Abstract: Biotite–melt Nb and Ta partition coefficients (D_Nb and D_Ta) are crucial for understanding Nb−Ta enrichment and fractionation in rare metal granites (RMGs). However, the key factor(s) affecting biotite–melt D_Nb, D_Ta, and D_Nb/D_Ta values remain unclear. To elucidate the physicochemical factors that control the partition coefficients, we performed piston−cylinder experiments at 0.5−1.0 GPa and 850−1000°C with H₂O-added (4−10 wt.%) mixtures of granitic and biotitic glasses as starting materials. Two series of experiments (graphite-buffered and unbuffered fO₂ conditions) were conducted with calculated fO₂ values ranging from ∼FMQ–1.5 to ∼FMQ+4. Under these experimental conditions, biotite–melt D_Nb, D_Ta, and D_Nb/D_Ta values are 0.30–2.63, 0.24−1.02, and 1.01−2.15, respectively. Biotite–melt D_Nb, D_Ta, and D_Nb/D_Ta values increase with decreasing melt NBO/T value (non-bridging oxygens per tetrahedron), melt H₂O content, and biotite Mg#^T value [molar 100 × MgO/(MgO + FeO^T)]. In addition, D_Nb and D_Ta exhibit good correlations with D_Ti, suggesting that D_Nb and D_Ta are predictable via D_Ti values. With our and literature data, we used multiple linear regressions to obtain empirical expressions of D_Nb and D_Ta as functions of the three parameters. By applying the empirical models to granite differentiation process, we found that ∼99% crystallization of biotite ± muscovite-bearing assemblages results in an enrichment in magma Ta contents by >10 times with a decrease in Nb/Ta values from 10−13 to ∼1, which reproduces the Ta–Nb/Ta features of most RMGs. However, additional processes, such as columbite-group mineral precipitation, may be required to account for the extremely low Nb/Ta values (<1) of some RMGs.

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Abstract: Draining into the northern Baltic Sea, River Simojoki is an important spawning river for Atlantic salmon. The present study aimed to preliminary explore the potential of analysing the elemental composition of otoliths to distinguish the within-river nursery area of origin for salmon. Parr were sampled at three nursery areas in the river and smolts of unknown origin were sampled near the river mouth during the migration to the sea. The concentrations of multiple elements and the strontium ⁸⁷Sr/⁸⁶Sr isotopic ratio in the otoliths were analysed using single- and multi-collector laser ablation inductively coupled plasma mass spectrometry, respectively. Based on the otolith elemental variables, parr could be reclassified to the sampled nursery areas using discriminant function analysis and random forest with a success rate of 53.3% and 63.3%, respectively. However, for parr sampled at the uppermost nursery area in the river, the success rates were 90% and 100%, respectively. Applying the classification models trained on the parr samples to determine which nursery area sampled smolt originated from was constrained by the limited sampling of parr, both in sample sizes and the coverage of the nursery areas found in the river.

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Abstract: In an era of rapid environmental change and increasing human presence, researchers need efficient tools for tracking contaminants to monitor the health of Antarctic flora and fauna. Here, we examined the utility of leopard seal whiskers as a biomonitoring tool that reconstructs time-series of significant ecological and physiological biomarkers. Leopard seals (Hydrurga leptonyx) are a sentinel species in the Western Antarctic Peninsula due to their apex predator status and top-down effects on several Antarctic species. However, there are few data on their contaminant loads. We analyzed leopard seal whiskers (n = 18 individuals, n = 981 segments) collected during 2018–2019 field seasons to acquire longitudinal profiles of non-essential (Hg, Pb, and Cd) and essential (Se, Cu, and Zn) trace elements, stable isotope (ẟ15N and ẟ13C) values and to assess Hg risk with Se:Hg molar ratios. Whiskers provided between 46 and 286 cumulative days of growth with a mean ~ 125 days per whisker (n = 18). Adult whiskers showed variability in non-essential trace elements over time that could partly be explained by changes in diet. Whisker Hg levels were insufficient (<20 ppm) to consider most seals being at “high” risk for Hg toxicity. Nevertheless, maximum Hg concentrations observed in this study were greater than that of leopard seal hair measured two decades ago. However, variation in the Se:Hg molar ratios over time suggest that Se may detoxify Hg burden in leopard seals. Overall, we provide evidence that the analysis of leopard seal whiskers allows for the reconstruction of time-series ecological and physiological data and can be valuable for opportunistically monitoring the health of the leopard seal population and their Antarctic ecosystem during climate change.

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Abstract: Studying the lacustrine microbialites in the Qaidam Basin may provide clues to the occurrence and mineralization processes of microbial communities in extremely harsh terrestrial environments. In the Eocene lacustrine systems of the Qaidam Basin, thick thrombolites (~0.4 to 1 m thick) generally formed in near-shore settings with rare to plentiful terrigenous admixtures and are characterized by four different clotted structures (i.e., maze-like, cortoid-like, tightly bound, and aggregated). In contrast, the small-scale stromatolitic, thrombolitic, and composite clotted-laminated microbialites (cm level) exhibit domical, columnar, and stratiform shapes, likely indicating that they developed in very shallow settings (e.g., a lagoon). The early lithification of the outer crusts and the internally laminated and clotted textures facilitated the preservation of the microbialites. The laminated and clotted textures of the Eocene microbialites analyzed in this study were composed of crypto- to micro-crystalline (mimetic) dolomite, which likely formed during the early mineralization process. This was likely caused by the strong evaporative lacustrine conditions on the Qinghai-Tibetan Plateau during the Eocene-Oligocene climate transition. The microbial mineralization process in dolomite-supersaturated pore fluids may also have contributed to early dolomitization. In contrast, the medium to coarsely crystalline components of the microbialites are composed of calcite minerals, implying that these components experienced cementation/recrystallization during diagenesis. In addition, large quantities of authigenic sulfate (celestite-barite) and sulfide (framboidal pyrite) minerals are exclusively distributed within the mimetically-dolomitized, laminated and clotted microbial structures. It is inferred that the saline lake conditions and the mineral dissolution (both carbonate and terrigenous particles) contributed to the SrSO4- and BaSO4-supersaturated fluid conditions and enabled the crystallization of celestite-barite. The development of Eocene lacustrine microbialites on the northeastern Qinghai-Tibetan Plateau provides a case for comparison with widely-distributed records of lake microbial carbonates, and the microstructural characteristics and analytical tools used in this study may offer a new perspective to explore the complex mineralization processes of microbialites.

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Abstract: Studying the lacustrine microbialites in the Qaidam Basin may provide clues to the occurrence and mineralization processes of microbial communities in extremely harsh terrestrial environments. In the Eocene lacustrine systems of the Qaidam Basin, thick thrombolites (~0.4 to 1 m thick) generally formed in near-shore settings with rare to plentiful terrigenous admixtures and are characterized by four different clotted structures (i.e., maze-like, cortoid-like, tightly bound, and aggregated). In contrast, the small-scale stromatolitic, thrombolitic, and composite clotted-laminated microbialites (cm level) exhibit domical, columnar, and stratiform shapes, likely indicating that they developed in very shallow settings (e.g., a lagoon). The early lithification of the outer crusts and the internally laminated and clotted textures facilitated the preservation of the microbialites. The laminated and clotted textures of the Eocene microbialites analyzed in this study were composed of crypto- to micro-crystalline (mimetic) dolomite, which likely formed during the early mineralization process. This was likely caused by the strong evaporative lacustrine conditions on the Qinghai-Tibetan Plateau during the Eocene-Oligocene climate transition. The microbial mineralization process in dolomite-supersaturated pore fluids may also have contributed to early dolomitization. In contrast, the medium to coarsely crystalline components of the microbialites are composed of calcite minerals, implying that these components experienced cementation/recrystallization during diagenesis. In addition, large quantities of authigenic sulfate (celestite-barite) and sulfide (framboidal pyrite) minerals are exclusively distributed within the mimetically-dolomitized, laminated and clotted microbial structures. It is inferred that the saline lake conditions and the mineral dissolution (both carbonate and terrigenous particles) contributed to the SrSO4- and BaSO4-supersaturated fluid conditions and enabled the crystallization of celestite-barite. The development of Eocene lacustrine microbialites on the northeastern Qinghai-Tibetan Plateau provides a case for comparison with widely-distributed records of lake microbial carbonates, and the microstructural characteristics and analytical tools used in this study may offer a new perspective to explore the complex mineralization processes of microbialites.

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