PO4 Ratio Research Articles

Novel insights into the amorphous feature of granulated blast furnace slag-supplemented magnesium potassium phosphate cement and its effect on bulk properties

This paper reports the effects of MgO:PO4 (3, 9, and 15) ratio and granulated blast furnace slag dosage (0 wt%, 40 wt%, and 80 wt%) on the phase formation, microstructure, and bulk properties of magnesium potassium phosphate cement (MKPC). Results show that the supplementary of slag and the increment in MgO:PO4 inhibit the formation of K-struvite via X-ray diffraction. While the detections of 29Si magic-angle spinning nuclear magnetic resonance spectroscopy and scanning electron microscope-energy dispersion spectrum further unveil the dissolution of slag and the formation of Q4 amorphous structure in slag supplemented MKPCs. Although the Q4 structure increases the interplanar spacing of K-struvite even leads to its amorphization in MKPCs with high MgO:PO4 (>9), the optimum coexisting of K-struvite and Q4 structure minimizes the porosity and maximizes the compressive strength of MKPCs with MgO:PO4=3 and 40 wt% slag. These results are crucial to developing optimal mixture formulations of MKPC with superior mechanical performance and lower costs associated with their production.

Characterization of rat vertebrae cortical bone microstructures using confocal Raman microscopy combined to tomography and electron microscopy

BackgroundThe rat vertebrae is a good model to study bone regeneration after implantation of biomaterials used to treat bone loss, a major problem in oral and dental surgery. However, the precise characterization of bone microstructures in the rat vertebrae has not been reported. Therefore, the aim of this study was to achieve the complete analysis of such bone, at different scales, in order to have a clear model of healthy bone for comparison with regenerated bone. MethodsIn order to image the cortical bone of rat caudal vertebra, confocal Raman microscopy was combined with high resolution X-ray micro computed tomography (micro-CT), with scanning electron microscopy (SEM) using backscatter electron imaging and with more conventional histology coloration techniques. SEM and Raman microscopy were done in various regions of the cortical bone corresponding to external, middle and internal areas. The spongy bone was imaged in parallel. Micro-CT was performed on the whole vertebra to monitor the network of haversian canals in the cortical bone. Osteonic canals characteristics, and relative chemical composition were analysed in several regions of interest, in cortical and spongy bone. Five rats were included in this study. ResultsOn micro-CT images, differences in intensity were observed in the cortical bone, substantiated by SEM. Chemical analysis with Raman spectra confirmed the difference in composition between the different regions of the cortical and spongy bone. PCA and k-mean cluster analysis separated these groups, except for the external and middle cortical bone. Peak intensity ratio confirmed these results with a CO3 to ν2 PO4 ratio significantly different for the internal cortical bone. Grayscale images stack extracted from micro-CT showed that global architecture of cortical bone was characterized by a dense and complex network of haversian osteonic canals, starting from the surface towards the vertebrae center. The mean diameter of the canals was 18.4 µm (SD 8.6 µm) and the mean length was 450 µm (SD 152 µm). Finally, Raman reconstructed images of the lamellar bone showed an enlargement of the lamellar layer width, both in circumferential lamellar bone and around haversian canals. ConclusionsMicro-CT and confocal Raman microscopy are good tools to complete classical analysis using optical and electron microscopy. The results and measurements presented in a rat model known for its small inter-individual differences provide the main characteristics of a mature bone. This study will allow the community working on this rat vertebrate model to have a set of characteristics, in particular on the structure of the haversian canals.

Superprotonic conductivity in RbH2-3y(PO4)1-y: a phosphate deficient analog to cubic CsH2PO4 in the (1 - x)RbH2PO4 - xRb2HPO4 system.

In contrast to CsH2PO4 (cesium dihydrogen phosphate, CDP), a material with a well-established superprotonic transition to a high conductivity state at 228 °C, RbH2PO4 (rubidium dihydrogen phosphate, RDP) decomposes upon heating under ambient pressure conditions. Here we find, from study of the (1 - x)RbH2PO4 - xRb2HPO4 system, the remarkable occurrence of cubic, off-stoichiometric RbH2-3y(PO4)1-y, or α-RDP, with a variable Rb : PO4 ratio. Materials were characterized by simultaneous thermal analysis and in situ X-ray powder diffraction performed under high steam partial pressure, from which the phase diagram between RbH2PO4 (x = 0) and Rb5H7(PO4)4 (x = 1/4) was established. The system displays eutectoid behavior, with a eutectoid transition temperature of 242.0 ± 0.5 °C and eutectoid composition of x = 0.190 ± 0.004. Even the end-member Rb5H7(PO4)4 appears to transform to α-RDP, implying y in the chemical formula of 0.2 and a phosphate site vacancy concentration as high as 20%. Charge balance is attained by a decrease in the average number of protons on the remaining phosphate groups. The cubic lattice parameter at x = 0.180, near the eutectoid composition, and at a temperature of 249 °C is 4.7138(2) Å. This value is substantially smaller than the estimated ambient-pressure lattice parameter of stoichiometric RbH2PO4 of 4.837(12) Å, consistent with the proposal of phosphate site vacancies in the former. The superprotonic conductivity of the x = 0.180 material is 6 × 10-3 S cm-1 at 244 °C, a factor of three lower than that of CDP at the same temperature. While the engineering properties of α-RDP do not suggest immediate technological relevance, the discovery of a superprotonic solid acid with a high concentration of phosphate site vacancies opens new avenues for developing proton conducting electrolytes, and in particular, for controlling their transition behavior.

Precipitation of potassium as hazenite from washing water of spent alkaline batteries

Hazenite (KNaMg2(PO4)2 × 14 H2O), a new type of struvite mineral, was precipitated from the potassium-rich washing water of spent alkaline battery black mass. Hazenite can be used as a fertilizer, which would be an additional benefit derived from the sustainable recovery of battery materials. Precipitation experiments were performed using different pH values (9.5–12), Mg:K:PO4 ratios ((1.0–1.5):1:(1.0–1.5)) and temperatures (10–40 °C). Based on the results, hazenite precipitated in a wide pH range under alkaline conditions. The precipitation kinetics were fast, and the purity of the hazenite was high. Overall, hazenite can be precipitated at room temperature without the addition of excess chemicals, which minimizes the consumption of chemicals and energy.

Are alternative magnesium sources the key for a viable downstream transfer of struvite precipitation? Assessment of process feasibility and precipitate characteristics

Phosphorus (P) recovery in source-separated decentralised wastewater treatment processes is an eco-efficient strategy in accordance with a circular economy perspective. Struvite (MgNH4PO4.6H2O) capture allows a reduction of P discharged to surface waters and generates a product known for its slow-release fertiliser properties. However, the cost and availability of current commercial Mg2+ sources hinder the downstream transfer of struvite precipitation. Although some alternative sources are available, there is a lack of information on how they compare to conventional sources; it is also not known how the Mg:PO4 ratio affects process performance or fertiliser product suitability. Therefore, this research evaluated the performance of two alternative sources, seasalt and seawater bittern, at different Mg:PO4 ratios. The results indicate that seasalt may be a problematic option owing to its high levels of NaCl, regardless of the Mg:PO4 level, which could affect soil fertility. Bittern, meanwhile, showed a high yield at pH 8.5 and Mg:PO4 1.2:1, achieving 99% recovery of PO4 and increasing also the recovery yield from 60% (using conventional sources) to 82% at Mg:PO4 1:2. In addition, bittern showed larger X-type crystals than commercial sources. The precipitate is composed mainly of struvite and Newberyite (MgHPO4.3H2O), with traces of K+, and no presence of NaCl at Mg:PO4 1.2:1; while at Mg:PO4 1:2 it forms a mixture of struvite with presence of Ca and K phosphates. In conclusion, bittern is an effective raw material to improve the downstream transfer of struvite precipitation into urine-diverting toilets in wastewater treatment systems.

Sectional Distribution Patterns of Cd, Ni, Zn, and Cu in the North Pacific Ocean: Relationships to Nutrients and Importance of Scavenging

AbstractThe North Pacific Ocean is located at the end of the thermohaline circulation of deep water. This study reports on basin‐scale full‐depth sectional distributions of total dissolvable (td), dissolved (d), and labile particulate (lp) Cd, Ni, Zn, and Cu along three transects: the GEOTRACES transects GP18 (165°E) and GP02 (47°N), and along 160°W. We find that scavenging is an important factor that significantly affects the distributions of dZn, dNi, and dCu, of which the magnitude of influence increases in the order of Cd < Ni, Zn < Cu. The relationships between the four dissolved metals with Si(OH)4 and PO4 differed considerably from those in other oceans. The spot concentration ratio of dCd/PO4 was 0.34 ± 0.02 nmol/μmol (n = 296) in waters >800 m deep, which is in the range of the phytoplankton Cd/P ratio. This is indicative of the dominant effect of water circulation and biological processes on dCd distribution. The dissolved metals (dMs) to PO4 ratios of other examined metals were either partially or completely outside the range of typical biomass ratios. They generally increased with depth in waters >800 m deep; the magnitude of increase was the highest for Cu and moderate for Ni and Zn. Below 800 m, an increase in the apparent oxygen utilization from 150 to 300 μmol/kg was concurrent with a decrease in the dMs/PO4 ratios: 4 ± 3% for Cd, 21 ± 4% for Zn, 21 ± 3% for Ni, and 69 ± 7% for Cu.

The dynamic uptake of lead and its radionuclides by natural and synthetic aluminium-phosphate-sulfates

The ability of aluminium-phosphate-sulfate (APS) phases to preferentially sorb lead and its radionuclides, particularly 210Pb, from metallurgical processing streams has been recently recognised empirically. This suggests that APS minerals may be suitable for the removal of lead from environmental and anthropogenic processes. We investigated the Pb sorption capabilities of APS with different Ca:Sr and SO4:PO4 ratios over a range of aqueous Pb concentrations (10–1000 ppm) and pH (1.5–5.5) typical of metallurgical processes and acid drainage conditions. Through a combination of characterization techniques including electron probe microanalysis, (laser ablation-) inductively coupled plasma mass spectrometry and X-ray absorption spectroscopy, we confirm the rapid (< 8 h) incorporation of Pb into the crystal lattice of APS phases. We also provide a mechanistic pathway for the sorption mechanism, with Pb sorption favoured at pH 3.5–5.5 via the direct replacement of lattice-bound Ca by Pb within the APS crystal structure. The observed Pb-incorporation dynamics of APS minerals, along with their insolubility and high thermodynamic stabilities, support the use of APS minerals as a novel agent for the uptake of Pb, radiogenic and nonradiogenic, from process-, surface-, and groundwaters. Since Pb quickly enters the crystal structure of environmentally stable APS minerals, these phases have much potential for long-term storage of Pb waste, and in particular for sequestration of the highly radioactive 210Pb isotope enriched in U-bearing geological materials.

The Utility of the Cl:PO4 Ratio in Patients With Variant Versions of Primary Hyperparathyroidism

To determine the significance and impact of additional chloride testing as part of a diagnostic laboratory test battery for borderline primary hyperparathyroidism (pHPT). Retrospective database review of parathyroidectomy patients. A tertiary care, academic health sciences center. Patients referred to a head and neck endocrine clinic for evaluation and treatment for pHPT. After exclusions, there were a total of 226 patients who underwent parathyroidectomy for primary hyperparathyroidism with the requisite preoperative and postoperative labs. Seventy-seven additional patients who had a thyroid operation for a nonmalignant cause were included as controls. Of the 303 total patients, 166 had normal calcium levels (<10.4 mg/dL), and 54 (32.5%) also exhibited hyperchloremia (>106 mmol/L). Of the 47 patients with normal calcium and parathyroid hormone (PTH) levels (<88 pg/mL), 6 (12.8%) had hyperchloremia, and of the 118 patients with normocalcemic pHPT, 48 (40.7%) were hyperchloremic. The area under the curve for the Cl:PO4 was 0.712. When using a cutoff of 33, the reported sensitivity and specificity of the curve were 58.4% and 28.6%, respectively. The Cl:PO4 ratio was a moderately sensitive test for the diagnosis of the borderline variants of primary hyperparathyroidism. The Ca:PO4 ratio was superior to the Cl:PO4 ratio. Our data also showed the superiority of preoperative calcium and ionized calcium over PTH when predicting the presence of pHPT.

Ammonia and COD Removal From Landfill Leachate Using MAP Precipitation Method

&lt;p&gt;Most of the major cities in our country are opposed to the problem of water pollution due to the uncontrolled leachate resulting from the decomposition of solid wastes in irregular landfills. The waste waters that have high nitrogen content such as leachate cause various problems like eutrophication. In this study; the preliminary treatment of leachate which formed on the landfill site storing solid wastes of Samsun Metropolitan Municipality by MAP (Magnesium ammonium phosphate) precipitation was examined. For this purpose, optimization of the parameters that affecting the MAP precipitation was performed and the conditions for optimum removal efficiency were investigated. As a result of MAP precipitation, various mole ratios were tested with the aim of providing the best ammonia removal efficiency. The maximum ammonia removal was found to be 90.63% at pH 9.5 and at Mg:NH4:PO4 ratio of 4: 1: 2.2. At this conditions the ammonia concentration was decreased from 1792 mg/L to 168 mg/L. Experimental data were also evaluated and the regression equations of ammonia and COD removal were obtained using Minitab 16 statistical software.&lt;/p&gt;&#x0D;

Ternary Complex Formation of Phosphate with Ca and Mg Ions Binding to Ferrihydrite: Experiments and Mechanisms

Calcium (Ca) and magnesium (Mg) are the most abundant alkaline-earth metal ions in nature, and their interaction with ferrihydrite (Fh) affects the geochemical cycling of relevant ions, including phosphate (PO4). The interfacial interactions of Ca and Mg (M2+) with PO4 have not been analyzed yet for freshly precipitated Fh. Here, we studied experimentally this interaction in binary M2+-PO4 systems over a wide range of pH, M2+/PO4 ratios, and ion loadings. The primary adsorption data were scaled to the surface area of Fh using a recent ion-probing methodology that accounts for the size-dependent chemical composition of this nanomaterial (FeO1.4(OH)0.2·nH2O). The results have been interpreted with the charge distribution (CD) model, combined with a state-of-the-art structural surface model for Fh. The CD coefficients have been derived independently using MO/DFT/B3LYP/6-31+G** optimized geometries. M2+ and PO4 mutually enhance their adsorption to Fh. This synergy results from the combined effect of ternary surface complex formation and increased electrostatic interactions. The type of ternary complex formed (anion- vs cation-bridged) depends on the relative binding affinities of the co-adsorbing ions. For our Ca-PO4 systems, modeling suggests the formation of two anion-bridged ternary complexes, i.e., ≡(FeO)2PO2Ca and ≡FeOPO3Ca. The latter is most prominently present, leading to a relative increase in the fraction of monodentate PO4 complexes. In Mg-PO4 systems, only the formation of the ternary ≡FeOPO3Mg complex has been resolved. In the absence of Ca, the pH dependency of PO4 adsorption is stronger for Fh than for goethite, but this difference is largely, although not entirely, compensated in the presence of Ca. This study enables the use of Fh as a proxy for the natural oxide fraction, which will contribute to improved understanding of the mutual interactions of PO4 and M2+ in natural systems.

Significant Release of Dissolved Inorganic Nutrients From the Shallow Submarine Volcano Tagoro (Canary Islands) Based on Seven-Year Monitoring

Tagoro, the shallow submarine volcano that erupted south of El Hierro (Canary Islands, Spain) in October 2011, has been intensely monitored for over 7 years, from the early eruptive stage to the current degassing stage characterized by moderate hydrothermal activity. Here, we present a detailed study of the emissions of inorganic macronutrients (NO2-+NO3-, PO4, and Si(OH)4) comprising a dataset of over 3300 samples collected through three different sampling methodologies. Our results show a significant nutrient enrichment throughout the whole studied period, up to 8.8-fold (nitrate), 4.0-fold (phosphate) and 16.3-fold (silicate) in the water column, and larger enrichments of phosphate (10.5-fold) and silicate (325.4-fold), but not of nitrate, in the samples collected directly from the vents. We also provide some preliminary results showing ammonium (NH4+) concentrations up to 1.97 µM in the vent fluids as compared to 0.02 µM in the surrounding waters. Nutrient fluxes from the volcano during the degassing stage were estimated as 3.19 ± 1.17 mol m-2 yr-1 (NO2-+NO3-), 0.02 ± 0.01 mol m-2 yr-1 (PO4), and 0.60 ± 1.35 mol m-2 yr-1 (Si(OH)4), comparable to other important nutrient sources in the region such as fluxes from the NW-African upwelling. Nutrient ratios were affected, with a minimum (NO3-+NO2-):PO4 ratio of 2.36:1; moreover, a linear correlation between silicate and temperature allowed to use this nutrient as a mixing tracer. This study is bound to shed light on how shallow hydrothermal systems impact the nutrient-poor upper waters of the ocean.

Strong seasonality in the cadmium and phosphate cycling at the subtropical convergence, south-eastern New Zealand

The global distribution of dissolved cadmium (Cd) in the world’s oceans is generally well understood. However, information on seasonal variability of this and other trace metals in the open ocean is difficult to obtain and, therefore, our understanding is limited. Here, we present a 3-year time series of field measurements of dissolved and particulate Cd and phosphate (PO4) from a transect across the subtropical convergence, south-eastern New Zealand. In the final year of study, the bioactive trace metals (iron, Fe; zinc, Zn; cobalt, Co) and nutrients (nitrate, NO3; silicate, Si(OH)4) were also measured to identify their influence on Cd cycling in the region. Cadmium varied seasonally from 0.009 to 0.137nM in the sub-Antarctic surface waters (SASW). Zinc in SASW varied between 0.03 and 0.011nM, which is low enough to suggest Zn limitation year-round. The seasonal input of dissolved Fe may stimulate phytoplankton growth in summer where microplankton (especially diatoms) dominate the phytoplankton distribution. The Cd:PO4 ratio also varied strongly with season (0.015×10–3 to 0.05×10–3). This seasonal variation in the Cd:PO4 ratio is productivity driven as revealed in the characteristic trend in the Cd:PO4 ratio, particulate Cd and chlorophyll-a measurements. The high seasonal variability between Cd and PO4 complicates the application of the Cd proxy for the reconstruction of historical PO4 concentrations in SASW.

Recovery of phosphates as struvite from urine-diverting toilets: optimization of pH, Mg:PO4 ratio and contact time to improve precipitation yield and crystal morphology.

Phosphate (P) recovery from urban wastewaters is an effective strategy to address environmental protection and resource conservation, aiming at an effective circular economy. Off-grid wastewater treatment systems like urine-diverting toilets (UDT) can contribute to source separation towards nutrient recovery, namely phosphorus recovery. Effectiveness of P precipitation requires a process-based knowledge regarding pH, Mg:PO4, contact time and their interactions in P recovery and crystal morphology. Several studies failed to see the process as a whole and how factors influence both morphology and P recovery for UDT hydrolysed urine. This study addressed the above-mentioned factors and their interactions, and results showed that pH and Mg:PO4 ratio are the key factors for struvite precipitation, whereas contact time is relevant for crystal growth. The recommended set of factors proposed (pH 8.5, Mg:PO4 ratio of 1.2:1 and 30 minutes contact time) not only promotes a high precipitation yield - 99% of P with co-precipitation of at least 21% of ammonium (NH4 +) - but also leads to larger crystals with lower water solubility (10% less crystals dissolved in water after 3 days). The obtained outcome facilitates the downstream process and leads to a more efficient slow-release fertiliser, as less P is wasted to receiving waters by leaching, minimising eutrophication processes.

Response of the photosynthetic activity and biomass of the phytoplankton community to increasing nutrients during cyanobacterial blooms in Meiliang Bay, Lake Taihu

Nutrient enrichment facilitates algal outbreaks in eutrophic shallow lakes. To further understand the influence of various inorganic nutrient forms on cyanobacterial blooms, a nitrate (NO3 ), ammonium (NH4 ), and orthophosphate (PO4 ) amendment experiment was conducted in a large shallow lake of China (Lake Taihu) during summer. The results showed that the photosynthetic performance of phytoplankton responded more positively to phosphorus (P) than nitrogen (N), and NH4 addition stimulated higher algal photosynthetic activities in P-enriched waters. Individual inorganic N or PO4 addition significantly activated cyanobacteria and green algae. Meanwhile, the N plus P amendment promoted higher biomass of the planktonic microbial community, and the dual addition of NH4 +PO4 yielded the highest chlorophyll a concentration. NH4 additions provisionally promoted higher green algae than cyanobacteria biomass in the beginning, while cyanobacteria dominated again with increasing NH4 :PO4 ratios. These results revealed that increasing ammonium would enhance the increase in phytoplankton biomass in advance and prolong the duration of algal blooms. Hence, based on the control of P loading, the reduction in external inorganic N focusing on ammonium sources (such as ammonia N fertilizer) at the watershed scale would help to alleviate eutrophication and cyanobacterial blooms over the long term in Lake Taihu. PRACTITIONER POINTS: Ammonium addition stimulated higher algal photosynthetic activities in P-enriched waters. Individual inorganic N or PO4 addition significantly activated cyanobacteria and green algae. The dual addition of NH4 +PO4 yielded the highest chlorophyll a concentration. Increasing NH4 would enhance the increase in phytoplankton biomass in advance and prolong the duration of cyanobacterial blooms.

On the origin of the marine zinc–silicon correlation

The close linear correlation between the distributions of dissolved zinc (Zn) and silicon (Si) in seawater has puzzled chemical oceanographers since its discovery almost forty years ago, due to the apparent lack of a mechanism for coupling these two nutrient elements. Recent research has shown that such a correlation can be produced in an ocean model without any explicit coupling between Zn and Si, via the export of Zn-rich biogenic particles in the Southern Ocean, consistent with the observation of elevated Zn quotas in Southern Ocean diatoms. Here, we investigate the physical and biological mechanisms by which Southern Ocean uptake and export control the large-scale marine Zn distribution, using suites of sensitivity simulations in an ocean general circulation model (OGCM) and a box-model ensemble. These simulations focus on the sensitivity of the Zn distribution to the stoichiometry of Zn uptake relative to phosphate (PO4), drawing directly on observations in culture. Our analysis reveals that OGCM model variants that produce a well-defined step between relatively constant, high Zn:PO4 uptake ratios in the Southern Ocean and low Zn:PO4 ratios at lower latitudes fare best in reproducing the marine Zn–Si correlation at both the global and the regional Southern Ocean scale, suggesting the presence of distinct Zn-biogeochemical regimes in the high- and low-latitude oceans that may relate to differences in physiology, ecology or (micro-)nutrient status. Furthermore, a study of the systematics of both the box model and the OGCM reveals that regional Southern Ocean Zn uptake exerts control over the global Zn distribution via its modulation of the biogeochemical characteristics of the surface Southern Ocean. Specifically, model variants with elevated Southern Ocean Zn:PO4 uptake ratios produce near-complete Zn depletion in the Si-poor surface Subantarctic Zone, where upper-ocean water masses with key roles in the global oceanic circulation are formed. By setting the main preformed covariation trend within the ocean interior, the subduction of these Zn- and Si-poor water masses produces a close correlation between the Zn and Si distributions that is barely altered by their differential remineralisation during low-latitude cycling. We speculate that analogous processes in the high-latitude oceans may operate for other trace metal micronutrients as well, splitting the ocean into two fundamentally different biogeochemical, and thus biogeographic, regimes.

Nitrogen and Phosphorus Budgets in the Northwestern Mediterranean Deep Convection Region

AbstractThe aim of this study is to understand the biogeochemical cycles of the northwestern Mediterranean Sea (NW Med), where a recurrent spring bloom related to dense water formation occurs. We used a coupled physical‐biogeochemical model at high resolution to simulate realistic 1 year period and analyze the nitrogen (N) and phosphorus (P) cycles. First, the model was evaluated using cruises carried out in winter, spring, and summer and a Bio‐Argo float deployed in spring. Then, the annual cycle of meteorological and hydrodynamical forcing and nutrients stocks in the upper layer were analyzed. Third, the effect of biogeochemical and physical processes on N and P was quantified. Fourth, we quantified the effects of the physical and biological processes on the seasonal changes of the molar NO3:PO4 ratio, particularly high compared to the global ocean. The deep convection reduced the NO3:PO4 ratio of upper waters, but consumption by phytoplankton increased it. Finally, N and P budgets were estimated. At the annual scale, this area constituted a sink of inorganic and a source of organic N and P for the peripheral area. NO3 and PO4 were horizontally advected from the peripheral regions into the intermediate waters (130–800 m) of the deep convection area, while organic matter was exported throughout the whole water column toward the surrounding areas. The annual budget suggests that the NW Med deep convection constitutes a major source of nutrients for the photic zone of the Mediterranean Sea.

Understanding the unique biogeochemistry of the Mediterranean Sea: Insights from a coupled phosphorus and nitrogen model

AbstractThe Mediterranean Sea (MS) is an oligotrophic basin whose offshore water column exhibits low dissolved inorganic phosphorus (P) and nitrogen (N) concentrations, unusually high nitrate (NO3) to phosphate (PO4) ratios, and distinct biogeochemical differences between the Western Mediterranean Sea (WMS) and Eastern Mediterranean Sea (EMS). A new mass balance model of P and N cycling in the WMS is coupled to a pre‐existing EMS model to understand these biogeochemical features. Estimated land‐derived inputs of reactive P and N to the WMS and EMS are similar per unit surface area, but marine inputs are 4 to 5 times greater for the WMS, which helps explain the approximately 3 times higher primary productivity of the WMS. The lateral inputs of marine sourced inorganic and organic P support significant fractions of new production in the WMS and EMS, similar to subtropical gyres. The mass balance calculations imply that the MS is net heterotrophic: dissolved organic P and N entering the WMS and EMS, primarily via the Straits of Gibraltar and Sicily, are mineralized to PO4 and NO3 and subsequently exported out of the basin by the prevailing anti‐estuarine circulation. The high deepwater (DW) molar NO3:PO4 ratios reflect the high reactive N:P ratio of inputs to the WMS and EMS, combined with low denitrification rates. The lower DW NO3:PO4 ratio of the WMS (21) compared to the EMS (28) reflects lower reactive N:P ratios of inputs to the WMS, including the relatively low N:P ratio of Atlantic surface water flowing into the WMS.

Severe hypercalcaemia and hypophosphataemia with an optimised preterm parenteral nutrition formulation in two epochs of differing phosphate supplementation

ObjectiveTo compare in two epochs of differing phosphate provision serum calcium, phosphate, potassium, and sodium concentrations and the frequency of abnormality of these electrolytes and of sepsis in preterm infants...

Tooth enamel maturation reequilibrates oxygen isotope compositions and supports simple sampling methods

Oxygen isotope and major element zoning patterns of several disparate ungulate teeth were collected to evaluate the timing and geometry of enamel formation, records of isotope zoning, and tooth enamel sampling strategies. Isotopic zoning in mammalian tooth enamel encodes a sub-annual time series of isotopic variation of an animal’s body water composition, with a damping factor that depends on the specifics of how enamel mineralizes. Enamel formation comprises two stages: precipitation of appositional enamel with a high CO3:PO4 ratio, followed by precipitation of maturational enamel with a lower CO3:PO4. If appositional and maturational enamel both contribute to isotope compositions (but with different CO3:PO4), and if isotope compositions vary seasonally, paired δ18O values from CO3 and PO4 profiles should show a spatial separation. CO3 isotope patterns should be shifted earlier seasonally than PO4 isotope patterns. Such paired profiles for new and published data show no resolvable shifts, i.e. CO3 and PO4 δ18O profiles show coincident maxima and minima. This coincidence suggests that enamel maturation reequilibrates appositional isotope compositions. If enamel maturation establishes enamel isotope compositions, the geometry of maturation, not apposition, should be considered when devising sampling protocols. X-ray maps of Ca zoning show that the majority of enamel (inner and middle layers) mineralizes heavily at a high angle to the external tooth surface and the enamel-dentine junction over length scales of 2–4mm, while the outer enamel surface mineralizes more slowly. These data suggest that isotopic sampling strategies should parallel maturational geometry and focus on interior enamel to improve data fidelity. The magnitude of isotopic damping is also smaller than implied in previous studies, so tooth enamel zoning more closely reflects original body water isotopic variations than previously assumed.

Effect of nutrient release from sea floor on Si:P ratio in the Buzen-Kai, western Seto Inland Sea, in summer

The concentrations of silicic acid [Si(OH)4] and phosphate (PO4) in the Buzen-Kai (southwestern Seto Inland Sea) increased by a rate of 93:1 from April through July 2013. Using the core incubation method, the Si(OH)4:PO4 ratio of the release rate and the release amount from the sediment were estimated to be 92:1 and 86:1, which generally agreed with the increased ratio in seawater (93:1). These findings indicate that the Si(OH)4:PO4 ratio in seawater in the Buzen-Kai is considered to reflect the nutrient release ratio from the sea floor, probably much influenced by the temperature or redox state in summer.