Homogeneous Composition Research Articles

Simplified fish larval supply in coastal areas after a dam burst in Brazil

Coastal and estuarine systems play an important role in the maintenance of marine biodiversity, providing nursery, feeding, developmental and reproductive areas for terrestrial and aquatic species. The Fundão dam collapse is considered one of the biggest environmental disasters in Brazil, causing great social, economic and ecological damage in the affected areas. In our study, we used beta diversity and its components as a tool to monitor the spatio-temporal variation of fish larvae in four marine areas adjacent to the Doce River. The results show that the four areas undergo different spatio-temporal dynamics, with the composition of fish larvae in the Doce being simplified in the last years after the dam burst, compared to the other adjacent marine areas. In addition, turbidity is an important factor that has caused the homogenization of the larval composition of the Doce, demonstrating that mud resuspension events can cause a decrease in diversity and also suggesting the toxicity of the mud composition. The change from negative to positive additive and colonizing components in recent years suggests a slight recovery of diversity in the Doce compared to other marine areas. Finally, we have shown that some species may be tolerant to the impact, but with probable behavioral, energetic and physiological costs, which justifies the constant monitoring of these areas.

Suppression of crack formation in wafer-scale amorphous SiNx films by residual hydrogen-ligands manipulation

Plasma-Enhanced Chemical Vapor Deposition (PECVD) of amorphous silicon nitride (SiNx) thin films is a critical procedure in microelectronics serving as a surface passivation layer and dielectric barrier. However, intrinsic film stress continuously builds up along with PECVD growth, leading to film cracking. How to achieve crack-free PECVD amorphous SiNx film within a large thickness range remains a critical unresolved challenge in semiconductor industry. In this study, we revealed that high residual NH ligands from the NH3 precursor could induce excessive tensile strain at the SiNx/Si wafer interface and consequently aggravate SiNx film crack formation. With a heating pretreatment on the wafer, residual H ligands were effectively reduced to achieve homogenous chemical composition in SiNx film. As a result, the crack number declined ∼42% and the remaining crack length was substantially shorter in contrast to the original SiNx film. This work demonstrates the crucial role of residual ligands on internal strain regulation and points out a pathway to achieve crack-free PECVD SiNx films in industrial manufacturing.

Heterostructure Interface Construction of Cobalt/Molybdenum Selenides toward Ultra‐Stable Sodium‐Ion Half/Full Batteries

AbstractTransition metal selenides (TMSes) are considered promising candidates for the anodes of sodium‐ion batteries (SIBs) due to their substantial theoretical capacity. However, TMSes still face with inferior cycling lifespan caused by sluggish Na+ diffusion kinetics and vigorous volume variations during dis/charge processes. Engineering heterostructure is an attractive solution for rapid Na+ transfer, and introducing carbonaceous materials also facilitates enhanced conductivity and structural stability. Herein, CoSe/MoSe2 heterostructure combined with homogeneous carbon composites are rational designed. The kinetic analysis and theoretical calculations verified that heterointerface engineering induced build‐in electric field effect can amplifies the Na+ diffusion kinetics, while carbon contributes to enhanced electrical conductivity and structural stability. Expectedly, the CoSe/MoSe2‐C exhibits high capacity and extremely ultra‐long lifespan (320.9 mAh g−1 at 2.0 A g−1 over 10,000 cycles with an average decay of only 0.01781 mAh g−1 per cycle). Furthermore, in situ X‐ray diffraction (XRD), ex situ X‐ray photoelectorn (XPS), and high‐resolution electron microscopy (HRTEM) are exploited to explore the Na+ storage mechanism. In addition, the Na3V2(PO4)3@rGO//CoSe/MoSe2‐C (NVP@rGO//CoSe/MoSe2‐C) pouch‐type full‐cells are successfully assembled and delivered satisfactory performance. This research presents a viable strategy for the targeted engineering of TMSes aimed at enhancing the efficiency of SIBs.

Selenization-induced [001]-oriented Sb2Se3 film formation and its photo-sensing characteristics

Antimony selenide (Sb2Se3) is emerging as a promising material for optoelectronic applications owing to its exceptional properties. Achieving c-axis oriented [001] Sb2Se3 films, which is crucial for optimizing charge carrier transport has consistently been challenging. In this work, a facile route involving reactive selenization of antimony films deposited on glass substrates via thermal evaporation was employed to obtain [001] oriented Sb2Se3 thin films. The resultant films were comprehensively characterized using X-ray diffraction, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy to confirm phase purity and compositional homogeneity, elucidating the role of selenization temperature in the formation of Sb2Se3 through this method. XPS analysis was carried out to confirm the oxidation states of Sb and Se. Optical analysis revealed a high absorption coefficient of ∼1.75 × 105 cm−1 with the desired direct band gap values in the range of 1.23 eV–1.20 eV. All these favourable properties, steered to observe a photocurrent of 143 nA at a 5V applied bias in 375°C selenized films under AM1.5 G illumination conditions. An n-Si/Sb2Se3 heterojunction was fabricated and a photocurrent of 2.8 μA was observed with responsivity and detectivity values of 8.18 × 10−5 A/W and 4.26 × 109 Jones respectively at zero applied bias and AM1.5 illumination conditions, showing the favourable prospects of Sb2Se3 thin films prepared via the selenization of antimony films in optoelectronic applications.

Analytical Modeling of Wave Absorption Performance in Gradient Graphene/Polymer Nanocomposites.

Due to the low impedance matching caused by the high dielectric permittivity of graphene, the strong absorption of electromagnetic waves by graphene/polymer nanocomposites is challenging. In this paper, an analytical model for microwave absorption based on Maxwell's equation and the effective medium theory, considering the interface effect, was constructed to explore the effect of the gradient distribution of graphene in the polymer matrix on its microwave absorption performance. The outcome indicated that the impedance of the composites matched well with the air, and its attenuation ability for electromagnetic waves was obviously improved as the graphene concentration was distributed in a gradient form. For instance, when the thickness of the material is 10 mm, based on the optimal concentration of the homogeneous composites being 0.7 wt%, the graphene concentration range of the gradient composites is set to 0.7-0.9 wt% and distributed in three gradient forms of linear, parabolic, and 0.5 power. The results show that the microwave absorption performance is significantly improved compared with the homogeneous composites. Among them, the effective bandwidth on the 0.5 power distribution is 5.2 GHz, 0.5 GHz higher than that of the homogeneous composites. The minimum reflection loss (RL) is as low as -54.7 dB, which is 26.26 dB lower than that of the homogeneous composites. This paper contributes to the design and application of gradient absorbing structures.

Carbon Macrosegregation Pattern in 30Cr15Mo1N Ingot: Impact of Pouring Rate

The effect of the pouring rate on the carbon macrosegregation in 30Cr15Mo1N ingots has been clarified by investigating changes in the content of carbon‐containing precipitated phases, cooling rate, secondary dendrite arm spacing (SDAS) and the flow characteristics of molten steel. During the solidification process, the solute‐enriched liquid steel migrates toward the center of the ingot under the action of convection, resulting in an increasing segregation ratio from the edge to the center. However, the growth of equiaxed grains partially restricts the flow of solute‐enriched liquid steel, which leads to a maximum segregation ratio not at the center but at approximately a quarter radius from the center. Furthermore, due to the upward flow of molten steel in the center, positive segregation occurs at the top. An increment in the pouring rate reduces the SDAS by enhancing the cooling rate, and thus the permeability decreases. It aggravates the carbon macrosegregation horizontally. However, increasing the pouring rate decreases the carbon macrosegregation vertically. This is due to the more intense flow of molten steel and the larger liquid phase region at higher pouring rate, which reduces the solute enrichment degree and promotes compositional homogeneity above and below the ingot.

Innovative Bioactive Ca-SZ Coating on Titanium Dental Implants: A Multidimensional Structural and Elemental Analysis.

The design of new, biomimetic biomaterials is of great strategic interest and is converging for many applications, including in implantology. This study explores a novel approach to improving dental implants. Although endosseous TA6V alloy dental implants are widely used in oral implantology, this material presents significant challenges, notably the prevalence of peri-implantitis. Therefore, in this study, we investigate a new advance in the design of hybrid medical devices. This involves the design of a Ca-SZ coating deposited by PVD on a TA6V substrate. This approach aims to overcome the inherent limitations of each of these materials, namely TA6V's susceptibility to peri-implantitis on the one hand and zirconia's excessively high Young's modulus compared with bone on the other, while benefiting from their respective advantages, such as the ductility of TA6V and the excellent biocompatibility of zirconia, offering relevant prospects for the design of high-performance implantable medical devices. This study integrates characterisation techniques, focusing on the structural and elemental analysis of the Ca-SZ coating by XRD and TEM. The results suggest that this coating combines a tetragonal structure, a uniform morphology with no apparent defects, a clean interface highlighting good adhesion, and a homogeneous composition of calcium, predisposing it to optimal biocompatibility. All of these findings make this innovative coating a particularly suitable candidate for application in dental implantology.

Age, composition and spatial distribution of sandy loess in north‐eastern Germany (Fläming, Brandenburg)

AbstractThe sandy loess deposits in the lowlands of northern Germany present a valuable sedimentary archive for late Weichselian periglacial geomorphodynamics. While other aeolian sediments from the Late Quaternary, especially loess deposits and sand dunes, have been studied and dated in some detail in the last decades, sandy loess has received less scientific attention with respect to its genesis, composition, age and provenance as well as distribution patterns. In this study, we present detailed results for three sediment sections located on the Fläming ridge in the south of the state of Brandenburg. According to our results from luminescence dating, the sandy loess deposits of this area were deposited during the late MIS 2 (19–14 ka) with a highly variable thickness of at least up to 4 m, followed by a deposition of periglacial coversands shortly thereafter. The sandy loess deposits display a homogeneous geochemical composition and grain size characteristics similar to loess sections in the main loess areas to the west and south. Furthermore, we analysed a large dataset of geological drill data and performed a spatial interpolation of sandy loess distribution in the Western Fläming. Despite the strongly dissected modern landscape of the Fläming ridge which is partly the result of intense Holocene soil erosion processes, general patterns of the original loess distribution could be deduced. Based on these findings, we were able to identify the low‐lying areas to the north and north‐east of the study area to be the most likely source areas for the sandy loess as a result of katabatic winds originating from the Fennoscandian Ice Shield. Thereby, this study yields important insights regarding aeolian transport and deposition patterns under periglacial conditions in the Central European Lowlands.

Two-dimensional medium-entropy SeSI composite cathodes with cascaded redox reactions for advanced sodium batteries

Na−S/Se/I2 batteries represent a promising rechargeable Na battery system because of high theoretical energy density and low raw material cost. However, the inherent electrical insulation and poor structural stability of S/Se/I2 cathodes result in the unsatisfactory battery performance. Here we develop a new medium-entropy Se-S-I composite cathode via a straight chemical reaction of 2xSe+yI2+CS2=2SexSIy+C, simultaneously consolidating a ternary Se-S-I compound within carbon nanocage, forming a SeSI@C core-shell structure. In the composite, SeSI has a distinctive single crystal structure with homogeneous elemental composition, while carbon shell shows a uniform annular nanoscale that can completely envelop SeSI active mass. The cathode structural design bears high electrical conductivity, fast synergistic activation and excellent structural integrity, accordingly enabling a high capacity with an ultralong cycle life in a representative Na−Se-S-I battery (425.4 mAh g−1 at 10.0 A g−1, 91.6 % retention for 2000 cycles). Notably, a tertiary cascade of Se, S, and I redox has been demonstrated for providing high capacity, and an in-situ grown carbon shell ensures electrical conductivity and structural stability through the entire cathode. This SeSI@C cathode architecture significantly alleviates issues of traditional S/Se/I2-based cathodes, and makes the Na−Se-S-I battery more promising for application.

Microstructural Evolution and Phase Transformation on Sn–Ag Solder Alloys under High‐Temperature Conditions Focusing on Ag3Sn Phase

This study investigates the microstructural and phase transformations in Sn–Ag solder alloys under high‐temperature conditions, utilizing X‐ray diffraction, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) analyses. Analytical techniques are employed pre‐ and postcontrolled thermal cycling from 30 to 180 °C, aimed at emulating solder reflow processes. The analysis at room temperature demonstrates pronounced crystalline peaks, suggesting a preferred orientation within the crystal structure. Upon heating, peak broadening suggests grain growth and the onset of recrystallization. SEM and energy‐dispersive spectroscopy analyses corroborate these findings, displaying a fine‐grained, well‐distributed microstructure with a homogenous composition of Sn and Ag elements. EBSD provides insights into the orientation and texture of grains, revealing a weak‐to‐moderate texture across the phases. Postexperiment data indicate a dominant presence of larger grains and significant variation in grain size, with an area‐weighted mean grain size of 68.47 μm and a standard deviation of 8.68 μm; this suggests significant grain growth and coarsening of the Ag3Sn intermetallic compounds. These structural evolutions have crucial implications for the mechanical properties and reliability of the solder alloy in electronic assemblies, underscoring the need for further exploration of lead‐free solder materials in the electronics industry.

Cd0.90Mn0.10Te single crystal for γ – Ray detector application: A comprehensive analysis of structural and compositional homogeneity

This study provides a comprehensive examination of the Cd0.90Mn0.10Te (CMT) single crystal in its role as a radiation detector. Covering aspects from the growth process to detector performance, the primary emphasis is placed on ensuring the uniformity of composition along the growth axis. A cost-effective custom-built vertical Bridgman (VB) setup is developed for the growth of highly homogeneous Cd0.90Mn0.10Te (CMT) single crystal. CMT single crystals of 10 mm diameter and 130 mm length with near uniform stoichiometry along the growth axis were grown using VB method. Laue diffraction confirms the single crystallinity of the grown crystal. The measured lattice constant is comparable to the theoretical value calculated using Vegard’s law. The two mode vibrations of the CdTe and MnTe sublattices were confirmed by Raman spectroscopy. The observed high optical transmittance in the mid-infra-red (IR) region and a nearly constant bandgap of ∼1.6 eV for the wafers taken at different locations along the growth axis reveals the IR transparency and compositional uniformity of the grown crystal. The energy dispersive X-ray spectroscopy proved that the elemental distribution is uniform in the grown crystal. The IR microscopic imaging shows Te inclusions with a number density in the range of ∼2.6–4.5 × 104 cm−2. The resistivity of the CMT crystal for all wafers was found to be in the order of 109 Ωcm. The γ–ray spectral resolution of ∼22 % of 59.5 keV irradiation from 241Am source is achieved.

In Situ MOF-74-Pyrolysis-Generated Porous Carbon Supporting Spinel Cu0.15Co2.85O4/C Boosts Ammonium Perchlorate Accelerating Decomposition: Precise Cu Doping Modulating Oxygen Vacancy Concentration.

As one of the main components of solid propellant, ammonium perchlorate (AP) shows slow sluggish decomposition kinetics with unconcentrated heat release. To achieve efficient catalytical decomposition, it is a significant challenge to design reasonable catalyst structure and explore the interaction between catalyst and AP. Herein, a series of porous carbon supported spinel-typed homogeneous heterometallic composites CuxCo3-xO4/C via pyrolysis of MOF-74-Co doped Cu. On basis of precise electronic-structure-tuning through modulating Cu/Co ratio in MOF-74, Cu0.15Co2.85O4/C with 5% Cu-doping featuring oxygen vacancy concentration of 26.25% exhibits the decrease to 261.5°C with heat release up to 1222.1 J g-1 (456.9°C and 669.2 J g-1 for pure AP). The detail process of AP accelerated decomposition is approved by TG-DSC-FTIR-MS technique. Density functional theory calculation revealed that in the Cu0.15Co2.85O4/C, the distinctive ability for NH3 catalyzed oxidation assisted with absorption performance of active porous C boosts accelerating AP decomposition. The findings would provide an insight for perceiving and understanding AP catalytic decomposition.

Compositional Diversity of Early Mesozoic Granites in South Qinling: Derivation from Heterogenous Basement Rocks in the Orogenic Belt

Granitic rocks forming in the syn- to post-orogenic stages can trace the compositional and structural complexity of the crust beneath an orogenic belt. The Qinling orogenic belt undertook multiple stages of tectonics and magmatism, resulting in the multifaceted evolution and compositional diversity of the crust. In the present study, the Guangtoushan and Miba plutons in South Qinling were chosen to reveal the crustal heterogeneity in study area via isotopic geochemistry and zircon geochronology. The Guangtoushan pluton was emplaced between ~215 Ma and ~202 Ma and the Miba pluton formed at ~213 Ma, as constrained by zircon U-Pb isotopic dating. Granitic rocks of the Miba pluton are characterized by amphibole bearing and homogeneous composition, with relatively depleted Sr-Nd isotopic compositions (initial 87Sr/86Sr values of 0.7060 to 0.7084 and initial εNd values of −5.4 to −9.5) and high Pb isotopic values. The Guangtoushan pluton contains muscovite and complex inherited zircon grains and has variable Sr-Nd isotopic composition (initial 87Sr/86Sr values of 0.7050 to 0.7091 and initial εNd values of −4.5 to −12.9) and low Pb isotopic values. Felsic magmas of the Guangtoushan pluton should be derived mainly from meta-sedimentary rocks beneath South Qinling, while the Miba pluton originated primarily from partial melting of meta-igneous rocks. The compositional diversity recorded in the Early Mesozoic plutons was caused by the heterogeneous crust, and partial melting was induced by heating of the up-welling asthenosphere in a post-collision setting.

Constraints on crustal compositional architecture across the North China-Altaids transition and implications for craton margin reworking

Abstract The phase of secular evolution of continents is manifested as the degree of compositional differentiation, modification, and maturation of continental crusts, which is vital in understanding the mechanism of continental evolution but is difficult to quantify. Here we use integrated passive- and active-source seismic profiling to conduct joint analysis and inversion and derive Vs and Vp/Vs section models across the North China craton (NCC) to southeastern Altaids boundary zone that bears a tectonic transition from a reworked ancient craton margin to a Phanerozoic accretionary orogen. We systematically exploited the imaged multiple physical properties as precise and delicate proxies to constrain the compositional architecture in the crust across this important tectonic transition subject to various crustal evolutional phases. Our Vs and Vp/Vs imaging, together with the existing isotopic data, characterizes the Yin Shan-Yan Shan belt as the northern NCC margin with layered homogeneous compositions that point to an evolved crust. However, the lower-crustal low-Vs/high-Vp/Vs signature that overlaps the shallowly dipping to horizontal reflective fabrics suggests the crust of the northern NCC margin has undergone considerable reworking through lower-crustal-stretching assisted melt migration and mixing since the late-Paleozoic to Mesozoic era. The process probably involved crust-mantle interaction and thus resulted in a compositionally modified ancient crustal basement. On the contrary, the southeastern Altaids domain manifests crustal complexity in compositions and structures inferred to be indicative of a juvenile crust of the Phanerozoic accretionary orogen. Our results provide deep physical-property constraints that shed new light on the crustal evolution of a complex craton margin.

Distance decay effects predominantly shape spider but not carabid community composition in crop fields in north-western Europe

Agricultural intensification and expansion are regarded as main drivers of biodiversity loss. This conclusion is mainly based on observed declines of local diversity (α-diversity), while effects on community composition homogenization (decrease of β-diversity) at a larger spatial scale are less well understood. Carabid beetles and spiders represent two widespread guilds and are important predators of pest species. Here we surveyed carabid beetles and spiders in 66 winter wheat fields in four northwestern European countries (Germany, the Netherlands, Sweden and UK) and analyzed how their community composition was related to geographic distance (separation distance between any pairwise fields) and three environmental variables: crop yield (proxy for land-use intensity), percentage cropland (proxy for landscape complexity) and soil organic carbon content (proxy for local soil conditions). We further analyzed whether the relationship between carabid beetle and spider community composition and geographic distance was influenced by environmental variables. We found that, 55 % and 75 % of all observed carabid and spider individuals, respectively, belonged to species that occurred in all four countries. However, individuals of species that were unique to a particular country only accounted for 3 % of all collected individuals for both taxa. Furthermore, we found a negative relationship between distance and similarity of spider communities but not for carabid beetle communities. None of the environmental variables were related to similarity of carabid beetle and spider communities, nor moderated the effects of distance. Our study indicates that across a great part of the European continent, arthropod communities (especially carabid beetles) in agricultural landscapes are composed of very similar species that are robust to current variations in environment and land-use.

Zinc isotopes of high silica granites in the Qilian Orogenic belt and implications for mineralization potential

Many high silica granites (>70 wt% SiO2) are closely linked to ore deposits. There has been an ongoing debate about whether they are formed through extensive fractional crystallization or partial melting, as traditional major-trace element and radiogenic isotopes make it challenging to distinguish among these mechanisms. Recent studies suggest that zinc isotopes have the potential to trace crustal differentiation and monitor fluid evolution during the late stage of magma evolution. In this study, we investigated the Lenglongling leucogranites in the North Qilian Orogenic belt, characterized by high SiO2 contents ranging from 72 % to 78 wt%, extremely low Zr/Hf ratios (15.8–21), low Nb/Ta ratios (3.8–9.3), and strongly negative Eu/Eu* anomalies (0.04–0.32). The invariant and basalt-like zinc isotopic compositions of the Lenglongling high silica leucogranites (0.27 ‰ ±0.03 ‰ to 0.38 ‰ ± 0.03 ‰) reveal that they did not undergo extensive fractional crystallization or fluid exsolution. Instead, their homogeneous zinc isotope compositions and distinct geochemical characteristics were inherited from their protoliths during partial melting.

3D characterisation of a large high rate algal pond for wastewater treatment

The Peterborough high rate algal pond (HRAP) is a large scale (5000 m2) wastewater treatment system using microalgae, located in South Australia. The purpose of the study was to assess the homogeneity of wastewater composition in this meandering 1 km-long, 30 cm-depth, 4 m-wide channel, mixed by paddlewheel. In situ measurements of flow velocity, dissolved oxygen, pH and contemporaneous wastewater sampling were conducted along the length, depth and width of HRAP. The mean flow velocity, 0.2 m.s−1, was conserved along the channel with deviations observed near the pond bottom and the 180° bends. The chlorophyll a was constant through the channel length. The HRAP wastewater was homogeneously over saturated with photosynthetically derived dissolved oxygen (DO >20 mg.L−1) at midday. However, solids sedimentation occurred near the bends where flow velocities decreased to <0.05 m.s−1 on the inner bank. Nitrification was occasionally incomplete and varied along the channel length and through depth. Given alkalinity and DO was sufficient, factors impacting nitrification included the relative proportion of ammonia and nitrite-oxidizing bacteria as well as the stability and/or presence of algal-bacterial flocs affecting substrate access. Nitrification showed less variability when these flocs were absent, and the algal population was unicellular/colonial. The wastewater composition within the 1 km-long HRAP was predominantly homogenous and efficiently mixed by the paddlewheel driven by an electric motor with an energy consumption of 0.85 kWh. Further investigations are needed to clarify associations amongst mixing, flocs size, nitrification and denitrification in micro anaerobic zones within flocs.

Low temperature crystallization of atomic-layer-deposited SrTiO3 films with an extremely low equivalent oxide thickness of sub-0.4 nm

Despite SrTiO3(STO) possessing a high dielectric constant, its application as a capacitor dielectric in dynamic random-access memory(DRAM) capacitors faces challenges due to the high-temperature annealing for crystallization, its compositional inhomogeneity, and the high leakage currents of STO films. To address these issues, we employ atomic layer deposition(ALD) of STO films onto Pt substrates at elevated temperatures(340–380 °C). The use of low-reactivity Pt electrodes effectively mitigates the initial growth of excess Sr, ensuring enhanced compositional uniformity along the film growth direction. Coupled with ALD at high temperatures, this approach facilitates the crystallization of STO films in the as-grown state, further enhancing the crystallinity with increasing film thickness. Subsequent low-temperature post-deposition annealing (PDA) at 400 and 500 °C achieves full crystallization. This process results in a remarkable increase in the dielectric constant, reaching approximately 150. Furthermore, the absence of microcracks after PDA, attributed to the formation of adequately dense films, contributes to substantially improved dielectric properties. Consequently, these STO films exhibit an exceptionally low equivalent oxide thickness of 0.34 nm coupled with an ultralow leakage current of 3.7 × 10−8 A/cm2 at an operation voltage of 0.8 V, promising for advancing DRAM capacitors. This study presents a pathway for the sustainable scaling of DRAMs, addressing challenges in ALD-grown STO films.

The Late Holocene deglaciation of James Ross Island, Antarctic Peninsula: OSL and 14C-dated multi-proxy sedimentary record from Monolith Lake

Lentic waterbodies provide terrestrial sedimentary archives of palaeoenvironmental change in deglaciated areas of the Antarctic. Knowledge of the long-term evolution of Antarctic palaeoenvironments affords important context to the current marked impacts of climate change in the Polar regions. Here, we present a comprehensively dated, multi-proxy sedimentary record from Monolith Lake, a distal proglacial lake in one of the largest ice-free areas of the Antarctic Peninsula region. Of the two defined sedimentary units in the cores studied, the lower Unit 1 exhibits a homogeneous composition and unvarying proxy data profiles, suggesting rapid clastic deposition under uniform, ice-proximal conditions with a sedimentation rate of ∼1 mm yr−1. 14C and optically stimulated luminescence (OSL) dating bracket the deposition interval to 1.5–2.5 ka BP, with the older age being more probable when compared to independent dating of the local deglaciation. The uppermost 11 cm of the record spans the last ∼2.2 ka BP (maximum age), suggesting a markedly decreased sedimentation rate of ∼0.05 mm yr−1 within Unit 2. Whereas Unit 1 shows only scarce evidence of biological activity, Unit 2 provides an uninterrupted record of diatoms (with 29 species recorded) and faunal subfossils, including the fairy shrimp Branchinecta gaini. Concentrations of organically-derived elements, as well as diatoms and faunal remains, are consistent, implying a gradual increase in lake productivity. These results provide an example of long-term Antarctic ‘greening’ (i.e. increasing organic productivity in terrestrial habitats) from a palaeolimnological perspective. The boundary between Units 1 and 2, therefore, marks the timing of local deglaciation at the final stages of a period of negative glacier mass balance, i.e. the Mid-Late Holocene Hypsithermal. Subsequent Neoglacial cooling is evidenced by the abated influence of glacial meltwater streams and turbidity decline linked to reduced glacier runoff, although most proxy responses mirror the natural proglacial lake ontogeny.

Above and below-ground bacterial communities shift in seagrass beds with warmer temperatures

Current rates of ocean warming are predicted to exacerbate ongoing declines in seagrass populations. Above-ground responses of seagrass to increasing temperatures have been studied from a direct physiological perspective while indirect effects, including changes to microbially-mediated below-ground processes, remain poorly understood. To test potential effects of increased temperature on seagrass growth and associated microbial communities, we sampled seagrass beds experiencing ambient and elevated water temperatures at Lake Macquarie, Australia. Sites with warmer water were associated with a plume from a power station discharge channel with temperatures analogous to conditions predicted by 2100 under current rates of ocean warming (+3°C). The microbial community composition in both sediments and leaf tissues varied significantly between warm and ambient water temperatures with higher relative abundances of putative sulphate-reducing bacteria such as Desulfocapsaceae, Desulfobulbaceae and Desulfosarcinaceae in sedimentary communities in warm water. Above-ground biomass and seagrass growth rates were greater at warm sites while below-ground biomass and detrital decomposition rates showed no difference suggesting potential buffering of temperature effects below-ground. These findings suggest a 3°C rise in temperate regions is unlikely to induce mortality in seagrass however, it may shift microbial communities towards more homogenous structure and composition.