Outline. 1 Phosphorus. 2 Nitrogen. 3 Silicon. 4 Other nutrients. 5 Quantitative relationships. 6 Initial nutrients

Transcription

1 8 Nutrients

2 Outline 1 Phosphorus 2 Nitrogen 3 Silicon 4 Other nutrients 5 Quantitative relationships 6 Initial nutrients

3 Outline 1 Phosphorus 2 Nitrogen 3 Silicon 4 Other nutrients 5 Quantitative relationships 6 Initial nutrients

4 Crustal abundance and geochemical transport granites, basalts, shales ( % as PO 4 ) Humans have more than doubled the total geochemical transport of phosphorus.

5 Inorganic phosphate Essentially no undissociated H 3 PO 4 is present in normal seawater. Strong ion-pairing with calcium and magnesium

6 Polyphosphates Polyphosphates, often highly polymerized, are made in large amounts by certain algae and bacteria, where they may act as storage products. They are present only in small or undetectable amounts under usual conditions.

7 Organic phosphorus (1) (2) (1) easily hydrolyzed (2) The direct carbon phosphorus bond is so difficult to break. 25% of the phosphorus in high-molecular-weight dissolved organic matter; this fraction appears constant in the deep water of all ocean basins.

8 Colorimetric quantification of phosphorus Mo: molybdenum, Sb: Antimony molybdenum blue

9 Vertical distribution of inorganic phosphate 0 3 µmol kg 1 Biological transport (mostly downward transport by sinking biological detritus and subsequent metabolic release) The large-scale features of oceanic circulation ( ocean conveyor belt )

10 Redistribution within the ocean of many biologically transported substances During its long path the deep water continually receives falling debris from the surface, and thus is continually enriched with nutrients and other substances.

11 Occurrence of organic phosphorus DOP = TDP - DIP Occurrence of organic phosphorus at all depths fairly stable and long-lived compounds. In surface waters the DOP may comprise more than half the total.

12 Seasonal cycles in Narragansett Bay 33-year mean of the monthly means of approximately weekly observations in Narragansett Bay, Rhode Island. summer: sediment water winter: water sediment

13 Phosphorus-poor regions Mediterranean and the great central gyres of all the major oceans blue is the desert color of the sea - Sverdrup Arsenate (AsO 3 4 ): (1) chemically very similar to phosphate (Group 15) (2) it forms a blue-colored arsenomolybdenum compound Arsenate disrupts some normal biochemical activities in cells. Marine meat (fish and shell fish) may have up to 10 times the concentration of arsenic as terrestrial meat.

14 Phosphorite minerals Phosphorite is a general term for sedimentary rocks that contain large amounts of phosphorous. apatites - the most abundant group of phosphorite minerals in general formula: Ca 5 (PO 4 ) 3 (X), where X may be Cl, F, OH. Present-day oceanic conditions are apparently not conducive to the formation of massive deposits. Phosphorites always seem to be found in regions of intensive coastal upwelling and low oxygen concentration, such as off Peru and Namibia, where they appear to be forming in the organic-rich and anoxic sediments.

15 Outline 1 Phosphorus 2 Nitrogen 3 Silicon 4 Other nutrients 5 Quantitative relationships 6 Initial nutrients

16 Reservoirs of nitrogen on Earth One third of all nitrogen on Earth is in the atmosphere.

17 Various forms of inorganic nitrogen The oxidation states of inorganic nitrogen range from a valence of 3 to +5. In seawater, most nitrogen is present as the dissolved molecular form, N 2.

18 Nitrogen fixation fixed nitrogen or reactive nitrogen - the non-n 2 inorganic forms (and the organic forms as well) In lightning and fires - NO and NO 2, collectively known as NOx Biological fixation - ammonia (NH 3 ) Humans - manufacture of NH 3 for fertilizers combustion of fossil fuels

19 Industrial nitrogen fixation Haber Bosch process (in 1909): N H 2 2 NH 3 NH 3 production ( tons/yr) consumes the equivalent of 3 to 4% of the world s total natural-gas production. Some NH 3 is applied directly to the soil, and a greater amount is applied in the form of urea [(NH 2 ) 2 CO], which is easy and safe to transport long distances. About 87% of the ammonia fixed is used as fertilizer.

20 Biological nitrogen fixation Rhizobium ( 뿌리혹박테리아 ) - a nitrogen-fixing bacterium that is common in the soil, especially in the root nodules of leguminous plants. on land: 144 Mt yr 1 in the oceans: 135 Mt yr 1 (nitrogen-fixing cyanobacteria of the genus Trichodesmium)

21 Trichodesmium ( sea sawdust ) Trichodesmium fixes atmospheric nitrogen into ammonium, a nutrient used by other organisms (80 Mt yr 1 ). They are found in nutrient poor tropical and subtropical ocean waters.

22 Denitrification A microbially facilitated process of nitrate reduction that may ultimately produce molecular nitrogen (N 2 ) through a series of intermediate gaseous nitrogen oxide products. Benthic foraminifera can accumulate large concentrations of NO 3 and use it as an electron acceptor for respiration. Overall reaction: A series of steps carried out by complex biochemical machinery Different enzymes or enzyme complexes are involved for each step.

23 Places for denitrification Denitrification processes occur in all regions where nitrate is present and oxygen is low or absent (anoxic basins, sediments, and O 2 -minimum zone). Profiles of nitrous oxide and oxygen in the Pacific Ocean

24 N 2 O N 2 O is chemically quite unreactive, it cannot be used by plants, and much of it diffuses into the atmosphere. There is usually a flux of N 2 O from the ocean to the atmosphere. Residence time in the atmosphere 120 years. An important green house gas (GWP: 298 CO 2 ) 323 ppbv in the atmosphere (0.76 ppbv/yr )

25 Anammox ANaerobic AMMonium OXidation primary energy source for Candidatus sp. Candidatus sp. - They are the only organisms known that make and store hydrazine (N 2 H 4 ), a very toxic substance; These bacteria are also unusually slow growing, doubling in about two weeks.

26 Geochemical importance of anammox At least one-half of NO 3 is perhaps due to the anammox reaction. Anammox vs. tranditional denitrification autotrophic denitrification vs. (heterotrophic) denitrification

27 Biological nitrogen cycles Cultures of diatoms in large glass carboys of seawater in the dark. The first major nitrogenous product of decay of plant material is ammonia. Ammonia is oxidized to nitrite, NO 2, by organisms (bacteria) which develop in numbers when the ammonia supply is adequate, and O 2 is present. Nitrite is oxidized to nitrate, NO 3, by a different set of bacteria which develop when the nitrite supply is adequate; again, O 2 must be present.

28 When the carboys placed in a lighted window... Ammonia was taken up during the formation of organic matter as diatoms re-grew to their original density. Plants prefer ammonia, because it is in this form that it enters the biosynthetic pathways. Essentially all the inorganic fixed nitrogen in deep water is in the form of nitrate.

29 Biochemical cycles of nitrogen in ocean waters

30 Dissolved organic nitrogen DON = TDN - DIN (NO 3 ) 2 10 µmol kg 1 (Urea <0.5, Amino acids < 0.6) Most of DON are uncharacterized Nearly all of the DON in deep water and a considerable portion of that in surface water appears to be highly resistant to bacterial attack and very long-lived.

31 Geochemical fluxes of fixed nitrogen In a ton of continental crust: 7 mol (N) vs. 25 mol (P)

32 Short residence time of fixed nitrogen There is little fixed nitrogen in continental rocks. The rocks play only a minor role in the modern geochemical pathways of nitrogen. * * * Total pool of fixed nitrogen amounts to about t (Table 8.3). Global fixation rate is about t/yr (Table 8.6). 1,500 years for an apparent residence time of the fixed nitrogen pool. Higher human impact on the cycle? (e.g., 50% increase of N fixation by human)

33 Outline 1 Phosphorus 2 Nitrogen 3 Silicon 4 Other nutrients 5 Quantitative relationships 6 Initial nutrients

34 Silica as a nutrient Silica (SiO2 ) makes up nearly 58% of the mass of Earth s crust. *** Radiolaria[방산충] make skeletons out of silica. Diatoms[규조류] make shells (called tests or frustules) out of precipitated amorphous silica (opal).

35 Occurrence and forms of silica Si(OH) 4, Si(OH) 2 2+, Si(OH) 6 2 polymers (when concentration >1800 µm) In ordinary seawater (i.e., <200 µm) dissolved silica should be exclusively monomeric.

36 Silica and salinity Silica in solution is mostly not ionized (< 5%) a negligible effect on the conductivity of the water. broad range: 1 µmol kg 1 in surface waters of Atlantic tropical regions 210 µmol kg 1 in deep water of the North Pacific. Silica must cause the density to depart from that calculated according to the usual relationship from the salinity as measured by a conductive salinometer. S P vs. S A

37 Difficulty in measuring solubility of silica Extreme slowness of the reaction It also depends on surface area, presence of coatings and metal ions, etc.

38 Effects of temperature and pressure on the solubility The best estimate is that the solubility of pure amorphous silica is about 1800 µm at 25 C (Alexander et al. 1954) Almost all natural waters are undersaturated with amorphous silica (e.g., seawater <200µM). temperature, pressure (and ph) solubility

39 Geochemical cycles of silica Unlike nitrogen and phosphorus, there are no significant inputs of dissolved silica by humans. Decrease of silica concentration is greatly enhanced by the construction of dams on most of the world s rivers.

40 Diffusion from sediments The source of the diffusive flux is slow dissolution of the frustules of diatoms and skeletons of radiolaria, buried in the sediment g yr 1 (Treguer et al., 1995). φ is the porosity - the fraction of sediment volume occupied by water θ is the tortuosity - the increased diffusive path length around sediment particles

41 Silica budget in the water column Most of the silica that is biologically converted to opaline diatom frustules and radiolarian skeletons must be re-dissolved in the water column.

42 Outline 1 Phosphorus 2 Nitrogen 3 Silicon 4 Other nutrients 5 Quantitative relationships 6 Initial nutrients

43 Micro- vs. nano-nutrients Phosphorus, nitrogen, and silicon - conventionally called, nutrient elements or macro-nutrient elements micro-nutrient elements ( present in concentrations in units of µmol kg 1 ) gross composition of living organisms - water (70 to 95% of total mass), carbon (45% of dry matter), oxygen, nitrogen, sulfur, phosphorus nano-nutrient elements, including Fe, Cu, Zn, Mn, Co, and so on... ( requirements by marine organisms usually can be satisfied by nanomolar concentrations)

44 Limiting nutrient Law of the Minimum (Justus von Liebig in mid-1800) - for each species, nutrients are required in a fixed proportion, and when one of these nutrients is used up, the plant will cease to grow. However, multiple factors are usually at work in nature. Examples include light, temperature, multiple nutrients and other environmental limtations.

45 Fe addition to the surface waters of Ocean Station PAPA (north-east Pacific subarctic) Martin and Fitzwater (1988) The addition of nmol amounts of dissolved iron resulted in the nearly complete utilization of excess NO 3. Fe deficiency is limiting phytoplankton growth in high-nutrient low-chlorophyll (HNLC) regions (North Pacific, Eastern equatorial Paicifc, and Southern Ocean).

46 Annual surface mixed-layer nitrate (µmol/l) Boyd et al. (2007)

47 Boyd et al. (2007) Mechanisms responsible for perturbations in Fe supply A: A purposeful in situ Southern Ocean FeAX B: An FeNX near Crozet C: An atmospheric dust deposition event (g m 2 year 1 ) D: Fe supply to the Southern Ocean during the glacial maxima.

48 Outline 1 Phosphorus 2 Nitrogen 3 Silicon 4 Other nutrients 5 Quantitative relationships 6 Initial nutrients

49 Redfield (1934) showed the linear relationship between N and P, with a slope of about 16. Redfield et al. (1963) The slope ( 16) should reflect the average composition of the organic debris that is metabolized and mineralized in the deep sea and, by extension, the average composition of the plankton that produces the organic debris.

50 Redfield ratio Redfield et al. (1963) - 1P : 16N : 106C : 138O 2 Redfield molecule Photosynthesis with ammonia:

51 Photosynthetic and respiratory quotients PQ = O 2 produced CO 2 fixed RQ = O 2 consumed CO 2 produced The ratios are necessary to calculate the organic matter produced from changes in the concentration of oxygen, or changes in oxygen from other measurements of the rate of carbon fixation.

52 Reevaluation of the Redfield ratio (Pilson, 2013) There is a little more carbon per unit phosphorus, and a little more oxygen is required per unit carbon to oxidize the carbon part of the Redfield molecule. Inclusion of the lipid component as 20CH 2 units. Published values for the oxygen-to-phosphate ratio are in the range of Laws (1991) estimate of the PQ appropriate for the biosynthesis of most phytoplankton was 1.3 to 1.4 when growing on nitrate (1.34 = 166/124).

53 Stoichiometric "Redfield" ratios

54 Potential fertility The quantity of organic matter that could be produced by photosynthesis in a unit volume of water if it were brought from depth to the surface and illuminated there until the limiting nutrients are exhausted. seawater from about 500 m depth in the North Pacific Over the oceans as a whole the concentration of plankton in surface water probably averages less than 1% of these values.

55 Relationships between nutrient and oxygen data from east of Barbados The depths of the phosphate and nitrate maxima coincide, while the upper silicate maximum is a little deeper. ( Slower dissolution of silicate from sinking particles) The increased silicate concentration near the bottom is due to the influence of AABW.

56 Ratios of N-to-P in the Atlantic and Pacific The Pacific is a region where denitrification is more important than in the Atlantic. * Low O 2 at mid-waters * Old deep water has more time to be exposed to sediments The same ratios at the very deepest water of both oceans. ( a considerable input directly from Antarctic Bottom Water)

57 The ratios in coastal and estuarine regions Narragansett Bay Denitrification is most active in the summer during times of warm temperatures. The major limiting nutrient is nitrogen in the regions (shallow waters over continental shelves).

58 Outline 1 Phosphorus 2 Nitrogen 3 Silicon 4 Other nutrients 5 Quantitative relationships 6 Initial nutrients

59 Calculation of the nutrients released during metabolism of organic matter 1. Assume the water was in equilibrium with the atmosphere when O 2 was at surface. 2. Calculate [O 2 ] sat from potential temperature and salinity 3. AOU = [O 2 ] sat - [O 2 ] obs, Apparent Oxygen Utilization 4. Calculate the concentrations of nitrate and phosphate that must have been released based on the Redfield ratio. There is always more phosphate and nitrate than can be accounted for by the AOU (166O 2 :1P). Much of the water sinking in the regions that generate the deep water of the world ocean is, in fact, not completely depleted in nutrients prior to equilibration with the atmosphere and sinking.

60 The distributions of initial nutrients in the oceans Initial P = Measured P - (AOU/166) Initial NO 3 = Measured NO 3-16 (AOU/166)

61 Initial nutrients (aka preformed nutrients ) Remarkably uniform concentration of initial phosphate in water below about 900 m. They constitute the ultimate reservoir of nutrients dissolved in the ocean that have not been utilized to make organic matter. accessed to increase the organic production in the ocean to reduce the atmospheric concentration in glacial times?