Redfield ratio
Encyclopedia
Redfield ratio or Redfield stoichiometry is the molecular ratio of carbon
, nitrogen
and phosphorus
in plankton
. This empirically developed stoichiometric ratio is found to be C:N:P = 106:16:1. This term is named after the American oceanographer Alfred C. Redfield
, who first described this ratio in an article written in 1934 (Redfield 1934). As a physiologist, Redfield participated in several voyages on board the research vessel Atlantis
. Alfred Redfield analyzed thousands of samples of marine biomass
across all of the ocean regions. From this research he found that globally the elemental composition of marine organic matter (dead and living) was remarkably constant across all of the regions. The stoichiometric ratios of carbon, nitrogen, phosphorus remain relatively consistent from both the coastal to open ocean regions.
to phosphate
(16:1).
Redfield felt that it wasn’t purely a coincidence that the large oceans would have a chemistry perfectly suited for the requirements of life.
In his hypothesis
he suggested that if the ocean were to be devoid of life then the chemical compositions would be significantly different from its actual composition. He determined this ratio empirically by analyzing thousands of samples of marine biomass from all of the ocean regions.
In 1958, almost a quarter century after first discovering the ratios, Redfield proposed the seminal idea of "the biological control of chemical factors" in the ocean (Redfield, 1958). He considered how the cycles of not just N and P but also C and O could interact to result in this match.
conditions, oxidize the organic matter to form dissolved inorganic nutrients, mainly carbon dioxide
, nitrate, and phosphate.
Redfield explained the remarkable congruence between the chemistry of the deep ocean and the chemistry of living things such as phytoplankton in the surface ocean. Both have N:P ratios of about 16:1 in terms of atoms. When nutrients are not limiting
, the molar elemental ratio C:N:P in most phytoplankton is 106:16:1. Redfield thought it wasn't purely coincidental that the vast oceans would have a chemistry perfectly suited to the requirements of living organisms.
Although the Redfield ratio is remarkably stable in the deep ocean, phytoplankton may have large variations in the C:N:P composition, and their life strategy play a role in the C:N:P ratio, which has made some researchers speculate that the Redfield ratio perhaps is a general average rather than specific requirement for phytoplankton growth (e.g., Arrigo 2005) as no theoretical justification for Redfield ratio has ever been found.
. This was later supported by hundreds of independent measurements. However, looking at the composition of individual species
of phytoplankton grown with nitrogen and phosphorus limitation shows that this nitrogen to phosphorus ratio can vary anywhere from 6:1 to 60:1. While understanding this problem, Redfield never attempted to explain it with the exception of noting that the N:P ratio of inorganic nutrients in the ocean interior was an average with small scale variability to be expected.
Despite reports that the elemental composition of organisms such as marine phytoplankton in an oceanic region do not conform to the Redfield ratio, the fundamental concept of this ratio continues to remain valid. That the nitrate to phosphate ratio in the interior of all of the major ocean basins is highly similar to the N:P ratio is due to the residence times of these elements in the ocean relative to the oceans circulation time, roughly 10,000 years and 1000 years, respectively. The fact that the residence times of these elements are greater than the mixing times by an order of magnitude results in the ratio of nitrate to phosphate in the ocean interior remaining fairly constant.
, Sulfur
, Zinc
, Copper
, and Iron
are also important in the ocean chemistry. In particular, iron (Fe) was considered of great importance as early biological oceanographers hypothesized that iron may also be a limiting factor for primary production
in the ocean. As a result a Modified Redfield Ratio was developed to include this as part of this balance. This new stoichiometric ratio states that the ratio should be 106 C:16 N:1 P:0.1-0.001 Fe. The variation in iron is the result of “…iron contamination on ships and in labs is large and difficult to control. No one has been able to beat this nearly insuperable combination of difficulties.” (Broecker and Peng (1982)). It is this contamination
that resulted in early evidence suggesting that iron concentrations were high and not a limiting factor in marine primary production.
to create biogenic silica
for their frustules (cell walls). As a result of this the Redfield-Brzezinski nutrient ratio was proposed for diatoms and stated to be C:Si:N:P = 106:15:16:1 (Brzezinski, 1985).
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
in plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
. This empirically developed stoichiometric ratio is found to be C:N:P = 106:16:1. This term is named after the American oceanographer Alfred C. Redfield
Alfred C. Redfield
Alfred Clarence Redfield was an American oceanographer.He is especially known for having discovered the Redfield ratio, which describes the ratio between nutrients in plankton and ocean water. In 1966, he received the Eminent Ecologist Award from the Ecological Society of America...
, who first described this ratio in an article written in 1934 (Redfield 1934). As a physiologist, Redfield participated in several voyages on board the research vessel Atlantis
RV Atlantis
RV Atlantis is a sailboat that served as the first and also the main research vessel for the Woods Hole Oceanographic Institution from 1931 to 1964. Several ships, including RV Atlantis and the Space Shuttle Atlantis were named after Atlantis...
. Alfred Redfield analyzed thousands of samples of marine biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
across all of the ocean regions. From this research he found that globally the elemental composition of marine organic matter (dead and living) was remarkably constant across all of the regions. The stoichiometric ratios of carbon, nitrogen, phosphorus remain relatively consistent from both the coastal to open ocean regions.
History
In his 1934 paper, Alfred Redfield proposed that the ratio of Nitrogen to Phosphorus in plankton resulted in the global ocean having a remarkably similar ratio of dissolved nitrateNitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
to phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
(16:1).
Redfield felt that it wasn’t purely a coincidence that the large oceans would have a chemistry perfectly suited for the requirements of life.
In his hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
he suggested that if the ocean were to be devoid of life then the chemical compositions would be significantly different from its actual composition. He determined this ratio empirically by analyzing thousands of samples of marine biomass from all of the ocean regions.
In 1958, almost a quarter century after first discovering the ratios, Redfield proposed the seminal idea of "the biological control of chemical factors" in the ocean (Redfield, 1958). He considered how the cycles of not just N and P but also C and O could interact to result in this match.
Uses
This research has resulted in this ratio has become a fundamental feature in the understanding of the biogeochemical cycles of the oceans. They also help in determining which nutrients are limiting in a localized system, if there is a limiting nutrient. The ratio can also be used to understand the formation of phytoplankton blooms and subsequently hypoxia by use of comparison of the ratio between different regions, such as a comparison of the Redfield Ratio of the Mississippi River to the ratio of the northern Gulf of Mexico.Explanation
In the ocean a large portion of the biomass is found to be nitrogen-rich plankton. Many of these plankton are consumed by other plankton biomass which have similar chemical compositions. This results in a similar nitrogen to phosphorus ratio, on average, for all the plankton throughout the world’s ocean, averaging approximately 16:1. When these organisms sink into the ocean interior, their energy-rich bodies are consumed by bacteria that, in aerobicAerobic organism
An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment.Faculitative anaerobes grow and survive in an oxygenated environment and so do aerotolerant anaerobes.-Glucose:...
conditions, oxidize the organic matter to form dissolved inorganic nutrients, mainly carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, nitrate, and phosphate.
Redfield explained the remarkable congruence between the chemistry of the deep ocean and the chemistry of living things such as phytoplankton in the surface ocean. Both have N:P ratios of about 16:1 in terms of atoms. When nutrients are not limiting
Limiting
Limiting: Any process by which a specified characteristic of the output of a device is prevented from exceeding a predetermined value....
, the molar elemental ratio C:N:P in most phytoplankton is 106:16:1. Redfield thought it wasn't purely coincidental that the vast oceans would have a chemistry perfectly suited to the requirements of living organisms.
Although the Redfield ratio is remarkably stable in the deep ocean, phytoplankton may have large variations in the C:N:P composition, and their life strategy play a role in the C:N:P ratio, which has made some researchers speculate that the Redfield ratio perhaps is a general average rather than specific requirement for phytoplankton growth (e.g., Arrigo 2005) as no theoretical justification for Redfield ratio has ever been found.
Errors with the Redfield Ratio
This ratio was initially derived empirically from measurements of the elemental composition of plankton in addition to the nitrate and phosphate content of seawater collected from a few stations in the Atlantic OceanAtlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
. This was later supported by hundreds of independent measurements. However, looking at the composition of individual species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of phytoplankton grown with nitrogen and phosphorus limitation shows that this nitrogen to phosphorus ratio can vary anywhere from 6:1 to 60:1. While understanding this problem, Redfield never attempted to explain it with the exception of noting that the N:P ratio of inorganic nutrients in the ocean interior was an average with small scale variability to be expected.
Despite reports that the elemental composition of organisms such as marine phytoplankton in an oceanic region do not conform to the Redfield ratio, the fundamental concept of this ratio continues to remain valid. That the nitrate to phosphate ratio in the interior of all of the major ocean basins is highly similar to the N:P ratio is due to the residence times of these elements in the ocean relative to the oceans circulation time, roughly 10,000 years and 1000 years, respectively. The fact that the residence times of these elements are greater than the mixing times by an order of magnitude results in the ratio of nitrate to phosphate in the ocean interior remaining fairly constant.
Modified Redfield Ratio
Some feel that there are other elements, such as PotassiumPotassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
, Sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
, Zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, Copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, and Iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
are also important in the ocean chemistry. In particular, iron (Fe) was considered of great importance as early biological oceanographers hypothesized that iron may also be a limiting factor for primary production
Primary production
400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...
in the ocean. As a result a Modified Redfield Ratio was developed to include this as part of this balance. This new stoichiometric ratio states that the ratio should be 106 C:16 N:1 P:0.1-0.001 Fe. The variation in iron is the result of “…iron contamination on ships and in labs is large and difficult to control. No one has been able to beat this nearly insuperable combination of difficulties.” (Broecker and Peng (1982)). It is this contamination
Contamination
Contamination is the presence of a minor and unwanted constituent in material, physical body, natural environment, at a workplace, etc.-Specifics:"Contamination" also has more specific meanings in science:...
that resulted in early evidence suggesting that iron concentrations were high and not a limiting factor in marine primary production.
Redfield Ratio in Diatoms
Diatoms need, among other nutrients, silicic acidSilicic acid
Silicic acid is a general name for a family of chemical compounds of the element silicon, hydrogen, and oxygen, with the general formula [SiOx4-2x]n...
to create biogenic silica
Biogenic silica
Biogenic silica , also referred to as opal, biogenic opal, or amorphous opaline silica, forms one of the most widespread biogenic minerals. Silica is an amorphous metal oxide formed by complex inorganic polymerization processes. This is opposed to the other major biogenic minerals, comprising...
for their frustules (cell walls). As a result of this the Redfield-Brzezinski nutrient ratio was proposed for diatoms and stated to be C:Si:N:P = 106:15:16:1 (Brzezinski, 1985).