We present evolution equations for a family of paths that results from anisotropically weighting curve energies in non-linear statistics of manifold valued data. This situation arises when performing ...inference on data that have non-trivial covariance and are anisotropic distributed. The family can be interpreted as most probable paths for a driving semi-martingale that through stochastic development is mapped to the manifold. We discuss how the paths are projections of geodesics for a sub-Riemannian metric on the frame bundle of the manifold, and how the curvature of the underlying connection appears in the sub-Riemannian Hamilton-Jacobi equations. Evolution equations for both metric and cometric formulations of the sub-Riemannian metric are derived. We furthermore show how rank-deficient metrics can be mixed with an underlying Riemannian metric, and we relate the paths to geodesics and polynomials in Riemannian geometry. Examples from the family of paths are visualized on embedded surfaces, and we explore computational representations on finite dimensional landmark manifolds with geometry induced from right-invariant metrics on diffeomorphism groups.
A meaningful application of Mo as a paleo-redox proxy requires an understanding of Mo cycling in modern reducing environments. Stagnant euxinic basins such as the Black Sea are generally regarded as ...model systems for understanding euxinic systems during early Earth history. However, drawing direct parallels between the Black Sea and open-marine euxinic margins is somewhat complicated by differences in the seawater residence time between these two environments. We report sediment and pore water Mo, U, Mn and Fe data for a euxinic basin with a short seawater residence time; the weakly restricted Gotland Deep in the Baltic Sea. Here, prolonged periods of euxinia alternate with brief inflow events during which well-oxygenated, saline water penetrates into the basin. During these inflow events, dissolved Mn and Fe that has accumulated within the euxinic deep water can be oxidized and precipitated. Co-variations of Mo and U within the sediment suggest that these inflow and oxygenation events may favor Mo accumulation in the sediment through adsorption to freshly oxidized Mn and Fe solid phases. Once Mo is sequestered within the deeper euxinic water and sediments, Mo retention can be further facilitated by conversion to thiomolybdate species and interactions with organic matter and metal sulfides. By comparing our data with those from previous studies where a Mn and Fe “shuttle” for Mo has been demonstrated, we identify two prerequisites for the occurrence of this mechanism. First, there must be a water column oxic–anoxic redox-boundary; this provides a solubility contrast for Mn and Fe. Second, the residence time of seawater in the system has to be short (weeks to a few years). The latter criterion can be met through regular inflow in weakly restricted basins or upwelling in oxygen minimum zones at open-marine continental margins. Based on prior work, we suggest that similar conditions to those currently represented by the Gotland Deep may have prevailed at euxinic ocean margins during the Proterozoic. A boundary between euxinic and oxic water masses overlying the continental shelf may have resulted in accelerated Mo transport through the water column with Mn and Fe (oxyhydr)oxides. We propose that this mechanism, along with Mo isotope fractionation during adsorption, could contribute to the light Mo isotope composition observed in open-marine euxinic sediment facies of the Proterozoic.
•There is coupled Mn, Fe and Mo delivery to euxinic sediments of the Gotland Deep.•A Mn and Fe shuttle for Mo is a common feature in dynamic anoxic systems.•This shuttle mechanism may contribute to the Mo isotope composition of Proterozoic black shales.
Poly(vinyl chloride) (PVC) is today one of the most important commodity polymers. Its broad range of applications is due to the presence of plasticizers whose concentration largely impacts the ...microscopic and the macroscopic properties. Quantifying the concentration of plasticizer in PVC products is therefore of fundamental importance. Thus, in this paper, the applicability of terahertz (THz) time-domain spectroscopy for the characterization of plasticized PVC is for the first time evaluated in a systematic way. It could be demonstrated that the method is able to distinguish between PVC samples with different types and concentrations of plasticizers. Furthermore, a simple, fast, and efficient method is introduced to quantify the concentration of plasticizer in PVC samples of known plasticizer type but different thermal histories. The presented results are of key importance due to the need of reliable noninvasive and nondestructive analytical methods which can deliver onsite information about the remaining plasticizer concentration inside PVC products. Furthermore, it is expected that the proposed approach can be easily extended to other plasticized polymers.
Benthic foraminifera populate a diverse range of marine habitats. Their ability to use alternative electron acceptors—nitrate (NO₃⁻) or oxygen (O₂)—makes them important mediators of benthic nitrogen ...cycling. Nevertheless, the metabolic scaling of the two alternative respiration pathways and the environmental determinants of foraminiferal denitrification rates are yet unknown. We measured denitrification and O₂ respiration rates for 10 benthic foraminifer species sampled in the Peruvian oxygen minimum zone (OMZ). Denitrification and O₂ respiration rates significantly scale sublinearly with the cell volume. The scaling is lower for O₂ respiration than for denitrification, indicating that NO₃⁻ metabolism during denitrification is more efficient than O₂ metabolism during aerobic respiration in foraminifera from the Peruvian OMZ. The negative correlation of the O₂ respiration rate with the surface/volume ratio is steeper than for the denitrification rate. This is likely explained by the presence of an intracellular NO₃⁻ storage in denitrifying foraminifera. Furthermore, we observe an increasing mean cell volume of the Peruvian foraminifera, under higher NO₃⁻ availability. This suggests that the cell size of denitrifying foraminifera is not limited by O₂ but rather by NO₃⁻ availability. Based on our findings, we develop a mathematical formulation of foraminiferal cell volume as a predictor of respiration and denitrification rates, which can further constrain foraminiferal biogeochemical cycling in biogeochemical models. Our findings show that NO₃⁻ is the preferred electron acceptor in foraminifera from the OMZ, where the foraminiferal contribution to denitrification is governed by the ratio between NO₃⁻ and O₂.
Dissolved silicon isotope compositions have been analysed for the first time in pore waters (δ30SiPW) of three short sediment cores from the Peruvian margin upwelling region with distinctly different ...biogenic opal content in order to investigate silicon isotope fractionation behaviour during early diagenetic turnover of biogenic opal in marine sediments. The δ30SiPW varies between +1.1‰ and +1.9‰ with the highest values occurring in the uppermost part close to the sediment–water interface. These values are of the same order or higher than the δ30Si of the biogenic opal extracted from the same sediments (+0.3‰ to +1.2‰) and of the overlying bottom waters (+1.1‰ to +1.5‰). Together with dissolved silicic acid concentrations well below biogenic opal saturation, our collective observations are consistent with the formation of authigenic alumino-silicates from the dissolving biogenic opal. Using a numerical transport-reaction model we find that approximately 24% of the dissolving biogenic opal is re-precipitated in the sediments in the form of these authigenic phases at a relatively low precipitation rate of 56μmolSicm−2yr−1. The fractionation factor between the precipitates and the pore waters is estimated at −2.0‰. Dissolved and solid cation concentrations further indicate that off Peru, where biogenic opal concentrations in the sediments are high, the availability of reactive terrigenous material is the limiting factor for the formation of authigenic alumino-silicate phases.
The possibility to adapt chemometrics approaches for the quantitative estimation of heavy metals in soils polluted by a mining accident was explored. In April 1998, the dam of a mine tailings pond in ...Aznalcóllar (Spain) collapsed and flooded an area of more than 4000 ha with pyritic sludge contaminated with high concentrations of heavy metals. Six months after the end of the first remediation campaign, soil samples were collected for chemical analysis and measurement of visible to near-infrared reflectance (0.35−2.4 μm). Concentrations for As, Cd, Cu, Fe, Hg, Pb, S, Sb, and Zn were well above background values. Prediction of heavy metals was achieved by stepwise multiple linear regression analysis (MLR) and an artificial neural network (ANN) approach. It was possible to predict six out of nine elements with high accuracy. Best R 2 between predicted and chemically analyzed concentrations were As, 0.84; Fe, 0.72; Hg, 0.96; Pb, 0.95; S, 0.87; and Sb, 0.93. Results for Cd (0.51), Cu (0.43), and Zn (0.24) were not significant. MLR and ANN both achieved similar results. Correlation analysis revealed that most wavelengths important for prediction could be attributed to absorptions features of iron and iron oxides. These results indicate that it is feasible to predict heavy metals in soils contaminated by mining residuals using the rapid and cost-effective reflectance spectroscopy.
Fossil benthic foraminifera are used to trace past methane release linked to climate change. However, it is still debated whether isotopic signatures of living foraminifera from methane-charged ...sediments reflect incorporation of methane-derived carbon. A deeper understanding of isotopic signatures of living benthic foraminifera from methane-rich environments will help to improve reconstructions of methane release in the past and better predict the impact of future climate warming on methane seepage. Here, we present isotopic signatures (δ
C and δ
O) of foraminiferal calcite together with biogeochemical data from Arctic seep environments from c. 1200 m water depth, Vestnesa Ridge, 79° N, Fram Strait. Lowest δ
C values were recorded in shells of Melonis barleeanus, - 5.2‰ in live specimens and - 6.5‰ in empty shells, from sediments dominated by aerobic (MOx) and anaerobic oxidation of methane (AOM), respectively. Our data indicate that foraminifera actively incorporate methane-derived carbon when living in sediments with moderate seepage activity, while in sediments with high seepage activity the poisonous sulfidic environment leads to death of the foraminifera and an overgrowth of their empty shells by methane-derived authigenic carbonates. We propose that the incorporation of methane-derived carbon in living foraminifera occurs via feeding on methanotrophic bacteria and/or incorporation of ambient dissolved inorganic carbon.
Marine silicate alteration plays a key role in the global carbon and cation cycles, although the timeframe of this process in response to extreme weather events is poorly understood. Here we ...investigate surface sediments across the Peruvian margin before and after extreme rainfall and runoff (coastal El Niño) using Ge/Si ratios and laser-ablated solid and pore fluid Si isotopes (δ
Si). Pore fluids following the rainfall show elevated Ge/Si ratios (2.87 µmol mol
) and δ
Si values (3.72‰), which we relate to rapid authigenic clay formation from reactive terrigenous minerals delivered by continental runoff. This study highlights the direct coupling of terrestrial erosion and associated marine sedimentary processes. We show that marine silicate alteration can be rapid and highly dynamic in response to local weather conditions, with a potential impact on marine alkalinity and CO
-cycling on short timescales of weeks to months, and thus element turnover on human time scales.
Ever-increasing human pressures on cave biodiversity have amplified the need for systematic, repeatable, and intensive surveys of cave-dwelling arthropods to formulate evidence-based management ...decisions. We examined 110 papers (from 1967 to 2018) to: (i) understand how cave-dwelling invertebrates have been sampled; (ii) provide a summary of techniques most commonly applied and appropriateness of these techniques, and; (iii) make recommendations for sampling design improvement. Of the studies reviewed, over half (56) were biological inventories, 43 ecologically focused, seven were techniques papers, and four were conservation studies. Nearly one-half (48) of the papers applied systematic techniques. Few papers (24) provided enough information to repeat the study; of these, only 11 studies included cave maps. Most studies (56) used two or more techniques for sampling cave-dwelling invertebrates. Ten studies conducted >10 site visits per cave. The use of quantitative techniques was applied in 43 of the studies assessed. More than one-third (42) included some level of discussion on management. Future studies should employ a systematic study design, describe their methods in sufficient detail as to be repeatable, and apply multiple techniques and site visits. This level of effort and detail is required to obtain the most complete inventories, facilitate monitoring of sensitive cave arthropod populations, and make informed decisions regarding the management of cave habitats. We also identified naming inconsistencies of sampling techniques and provide recommendations towards standardization.
The thermophilic ant genera
Cataglyphis and
Ocymyrmex share a variety of specialisations that enable them to engage in high-speed foraging at considerably higher temperatures than less heat-tolerant ...species. In the present account we test the hypothesis that thermophilic ants have longer legs than closely related species from more mesic habitats. By comparing large-sized, medium-sized, and small-sized species of
Cataglyphis and
Ocymyrmex with size-matched species of the closely related non-thermophilic genera
Formica (Formicinae) and
Messor (Myrmicinae), respectively, we show that the thermophilic species are equipped with considerably longer legs than their less heat-tolerant relatives. Hence phylogenetically, extreme long-leggedness has evolved at least twice in desert ants: in the Formicinae and the Myrmicinae. Functionally, this morphological trait is adaptive for a number of reasons. The long legs raise the body into cooler layers of air and enable higher running speeds, which increase convective cooling and reduce foraging time. These are important adaptations all the more as due to the low food density prevailing in desert habitats foraging
Cataglyphis and
Ocymyrmex ants have to cover large distances within their physically demanding foraging grounds.
► Thermophilic ants have significantly longer legs than non-thermophilic ants. ► Leg length increases with decreasing geographical latitude. ► Extreme long-leggedness is a highly adaptive trait in thermophilic desert ants. ► In thermophilic ants extreme long-leggedness has evolved at least twice.
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