Phosphorus Geochemistry Research Articles

On the potential roles of phosphorus in the early evolution of energy metabolism.

Energy metabolism in extant life is centered around phosphate and the energy-dense phosphoanhydride bonds of adenosine triphosphate (ATP), a deeply conserved and ancient bioenergetic system. Yet, ATP synthesis relies on numerous complex enzymes and has an autocatalytic requirement for ATP itself. This implies the existence of evolutionarily simpler bioenergetic pathways and potentially primordial alternatives to ATP. The centrality of phosphate in modern bioenergetics, coupled with the energetic properties of phosphorylated compounds, may suggest that primordial precursors to ATP also utilized phosphate in compounds such as pyrophosphate, acetyl phosphate and polyphosphate. However, bioavailable phosphate may have been notably scarce on the early Earth, raising doubts about the roles that phosphorylated molecules might have played in the early evolution of life. A largely overlooked phosphorus redox cycle on the ancient Earth might have provided phosphorus and energy, with reduced phosphorus compounds potentially playing a key role in the early evolution of energy metabolism. Here, we speculate on the biological phosphorus compounds that may have acted as primordial energy currencies, sources of environmental energy, or sources of phosphorus for the synthesis of phosphorylated energy currencies. This review encompasses discussions on the evolutionary history of modern bioenergetics, and specifically those pathways with primordial relevance, and the geochemistry of bioavailable phosphorus on the ancient Earth. We highlight the importance of phosphorus, not only in the form of phosphate, to early biology and suggest future directions of study that may improve our understanding of the early evolution of bioenergetics.

Porewater and solid phase speciation geochemistry of phosphorus in the Western Bay of Bengal: An assessment of depositional pathways

In this study, we used a combination of porewater phosphate and solid-phase P speciation to examine the present-day benthic biogeochemical cycling and pathways of phosphorus (P) deposition at four sites in the western Bay of Bengal (BoB). We concentrate on two regions, with 2 sediment cores from each region. One is the Palar basin where ancient phosphorites and phosphatic grains were discovered before, and the other in the Cauvery basin, where no phosphories are known to occur. Both of these regions fall in the depths of the oxygen minimum zone (OMZ). Our results suggest that the influx of lithogenic material, or lack of it, largely regulates the sedimentary cycling of P in BoB. Both locations lack active phosphogenesis due to substantial inputs of non-reactive P relative to reactive P from river runoff and its quick burial by the ballasting effect, which appears to prevent P from transforming into an authigenic phase. Despite the oxygen-depleted conditions, low bacterial respiration limits the microbial reduction of iron oxyhydroxide and makes the redox cycling of iron a weak player in the sedimentary cycling of P in the studied cores. The burial efficiency of P is relatively high in the Cauvery basin cores owing to the high sediment accumulation rate and suggests that most of the sedimentary P is undergoing burial with a minimum regeneration. Lack of/Very low recent sedimentation in the Palar basin is possibly due to the reported migration of river course towards the south during the mid-to Late Holocene.

Main Patterns of Geochemistry of Phosphorus

Main Patterns of Geochemistry of Phosphorus

Titanium Barrier in Phosphorus Geochemistry

Titanium Barrier in Phosphorus Geochemistry

Iron and phosphorus geochemistry in the core sediments of an urbanized mangrove ecosystem, Southwest coast of India

This study has been carried out to understand the geochemistry of elements namely, iron (Fe) and phosphorus (P) in the core sediments of an urbanized tropical mangrove ecosystem along the Southwest coast of India. The study revealed the coupling of iron and phosphorus in which the reductive conditions induced reductive dissolution and upward transport of Fe, causing surface coprecipitation of phosphorus incorporated Fe oxyhydroxides. The accumulation and transformation of phosphorus were significantly influenced by processes viz., phosphorus regeneration due to organic matter mineralization and adsorption to inorganic iron oxides/Ca bound minerals in the surface sediments, and phosphorus retention in the sedimentary column by transformation into refractory organic phosphates. Bioavailable phosphorus (BAP) accounted for more than 50% of TP, so that the mangrove sediments act as an important internal nutrient source of iron and phosphorus for coastal eutrophication.

The Main Features of Phosphorus Transport in World Rivers

Data on the geochemistry of phosphorus in the continental runoff of dissolved and solid substances were systematized and generalized, with a separate consideration of the processes of runoff transformation in river mouth areas. It has been established that atmospheric deposition, which many authors consider to be an important source of phosphorus in river runoff and not associated with mobilization processes in catchments, actually contains phosphorus from soil-plant recycling. This is confirmed by the fact that the input of phosphorus from the atmosphere into catchments exceeds its removal via water runoff. An analysis of the mass ratio of phosphorus in the adsorbed form and in the form of its own minerals was carried out. It was shown that the maximum mass of adsorbed phosphorus is limited by the solubility of its most stable minerals. The minimum concentrations of dissolved mineral and total phosphorus were observed in the rivers of the Arctic and subarctic belts; the maximum concentrations were confined to the most densely populated temperate zone and the zone of dry tropics and subtropics. In the waters of the primary hydrographic network, the phosphorus concentration exhibited direct relationships with the population density in the catchments and the mineralization of the river water and was closely correlated with the nitrogen content. This strongly suggests that economic activity is one of the main factors in the formation of river phosphorus runoff. The generalization of the authors’ and the literature’s data on the behavior of phosphorus at the river–sea mixing zone made it possible to draw a conclusion about the nonconservative distribution of phosphorus, in most cases associated with biological production and destruction processes. The conservative behavior of phosphorus was observed only in heavily polluted river mouths with abnormally high concentrations of this element.

Main empirical regularities of the phosphorus geochemistry in the hypergenesis

Research subject. The study investigates the distribution of phosphorus (as percentages of P2O5 and P) and 4 phosphorus modules introduced by the authors - phosphorus-titanium FTM (P2O5/TiO2), phosphorus-calcium FCM (P2O5/CaO), phos-phorus-iron FIM (P2O5/Fe2O3) and phosphorus-general-iron FGiM (P2O5/(Fe2O3 + FeO)) - in the main types of sedimentary rocks, such as psammites, pelites, carbonates, silicites, in volcanic-sedimentary rocks (tuffoids), as well as in soils, sediments and such specific rocks as nodules and weathering crusts. Methods. On the basis of a large data bank (several tens of thousands of silicate analyses), new clarks of phosphorus were calculated. Clark estimates were based on average median contents for all the above-mentioned rock groups. For the first time, lithochemistry methods were successfully applied to characterize the composition of phosphorites. Correlation analysis was used to identify forms of phosphorus in rocks. Only the most reliable linear correlation coefficients of phosphorus and phosphorus modules with rock-forming components were considered significant - with a significance level no greater than 0.01 and 0.05.Results and conclusions. In some cases, new estimates of clarks differed markedly from the estimates of our predecessors. For a number of objects, clarks were determined for the first time. Interpretation of the revealed relationships allowed us to identify the following main correlations and corresponding forms of phosphorus in sedimentary rocks and their analogues (soils and sediments): positive correlation with CaO - phosphorus in the form of accessory apatite or francolite dominated; positive correlation with Fe2O3 - phosphorus sorbed on iron hydroxides dominates; positive correlation with MgO - phosphorus dominated in the composition of smectite or chlorite, initially sorbed on the clay substance of precipitation; positive correlation with TiO2 - phosphate sorbed on leucoxene, dominates. Thus, in addition to the previously known calcium and iron hydroxide, a titanium geochemical barrier for phosphorus was first identified.

Geochemistry of phosphorus and the behavior of apatite during crustal anatexis: Insights from melt inclusions and nanogranitoids

AbstractThe solubility of apatite in anatectic melt plays an important role in controlling the trace-element compositions and isotopic signatures of granites. The compositions of glassy melt inclusions and nanogranitoids in migmatites and granulites are compared with the results of experimental studies of apatite solubility to evaluate the factors that influence apatite behavior during prograde suprasolidus metamorphism and investigate the mechanisms of anatexis in the continental crust. The concentration of phosphorus in glassy melt inclusions and rehomogenized nanogranitoids suggests a strong control of melt aluminosity on apatite solubility in peraluminous granites, which is consistent with existing experimental studies. However, measured concentrations of phosphorus in melt inclusions and nanogranitoids are generally inconsistent with the concentrations expected from apatite solubility expressions based on experimental studies. Using currently available nanogranitoids and glassy melt inclusion compositions, we identify two main groups of inclusions: those trapped at lower temperature and showing the highest measured phosphorus concentrations, and melt inclusions trapped at the highest temperatures having the lowest phosphorus concentrations. The strong inconsistency between measured and experimentally predicted P concentrations in higher temperature samples may relate to apatite exhaustion during the production of large amounts of peraluminous melt at high temperatures. The inconsistency between measured and predicted phosphorus concentrations for the lower-temperature inclusions, however, cannot be explained by problems with the electron microprobe analyses of rehomogenized nanogranitoids and glassy melt inclusions, sequestration of phosphorus in major minerals and/or monazite, shielding or exhaustion of apatite during high-temperature metamorphism, and apatite–melt disequilibrium. The unsuitability of the currently available solubility equations is probably the main cause for the discrepancy between the measured concentrations of phosphorus in nanogranites and those predicted from current apatite solubility expressions. Syn-entrapment processes such as the generation of diffusive boundary layers at the mineral-melt interface may also be responsible for concentrations of P in nanogranitoids and glassy melt inclusions that are higher than those predicted in apatite-saturated melt.

Sulfur, iron, and phosphorus geochemistry in an intertidal mudflat impacted by shellfish aquaculture.

Dissolved sulfide, iron (Fe), and phosphorus (P) in a mudflat (Jiaozhou Bay, China) impacted by shellfish aquaculture were measured in situ by the diffusive gradients in thin films (DGT) technique. A combination of porewater and solid-phase chemistry was used to characterize the interplays of Fe and S, and their control on P mobilization. Below the subsurface layer, two times higher fluxes (FDGT) of dissolved Fe2+ from porewater to the DGT device than those of dissolved sulfide indicate that dissimilatory iron reduction (DIR) dominates over sulfate reduction (SR). Spatial coupling of dissolved Fe2+ and P points to P release driven mainly by reductive dissolution of Fe. Much higher FDGT values of dissolved Fe2+ relative to dissolved P imply that oxidative regeneration of Fe oxides at the sediment-water interfaces (SWIs) of the transitional mudflat serves as an effective "iron curtain" of upward diffusing P. In the mudflat sediments of DIR prevalence, the accumulation of total reduced inorganic sulfur (TRIS) is dampened, which can largely ascribed to enhanced oxidative loss of sulfide and/or limited availability of degradable organic carbon in the dynamic regimes. Low dissolved sulfide concentrations in the sediments leave the majority of reactive Fe unsulfidized and thus abundantly available to buffer newly produced sulfide.

The biogeochemical characteristics of phosphorus in coastal sediments under high salinity and dredging conditions

The geochemistry of phosphorus (P) can usually be related to prevailing environmental conditions. To investigate sedimentary P cycling mechanism and biogeochemical characteristics under high salinity and dredging conditions in polluted coastal sediments, thirty-three surface sediment samples were collected from the Jiehe River (JH), Jiaolai River (JL) and their estuarine and offshore areas in the Bohai Sea. Analyses included the Standards, Measurements and Testing method (SMT), Ivanoff organic P (OP) fractionation, and nuclear magnetic resonance (31P-NMR) of soluble P and indicated that HCl-P was the dominant fraction in sediments under high salinity stress. However, under dredging conditions in freshwater river sediments, NaOH-P was the dominant fraction. The potential activity of the OP fraction was reactive in freshwater river sediments, while it was unreactive under high salinity conditions.NaOH-P and HCl-P were found to be mainly derived from anthropogenic inputs, whereas both in-situ biological and anthropogenic inputs were important sources of the OP fractions. High salinity had the potential to increase NaOH-P content in acidic river sediments, resulting in the OP being relatively stable with a low risk level. Sediment dredging potentially increased the regeneration of P from HCl-P and OP and increased the potential activity of OP and IP. Seawater was found to induce removal of the NaOH-P and OP from offshore sediments, resulting in the regeneration of the remaining P at a low level.

Apatite in carbonatitic rocks: Compositional variation, zoning, element partitioning and petrogenetic significance

Apatite-group phosphates are nearly ubiquitous in carbonatites, but our understanding of these minerals is inadequate, particularly in the areas of element partitioning and petrogenetic interpretation of their compositional variation among spatially associated rocks and within individual crystals. In the present work, the mode of occurrence, and major- and trace-element chemistry of apatite (sensu lato) from calcite and dolomite carbonatites, their associated cumulate rocks (including phoscorites) and hydrothermal parageneses were studied using a set of 80 samples from 50 localities worldwide. The majority of this set represents material for which no analytical data are available in the literature. Electron-microprobe and laser-ablation mass-spectrometry data (~600 and 400 analyses, respectively), accompanied by back-scattered-electron and cathodoluminescence images and Raman spectra, were used to identify the key compositional characteristics and zoning patterns of carbonatitic apatite. These data are placed in the context of phosphorus geochemistry in carbonatitic systems and carbonatite evolution, and compared to the models proposed by previous workers. The documented variations in apatite morphology and zoning represent a detailed record of a wide range of evolutionary processes, both magmatic and fluid-driven. The majority of igneous apatite from the examined rocks is Cl-poor fluorapatite or F-rich hydroxylapatite (≥0.3apfu F) with 0.2–2.7wt.% SrO, 0–4.5wt.% LREE2O3, 0–0.8wt.% Na2O, and low levels of other cations accommodated in the Ca site (up to 1000ppm Mn, 2300ppm Fe, 200ppm Ba, 150ppm Pb, 700ppm Th and 150ppm U), none of which show meaningful correlation with the host-rock type. Silicate, (SO4)2− and (VO4)3− anions, substituting for (PO4)3−, tend to occur in greater abundance in crystals from calcite carbonatites (up to 4.2wt.% SiO2, 1.5wt.% SO3 and 660ppm V). Although (CO3)2− groups are very likely present in some samples, Raman micro-spectroscopy proved inconclusive for apatites with small P-site deficiencies and other substituent elements in this site. Indicator REE ratios sensitive to redox conditions (δCe, δEu) and hydrothermal overprint (δY) form a fairly tight cluster of values (0.8–1.3, 0.8–1.1 and 0.6–0.9, respectively) and may be used in combination with trace-element abundances for the development of geochemical exploration tools. Hydrothermal apatite forms in carbonatites as the product of replacement of primary apatite, or is deposited in fractures and interstices as euhedral crystals and aggregates associated with typical late-stage minerals (e.g., quartz and chlorite). Hydrothermal apatite is typically depleted in Sr, REE, Mn and Th, but enriched in F (up to 4.8wt.%) relative to its igneous precursor, and also differs from the latter in at least some of key REE ratios [e.g., shows (La/Yb)cn≤25, or a negative Ce anomaly]. The only significant exception is Sr(± REE,Na)-rich replacement zones and overgrowths on igneous apatite from some dolomite(-bearing) carbonatites. Their crystallization conditions and source fluid appear to be very different from the more common Sr-REE-depleted variety. Based on the new evidence presented in this work, trace-element partitioning between apatite and carbonatitic magmas, phosphate solubility in these magmas, and compositional variation of apatite-group minerals from spatially associated carbonatitic rocks are critically re-evaluated.

The effects of sulfur amendments on the geochemistry of sulfur, phosphorus and iron in the mangrove plant (Kandelia obovata (S. L.)) rhizosphere

P (phosphorus) and Fe (iron) are limiting elements and S (sulfur) is an important element of the biogeochemical cycle in the mangrove environment. To assess the effects of sulfur on the geochemical cycling of Fe and P at the sediment-plant interface, the speciation distributions of Fe, P and S in sediments were examined. The data showed that higher proportions of amorphous Fe, Fe-bound phosphate, chromium reducible sulfur and elemental sulfur were found in the rhizosphere, while more crystalline Fe, exchangeable phosphate and acid-volatile sulfide were determined in the non-rhizosphere. Sulfate application induced an increase in the Ex-P concentration, high P accumulation and high iron plaque deposition in the roots. In conclusion, sulfate applications had a significant influence on the geochemical cycling of Fe and P in the sediments. It significantly curtailed the Fe and P limit to plant growth and enhanced plant resistance to the rugged surroundings in mangrove.

Geochemistry of phosphorus in sediment cores from Sishili Bay, China

This paper presents the distribution of total phosphorus (P), inorganic P (IP) and organic P in sediment cores from Sishili Bay, China. Their concentrations (μmolg−1) ranged from 15.04 to 21.59, 12.43 to 18.27 and 0.15 to 5.11, respectively, showing 87.6–96.9% of TP is IP. The distribution of the fractionation of IP , obtained by a sequential extraction technique, was 1.9–3.2% for soluble and loosely bound P (Ex-P), 8.5–13.1% for Al-bound from (Al-P), 7.4–9.5% for Fe-bound P (Fe-P), 5.0–12.4% for reductant-soluble P (Oc-P), 9.7–15.6% for CaCO3-bound P (ACa-P) and 45.9–54.6% for detritus P (Det-P). The P distribution and concentration was consistent with other Chinese coastal seas. No significant difference was found for the sedimentary P forms between scallop cultivation area and background area, indicating that shellfish aquaculture did not have significant effect on the depositional environment in the studied area, at least in case of P.

Interaction of Peat Soil and Sulphidic Material Substratum: Role of Peat Layer and Groundwater Level Fluctuations on Phosphorus Concentration

Phosphorus (P) often becomes limiting factor for plants growth. Phosphorus geochemistry in peatland soil is associated with the presence of peat layer and groundwater level fluctuations. The research was conducted to study the role of peat layer and groundwater level fluctuations on P concentration in peatland. The research was conducted on deep, moderate and shallow peat with sulphidic material as substratum, peaty acid sulphate soil, and potential acid sulphate soil. While P concentration was observed in wet season, in transition from wet to dry season, and in dry season. Soil samples were collected by using peat borer according to interlayer and soil horizon. The results showed that peat layer might act as the main source of P in peatland with sulphidic material substratum. The upper peat layer on sulphidic material caused by groundwater level fluctuations had no directly effect on P concentration in the peat layers. Increased of P concentration in the lowest sulphidic layer might relate to redox reaction of iron in the sulphidic layer and precipitation process. Phosphorus concentration in peatland with sulphidic material as substratum was not influenced by peat thickness. However, depletion or disappearance of peat layer decreased P concentration in soil solution. Disappearance of peat layer means loss of a natural source of P for peatland with sulphidic material as substratum, therefore peat layer must be kept in order to maintain of peatlands. [How to Cite: Arifin F, B Radjagukguk and BH Purwanto. 2014. Interaction of Peat Soil and Sulphidic Material Substratum: Role of Peat Layer and Groundwater Level Fluctuations on Phosphorus Concentration. J Trop Soils 19: 171-179. Doi: 10.5400/jts.2014.19.3.171]

Impact of harbour, industry and sewage on the phosphorus geochemistry of a subtropical estuary in Brazil

The distribution of different forms of phosphorus in surface sediment from 17 sites were investigated by SEDEX method. The sites were divided into three sectors: Santos Channel (SC – influenced by harbour, fertilizers plants and phosphogypsum mountains), São Vicente Channel (SVC– domestic waste) and Santos Bay (SB – sewage outfall). The average percentage of each P fraction of the surface sediments in this region followed the sequence P–Fe (38%)>Porg (27%)>Pexch (13%)>Detrital – P (12%)>Auth – P (10%). Ptotal varied from 3.57 to 74.11μmolg−1 in both seasons. In SVC, Pexch ranged from 13% to 27% and Porg varied from 12% to 56%. These high percentages of Pexch/Ptotal (greater than 20%) may be related to low oxygen resulting from oxygen consumed by intensive organic matter decomposition as well as the salty water that leads to cation and anion flocculation. Also, the possibility of an influence related to the industrial source of Pexch is not ruled out. No significant seasonal differences were found among sites, except for sewage outfall, with changing in the grain size and hence, the P geochemistry. During the summer in the sewage outfall station, Porg represented 37% of Ptotal, which decreased to 13% in the winter. These results suggest that high percentages of organic phosphorus cannot be attributed only to autochthonous and allochthonous organic matter, but also to detergents and/or domestic waste. In contrast, spatial differences among sectors were observed, with the highest values of each fraction associated with sites near industrial and domestic waste activities.

Phosphorus geochemistry in a Brazilian semiarid mangrove soil affected by shrimp farm effluents.

Wastewater discharge from shrimp farming is one of the main causes of eutrophication in mangrove ecosystems. We investigated the phosphorus (P) geochemistry in mangrove soils affected by shrimp farming effluents by carrying out a seasonal study of two mangrove forests (a control site (CS); a site affected by shrimp farm effluents (SF)). We determined the soil pH, redox potential (Eh), total organic carbon (TOC), total phosphorus (TP), and dissolved P. We also carried out sequential extraction of the P-solid phases. In SF, the effluents affected the soil physicochemical conditions, resulting in lower Eh and higher pH, as well as lower TOC and higher TP than in CS. Organic P forms were dominant in both sites and seasons, although to a lesser extent in SF. The lower TOC in SF was related to the increased microbial activity and organic matter decomposition caused by fertilization. The higher amounts of P oxides in SF suggest that the effluents alter the dominance of iron and sulfate reduction in mangrove soils, generating more reactive Fe that is available for bonding to phosphates. Strong TP losses were recorded in both sites during the dry season, in association with increased amounts of exchangeable and dissolved P. The higher bioavailability of P during the dry season may be attributed to increased mineralization of organic matter and dissolution of Ca-P in response to more oxidizing and acidic conditions. The P loss has significant environmental implications regarding eutrophication and marine productivity.

Quaternary paleolake nutrient evolution and climatic change in the western Qaidam Basin deduced from phosphorus geochemistry record of deep drilling core SG-1

Phosphorus (P) provides an important biologically limiting nutrient in lake ecosystems, and its concentrations furnish significant information on lake nutrient status, climatic change, and landscape development within a drainage area. This study explores the potential of calcium-bound P and iron-bound P in calcareous lacustrine sediments to reveal variations of the paleolake nutrient status and its related climatic changes. Data come from the nearly 1000-m long core (SG-1) from the western Qaidam Basin (NE Tibetan Plateau), which has been well-dated by paleomagnetism to between 2.77 and 0.1 Ma. Calcium-bound P and iron-bound P make up the two most frequent phases of inorganic phosphorus pools in the calcareous sediment. This study compares the variations of calcium-bound P and iron-bound P with the independent proxy for biologic production proxy Total Organic Carbon (TOC) as well as a climatic proxy for lake level fluctuation from the borehole. Those results indicate that calcium-bound P responds sensitively to paleolake nutrients and climatic changes, while the iron-bound P responds to more complex factors, more specific, to the content of iron oxides. Variations of the calcium-bound P in the core SG-1 show a long-term, stepwise decrease, with shifts at ∼2.5 Ma, 1.8 Ma, 1.2 Ma, and 0.6 Ma, indicating a long-term stepwise decrease of the paleolake nutrient supply in the drainage. This suggests that the ecologic systems experienced a long-term deterioration, and the climate in central Asia became increasingly arid since after the late Pliocene.

Efectos del uso urbano de la tierra en la distribución de fosfatos en el agua subterránea en un acuífero somero, Cuenca del Río Nanfei, China

Groundwater, surface water, soil and river sediment samples, and information on land use in the Nanfei River basin (NRB) of China have been analyzed to study the geochemistry, distribution, and mobilization of phosphorus. The distribution of phosphate (PO 4 3– ) and the relationships between PO 4 3– and several constituents in groundwater were studied. Partial correlation analysis relating PO 4 3– to types of land use was conducted using the data analyzing tool SPSS 15.0. The processes controlling the transport of PO 4 3– are discussed. The conclusions from this study are: (1) urban land use has obvious impact on PO 4 3– in groundwater, the average concentration of PO 4 3– being 4.37 mg/L, greater than that resulting from farmland and mixed land use, which have average PO 4 3– concentrations of 0.10 and 0.18 mg/L, respectively; (2) the partial correlation between PO 4 3– and types of land use is significant with a coefficient of 0.760; (3) the PO 4 3– concentrations in surface water are generally higher than those in groundwater, and the total phosphorus (TP) concentrations in river sediments are generally higher than those in soil samples; (4) groundwater is a carrier of PO 4 3– and is likely responsible for the redistribution of PO 4 3– in different regions of NRB.

Phosphate rock formation and marine phosphorus geochemistry: The deep time perspective

The role that phosphorite formation, the ultimate source rock for fertilizer phosphate reserves, plays in the marine phosphorus (P) cycle has long been debated. A shift has occurred from early models that evoked strikingly different oceanic P cycling during times of widespread phosphorite deposition to current thinking that phosphorite deposits may be lucky survivors of a series of inter-related tectonic, geochemical, sedimentological, and oceanic conditions. This paradigm shift has been facilitated by an awareness of the widespread nature of phosphogenesis—the formation of authigenic P-bearing minerals in marine sediments that contributes to phosphorite formation. This process occurs not just in continental margin sediments, but in deep sea oozes as well, and helps to clarify the driving forces behind phosphorite formation and links to marine P geochemistry. Two processes come into play to make phosphorite deposits: chemical dynamism and physical dynamism. Chemical dynamism involves the diagenetic release and subsequent concentration of P-bearing minerals particularly in horizons, controlled by a number of sedimentological and biogeochemical factors. Physical dynamism involves the reworking and sedimentary capping of P-rich sediments, which can either concentrate the relatively heavy and insoluble disseminated P-bearing minerals or provide an episodic change in sedimentology to concentrate chemically mobilized P. Both processes can result from along-margin current dynamics and/or sea level variations. Interestingly, net P accumulation rates are highest (i.e., the P removal pump is most efficient) when phosphorites are not forming. Both physical and chemical pathways involve processes not dominant in deep sea environments and in fact not often coincide in space and time even on continental margins, contributing to the rarity of high-quality phosphorite deposits and the limitation of phosphate rock reserves. This limitation is becoming critical, as the human demand for P far outstrips the geologic replacement for P and few prospects exist for new discoveries of phosphate rock.

Rethinking early Earth phosphorus geochemistry.

Phosphorus is a key biologic element, and a prebiotic pathway leading to its incorporation into biomolecules has been difficult to ascertain. Most potentially prebiotic phosphorylation reactions have relied on orthophosphate as the source of phosphorus. It is suggested here that the geochemistry of phosphorus on the early Earth was instead controlled by reduced oxidation state phosphorus compounds such as phosphite (HPO(3)(2-)), which are more soluble and reactive than orthophosphates. This reduced oxidation state phosphorus originated from extraterrestrial material that fell during the heavy bombardment period or was produced during impacts, and persisted in the mildly reducing atmosphere. This alternate view of early Earth phosphorus geochemistry provides an unexplored route to the formation of pertinent prebiotic phosphorus compounds, suggests a facile reaction pathway to condensed phosphates, and is consistent with the biochemical usage of reduced oxidation state phosphorus compounds in life today. Possible studies are suggested that may detect reduced oxidation state phosphorus compounds in ancient Archean rocks.