Global variability in seawater Mg:Ca and Sr:Ca ratios in the modern ocean.

Seawater Mg:Ca and Sr:Ca ratios are biogeochemical parameters reflecting the Earth-ocean-atmosphere dynamic exchange of elements. The ratios' dependence on the environment and organisms' biology facilitates their application in marine sciences. Here, we present a measured single-laboratory dataset, combined with previous data, to test the assumption of limited seawater Mg:Ca and Sr:Ca variability across marine environments globally. High variability was found in open-ocean upwelling and polar regions, shelves/neritic and river-influenced areas, where seawater Mg:Ca and Sr:Ca ratios range from ∼4.40 to 6.40 mmol:mol and ∼6.95 to 9.80 mmol:mol, respectively. Open-ocean seawater Mg:Ca is semiconservative (∼4.90 to 5.30 mol:mol), while Sr:Ca is more variable and nonconservative (∼7.70 to 8.80 mmol:mol); both ratios are nonconservative in coastal seas. Further, the Ca, Mg, and Sr elemental fluxes are connected to large total alkalinity deviations from International Association for the Physical Sciences of the Oceans (IAPSO) standard values. Because there is significant modern seawater Mg:Ca and Sr:Ca ratios variability across marine environments we cannot absolutely assume that fossil archives using taxa-specific proxies reflect true global seawater chemistry but rather taxa- and process-specific ecosystem variations, reflecting regional conditions. This variability could reconcile secular seawater Mg:Ca and Sr:Ca ratio reconstructions using different taxa and techniques by assuming an error of 1 to 1.50 mol:mol, and 1 to 1.90 mmol:mol, respectively. The modern ratios' variability is similar to the reconstructed rise over 20 Ma (Neogene Period), nurturing the question of seminonconservative behavior of Ca, Mg, and Sr over modern Earth geological history with an overlooked environmental effect.

An All-Solid-State Silicate Ion-Selective Electrode Using PbSiO3 as a Sensitive Membrane.

Ion-Selective Electrode (ISE) is an emerging technology for in situ monitoring of the chemical concentrations of an aqueous environment. In this work, we reported a novel all-solid-state silicate ISE, using an Ag/Pb/PbSiO3 electrode. This electrode responded to aqueous SiO32- with a reasonable slope of -31.34 mV/decade and a good reproductivity. The linear range covered from 10-5 M to 10-1 M, for the Na2SiO3 solutions and the response time was generally less than 5 s. Its potentiometric response to pH and silicate indicated that the prepared electrode was sensitive to silicate, rather than pH. Compared to the traditional liquid ISE, our all-solid-state silicate electrode was resistant to high pressure and could be used in situ, in deep water. In addition, the miniaturized electrodes (diameter of 0.4 mm and a length of 2⁻3 cm) could be easily integrated into a multi-modal sensor, which could simultaneously determine multiple parameters. Our prepared silicate ISE could potentially be used to determine the presence of silicate in a low-chloride aqueous environment, where the ISE exhibited better selectivity for silicate, over interfering ions such as, SO4²-, NO3-, CH3COO-, CO3²-, and PO4³-.

Comparative Study on the Elucidation of Sedimentary Phosphorus Species Using Two Methods, the SMT and SEDEX Methods.

Sedimentary phosphorus (P) forms are important representatives of P sources and their bioavailability as well as the potential of sediments to release P in water. In this study, surface sediments along a transect of the Changjiang Estuary and two transects along the Andong salt marsh in the southwest of Hangzhou Bay were subjected to the elucidation of sedimentary P species using the standards, measurements, and testing (SMT) and sequential extraction (SEDEX) methods. The results showed that the mean sedimentary P forms elucidated by the SMT method were as follows: organic P (OP; ∼11-14 mg/kg; ∼30-45% of total P; TP) > apatite P (∼5-15 mg/kg; ∼21-36% TP) > Fe/Al-P (∼8-14 mg/kg; ∼31-34% TP), with inorganic P (IP) composing 54-70% of TP. The mean sedimentary P forms elucidated by the SEDEX method were as follows: authigenic P (∼54-68 mg/kg; ∼41-46% TP) > extractable P (Ex-P; ∼36-53 mg/kg; ∼28-34%) > Fe-P (∼21-27 mg/kg; ∼13-19%) > OP (∼8.7-13 mg/kg; ∼5-8%) > detrital P (De-P; ∼2 mg/kg; ∼1-2% TP), with IP composed of ∼91-94% TP. These results showed that the SEDEX method elucidated higher concentrations of sedimentary P forms as well as the TP from these coastal sediments although the SMT method had the advantage of being more economic and faster. The results of both the SMT and SEDEX methods showed that the Andong salt marsh and Changjiang Estuary sediments had much bioavailable P. The mean percentages of bioavailable P from the SMT and SEDEX methods were ∼64-74% and 52-56% of TP, respectively, indicating that these sediments were prone to release P to the coastal areas.

Earthquake and typhoon trigger unprecedented transient shifts in shallow hydrothermal vents biogeochemistry.

Shallow hydrothermal vents are of pivotal relevance for ocean biogeochemical cycles, including seawater dissolved heavy metals and trace elements as well as the carbonate system balance. The Kueishan Tao (KST) stratovolcano off Taiwan is associated with numerous hydrothermal vents emitting warm sulfur-rich fluids at so-called White Vents (WV) and Yellow Vent (YV) that impact the surrounding seawater masses and habitats. The morphological and biogeochemical consequences caused by a M5.8 earthquake and a C5 typhoon ("Nepartak") hitting KST (12th May, and 2nd-10th July, 2016) were studied within a 10-year time series (2009-2018) combining aerial drone imagery, technical diving, and hydrographic surveys. The catastrophic disturbances triggered landslides that reshaped the shoreline, burying the seabed and, as a consequence, native sulfur accretions that were abundant on the seafloor disappeared. A significant reduction in venting activity and fluid flow was observed at the high-temperature YV. Dissolved Inorganic Carbon (DIC) maxima in surrounding seawater reached 3000-5000 µmol kg-1, and Total Alkalinity (TA) drawdowns were below 1500-1000 µmol kg-1 lasting for one year. A strong decrease and, in some cases, depletion of dissolved elements (Cd, Ba, Tl, Pb, Fe, Cu, As) including Mg and Cl in seawater from shallow depths to the open ocean followed the disturbance, with a recovery of Mg and Cl to pre-disturbance concentrations in 2018. The WV and YV benthic megafauna exhibited mixed responses in their skeleton Mg:Ca and Sr:Ca ratios, not always following directions of seawater chemical changes. Over 70% of the organisms increased skeleton Mg:Ca ratio during rising DIC (higher CO2) despite decreasing seawater Mg:Ca ratios showing a high level of resilience. KST benthic organisms have historically co-existed with such events providing them ecological advantages under extreme conditions. The sudden and catastrophic changes observed at the KST site profoundly reshaped biogeochemical processes in shallow and offshore waters for one year, but they remained transient in nature, with a possible recovery of the system within two years.

Preparation of hollow iron/halloysite nanocomposites with enhanced electromagnetic performances.

Nanostructures loaded on halloysite nanotubes (HNTs) have attracted global interest, because the nanotubular HNTs could extend the range of their potential applications. In this study, we fabricated a novel nanocomposite with hollow iron nanoparticles loaded on the surface of HNTs. The structure of the iron nanoparticles can be adjusted by ageing time. Owing to the increased remnant magnetization and coercivity values, the nanocomposites loaded with hollow iron nanoparticles showed better electromagnetic performance than that with solid iron nanoparticles. This study opens a new pathway to fabricate halloysite nanotubular nanocomposites that may gain applications in the catalytic degradation of organic pollutants and electromagnetic wave absorption.

Submarine Groundwater Discharge helps making nearshore waters heterotrophic.

Submarine groundwater discharge (SGD) is the submarine seepage of all fluids from coastal sediments into the overlying coastal seas. It has been well documented that the SGD may contribute a great deal of allochthonous nutrients to the coastlines. It is, however, less known how much carbon enters the ocean via the SGD. Nutrients (NO3, NO2, NH4, PO4, SiO2), alkalinity and dissolved inorganic carbon (DIC) in the submarine groundwater were measured at 20 locations around Taiwan for the first time. The total N/P/Si yields from the SGD in Taiwan are respectively 3.28 ± 2.3 × 104, 2.6 ± 1.8 × 102 and 1.89 ± 1.33 × 104 mol/km2/a, compared with 9.5 ± 6.7 × 105 mol/km2/a for alkalinity and 8.8 ± 6.2 × 105 mol/km2/a for DIC. To compare with literature data, yields for the major estuary across the Taiwan Strait (Jiulong River) are comparable except for P which is extremely low. Primary production supported by these nutrient outflows is insufficient to compensate the DIC supplied by the SGD. As a result, the SGD helps making the coastal waters in Taiwan and Jiulong River heterotrophic.

[Environmental magnetic properties and their spatial variability of topsoil in Shihezi City].

The 80 topsoil samples (0-10 cm) are collected from different land use types in built-up areas, northern new town (including chemical concentration area and concentrated residential areas) and suburban agricultural land at Shihezi oasis city in arid zone of Xinxiang, China. The aim of this study is to analysis the magnetic parameters of concentration, composition and particle size of magnetic properties for the urban topsoils, and to describe the spatial distribution under different circumstances of land use. The magnetic grain parameters show that the soils are dominated with coarser multi domain (MD) ferrimagnetic grain. The magnetic mineralogy parameters suggest that samples are dominated by ferrimagnetic minerals corresponding to magnetite-like minerals, but contain a small amount of anti-ferromagnetic material. From the spatial distribution, the concentration of magnetic minerals are ranked in the order of northern new town > built-up areas > suburban agricultural land. Particle size of magnetic minerals are ranked in the order of northern new town > suburban agricultural land > built-up areas. The high concentration of magnetic parameters areas is coincident with factories' area. However, the magnetic concentration in heavy chemical industry region (N1-N7) are low, and particle size of the magnetic particles is larger. XLF, SIRM and SOFT are effective magnetic parameter indexes indicating the light industrial zone of the study area. While, the discrimination in the heavy chemical industry area needs to combine with a magnetic particle parameters (XFD%) .

Hydrothermal removal of Sr2+ in aqueous solution via formation of Sr-substituted hydroxyapatite.

We removed Sr(2+) in simulating wastewater and simultaneously prepared Sr-substituted hydroxyapatite via chemical precipitation and hydrothermal treatment. Both higher initial pH value and higher molar ratio of Sr/(Sr+Ca) contributed to lower residual Sr(2+) concentration and higher removal efficiency. About two thirds of Sr(2+) residual in solution after chemical precipitation were further reduced by hydrothermal treatment. The optimal Sr removal result was 99.66% with an ultimate concentration of 2.0 mg L(-1) when the initial pH was 12 and Sr/(Sr+Ca) was 0.2. Sr-substituted hydroxyapatite phase with hexagonal structure was identified by XRD and EDS results. However, it was found that SrHPO(4) phase was formed in the samples with high Sr composition. The lattice constants became larger with the increase of Sr(2+) and the crystallinity became higher with the increase of pH value. Rod-like particles were observed in SEM images of synthesized Sr-substituted hydroxyapatite samples, with the size of 20-30 nm in width and 70-100 nm in length. With little secondary waste and simple treating procedure, this method is an effective and prospective measure to deal with (90)Sr in nuclear waste and industry wastewater.