting that bacterial DOC production could be important in marine systems. Viruses are the most abundant life forms in the oceans infecting all life forms including algae, bacteria and zooplankton. After infection, the virus either enters a dormant ( lysogenic ) or productive ( lytic ) state. The lytic cycle causes disruption of the cell(s) and release of DOC. Marine macrophytes (i.e., macroalgae and seagrass ) are highly productive and extend over large areas in coastal waters but their production of DOC has not received much attention. Macrophytes release DOC during growth with
7425-490: The organisms living there, including deep-sea fish and benthic organisms. Zooplankton play a critical role in shaping particle flux through ingestion and fragmentation of particles, production of fast-sinking fecal material and active vertical migration. Besides the importance of "exported" organic carbon as a food source for deep ocean organisms, the biological carbon pump provides a valuable ecosystem function: Exported organic carbon transports an estimated 5–20 Gt C each year to
7524-412: The pH of the water. DIC concentrations in freshwater range from about zero in acidic waters to 60 mg C L in areas with carbonate-rich sediments. POC can be degraded to form DOC; DOC can become POC by flocculation . Inorganic and organic carbon are linked through aquatic organisms . CO is used in photosynthesis (P) by for instance macrophytes , produced by respiration (R), and exchanged with
7623-429: The particle. Their light emission is shown as a bluish cloud around it. Blue dotted arrows represent the visual detection and the movement toward the particle of the consumer organisms. Increasing the visual detection allows a better detection by upper trophic levels, potentially leading to the fragmentation of sinking POC into suspended POC due to sloppy feeding. Sieve A sieve , fine mesh strainer , or sift ,
7722-443: The pollution of water with fecal bacteria , toxic metals or organic compounds. Life and particulate organic matter in the ocean have fundamentally shaped the planet. On the most basic level, particulate organic matter can be defined as both living and non-living matter of biological origin with a size of ≥0.2 μm in diameter, including anything from a small bacterium (0.2 μm in size) to blue whales (20 m in size). Organic matter plays
7821-437: The rate of decomposition by exposing soil organisms to oxygen and organic substrates ; ultimately, depleting POM. Reduction in POM content is observed when native grasslands are converted to agricultural land. Soil temperature and moisture also affect the rate of POM decomposition. Because POM is a readily available (labile) source of soil nutrients, is a contributor to soil structure, and is highly sensitive to soil management, it
7920-510: The right attempts to capture some of the predominant features that influence the shape of the sinking flux profile (red line). The sinking of organic particles produced in the upper sunlit layers of the ocean forms an important limb of the oceanic biological pump, which impacts the sequestration of carbon and resupply of nutrients in the mesopelagic ocean. Particles raining out from the upper ocean undergo remineralization by bacteria colonized on their surface and interior, leading to an attenuation in
8019-450: The same amount of carbon as in the atmosphere and up to 20% of all organic carbon. In general, organic carbon compounds are the result of decomposition processes from dead organic matter including plants and animals. DOC can originate from within or outside any given body of water. DOC originating from within the body of water is known as autochthonous DOC and typically comes from aquatic plants or algae , while DOC originating outside
8118-619: The same source and of the same age may have been subjected to different processing histories prior to accumulating within the same pool of DOM. Interior ocean DOM is a highly modified fraction that remains after years of exposure to sunlight, utilization by heterotrophs, flocculation and coagulation, and interaction with particles. Many of these processes within the DOM pool are compound- or class-specific. For example, condensed aromatic compounds are highly photosensitive, whereas proteins, carbohydrates, and their monomers are readily taken up by bacteria. Microbes and other consumers are selective in
8217-490: The same water/plankton community. When particles were made by different plankton communities, size alone was a bad predictor (e.g., Diercks and Asper, 1997) strongly supporting notions that particle densities and shapes vary widely depending on the source material. Packaging and porosity contribute appreciably to determining sinking velocities. On the one hand, adding ballasting materials, such as diatom frustules, to aggregates may lead to an increase in sinking velocities owing to
8316-492: The screen openings. Depending upon the types of particles to be separated, sieves with different types of holes are used. Sieves are also used to separate stones from sand. Sieving plays an important role in food industries where sieves (often vibrating) are used to prevent the contamination of the product by foreign bodies. The design of the industrial sieve is of primary importance here. Triage sieving refers to grouping people according to their severity of injury. The mesh in
8415-650: The second largest carbon sink (19–41 Tg C y ); only forests take up more carbon (125–223 Tg C y ). In marine systems DOC originates from either autochthonous or allochthonous sources. Autochthonous DOC is produced within the system, primarily by plankton organisms and in coastal waters additionally by benthic microalgae, benthic fluxes, and macrophytes, whereas allochthonous DOC is mainly of terrestrial origin supplemented by groundwater and atmospheric inputs. In addition to soil derived humic substances , terrestrial DOC also includes material leached from plants exported during rain events, emissions of plant materials to
8514-406: The sinking flux of organic matter with depth. The diagram illustrates a mechanistic model for the depth-dependent, sinking, particulate mass flux constituted by a range of sinking, remineralizing particles. Marine snow varies in shape, size and character, ranging from individual cells to pellets and aggregates, most of which is rapidly colonized and consumed by heterotrophic bacteria, contributing to
8613-407: The sinking fraction. Both DOC and POC play major roles in the carbon cycle , but POC is the major pathway by which organic carbon produced by phytoplankton is exported – mainly by gravitational settling – from the surface to the deep ocean and eventually to sediments , and is thus a key component of the biological pump . Soil organic matter is anything in the soil of biological origin. Carbon
8712-595: The soil column to the saturated zone . The concentration, composition, and bioavailability of DOC are altered during transport through the soil column by various physicochemical and biological processes, including sorption , desorption , biodegradation and biosynthesis . Hydrophobic molecules are preferentially partitioned onto soil minerals and have a longer retention time in soils than hydrophilic molecules. The hydrophobicity and retention time of colloids and dissolved molecules in soils are controlled by their size, polarity, charge, and bioavailability . Bioavailable DOM
8811-425: The soil negative electrical charges denitrification process, acid-base reactions in the soil solution, retention and translocation of nutrients ( cations ), and immobilization of heavy metals and xenobiotics . Soil DOM can be derived from different sources (inputs), such as atmospheric carbon dissolved in rainfall, litter and crop residues, manure, root exudates, and decomposition of soil organic matter (SOM). In
8910-444: The soil, DOM availability depends on its interactions with mineral components (e.g., clays, Fe and Al oxides) modulated by adsorption and desorption processes. It also depends on SOM fractions (e.g., stabilized organic molecules and microbial biomass) by mineralization and immobilization processes. In addition, the intensity of these interactions changes according to soil inherent properties, land use, and crop management. During
9009-414: The structure or function of phytoplankton communities is likely to alter the efficiency of the biological carbon pump, with feedbacks on the rate of climate change. The consumption of the bioluminescent POC by fish can lead to the emission of bioluminescent fecal pellets (repackaging), which can also be produced with non-bioluminescent POC if the fish gut is already charged with bioluminescent bacteria. In
9108-649: The surface ocean at a depth of 30 meters, the higher dissolved organic carbon concentrations are found in the South Pacific Gyre, the South Atlantic Gyre, and the Indian Ocean. At a depth of 3,000 meters, highest concentrations are in the North Atlantic Deep Water where dissolved organic carbon from the high concentration surface ocean is removed to depth. While in the northern Indian Ocean high DOC
9207-563: The top of the range and the middle of oceans may be near the bottom. Occasionally, high concentrations of organic carbon indicate anthropogenic influences, but most DOC originates naturally. The BDOC fraction consists of organic molecules that heterotrophic bacteria can use as a source of energy and carbon. Some subset of DOC constitutes the precursors of disinfection byproducts for drinking water. BDOC can contribute to undesirable biological regrowth within water distribution systems. The dissolved fraction of total organic carbon (TOC)
9306-460: The total amount of aquatic organic carbon. Its concentration ranges from 0.1 to >300 mg L . Likewise, inorganic carbon also consists of a particulate (PIC) and a dissolved phase (DIC). PIC mainly consists of carbonates (e.g., CaCO 3 ), DIC consists of carbonate (CO 3 ), bicarbonate (HCO 3 ), CO 2 and a negligibly small fraction of carbonic acid (H 2 CO 3 ). The inorganic carbon compounds exist in equilibrium that depends on
9405-455: The total mass of the particulate organic matter. In addition to carbon, POM includes the mass of the other elements in the organic matter, such as nitrogen, oxygen and hydrogen. In this sense POC is a component of POM and there is typically about twice as much POM as POC. Many statements that can be made about POM apply equally to POC, and much of what is said in this article about POM could equally have been said of POC. Particulate organic matter
9504-539: The transformation of compounds such as triglycerides, into more complex aromatic compounds, which are less degradable by microbes. Moreover, UV radiation can produce e.g., reactive oxygen species, which are harmful to microbes. The impact of photochemical processes on the DOC pool depends also on the chemical composition, with some studies suggesting that recently produced autochthonous DOC becomes less bioavailable while allochthonous DOC becomes more bioavailable to prokaryotes after sunlight exposure, albeit others have found
9603-421: The type of DOM they utilize and typically prefer certain organic compounds over others. Consequently, DOM becomes less reactive as it is continually reworked. Said another way, the DOM pool becomes less labile and more refractory with degradation. As it is reworked, organic compounds are continually being added to the bulk DOM pool by physical mixing, exchange with particles, and/or production of organic molecules by
9702-751: The use of a pre-filter or specially designed sampling intakes that repel swimming organisms. Sub-micron particles, including most marine prokaryotes , which are 0.2–0.8 μm in diameter, are often not captured but should be considered part of POC rather than dissolved organic carbon (DOC), which is usually operationally defined as < 0.2 μm. Typically POC is considered to contain suspended and sinking particles ≥ 0.2 μm in size, which therefore includes biomass from living microbial cells, detrital material including dead cells, fecal pellets , other aggregated material, and terrestrially-derived organic matter. Some studies further divide POC operationally based on its sinking rate or size, with ≥ 51 μm particles sometimes equated to
9801-404: The water density) and the square of particle diameter (i.e., linearly with the particle area). Building on these expectations, many studies have tried to relate sinking velocity primarily to size, which has been shown to be a useful predictor for particles generated in controlled environments (e.g., roller tanks. However, strong relationships were only observed when all particles were generated using
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