By:Daniel M. Sigman(Department that Geosciences, Princeton University)&Mathis P. Hain(Department that Geosciences, Princeton University)© Education

Citation:Sigman,D.M.&Hain,M.P.(2012)The organic Productivity of the education and learning Knowledge3(10):21




Productivity fuels life in the ocean, cd driver its chemical cycles, and lowers atmospheric carbon dioxide. Nutrient uptake and export interact with circulation come yield unique ocean regimes.

You are watching: During which season does primary productivity reach its peak in polar oceans?

What is s Productivity?

s productivity mainly refers come the production of organic matter by "phytoplankton," tree suspended in the ocean, most of which are single-celled. Phytoplankton space "photoautotrophs," harvesting light to convert inorganic to organic carbon, and they it is provided this essential carbon to varied "heterotrophs," organisms that achieve their energy solely indigenous the respiration of essential matter. Open ocean heterotrophs incorporate bacteria and also more facility single- and multi-celled "zooplankton" (floating animals), "nekton" (swimming organisms, including fish and also marine mammals), and also the "benthos" (the seafloor neighborhood of organisms).

The plenty of nested cycles of carbon connected with ocean productivity room revealed through the following definitions (Bender et al. 1987) (Figure 1). "Gross primary production" (GPP) refers to the full rate that organic carbon manufacturing by autotrophs, if "respiration" refers to the energy-yielding oxidation of organic carbon earlier to carbon dioxide. "Net primary production" (NPP) is GPP minus the autotrophs" own rate the respiration; that is therefore the price at which the full metabolism the phytoplankton produce biomass. "Secondary production" (SP) typically refers come the growth rate that heterotrophic biomass. Only a small portion of the organic matter ingested by heterotrophic organisms is supplied to grow, the majority being respired ago to dissolved not natural carbon and nutrients that have the right to be reused by autotrophs. Therefore, SP in the ocean is little in comparison to NPP. Fisheries depend on SP; therefore they count on both NPP and also the efficiency with which organic matter is transferred up the foodweb (i.e., the SP/NPP ratio). "Net ecosystem production" (NEP) is GPP minus the respiration by all organisms in the ecosystem. The worth of NEP counts on the limits defined because that the ecosystem. If one considers the sunlit surface s down to the 1% light level (the "euphotic zone") end the food of whole year, then NEP is equivalent to the particulate organic carbon sinking into the dark ocean inner plus the liquified organic carbon gift circulated the end of the euphotic zone. In this case, NEP is additionally often referred to as "export production" (or "new production" (Dugdale & Goering 1967), as discussed below). In contrast, the NEP because that the whole ocean, including its shallow sediments, is approximately equivalent to the slow burial of organic issue in the sediments minus the price of organic matter entering indigenous the continents.

Productivity in the surface ar ocean, the meanings used to explain it, and also its relations to nutrient cycling. The blue cycle for “net ecosystem production” (NEP) (i.e. “new” or “export” production) encompasses the “new” nutrient supply from the ocean interior, its absorb by autotrophic phytoplankton growth, packaging into large particles by heterotrophic grazing organisms, and sinking that organic matter out the the surface ar ocean. The red bicycle illustrates the fate of the bulk of essential matter produced in the surface ar ocean, i beg your pardon is to it is in respired by heterotrophic biology to fulfill their power requirements, thereby releasing the nutrients ago into the surface water wherein they have the right to be taken up by phytoplankton once again to fuel “regenerated production.” The eco-friendly cycle to represent the internal respiration the phytoplankton themselves, the is, their own use that the products of photosynthesis for purposes other than growth. This nested cycles incorporate to yield (1) “gross main production” (GPP) representing the pistol photosynthesis and (2) “net main production” (NPP) that represents phytoplankton biomass manufacturing that creates the communication of the food internet plus a lot smaller price of organic matter export from the surface. If the brand-new nutrient supply and export manufacturing are ultimately attached by massive balance, there may be inequalities on little scales of an are and time, allowing for brief accumulations of biomass.

There room no accumulations of living biomass in the marine setting that compare v the forests and grasslands on land (Sarmiento & Bender 1994). Nevertheless, s biology is responsible for the storage of an ext carbon away from the atmosphere than is the terrestrial biosphere (Broecker 1982). This is achieved by the sinking that organic issue out the the surface ocean and also into the s interior before it is went back to dissolved inorganic carbon and also dissolved nutrients by bacter decomposition. Oceanographers often refer come this procedure as the "biological pump," as it pumps carbon dioxide (CO2) the end of the surface ar ocean and also atmosphere and into the voluminous deep ocean (Volk & Hoffert 1985).

Only a fraction of the organic matter produced in the surface ocean has actually the fate of gift exported to the deep ocean. The the necessary matter created by phytoplankton (NPP), most is respired ago to liquified inorganic forms within the surface ar ocean and also thus recycle for use by phytoplankton (Eppley & Peterson 1979) (Figure 1). Many phytoplankton cells space too tiny to sink individually, for this reason sinking occurs only when they accumulation into larger particles or are packaged into "fecal pellets" by zooplankton. The stays of zooplankton are additionally adequately big to sink. If sinking is a reasonably rare fate for any type of given particle in the surface ocean, biomass and organic matter do no accumulate in the surface ar ocean, for this reason export the organic issue by sinking is the ultimate fate for every one of the nutrient that go into into the surface s in dissolved form — through the exceptions the (1) liquified nutrients have the right to be changed unused to the inner by the circulation in part polar regions (see below), and also (2) circulation also carries dissolved organic issue from the surface ocean right into the interior, a far-ranging process (Hansell et al. 2009) that we will not address further. As organic matter settles through the ocean interior and onto the seafloor, that is practically entirely decomposed earlier to liquified chemicals (Emerson & Hedges 2003, boy name et al. 1987). This high efficiency of decomposition is due to the reality that the organisms moving out the decomposition count upon it together their sole resource of chemical energy; in many of the open up ocean, the heterotrophs just leave behind the organic issue that is as well chemically resistant for it come be precious the investment to decompose. ~ above the whole, only a tiny fraction (typically much much less than 1%) of the organic carbon indigenous NPP in the euphotic zone survives come be buried in deep sea sediments.

Productivity in seaside ecosystems is often distinctive from that of the open ocean. Along the coasts, the seafloor is shallow, and also sunlight have the right to sometimes pass through all the way through the water pillar to the bottom, thus permitting bottom-dwelling ("benthic") organisms to photosynthesize. Furthermore, sinking organic issue isintercepted by the seabed, wherein it supports thriving benthic faunal communities, in the procedure being recycled back to liquified nutrients that room then immediately accessible for main production. The proximity come land and its nutrient sources, the interception of sinking organic issue by the shallow seafloor, and the propensity for seaside upwelling all result in highly productive ecosystems. Here, we mainly resolve the performance of the vast open ocean; nevertheless, many of the exact same concepts, albeit in modification form, apply to coastal systems.

What Does ocean Productivity Need?

Phytoplankton need a suite of chemicals, and those v the potential to be scarce in surface ar waters are typically identified together "nutrients." Calcium is an instance of an aspect that is swiftly assimilated by some plankton (for production of calcium carbonate "hard parts") yet is not typically considered a nutrient since of that uniformly high concentration in seawater. Dissolved inorganic carbon, i m sorry is the feedstock because that organic carbon production by photosynthesis, is likewise abundant and so is not typically provided among the nutrients. However, the acidic kind dissolved CO2 is frequently at adequately low concentrations to affect the development of at least some phytoplankton.

Broadly vital nutrients encompass nitrogen (N), phosphorus (P), steel (Fe), and also silicon (Si). There show up to be reasonably uniform needs for N and also P among phytoplankton. In the early 1900s, oceanographer Alfred Redfield uncovered that plankton develop their biomass v C:N:P stoichiometric ratios the ~106:16:1, to which we now refer as the Redfield ratios (Redfield 1958). As Redfield noted, the dissolved N:P in the deep ocean is close come the 16:1 proportion of plankton biomass, and also we will argue below that plankton i charged this ratio on the deep, not vice versa. Steel is found in biomass only in trace amounts, yet it is supplied for varied essential functions in organisms, and also it has come to be clear over the critical 25 years that iron"s scarcity often limits or affects performance in the open up ocean, specifically those areas where high-N and also -P deep water is lugged rapidly to the surface ar (Martin & Fitzwater 1988). Research is ongoing to understand the function of various other trace facets in efficiency (Morel et al. 2003). Silicon is a nutrient only for specific plankton taxa-diatoms (autotrophic phytoplankton), silicoflaggellates, and radiolaria (heterotrophic zooplankton) — which use it to make opal difficult parts. However, the common dominance of diatoms in Si-bearing waters, and also the tendency of diatom-associated organic issue to sink the end of the surface ar ocean, make Si ease of access a major factor in the wider ecology and biogeochemistry of surface waters.

Sunlight is the can be fried energy source — directly or indirectly — for almost all life on Earth, consisting of in the deep ocean. However, irradiate is absorbed and scattered such the very tiny of the penetrates listed below a depth that ~80 m (as deep as 150 m in the least productive subtropical regions, yet as shallow together 10 m in highly productive and coastal regions) (Figure 2). Thus, photosynthesis is largely limited to the upper light-penetrated skin that the ocean. Moreover, across most of the ocean"s area, consisting of the tropics, subtropics, and the warm zone, the absorption of sunlight reasons surface water come be much warmer than the underlying deep ocean, the latter being filled v water that sank native the surface in the high latitudes . Warm water is an ext buoyant than cold, which reasons the top sunlit layer come float top top the denser deep ocean, through the shift between the two recognized as the "pycnocline" (for "density gradient") or "thermocline" (the upright temperature gradient the drives thickness stratification across most the the ocean, number 2). Wind or another source of power is required to journey mixing throughout the pycnocline, and so the transfer of water through its dissolved chemicals between the sunlit surface and also the dark interior is sluggish. This dual effect of irradiate on photosynthesis and also seawater buoyancy is an important for the success of s phytoplankton. If the s did not have a thin buoyant surface ar layer, mixing would lug algae the end of the light and thus far from their energy source for many of the time. Rather of virtually neutrally buoyant solitary celled algae, larger, positive buoyant photosynthetic organisms (e.g., pelagic seaweeds) might dominate the open ocean. This hypothetical instance aside, back viable phytoplankton cells are uncovered (albeit at low concentrations) in depths waters, photosynthesis limits active phytoplankton development to the top skin that the ocean, while top ocean density stratification avoids them from being blended down into the dark abyss. Thus, many open s biomass, consisting of phytoplankton, zooplankton, and nekton, is uncovered within ~200 m of the ocean surface.

Typical problems in the subtropical ocean, as shown by data built up at the Bermuda Atlantic Time-series station in July, 2008. The thermocline (vertical temperature gradient) stratifies the top water column. During this certain station occupation, the shallow wind-mixed surface layer is not well defined, presumably since of solid insolation and also a absence of wind that allowed continuous stratification every the means to the surface. Very small sunlight penetrates deeper than ~100 m. Brand-new supply the the significant nutrients N and also P is restricted by the sluggish mixing throughout the upper thermocline (showing right here only the N nutrient nitrate, NO3-). Within the upper euphotic zone, the slow nutrient supply is completely consumed by phytoplankton in your growth. This expansion leads to the buildup of particulate organic carbon in the surface ocean, few of which is respired by bacteria, zooplankton, and also other heterotrophs, and also some of which is exported as sinking material. The deep chlorophyll maximum (DCM) wake up at the contact where there is sufficient light because that photosynthesis and yet far-reaching nutrient supply from below. The DCM should not it is in strictly interpreted as a depth best in phytoplankton biomass, together the phytoplankton in ~ the DCM have actually a an especially high inner chlorophyll concentration. The data displayed here is made easily accessible the Bermuda academy of ocean Sciences ( and the Bermuda Bio Optics job (

At the same time, the visibility of a slim buoyant surface ar layer conspires with various other processes to impose nutrient limitation on s productivity. The export the organic issue to depth depletes the surface s of nutrients, leading to the nutrients to accumulate in deep waters where there is no light easily accessible for photosynthesis (Figure 2). Because of the thickness difference in between surface water and the deep sea throughout most that the ocean, s circulation have the right to only very slowly reintroduce dissolved nutrients come the euphotic zone. Through driving nutrients out that the sunlit, buoyant surface ar waters, ocean productivity effectively boundaries itself.

Phytoplankton development limitation has actually traditionally been taken in the context of Liebig"s legislation of the Minimum, which claims that plant growth will be as good as enabled by the least obtainable resource, the "limiting nutrient" that sets the productivity of the system (de Baar 1994). If this watch is powerful, interactions among nutrients and between nutrients and also light can also control productivity. A basic but essential example of this potential for "co-limitation" comes from polar regions, where oblique solar insolation combines with deep mix of surface ar waters come yield short light availability. In together environments, greater iron supply can increase the efficiency with i m sorry phytoplankton capture light energy (Maldonado et al. 1999, Sunda & Huntsman 1997). An ext broadly, it has actually been argued that phytoplankton should usually seek a state that co-limitation by all the chemistry they require, including the plenty of trace metal nutrients (Morel 2008).

Who are the significant Players in ocean Productivity?

In contrast to the terrestrial biosphere, most naval photosynthesis is conducted by single-celled organisms, and the an ext abundant the the multicellular forms are structurally much simpler than the vascular tree on land. During much the the twenty century, the was believed that cells in the range of ~5 to ~100 microns diameter account for many phytoplankton biomass and productivity. This size selection is composed mainly of eukaryotes, organisms whose cells contain facility membrane-bound frameworks ("organelles"), including the cell"s nucleus and chloroplasts. Well-studied creates of eukaryotic bio phytoplankton include the opal-secreting diatoms, prymnesiophytes (including the CaCO3-secreting coccolithophorids), and also the organic wall-forming dinoflagellates. The centrality of these organisms in early oceanographic thought was due to their access by traditional light microscopy.

Only v recent technological advances have smaller organisms become readily observable, revolutionizing our watch of the plankton. In particular, the cyanobacteria, which are prokaryotes (lacking a nucleus and also most other organelles found in eukaryotes), room now recognized to be important amongst the phytoplankton. Initially, the cyanobacteria were established largely with early american forms such together Trichodesmium that play the an important role that "fixing" nitrogen (see below). However, significant discoveries end the last thirty years have revealed the prevalence throughout the an international ocean of unicellular cyanobacteria that ~0.5 come ~1.5 microns diameter. That is now known that two cyanobacterial genera — Synechoccocus and also Prochlorococcus — conquer phytoplankton numbers and biomass in the nutrient-poor tropical and also subtropical s (Waterbury et al. 1979, Chisholm et al. 1988). In addition, new methods, both microscopic and genetic, are revealing a formerly unappreciated diversity of smaller eukaryotes in the open ocean.

Mapping ecological and also biogeochemical features onto the hereditary diversity that the phytoplankton is an energetic area in biological and also chemical oceanography. Based on observations and theory, the smaller sized phytoplankton such as the uncellular cells cyanobacteria space thought to dominate regenerated manufacturing in countless systems, conversely, the larger eukaryotes appear to play a much more important duty in brand-new production (i.e., NEP, number 1; see below).

See more: The Pitch Of A Sound Is Most Closely Related To The, Hearing: 11

Just as large eukaryotes were as soon as thought to dominate the phytoplankton, it to be long believed that multicell zooplankton that ≥200 microns overcome heterotrophy — the tiny crustaceans recognized as copepods room the prototypical example. Us now understand that heterotrophy is often overcame by single-celled standard scale ("microzooplankton," that ~1 come ~200 microns) and also by bacteria (of ~0.3 to ~1 microns), the latter carrying out many of the essential carbon decomposition in the ocean.

The food source of a given kind of zooplankton is typically driven by its own size, v microzooplankton grazing top top the prokaryotes and also smaller eukaryotes and also multicellular zooplankton grazing on larger eukaryotes, both phytoplankton and also microzooplankton. Because of their relative physiological simplicity, microzooplankton space thought to it is in highly efficient grazers the strongly border the biomass buildup of their prey. In contrast, the multicell zooplankton, since they generally have more complicated life histories, have the right to lag behind the proliferation of their prey, enabling them to bloom and also sometimes protect against predation altogether and also sink directly. The multicellular zooplankton also often facilitate the production of sinking organic matter, for example, through the production of fecal pellets by copepods.

The diversity of the plankton interacts v open s environmental conditions to influence the performance of the bigger ecosystem (Michaels & silver 1988, Morel et al. 1991, Buesseler 1998) (Figure 3). In the nutrient-poor tropical and subtropical ocean, the (small) cyanobacteria tend to it is in numerically dominant, perhaps because they specialize in acquisition up nutrients at low concentrations. Small phytoplankton have actually a better surface area-to-volume ratio than do huge phytoplankton. A higher proportional surface area disclosure the uptake of nutrients across the cell boundary, a an essential process once nutrients space scarce, likely explaining why tiny phytoplankton conquer the biomass in the nutrient-poor ocean. The microzooplankton properly graze these little cells, staying clear of their biomass native accumulating and sinking directly. Moreover, this single-celled microzooplankton lack a digestive tract, so they execute not produce the fecal pellets that represent a significant mechanism the export. Instead, any residual organic matter remains in the top ocean, to be degraded by bacteria. Every told, microzooplankton grazing that phytoplankton biomass leader to the remineralization of most of its consisted of nutrients and also carbon in the surface ocean, and thus rises recycling loved one to organic issue export. This really efficient recycling elevates NPP loved one to NEP, yielding a short NEP:NPP ratio (~0.05–0.3) in nutrient-poor systems (Figure 3a). In contrast, bigger phytoplankton, such together diatoms, often overcome the nutrient-rich polar ocean, and these have the right to be grazed straight by multicell zooplankton. By cultivation adequately swiftly to outstrip the grazing rates of this zooplankton, the diatoms deserve to sometimes accumulate come high concentrations and produce plentiful sinking material. In addition, the zooplankton export organic matter as fecal pellets. In these productive systems, the less extensive upper s recycling reasons NEP and NPP come be much more similar, v an NEP:NPP ratio frequently near 0.5 (Figure 3b).

The most generally accepted paradigm for the controls on surface nutrient recycling efficiency. NPP is supported by both new nutrient it is provided from the deep ocean and also nutrients regenerated in ~ the surface ar ocean. The portion of NEP:NPP ratio appears to vary with the nutrient supply, since links to the ecology the the plankton. In the nutrient-poor tropical and subtropical s (a), the (small) cyanobacteria have tendency to it is in numerically dominant. The microzooplankton that graze these tiny cells execute so effectively, avoiding phytoplankton indigenous sinking directly. Moreover, these single-celled microzooplankton perform not create sinking fecal pellets. Instead, any residual organic issue remains to it is in degraded by bacteria. This increases recycling loved one to organic matter export, yielding a short NEP:NPP proportion (~0.1). In nutrient-rich areas (b), large phytoplankton are much more important, and also these can be grazed directly by multicell zooplankton. By cultivation adequately promptly to outstrip the grazing prices of zooplankton, the huge phytoplankton deserve to sometimes accumulate to high concentrations and also produce plentiful sinking material. In addition, the zooplankton export organic issue as fecal pellets. In these fertile systems, the less intensive upper ocean recycling reasons NEP and NPP to be much more similar, with an NEP:NPP ratio frequently near 0.5. The relationships in between nutrient supply, phytoplankton size, and also sinking thus conquer this view of upper ocean nutrient cycling.