Search

More than 100 volcanoes have been discovered in Antarctica, however, the sources of many Antarctic tephras are not yet constrained. In this study, four tephra samples recovered from the environment of Site 27 on an area of blue ice at Allan Hills, South Victoria Land, provide information on magma and crustal sources for the tephra erupted in Antarctica. We report data on the chemistry of Antarctic tephra glasses and minerals analysed by electron microscopy, electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry. The tephra amphibole chemistry indicates magma residence at ~1 GPa and ~1100 °C. Abundant Ca–Al–Si-rich minerals imply that the magma ascended from a reservoir at 29.4 ± 2.7 km depth was affected by the assimilation of calc-silicate crust. The high Fe and Ti contents in the magmatic minerals and the trace element patterns of the glasses typical of a hydrothermally altered oceanic crust suggest that the Allan Hills tephra originated from a mantle plume-derived magma. The fragmented morphology of the glasses implies that the magmatic activity was associated with explosive eruptions during the mid-Pleistocene. The chemistry of the glasses and the presence of rhönite and Al-rich spinel minerals suggest that the magma might be genetically related to the currently active McMurdo volcanic group. [ABSTRACT FROM AUTHOR]

Understanding supra-regional climate variability such as the changes in the North Atlantic realm is important to identify the drivers of the climate system. In this study maar lake sediments from the Eifel (western Germany) were analysed with a multi-proxy approach and compared to central and western European speleothem growth phases. C org (chlorins) and the pollen assemblage were analysed from two sediment cores of the Hoher List infilled maar lake. To generate C org (chlorins) and pollen records covering the entire last 130,000 yr b2k (years before year 2000 CE), the data from this study were stacked with published data from other Eifel maar lake sediment cores (Sirocko et al., 2013, 2021, 2022). The sediment cores from Hoher List infilled maar lake were dated by marker tephra layers giving chronological anchor points and the precise dating of the sediment cores was performed by the tuning of the C org (chlorins) records to the NGRIP δ18O record (Rasmussen et al., 2014). The speleothems, whose growth phases are compared to the lake sediment proxy records, were compiled from the literature as well as speleothems from Dechencave (western Germany) dated by the 230Th/U-method in this study. The C org (chlorins) variability shows the bioproductivity in the maar lake, which is related to water temperature and corresponds to the Greenland Interstadials (GIs) in the NGRIP δ18O record indicates its dependence on supra-regional climate variations in the North Atlantic. The pollen record shows three periods of forest with temperate forest species, during the Eemian, early Marine Isotope Stage (MIS) 3, and the Holocene. Speleothem growth in four caves in central and western Europe (Dechencave, Spannagel Cave, Hölloch Cave, Villars Cave) is predominantly sensitive to cold periods with glaciers and/or permafrost conditions above the caves inhibiting speleothem growth. The forested phases and phases of high bioproductivity in the Eifel correspond well with phases of speleothem growth indicating three warm phases in central Europe during the last glacial cycle. [ABSTRACT FROM AUTHOR]

Black manganese-rich crusts are found worldwide on the façades of historical buildings. In this study, they were studied exemplarily on the façade of the Freiburger Münster (Freiburg Minster), Germany, and measured in-situ by portable X-ray fluorescence (XRF). The XRF was calibrated to allow the conversion from apparent mass fractions to Mn surface density (Mn mass per area), to compensate for the fact that portable XRF mass fraction measurements from thin layers violate the assumption of a homogeneous measurement volume. Additionally, 200-nm femtosecond laser ablation-inductively coupled plasma-mass spectrometry (fs LA-ICP-MS) measurements, scanning transmission X-ray microscopy-near edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS), Raman spectroscopy, and imaging by light microscopy were conducted to obtain further insight into the crust material, such as potential biogenic contributions, element distributions, trace element compositions, and organic functional groups. While black crusts of various types are present at many places on the minster's facade, crusts rich in Mn (with a Mn surface density >150 μg cm −2 ) are restricted to a maximum height of about 7 m. The only exceptions are those developed on the Renaissance-Vorhalle (Renaissance Portico) at a height of about 8 m. This part of the façade had been cleaned and treated with a silicon resin as recently as 2003. These crusts thus accumulated over a period of only 12 years. Yet, they are exceptionally Mn-rich with a surface density of 1200 μg cm −2 , and therefore require an accumulation rate of about 100 μg cm −2 Mn per year. Trace element analyses support the theory that vehicle emissions are responsible for most of the Mn supply. Lead, barium, and zinc correlate with manganese, indicating that tire material, brake pads, and resuspended road dust are likely to be the element sources. Microscopic investigations show no organisms on or in the Mn-rich crusts. In contrast, Mn-free black crusts sampled at greater heights (>8 m) exhibited fungal and cyanobacterial encrustation. Carbon-rich spots were found by STXM-NEXAFS underneath one of the Mn-rich crusts. However, these carbon occurrences originate from soot and polycyclic aromatic hydrocarbons (PAHs) deposited on top of the crust, rather than from organisms responsible for the crust's formation, as shown by STXM-NEXAFS and Raman spectroscopic measurements. Our results suggest that the crusts develop abiogenically, with vehicle emissions as dominant element sources. [ABSTRACT FROM AUTHOR]

Abstract: Intra-bone rare earth element (REE) fractionation trends were studied by LA-ICPMS analysis to put constraints on (1) the mechanisms controlling REE fractionation within fossil bones; (2) the relative timing of REE uptake in various parts of fossil bone and (3) the origin of REE in fossil bones. We have evaluated REE bone profiles across 54 fossil bones from a broad range of well-characterised taphonomic settings ranging in age from Triassic to early Medieval. REE patterns and concentration gradients are highly variable and intra-bone fractionation trends in (La/Yb)N vs. (La/Sm)N space of few specimens cover almost the entire range previously observed for bulk samples. Intra-bone variability of Ce anomalies, as well as variable Y/Ho and (La/La∗)N is also observed. Sometimes, diagenetic fluids with fractionated, HREE enriched compositions have entered the bone from the marrow cavity, producing secondary REE uptake profiles. Theoretical intra-bone fractionation trends, modelled using lattice strain theory, concur with most REE data but some trends cannot be modelled using realistic boundary conditions. This fact, as well as the occurence of positive and negative Ce anomalies within the same fossil sample, hint towards changing REE compositions of diagenetic fluids over the timescales of REE uptake. Because apparent Ce anomalies frequently evolve over bone profiles and Ce anomalies can be inherited from previous fractionation events, Ce anomalies are a highly ambiguous tracer for constraining ambient redox conditions. In general, bioapatite REE signatures may not always reliably reflect ambient taphonomic or redox conditions and diagenetic fluid compositions. Therefore REE patterns and Ce anomalies of fossil bones must be interpreted cautiously as they vary spatially within skeletal remains and are affected by intra-bone fractionation processes as well as changing compositions of the diagenetic fluid. [Copyright &y& Elsevier]

Abstract Marine Isotope Stage 3 (MIS 3, 57–27 ka) was characterised by numerous rapid climate oscillations (i.e., Dansgaard-Oeschger (D/O-) events), which are reflected in various climate archives. So far, MIS 3 speleothem records from central Europe have mainly been restricted to caves located beneath temperate Alpine glaciers or close to the Atlantic Ocean. Thus, MIS 3 seemed to be too cold and dry to enable speleothem growth north of the Alps in central Europe. Here we present a new speleothem record from Bunker Cave, Germany, which shows two distinct growth phases from 52.0 (+0.8, −0.5) to 50.9 (+0.6, −1.3) ka and 47.3 (+1.0, −0.6) to 42.8 (±0.9) ka, rejecting this hypothesis. These two growth phases potentially correspond to the two warmest and most humid phases in central Europe during MIS 3, which is confirmed by pollen data from the nearby Eifel. The hiatus separating the two phases is associated with Heinrich stadial 5 (HS 5), although the growth stop precedes the onset of HS 5. The first growth phase is characterised by a fast growth rate, and Mg concentrations and Sr isotope data suggest high infiltration and the presence of soil cover above the cave. The second growth phase was characterised by drier, but still favourable conditions for speleothem growth. During this phase, the δ13C values show a significant decrease associated with D/O-event 12. The timing of this shift is in agreement with other MIS 3 speleothem data from Europe and Greenland ice core data. Highlights • Speleothem record from central Europe covering MIS 3. • 230Th/U dating shows two distinct growth phases during early MIS 3. • Growth stop is likely related to the Heinrich 5 event. • Multi-proxy data suggest humid phases during growth periods in MIS 3. [ABSTRACT FROM AUTHOR]

This study presents the first well-dated high resolution stable isotope ( δ 18 O and δ 13 C ) and trace element (Mg and Sr) speleothem records from southwestern Morocco covering the last 1000 yrs. Our records reveal substantial decadal to multidecadal swings between dry and humid periods, consistent with regional paleorecords with prevailing dry conditions during the Medieval Climate Anomaly (MCA), wetter conditions during the second part of the Little Ice Age (LIA), and a trend towards dry conditions during the current warm period. These coherent regional climate signals suggest common climate controls. Statistical analyses indicate that the climate of southwestern Morocco remained under the combined influence of both the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) over the last millennium. Interestingly, the generally warmer MCA and colder LIA at longer multidecadal timescales probably influenced the regional climate in North Africa through the influence on Sahara Low which weakened and strengthened the mean moisture inflow from the Atlantic Ocean during the MCA and LIA respectively. [ABSTRACT FROM AUTHOR]

• Time lag of 8 to 12 days between environmental signal and geochemical response. • Ba/Ca shell peaks are linked to specific diatom, dinoflagellate and flagellate blooms. • Mo/Ca shell chronologies reveal similarities with Gymnodinium spp. time-series. • Li/Ca shell peaks could be related to neurotoxin producing diatom blooms. Shells of the fast-growing bivalve Pecten maximus serve as a geochemical archive for the reconstruction of past phytoplankton dynamics. Specifically, high-resolution, temporally accurately aligned molar barium-to-calcium (Ba/Ca shell), molybdenum-to-calcium (Mo/Ca shell) and lithium-to-calcium ratios (Li/Ca shell) of the shell calcite revealed distinct peaks which are closely linked to phytoplankton dynamics. Yet, the development and applicability of these geochemical proxies is still at an early stage and needs further calibration. In this study, we examined the relationship between the timing and magnitude of Ba/Ca shell , Mo/Ca shell and Li/Ca shell peaks of P. maximus and the occurrence of various phytoplankton species (diatoms and dinoflagellates) from a statistical perspective. Studied shell samples (three specimens per calendar year) as well as detailed phytoplankton observation data were derived from the well-studied costal ecosystem of the Bay of Brest (France) over three years (2011, 2012 and 2019). An algorithm-based pseudo-random sampling simulation technique was established that analyzed the complex phytoplankton datasets with respect to the profiles of Ba/Ca shell , Mo/Ca shell and Li/Ca shell to identify potential patterns between phytoplankton and trace element time-series. The simulation results indicate that the timing and magnitude of Ba/Ca shell , Mo/Ca shell and Li/Ca shell peaks agreed best with the occurrence of specific phytoplankton blooms that developed ca. one to two weeks earlier. The data suggest that the formation of transient Ba/Ca shell peaks had a plurispecific origin, i.e., potentially linked to blooms of ingestible diatom, dinoflagellate and flagellate species enriched in Ba that occurred 8 to 12 days earlier. Observed peaks in Mo/Ca shell profiles demonstrably followed the timing and intensity of blooms of the dominant dinoflagellate genus Gymnodinium spp. after a short time lag of around 8 days, potentially linked to an enhanced enzyme activity of nitrate reductase that requires the presence of Mo in the dinoflagellate cells. In addition, Mo/Ca shell peaks agreed with periods of diatom aggregate formation which were hypothesized to induce the formation of Mo/Ca shell peaks in scallop shells. Li/Ca shell profiles revealed similar patterns as large blooms of the diatom Chaetoceros spp. as well as to neurotoxin producing diatoms of the genus Pseudo-nitzschia when considering a short time lag of 8 to 12 days. These findings highlight the great potential of using Ba/Ca shell , Mo/Ca shell and Li/Ca shell chronologies in P. maximus shells as proxies of past phytoplankton dynamics. [ABSTRACT FROM AUTHOR]

Abstract: The application of ostracod shell chemistry as a paleoenvironmental tool has grown within the past decades. Most studies have investigated Mg and Sr in ostracod shells as proxies for temperature and salinity, and the use of a wide range of trace elements as prospective paleoenvironmental indicators has yet to be developed for lacustrine systems. Only a few preliminary studies have used trace metals in paleolimnological studies such as Cd, Ba and Zn as paleonutrient indicators, or Mn, Fe and U as redox and oxygenation indicators. This paper reviews the state of the art of geochemical analyses in microfossils such as ostracods, foraminifera, and corals, and provides insights in new trace element proxies with the goal to promote the use of trace elements in ostracod shells as paleoenvironmental proxies. In paleoceanography, foraminifera and corals are most prominently used to reconstruct past climate conditions. Well-established proxies such as δ18O, Mg/Ca and Sr/Ca provide information about changes in sea surface temperatures. In addition, a great number of new proxies have been developed recently, such as radiogenic isotopes and redox sensitive trace elements. In paleolimnology, ostracod shell chemistry is widely used to assess paleohydrological changes. Reconstruction of temperature and salinity changes in lake environments is often achieved by oxygen isotopes as well as Mg/Ca and Sr/Ca ratios, but depending on the hydrological and geological settings of the lake system, local calibrations are needed to assess which proxy is suited to reflect which processes. New proxies need to be tested by novel techniques that recently have become available. Compared to conventional instrumentation used in ostracod shell chemistry, methods such as Laser Ablation ICP-MS and NanoSIMS allow single shell analysis and provide high-resolution data. The potential of ostracods in paleolimnology is not yet fully assessed, but can be developed by learning from paleoceanographic studies. [Copyright &y& Elsevier]

Abstract: The platinum-group elements (PGE) are exceptional tracers of planetary differentiation and therefore are useful discriminants of different high-temperature processes. Many of the initial efforts to understand how PGE behave during mantle melting involved experiments where PGE solubility in silicate melt was measured. The results of these experiments showed that PGE dissolve in silicate melts as oxide species, and that their saturation depends on oxygen partial pressure (pO2). However, the majority of these experimental studies were conducted on FeO and sulfur-free melt compositions that little resemble natural magmas. In particular, the role of sulfur has been downplayed because of its lower availability as a ligand to the PGE in silicate melt when compared to oxygen. However, magmatic sulfides from oceanic basalts and layered intrusions are greatly enriched in the PGE relative to the silicate melts in equilibrium with them, suggesting that the PGE are strongly chalcophile. The question then is whether the PGE are actively scavenged into sulfide melt after it exsolves from a silicate melt; or if the PGE are already associated with S2− in a silicate melt prior to sulfide saturation. Here we report the results of experiments where the solubilities of Ru and Pd have been measured in natural picritic melt, as a function of pO2 and in the presence of sulfur. Results show that the presence of sulfur in the silicate melt enhances the solubility of Ru in picrite by over an order of magnitude. These results can be used to quantify the preference that PGE have to associate with sulfur relative to oxygen. For example, Ru was found to be 880±410 times more likely to associate with sulfur than with oxygen at pO2 around the fayalite–magnetite–quartz redox equilibrium. The preferential association of the PGE with S2− ligand indicates that once a sulfide melt exsolves, it will already be enriched in PGE precluding the need for it to actively scavenge PGE from a silicate melt. [Copyright &y& Elsevier]

Abstract: The occurrence of aragonite in speleothems has commonly been related to high dripwater Mg/Ca ratios, because Mg is known to be a growth inhibitor for calcite. Laboratory aragonite precipitation experiments, however, suggested a more complex array of controlling factors. Here, we present data from Pleistocene to Holocene speleothems collected from both a dolostone and a limestone cave in northern Morocco. These stalagmites exhibit both lateral and stratigraphic calcite-to-aragonite transitions. Aragonite fabrics are well-preserved and represent primary features. In order to shed light on the factors that control alternating calcite and aragonite precipitation, elemental (Mg, Sr, Ba, U, P, Y, Pb, Al, Ti and Th) abundances were measured using LA-ICP-MS, and analysed with Principal Component Analysis. Samples were analyzed at 100–200μm resolution across stratigraphic and lateral transitions. Carbon and oxygen isotope ratios were analysed at 100μm resolution covering stratigraphic calcite-to-aragonite transitions. Results show that the precipitation of aragonite was driven by a decrease in effective rainfall, which enhanced prior calcite precipitation. Different geochemical patterns are observed between calcite and aragonite when comparing data from the Grotte de Piste and Grotte Prison de Chien. This may be explained by the increased dripwater Mg/Ca ratio and enhanced prior aragonite precipitation in the dolostone cave versus lower dripwater Mg/Ca ratio and prior calcite precipitation in the limestone cave. A full understanding for the presence of lateral calcite-to-aragonite transitions is not reached. Trace elemental analysis, however, does suggest that different crystallographic parameters (ionic radius, amount of crystal defect sites, adsorption potential) may have a direct effect on the incorporation of Sr, Mg, Ba, Al, Ti, Th and possibly Y and P. [Copyright &y& Elsevier]

Abstract: A variety of seemingly unrelated processes, such as core–mantle interaction, desulfurization, and direct precipitation from a silicate melt have been proposed to explain the formation of Ru–Os–Ir alloys (here referred to as osmiridiums) found in terrestrial mantle rocks. However, no consensus has yet been reached on how these important micrometer-sized phases form. In this paper we report the results of an experimental study on the solubilities of Ru, Os and Ir in sulfide melts (or mattes) as a function of alloy composition at 1300°C. Considering the low solubilities of Ru, Os, and Ir in silicate melts, coupled with their high matte/silicate-melt partition coefficients, our results indicate that these elements concentrate initially at the ppm level in a matte phase in the mantle source region. During partial melting, the extraction of sulfur into silicate melt leads to a decrease in fS2 that triggers the exsolution of osmiridiums from the refractory matte in the residue. The newly formed osmiridiums may persist in the terrestrial mantle for periods exceeding billions of years. [Copyright &y& Elsevier]

Abstract: In the present study we examined material from the Ashikule Basin of Tibet. Chemical analyses were performed by use of energy dispersive X-ray spectroscopy and electron probe microanalysis to clarify whether the varnish layers that had developed on the surface of the rhyolite are indeed composed of varnish bodies and silica glaze. Electron microscopic analyses revealed that the surface of the varnish is covered both by filamentous hyphae bacterial and cocci-shaped forms. Within the varnish mineral layer in those samples two forms of bacteria-like microorganisms exist; cocci as tightly packed bacterial aggregates [within varnish bodies], and bacillus-like microorganisms [within the varnish matrix, that surrounds the varnish bodies]. The bacillus-like forms are embedded in a network of filaments that have diameters between 35 and 45nm. These bacilli with the surrounding filaments are assumed to have been involved in biofilm formation (synthesis of extracellular polymeric substances) prior to their live burial. We concluded that the formation of the varnish layers was for the most part biogenically driven by microorganisms. [Copyright &y& Elsevier]

Abstract: Background: Spicules, the siliceous skeletal elements of the siliceous sponges, are synthesized enzymatically via silicatein. The product formed, bio-silica, constitutes their inorganic matrix. It remained unexplored which reactions are involved in molding of the amorphous bio-silica and formation of a solid and rigid biomaterial. Methods: Cell and molecular biological techniques have been applied to analyze processes resulting in the hardening of the enzymatically synthesized bio-silica. The demosponge Suberites domuncula has been used for the studies. Results: Cell aggregates (primmorphs) from the sponge S. domuncula, grown in the presence of Mn-sulfate, form spicules that comprise, instead of a smooth, a rough and porous surface which is decorated with irregular bio-silica deposits. During this process, the expression of the aquaporin-8 gene becomes down-regulated. Further in vitro studies showed that aquaporin is required for dehydration, and hardening of bio-silica following its enzymatic formation. The data show that in cell aggregates grown in the presence of Mn-sulfate, aquaporin-8 is down-regulated. We conclude that in cell aggregates grown in the presence of Mn-sulfate, the removal of reaction water, produced during the bio-silica polycondensation reaction, is inhibited. General significance: This study highlights that besides the silicatein-driven polycondensation reaction, the spicule formation also requires a phase of syneresis that results in a hardening of the material. [Copyright &y& Elsevier]

Abstract: Rare earth element (REE) patterns of fossil bones and teeth are widely used as proxies for provenance, taphonomy, and palaeoenvironment. In order to investigate if fossil bones behave as closed systems over geologic time, REE profiles were analysed by LA-ICPMS along cross sections of 54 bones from various well-characterised and well-dated settings. These include terrestrial and marine diagenetic environments, covering Early Triassic to Holocene ages. In general, all fossil bones exhibit the highest REE concentrations at the outer rim, gradually decreasing by up to four orders of magnitude toward the inner bone cortex. Intra-bone REE concentration gradients decrease significantly from Quaternary via Tertiary to Mesozoic specimens, suggesting long term REE uptake and open system behaviour of fossil bone. This view is further corroborated by 176Lu–176Hf dating of selected samples, all yielding significantly younger ages than the known chronostratigraphic ages. Hence, there is clear evidence for long term open system behaviour of fossil bones with respect to REE, which is in marked contrast to currently accepted models suggesting that REE uptake is only early diagenetic. Although unexpected, statistically significant four to seven point isochrons are observed for four fossil dinosaur bone samples and one Upper Triassic Mastodonsaurus tooth with MSWDs ranging from 0.083 to 4.5. Notably, mobility of Lu alone cannot account for the observed age patterns. Assuming constant Lu uptake rates over time, the radiometric ages should only be as low as half of the chronostratigraphic age. However, a six-point isochron defined by subsamples of a single Upper Triassic Mastodonsaurus tooth yields an age of 65.2±1.1Ma (MSWD=0.68), much younger than half of the stratigraphic age (ca. 234Ma). Hence, Hf must also undergo late diagenetic exchange. Likely mechanisms to account for the presence of statistically meaningful isochrons as well as for the late diagenetic exchange of both REE and Hf are diffusion, adsorption, and dissolution–reprecipitation processes. [Copyright &y& Elsevier]