Zn Flux Research Articles

Balancing the oceanic Zn isotope budget: The key role of deep-sea pelagic sediments

Abstract Oxygenated deep-sea pelagic sediments with Fe-Mn–oxide particles represent a key oceanic oxic sink for transition metals in the modern ocean. However, the isotopic composition of authigenic Zn in the pelagic zone remains poorly constrained, which hampers our understanding of the global budget of Zn isotopes. Here, we analyzed the Zn isotopic compositions of two deep-sea pelagic sediment columns collected from the Pacific Ocean. The results show that authigenic Zn in deep-sea sediments is primarily hosted by the Fe-Mn (oxyhydr)oxides. The light Zn isotopic signatures (δ66Zn: −0.02‰ to 0.34‰, n = 42; computed as the per mille deviation of the 66Zn/64Zn ratio from the JMC-Lyon standard) observed in deep-sea sediments are completely different from the previously assumed values of ~1.0‰ based on the Zn isotopic compositions of Fe-Mn crusts and nodules. Based on this observation (Zn flux of deep-sea sediments = 5.3 × 108 mol yr–1), we propose a new, balanced global budget for Zn isotopes.

A microcosm evaluation of metal cycling in an urbanized contaminated estuary varying with oxic-hypoxic-anoxic-reoxic transition: Behavior, fluxes, and mechanism

Water hypoxia and metal pollution are commonly co-existed in urbanized estuaries. This study focuses on the effect of an extended dissolved oxygen (DO) full-life dynamics (86 days) on metal behavior across the sediment-water interface through laboratory microcosms from two typical zones in Pearl River Estuary. Combining our time-series results of concentrations and fluxes, it showed that Co, Ni, and Zn consistently presented a release-precipitation-release trajectory with an oxic-hypoxic-anoxic-reoxic transition, characterized with highly variable behavior in the hypoxic-anoxic hotmoments. In parallel, changing DO dynamics significantly activated a repartitioning process of Co, Ni, and Zn among several species and elevated their risk in sediments, promoting the formation of more labile species in the 0–10 mm hotspots, where metals sensitively responded. Over DO transition, metal cycling was tightly co-related with Fe, Mn, and S elements. It was found that Mn was dominated in low oxygen-hypoxic period, but switched to S and Fe in anoxic stage, limiting sustained metal liberation to overlying water. Enlarging this experiment to practice, released Zn fluxes from sediments in hypoxic summer could contribute about ∼2.0% to their stocks in water column, while increase to 20% (1 m bottom water) in highly-stratified zones. This study has certain significance in understanding the long-term metal behavior and fate in estuarine regions, even lakes and reservoirs.

Potential risk, leaching behavior and mechanism of heavy metals from mine tailings under acid rain

The leaching of heavy metals from abandoned mine tailings can pose a severe threat to surrounding areas, especially in the regions influenced by acid rain with high frequency. In this study, the potential risks of heavy metals in the tailings collected from a small-scale abandoned multi-metal mine was assessed, and their leaching behavior and mechanism were investigated by batch, semi-dynamic and in situ leaching experiments under simulated and natural rainfall conditions. The results suggested that Zn, Cu, Pb, and Cd in the tailings could cause high/very high risks. Both batch and semi-dynamic leaching tests consistently confirmed that the leaching of heavy metals (particularly Cd) could lead to serious pollution of the surrounding environment. The leaching rates of heavy metals were pH-dependent and related to their chemical speciations in the mine tailings. The leaching behavior of Cu and Cd was dominated by surface wash-off, Zn was controlled by diffusion initially and then surface wash-off, and the leaching mechanisms of Pb and As varied with the pH conditions. It was estimated that acid rain could greatly elevate the release fluxes of Zn (20.8%), Cu (36.7%), Pb (49.9%) and Cd (35.3%) in the study area. These findings could improve the understanding of the leaching behavior of heavy metals from mine tailings and assist in developing appropriate management strategies.

Evaluating a mass balance model for soil trace metals using the historical data from the King’s Kitchen Garden (Versailles, France)

The mass balance of reconstituted Cd, Cu, Pb and Zn fluxes from 1683 to 2021 was compared to the current levels of the soil used only for vegetable production in the King's Kitchen Garden in Versailles (France). This comparison was made on the basis of 4 scenarios of organic matter application in the 18th and 19th centuries and by an uncertainty analysis over the entire period. The topsoil contamination falls within that of French kitchen gardens. Modelling of past fluxes predicted the correct trend (an increase) and order of magnitude of the soil metal contents. It produced a relatively accurate evaluation of the Cu and Zn contents. The model underestimated the Pb contents by about 80%, revealing a large and unknown source of soil contamination by this metal. The calculation overestimated the current Cd levels by about 100%, probably due to various biases, for example on atmospheric fallout or the composition of organic amendments. This assessment shows that modelling the mass balance of trace metal fluxes can be used to predict the long-term trend in the levels of these elements in cultivated soils, providing the input data are chosen according to realistic scenarios.

Trace Metal Fluxes of Cd, Cu, Pb and Zn From the Congo River Into the South Atlantic Ocean Are Supplemented by Atmospheric Inputs

AbstractThe Congo River supplies vast quantities of trace metals (TMs) to the South Atlantic Ocean, but TM budgets for the Congo plume derived using radium isotopes for GEOTRACES cruise GA08 suggest additional input other than the river outflow. Considering the tight correlations between most dissolved TMs and salinity in the plume and the high rainfall during the wet season over the Congo shelf, we hypothesized that wet atmospheric deposition is a TM source to the Congo plume. Observed TM concentrations in rainwaters across the Congo shelf were mostly comparable to values from previous work in the North Atlantic and Mediterranean Sea. Wet deposition contributed the equivalent of 43% dCd, 21% dCu, 20% dPb and 68% dZn of the Congo River fluxes. Our findings show an important role of wet deposition in supplying TMs to the South Atlantic overlapping with the region that receives substantial TM fluxes from the Congo River.

Benthic Respiration and Heavy Metal Benthic Fluxes in Artificial Shihwa Lake: Approaching In Situ Measurement

This study assessed the impact of intensive human activities on organic matter (OM) and heavy metal cycles in Shihwa Lake, South Korea. Sediment oxygen demand (SOD), benthic nutrient flux (BNF), and benthic heavy metal flux were estimated using in situ benthic chambers. The combined analysis of sediment trap and SOD showed that the vertical supply of OM was a major controlling factor for benthic respiration. The BNF accounted for 35–144% and 32–184% of the N and P required, respectively, for primary production (PP) in the water column. The higher SOD may have also accelerated the release of Mn, Fe, Co, and Ni from the sediment. Benthic fluxes of Cr, As, Cd, Pb, Cu, and Zn were highest near the industrial complex, with ranges of 1.3 ± 0.9, 6.4 ± 4.9, 0.2 ± 0.1, 0.5 ± 0.4, 7.7 ± 1.4, and 452 ± 133 μmol m−2 d−1, respectively. Mn, Fe, Co, As, Pb, Ni, and Cu contributed more than 10% of the sediment to the current standing stock at Shihwa Lake.

Lake Sediment Archive Reveals a Distinct Response to Anthropogenic Pb and Zn Deposition with Historical Periods: Pb-Zn Isotope Evidence.

Anthropogenic activities release large quantities of heavy metals into the atmosphere. In China, the input of these heavy metals through local and trans-boundary atmospheric deposition is poorly understood. To assess this issue, herein, we use Pb and Zn isotopes to constrain the sources of Pb and Zn in a 210Pb-dated sediment core collected from the enclosed lake in South China. We observed a progressive shift toward higher 208Pb/206Pb and Pb fluxes (0.79-4.02 μg·cm-2·a-1) from 1850 to 1950 and a consistent decrease in δ66ZnIRMM (as low as -0.097 ± 0.030‰) coupled with an increase in Pb (1.74-3.36 μg·cm-2·a-1) and Zn (8.07-10.44 μg·cm-2·a-1) fluxes after 1980. These distinguished isotopic signals and flux variations reveal the presence of trans-boundary Pb since 1900, with the addition of local industrial Pb and Zn pollution after 1980. Up to 72.3% of Pb deposited at our site can be attributed to long-distance transportation from previously industrialized countries, resulting in a noteworthy legacy of Pb in China since 1900. Despite the phasing out of leaded gasoline, Chinese gasoline still contributes an average of 20.9%. The contribution of China's mining and smelting activities to Pb has increased steadily since 1980 and remained stable at an average of 25.1% since 2000.

Tracing acid mine drainage and estuarine Zn attenuation using Cd and Zn isotopes

It has been estimated that the acid mine drainage (AMD) impacted Odiel river basin in southern Spain supplies 0.37% and 15% of the global riverine fluxes of Cd and Zn to the oceans, respectively (Sarmiento et al., 2009). However, the behaviour of Cd and Zn in the Ria of Huelva estuary, which connects the Odiel and Tinto watersheds with the Gulf of Cadiz, has yet to be fully investigated. Furthermore, very few studies have investigated Cd and Zn isotope behaviour in estuaries worldwide. This study presents Cd and Zn concentrations and isotopic compositions for the Ria of Huelva estuary and surrounding watersheds, sampled in 2017 and 2019. Sulfide-rich rock samples extracted from three mines yield Cd and Zn isotope compositions that range from –0.14‰ to +0.07‰ (n = 4) for δ114Cd and –0.01‰ to +0.29‰ (n = 4) for δ66Zn. However, a uniform riverine signal of about +0.02‰ for Cd and +0.17‰ for Zn indicates that tracing of individual mining regions using Cd and Zn isotopes is challenging. Limited variability was observed in dissolved δ114Cd values throughout the watershed, including AMD, the estuary, and the Gulf of Cadiz, with a mean value of ±0.00 ± 0.13‰ (n = 25, 2 SD; excludes one AMD outlier, at +0.48‰), including both 2017 and 2019 data. By contrast, δ66Zn values ranged from –0.12‰ to +0.35‰ (n = 28) for the same geographical and temporal scope. In May 2017, a large spill from an abandoned mine, La Zarza, resulted in a drastic increase in the concentrations of trace metals reaching the estuary compared to 2019, but no impact of this mine spill on Cd or Zn isotope compositions is observed. In 2019, an increase in δ66Zn values in the estuary coincided with high pH values (up to pH = 8.8) and chloride concentrations (2.73%), which may reflect an alkaline anthropogenic input from the active neighbouring industrial complex. Overall, Cd concentrations and isotope compositions in the estuary are largely consistent with conservative mixing behaviour. By contrast, Zn behaviour is non-conservative, with removal of 49–97% of dissolved riverine Zn in the estuary during the period 2017–2019, associated with a relatively small isotopic shift to lighter Zn isotope compositions. Removal of Zn to the particulate phase in the Ria of Huelva estuary therefore largely attenuates high riverine Zn fluxes from AMD, indicating that previously estimated Odiel river basin Zn fluxes were overestimated. Nevertheless, the variable but generally light AMD Cd and Zn isotope compositions, coupled with high dissolved metal concentrations, suggest that Cd and Zn isotopes may be useful tracers of regionally averaged AMD inputs to the Gulf of Cadiz and beyond.

The seasonal distribution and pollution potential of dissolved heavy metals and nutrients in subterranean estuaries in southern India

In order to better understand the distribution pattern, pollution degree and the submarine groundwater discharge (SGD) of dissolved heavy metals, 15 subterranean estuaries (STEs) along southwest Indian coast were sampled over three contrasting seasons. The average concentration of metals were ranked as, pre-monsoon > monsoon > post-monsoon with 3 to 12-fold higher groundwater metal concentrations than the adjacent seawater. Average SGD derived essential metal fluxes were five times higher than the toxic metal fluxes of which Fe and Zn together contributed >90 %. Using the Single Factor Contamination Index, the majority of sites were minimally contaminated with only two sites indicating moderate ecological risk due to As. Higher fluxes of Fe, Cu and Zn were likely a result of rising anthropogenic activities. The SGD derived nutrient fluxes were an important source of DIP for primary production in coastal waters and represented 30 % and 44 % of the DIN and DIP inputs respectively.

Insight into atmospheric deposition and contamination of toxic Zinc in remote glacier regions of the Northwestern China

Zinc (Zn) plays an important role in biogeochemical cycles. Its excessive supplies, however, are detrimental to living organisms. To figure out Zn contamination and migration along the atmosphere-glacier-meltwater runoff path in various glaciers of central Asia, this work investigated the concentration, enrichment factors (EFs), deposition and meltwater release fluxes of Zn in large-scale glaciers and snowpacks of the Northwestern China. Results showed that the concentration and EF value of Zn exhibited a heterogeneous geographic distribution from west to east, with higher values in the Zhaosu snowpack in Tienshan Mountains of the west and Northeastern Tibetan Plateau (NETP) glaciers (e.g., Qiyi Glacier) of the east, and lower values in the central region. A compilation of EF data of Zn showed that glacier areas in the Northwestern China have experienced significant anthropogenic Zn pollution, which has spread to the glacier meltwater. We found that there were different degrees of Zn enrichment in the NETP glacial basins, with the highest enrichment observed in the terminus and upper reaches. Furthermore, the estimated Zn release flux from the Laohugou Glacier was 11 ± 2 t a−1, which was significantly higher than that of the non-glacial river (3.7 ± 3.3 t a−1). This highlights a substantial release of Zn from the glacial basins. Based on the HYSPLT model, we deduced that aeolian dust and anthropogenic aerosols originating from central Asia (e.g., Kazakhstan), Xinjiang province, and local sources are the probable sources of Zn deposition in glacier regions in the Northwestern China. A conceptual model was provided to illustrate the multiple origins and transport dynamics of Zn along the atmosphere-glacier-meltwater runoff pathway. Therefore, this work provides a more complete view and understanding of Zn distribution and biogeochemical cycle in high-altitude glacial areas of the Northwestern China.

Isotope Compositions of Century‐Long Corals Reveal Significant Dissolved Cu, Zn Fluxes From Human‐Accelerated Weathering Into the Ocean

AbstractHuman activities have liberated substantial amounts of biologically active metals into oceans. However, identifying the sources and migration processes of these metals is challenging. Here we present first century‐long records of concentrations and isotope compositions of Zn and Cu (δ66Zn and δ65Cu) in two corals from the northern South China Sea. The results show dramatic enrichment in coral Zn and Cu concentrations since the 1980s, which coincide with δ66Zn and δ65Cu increases. Coupled with concurrent land use/cover changes, we suggest that the enrichment trends of Cu and Zn in corals are best explained by human‐induced rock weathering and soil erosion, which transferred isotopically heavy Zn and Cu fluxes into the coastal ocean. The metal releases due to land use/cover changes relative to direct anthropogenic sources could be even more significant in the future given that anthropogenic releases have been legally controlled and started to decline in recent decades.

Atmospheric dry deposition fluxes of trace metals over the Eastern China Marginal Seas: Impact of emission controls

Atmospheric deposition is an important exogenous input of trace metals to Eastern China Marginal Seas (ECMS), which is strongly affected by human activities. With emission control practices implemented in China, it still remains unknown what changes have taken place in the atmospheric dry depositions of the trace metals over ECMS. This study aimed to estimate the atmospheric dry depositions of Zn, Pb, Cu, and Cd over ECMS via Weather Research and Forecasting Model-Community Multiscale Air Quality Modeling System (WRF-CMAQ) in the two winter periods of January 2012 and January 2019 as well as to explore the impacts of emission control on the depositions. The anthropogenic metal emissions from China, the Korean Peninsula, Japan, and marine ships were investigated in this study. In 2012, the dry deposition fluxes of Zn, Pb, Cu, and Cd over ECMS were in the ranges of 0.50–3.4 μg m−2 d−1, 0.22–1.9 μg m−2 d−1, 0.14–0.90 μg m−2 d−1, and 12–88 ng m−2 d−1, respectively. The deposition fluxes of the four metals over Bohai Sea (BS) and Yellow Sea (YS) were 2–3 times those over East China Sea (ECS). Outflow of polluted air masses from East Asia increased the metal depositions by 3– 5-fold relative to clear days. Compared with 2012, a 5–85 % reduction in the metal depositions over ECMS were estimated in 2019, largest reductions were found over YS and BS. Meteorological variation was able to decrease or increase the metal depositions. However, the emission control only caused a reduction in the entire study region. The metal inputs to the sea were significantly lower from the ship emissions than from the continental anthropogenic emissions, although the proportion of the ship emissions in the total metal depositions rose slightly from 2012 to 2019.

Seasonal variation, contribution and dynamics of trace elements in the drainage basin and estuary of the Serinhaém river, BA

In the present study a mass balance calculation was used to quantify trace elements (Al, Ba, Cd, Cr, Cu, Fe, Mn, Pb, Ti, V and Zn) fluxes exported from the Serinhaém River estuary to the Atlantic Ocean. The studied elements exportation in the particulate fraction showed higher fluxes in the first sampling campaign and a high export rate to the Atlantic Ocean during this period. The physical-chemical parameters showed the highest values in sampling campaign 1. These variations are probably the cause of the different trace elements behavior in fluvial and estuarine areas, where removal and addition processes between particulate and dissolved phases took place, affecting distribution coefficient and fluxes to the Atlantic Ocean. EPA ecosystems present values in accordance with Brazilian legislation for pristine areas, however, monitoring programs must be carried out in the region, to avoid future environmental problems.

Can Zn isotopes in sediments record past eutrophication of freshwater lakes? A pilot study at Lake Baldegg (Switzerland)

In this study, the speciation and isotopic composition of Zn were traced across the sediments of a freshwater lake that experienced one hundred years of strong eutrophication, in order to assess the potential of sedimentary Zn isotopes to record such an environmental disturbance. The results indicate that the sedimentary Zn isotope signal varied with the change from pre-eutrophic to eutrophic conditions in the investigated lake. The average δ66ZnJMC value of the dominantly allochthonous lithogenic sediments deposited during the pre-eutrophic period was +0.27‰ ±0.05‰ (i.e. similar to the δ66ZnJMC value of +0.28‰ ±0.05‰ proposed for Bulk Silicate Earth), while enhanced autochthonous biochemical sedimentation during the eutrophic period resulted in significantly lower δ66ZnJMC values down to +0.04‰ ±0.06‰. Synchrotron-based X-ray absorption spectroscopy data revealed a concomitant change in Zn speciation from a dominant fraction of Zn in clay minerals during the pre-eutrophic period to a major fraction of Zn in ZnS during the eutrophic period. A linear regression relating the sedimentary Zn isotope signal to the fraction of Zn in ZnS indicated δ66ZnJMC values of +0.27‰ ±0.06‰ and 0.00‰ ±0.08‰ for Zn in clay minerals and in ZnS, respectively. The enrichment of light Zn in ZnS in the eutrophic sediments is tentatively attributed to enhanced biological uptake of light Zn in the water column, which resulted in an enhanced flux of organic-bound Zn towards the sediments and further transformation of organic Zn into ZnS upon biomass mineralization during early diagenesis. This hypothesis is in agreement with the fractionation towards lighter Zn reported for both biological uptake of Zn and ZnS precipitation. The results of this study emphasize the potential of sedimentary Zn isotopes to register past eutrophic periods in freshwater lakes, and thus to serve as a probe of paleo-environmental conditions and/or past land use at the catchment scale.

SU(N) fractional instantons and the Fibonacci sequence

We study, by means of numerical methods, new SU(N) self-dual instanton solutions on R × T3 with fractional topological charge Q = 1/N. They are obtained on a box with twisted boundary conditions with a very particular choice of twist: both the number of colours and the ’t Hooft ZN fluxes piercing the box are taken within the Fibonacci sequence, i.e. N = Fn (the nth number in the series) and left|overrightarrow{m}right| = left|overrightarrow{k}right| = Fn−2. Various arguments based on previous works and in particular on ref. [1], indicate that this choice of twist avoids the breakdown of volume independence in the large N limit. These solutions become relevant on a Hamiltonian formulation of the gauge theory, where they represent vacuum-to-vacuum tunneling events lifting the degeneracy between electric flux sectors present in perturbation theory. We discuss the large N scaling properties of the solutions and evaluate various gauge invariant quantities like the action density or Wilson and Polyakov loop operators.

Highly active crystal planes-oriented texture for reversible high-performance Zn metal batteries

Zn metal anodes with fast kinetics and stable thermodynamics is critical for developing reversible high-performance aqueous Zn-ion batteries. Herein, based on the characteristic of Zn hexagonal close-packed structure, a highly active reaction plane (HARP)-induced deposition strategy is developed by employing the selective reaction of weak oxidants ( e.g. , (NH 4 ) 6 Mo 7 O 24 ·4H 2 O) to crystal planes to build a thermodynamically stable ZnMoO 4 passivation layer on Zn metal surface. The selective reaction creates lots of lattice defects on the HARP as nuclei and orientation origin for Zn deposition showing the fast reaction kinetics. In addition, the ZnMoO 4 layer exhibits superior properties in inhibiting the corrosion and side reactions for Zn electrodes (stable thermodynamics), along with fast transport kinetics as uniform ion flux of Zn 2+ . Therefore, the Zn electrode delivers superb reversibility for stripping/plating over 6000 h with a low polarization of 40 mV at 0.5 mA cm −2 . This concept is universally valuable for constructing metal electrodes with fast kinetics, stable thermodynamics, and high-capacity.

Dendrite suppression with zirconium (IV) based metal–organic frameworks modified glass microfiber separator for ultralong-life rechargeable zinc-ion batteries

Metal–organic frameworks (MOFs) are increasingly employed in designing an active material for various battery systems due to the variety of structures, morphology, and controllable composition at a molecular level. Moreover, their high porosity enables a facile electrolyte penetration and ion transportation. In this work, we focus on the performance and life cycle of aqueous rechargeable zinc-ion batteries (ZIBs) using zirconium (IV) based MOFs, including UiO-66 and MOF-808 modified glass microfiber separators. The results demonstrated that the symmetrical cell using MOF-808 modified separator extended a relatively stable voltage plateau of symmetric Zn battery over 350 h owing to improved uniformity of Zn ion flux during striping/plating processes. For the capacity retention at the current density of 1.0 A g −1 , the ZIBs using UiO-66@GFC and MOF-808@GFC exhibited higher specific capacities than that using the pristine separator. In addition, the ZIBs with MOF-808 modified separators could prolong the cycle life to as high as 8000 cycles because the modified separators could inhibit non-uniform dendritic zinc growth on a zinc anode surface according to scanning electron micrographs. Hence, the UiO-66 and MOF-808 modified glass microfibers as separators are promising materials for high-performance aqueous zinc-ion batteries with long-life cycles. • No short-circuit of Zn|MnO 2 is achieved for over 8000 cycles at 1 A g −1 . • MOFs modified separators exhibit uniform Zn flux on striping/plating processes after cycling for 1000 cycles. • The percentage of capacitive retention of MOFs modified separators retain 50% after 3000 cycles. • MOFs modified separators were successfully by the one-step dip-coating process.

Zinc transport from the endoplasmic reticulum to the cytoplasm via Zip7 is necessary for barrier dysfunction mediated by inflammatory signaling in RPE cells.

Inflammatory signaling induces barrier dysfunction in retinal-pigmented epithelium (RPE) cells and plays a role in the pathology of age-related macular degeneration (AMD). We studied the role of Zn flux from the endoplasmic reticulum (ER) to the cytoplasm via Zip7 during inflammatory signaling in RPE cells. In ARPE-19 cells, Zip7 inhibition reduced impedance loss, FITC-dextran permeability and cytokine induction caused by challenge with IL-1β/TNF-α. Zip7 inhibition in iPS-derived RPE cells challenged with TNF- α reduced barrier loss in TER assays. In ARPE-19 cells, a Zn ionophore restored cytokine induction and barrier loss in cells challenged with IL-1 β /TNF- α despite Zip7 inhibition. A cell permeable Zn chelator demonstrated that Zn is essential for IL-1 β /TNF- α signaling. ER stress caused by Zip7 inhibition in ARPE-19 cells was found to partially contribute to reducing barrier dysfunction caused by IL-1 β /TNF- α. Overall, it was shown that Zn flux through Zip7 from the ER to the cytoplasm plays a critical role in driving barrier dysfunction caused by inflammatory cytokines in RPE cells.

Unraveling precipitation evolution and strengthening function of the Al-Zn-Mg-Cu alloys with various Zn contents: Multiple experiments and integrated internal-state-variable modeling

• The functions of Zn content in precipitation evolution and strengthening of Al-Zn-Mg-Cu alloys were systematically investigated. • The increased Zn content would promote the development of precipitates and enhance aging hardening. • The diffusion flux of soluble Zn and the coordination of Mg atom controlled the crystallographic microstructures. • An improved internal-state-variable physical model was developed by integrating precipitation development with electrical resistivity and hardness evolutions. • The unified model considered the intrinsic characteristic of precipitates and was adaptive to heat-treatment variables and chemical compositions. Zn content is one of the most concerned factors in the development of next generation ultra-strength Al-Zn-Mg-Cu alloys owing to its essential role in precipitation strengthening. In the present work, the underlying functions of Zn content in precipitation evolution and strengthening function of Al-Zn-Mg-Cu alloys were systematically investigated by combining multiple experiments and an integrated internal-state-variable model. The experimental results indicated that the increased Zn content in Al-Zn-Mg-Cu alloys would promote the development of precipitates and enhance aging hardening. The diffusion flux of soluble Zn and the coordination of Mg atom controlled the crystallographic microstructures evolution during precipitates nucleation, growth and transition processes. By integrating precipitation development with electrical resistivity and hardness evolutions, an improved internal-state-variable physical model was then developed for the aging responses of Al-Zn-Mg-Cu alloys. The unified model considered the intrinsic characteristics of precipitates such as crystallographic orientation, morphology, component, and distribution. The specific improvements were to balance the combined functions of Zn element and Mg element and consider the plate-like morphology and directed growth as indicated by experiments. This model was also adaptive to heat-treatment variables and chemical compositions, and owned the notable advantages to simultaneously rationalize the observed microstructural characteristics, mechanical and electrical properties following artificial aging of Al-Zn-Mg-Cu alloys. In addition, a preliminary model framework between electrical resistivity and hardness for Al-Zn-Mg-Cu alloys was established.

The zinc isotope composition of late Holocene open-ocean marine sediments

The controls on Zn burial fluxes into marine sediments are not well constrained by existing datasets. To address this problem, new Zn-isotope data have been generated from a globally distributed array of late-Holocene age sediments that accumulated in open ocean settings underneath a diverse range of depositional conditions (Namibian margin, West African margin, Arabian margin, Californian margin, Peruvian margin, Southern Ocean, Indian Ocean, North and South Atlantic Oceans, South China Sea). The mean non-detrital isotopic composition of Zn in the whole dataset (δ66/64Zn = 0.37 ± 0.25 ‰, 2. S.D., n = 33) is only slightly lower than the modern deep-ocean composition (0.45 ± 0.14 ‰). Locations with total organic carbon >1 wt% have greater non-detrital enrichments of Zn and higher Zn isotope compositions than organic-poor sites, although the uncertainties overlap. Zinc associated with organic matter burial (using Zn/C ratios) and/or oxyhydroxide burial (using Zn/Fe and Zn/Mn ratios) account for a combined total of ~16–73% of the total non-detrital Zn content of the investigated sediments, therefore requiring an additional burial flux of Zn to balance the sedimentary budget. This flux is probably related to ZnS formation although Zn incorporation into authigenic clays is also possible. The new data indicate that open-ocean marine sediments track the deep-ocean Zn isotope composition to within 0.1–0.2 ‰, except in areas where isotopically distinct Zn fractions dominate the non-detrital Zn budget. The fraction of Zn removed into different sedimentary components is used to calculate Zn residence times ranging from ~2.7 kyr to 13.5 kyr that are within the range of previous estimates based on input fluxes to the ocean.