Rapid grain boundary diffusion in foraminifera tests biases paleotemperature records.

The oxygen isotopic compositions of fossil foraminifera tests constitute a continuous proxy record of deep-ocean and sea-surface temperatures spanning the last 120 million years. Here, by incubating foraminifera tests in 18O-enriched artificial seawater analogues, we demonstrate that the oxygen isotopic composition of optically translucent, i.e., glassy, fossil foraminifera calcite tests can be measurably altered at low temperatures through rapid oxygen grain-boundary diffusion without any visible ultrastructural changes. Oxygen grain boundary diffusion occurs sufficiently fast in foraminifera tests that, under normal upper oceanic sediment conditions, their grain boundaries will be in oxygen isotopic equilibrium with the surrounding pore fluids on a time scale of <100 years, resulting in a notable but correctable bias of the paleotemperature record. When applied to paleotemperatures from 38,400 foraminifera tests used in paleoclimate reconstructions, grain boundary diffusion can be shown to bias prior paleotemperature estimates by as much as +0.86 to -0.46 °C. The process is general and grain boundary diffusion corrections can be applied to other polycrystalline biocarbonates composed of small nanocrystallites (<100 nm), such as those produced by corals, brachiopods, belemnites, and molluscs, the fossils of which are all highly susceptible to the effects of grain boundary diffusion.

A Unitary Association-based conodont biozonation of the Smithian-Spathian boundary (Early Triassic) and associated biotic crisis from South China.

The Smithian-Spathian boundary (SSB) crisis played a prominent role in resetting the evolution and diversity of the nekton (ammonoids and conodonts) during the Early Triassic recovery. The late Smithian nektonic crisis culminated at the SSB, ca. 2.7 Myr after the Permian-Triassic boundary mass extinction. An accurate and high-resolution biochronological frame is needed for establishing patterns of extinction and re-diversification of this crisis. Here, we propose a new biochronological frame for conodonts that is based on the Unitary Associations Method (UAM). In this new time frame, the SSB can thus be placed between the climax of the extinction and the onset of the re-diversification. Based on the study of new and rich conodont collections obtained from five sections (of which four are newly described here) in the Nanpanjiang Basin, South China, we have performed a thorough taxonomical revision and described one new genus and 21 new species. Additionally, we have critically reassessed the published conodont data from 16 other sections from South China, and we have used this new, standardized dataset to construct the most accurate, highly resolved, and laterally reproducible biozonation of the Smithian to early Spathian interval for South China. The resulting 11 Unitary Association Zones (UAZ) are intercalibrated with lithological and chemostratigraphical (δ13Ccarb) markers, as well as with ammonoid zones, thus providing a firm basis for an evolutionary meaningful and laterally consistent definition of the SSB. Our UAZ8, which is characterized by the occurrence of Icriospathodus ex gr. crassatus, Triassospathodus symmetricus and Novispathodus brevissimus, is marked by a new evolutionary radiation of both conodonts and ammonoids and is within a positive peak in the carbon isotope record. Consequently, we propose to place the SSB within the separation interval intercalated between UAZ7 and UAZ8 thus leaving some flexibility for future refinement and updating. Supplementary Information: The online version contains supplementary material available at 10.1186/s13358-022-00259-x.

Kinetic oxygen isotope fractionation upon acid liberation of CO2 from artificial and natural norsethite (BaMg(CO3 )2 ), a mineral analogue of dolomite.

RATIONALE: The analytical method to determine the stable oxygen isotope (18 O/16 O) composition of carbonates via phosphoric acid digestion leads to temperature- and solid-dependent kinetic isotope fractionation. Values for the double carbonate norsethite (BaMg(CO3 )2 ) have been unknown so far. METHODS: The temperature dependence of kinetic oxygen isotope fractionation during the reaction of synthetic and natural BaMg(CO3 )2 with orthophosphoric acid (H3 PO4 ) according to the overall reaction BaMg(CO3 )2 + 2H3 PO4 = Ba2+ + Mg2+ + 2HPO4 2- + 2CO2 + 2H2 O has been examined for the first time using separate carbonate decomposition via fluorination or phosphoric acid digestion, with the resulting gases analyzed by isotope ratio monitoring mass spectrometry. RESULTS: In the temperature range between 25 and 70°C the kinetic fractionation factor between acid-generated CO2 and artificial and natural norsethite is described by (T in K): [Formula: see text] with A = 4.15 and B = 6.47 for natural norsethite, and A = 4.77 and B = 5.94 for synthetic norsethite. The fractionation factor measured for a poorly crystallized synthetic carbonate agrees with those for the other samples at 25°C, but is slightly lower at 50 and 70°C. No carbon isotope fractionation was found during the unidirectional acid dissolution. CONCLUSIONS: The kinetic oxygen isotope fractionation during phosphoric acid liberation of CO2 from BaMg(CO3 )2 is quantified. Based on published results for endmember carbonates, the results at 25°C for other double carbonates are estimated.

Fast and pervasive diagenetic isotope exchange in foraminifera tests is species-dependent.

Oxygen isotope compositions of fossil foraminifera tests are commonly used proxies for ocean paleotemperatures, with reconstructions spanning the last 112 million years. However, the isotopic composition of these calcitic tests can be substantially altered during diagenesis without discernible textural changes. Here, we investigate fluid-mediated isotopic exchange in pristine tests of three modern benthic foraminifera species (Ammonia sp., Haynesina germanica, and Amphistegina lessonii) following immersion into an 18O-enriched artificial seawater at 90 °C for hours to days. Reacted tests remain texturally pristine but their bulk oxygen isotope compositions reveal rapid and species-dependent isotopic exchange with the water. NanoSIMS imaging reveals the 3-dimensional intra-test distributions of 18O-enrichment that correlates with test ultra-structure and associated organic matter. Image analysis is used to quantify species level differences in test ultrastructure, which explains the observed species-dependent rates of isotopic exchange. Consequently, even tests considered texturally pristine for paleo-climatic reconstruction purposes may have experienced substantial isotopic exchange; critical paleo-temperature record re-examination is warranted.

Sedimentary organic matter from a cored Early Triassic succession, Georgetown (Idaho, USA).

The plant fossil record from Lower Triassic sedimentary successions of the Western USA is extremely meager. In this study, samples from a drill core taken near Georgetown, Idaho, were analyzed for their palynological content as well as their stable carbon isotope composition. The concentration of palynomorphs is generally low. The lowermost part of the drilled succession represents Dinwoody/Woodside Formation and contains spore and pollen assemblages with Permian and Early Triassic affinity. Representatives of lycophytes (Densoisporites spp., Lundbladisporites spp.) were found in the overlying Meekoceras Limestone, in agreement with middle Smithian assemblages elsewhere. Ammonoids and conodonts are extremely rare, but confirm a middle Smithian age. Bulk organic and carbonate carbon isotope composition provide a stratigraphic framework. Carbonate carbon isotope compositions are compatible with the Smithian-Spathian global trend, with a middle Smithian shift towards lower δ13C values followed by a late Smithian shift towards higher values. Bulk organic carbon isotope compositions have been influenced by changes in the constitution of organic matter. A comparison with other paired carbon isotope datasets from the same basin is difficult due to lithostratigraphic inconsistencies (Hot Springs, ID) or biochemical mediated disturbance of isotope signals (Mineral Mountains, UT).

The driving mechanisms of the carbon cycle perturbations in the late Pliensbachian (Early Jurassic).

The Early Jurassic (late Pliensbachian to early Toarcian) was a period marked by extinctions, climate fluctuations, and oceanic anoxia. Although the causes of the early Toarcian Oceanic Anoxia Event (OAE) have been fairly well studied, the events that lead to the Toarcian OAE, i.e. the events in the late Pliensbachian, have not been well constrained. Scenarios of the driving mechanism of biotic and environmental changes of the late Pliensbachian have ranged from LIP volcanism (the Karoo-Ferrar LIP), ocean stagnation, and changing ocean circulation, to orbital forcing. The temporal relationship between the Karoo LIP and the late Pliensbachian (Kunae-Carlottense ammonite Zones) are investigated in an effort to evaluate a causal relationship. We present the first absolute timescale on the Kunae and Carlottense Zones based on precise high-precision U-Pb geochronology, and additional geochemical proxies, for a range of environmental proxies such as bulk organic carbon isotope compositions, Hg concentration, and Hg/TOC ratios, and Re-Os isotopes to further explore their causal relationship. The data presented here show that causality between the Karoo LIP and the late Pliensbachian events cannot be maintained.

Metamorphic pressure variation in a coherent Alpine nappe challenges lithostatic pressure paradigm.

Pressure-temperature-time paths obtained from minerals in metamorphic rocks allow the reconstruction of the geodynamic evolution of mountain ranges under the assumption that rock pressure is lithostatic. This lithostatic pressure paradigm enables converting the metamorphic pressure directly into the rock's burial depth and, hence, quantifying the rock's burial and exhumation history. In the coherent Monte Rosa tectonic unit, Western Alps, considerably different metamorphic pressures are determined in adjacent rocks. Here we show with field and microstructural observations, phase petrology and geochemistry that these pressure differences cannot be explained by tectonic mixing, retrogression of high-pressure minerals, or lack of equilibration of mineral assemblages. We propose that the determined pressure difference of 0.8 ± 0.3 GPa is due to deviation from lithostatic pressure. We show with two analytical solutions for compression- and reaction-induced stress in mechanically heterogeneous rock that such pressure differences are mechanically feasible, supporting our interpretation of significant outcrop-scale pressure gradients.

Unexpected large evasion fluxes of carbon dioxide from turbulent streams draining the world's mountains.

Inland waters, including streams and rivers, are active components of the global carbon cycle. Despite the large areal extent of the world's mountains, the role of mountain streams for global carbon fluxes remains elusive. Using recent insights from gas exchange in turbulent streams, we found that areal CO2 evasion fluxes from mountain streams equal or exceed those reported from tropical and boreal streams, typically regarded as hotspots of aquatic carbon fluxes. At the regional scale of the Swiss Alps, we present evidence that emitted CO2 derives from lithogenic and biogenic sources within the catchment and delivered by the groundwater to the streams. At a global scale, we estimate the CO2 evasion from mountain streams to 167 ± 1.5 Tg C yr-1, which is high given their relatively low areal contribution to the global stream and river networks. Our findings shed new light on mountain streams for global carbon fluxes.

Bacterial spores, from ecology to biotechnology.

The production of a highly specialized cell structure called a spore is a remarkable example of a survival strategy displayed by bacteria in response to challenging environmental conditions. The detailed analysis and description of the process of sporulation in selected model organisms have generated a solid background to understand the cellular processes leading to the formation of this specialized cell. However, much less is known regarding the ecology of spore-formers. This research gap needs to be filled as the feature of resistance has important implications not only on the survival of spore-formers and their ecology, but also on the use of spores for environmental prospection and biotechnological applications.

Neogene sharks and rays from the Brazilian 'Blue Amazon'.

The lower Miocene Pirabas Formation in the North of Brazil was deposited under influence of the proto-Amazon River and is characterized by large changes in the ecological niches from the early Miocene onwards. To evaluate these ecological changes, the elasmobranch fauna of the fully marine, carbonate-rich beds was investigated. A diverse fauna with 24 taxa of sharks and rays was identified with the dominant groups being carcharhiniforms and myliobatiforms. This faunal composition is similar to other early Miocene assemblages from the proto-Carribbean bioprovince. However, the Pirabas Formation has unique features compared to the other localities; being the only Neogene fossil fish assemblage described from the Atlantic coast of Tropical Americas. Phosphate oxygen isotope composition of elasmobranch teeth served as proxies for paleotemperatures and paleoecology. The data are compatible with a predominantly tropical marine setting with recognized inshore and offshore habitats with some probable depth preferences (e.g., Aetomylaeus groups). Paleohabitat of taxa particularly found in the Neogene of the Americas (†Carcharhinus ackermannii, †Aetomylaeus cubensis) are estimated to have been principally coastal and shallow waters. Larger variation among the few analyzed modern selachians reflects a larger range for the isotopic composition of recent seawater compared to the early Miocene. This probably links to an increased influence of the Amazon River in the coastal regions during the Holocene.

Application of δ(18)O, δ(13)CDIC, and major ions to evaluate micropollutant sources in the Bay of Vidy, Lake Geneva.

Waters were sampled monthly from a profile at the wastewater outlet and a reference point in the Bay of Vidy (Lake Geneva) for a year. The samples were analyzed for (18)O/(16)O of water, (13)C/(12)C of dissolved inorganic carbon (DIC), major ions, and selected micropollutant concentrations. δ(18)O values, combined with the major ion concentrations, allowed discharged waste and storm-drainage water to be traced within the water column. On the basis of δ(18)O values, mole fractions of wastewater (up to 45 %), storm-drainage (up to 16 %), and interflowing Rhône River water (up to 34 %) could be determined. The results suggest that the stormwater fractions do not influence micropollutant concentrations in a measurable way. In contrast, the Rhône River interflow coincides with elevated concentrations of Rhône River-derived micropollutants in some profiles. δ(13)C values of DIC suggest that an increase in micropollutant concentrations at the sediment-water interface could be related to remineralization processes or resuspension.

Linking megathrust earthquakes to brittle deformation in a fossil accretionary complex.

Seismological data from recent subduction earthquakes suggest that megathrust earthquakes induce transient stress changes in the upper plate that shift accretionary wedges into an unstable state. These stress changes have, however, never been linked to geological structures preserved in fossil accretionary complexes. The importance of coseismically induced wedge failure has therefore remained largely elusive. Here we show that brittle faulting and vein formation in the palaeo-accretionary complex of the European Alps record stress changes generated by subduction-related earthquakes. Early veins formed at shallow levels by bedding-parallel shear during coseismic compression of the outer wedge. In contrast, subsequent vein formation occurred by normal faulting and extensional fracturing at deeper levels in response to coseismic extension of the inner wedge. Our study demonstrates how mineral veins can be used to reveal the dynamics of outer and inner wedges, which respond in opposite ways to megathrust earthquakes by compressional and extensional faulting, respectively.

Caution on the use of NBS 30 biotite for hydrogen-isotope measurements with on-line high-temperature conversion systems.

RATIONALE: The supply of NBS 30 biotite is nearly exhausted. During measurements of NBS 30 and potential replacements, reproducible δ(2)HVSMOW-SLAP values could not be obtained by three laboratories using high-temperature conversion (HTC) systems. The cause of this issue has been investigated using the silver-tube technique for hydrogen-isotope measurements of water. METHODS: The δ(2)HVSMOW-SLAP values of NBS 30 biotite, other biotites, muscovites, and kaolinite with different particle sizes, along with IAEA-CH-7 polyethylene, and reference waters and NBS 22 oil that were sealed in silver-tube segments, were measured. The effect of absorbed water on mineral surfaces was investigated with waters both enriched and depleted in (2)H. The quantitative conversion of hydrogen from biotite into gaseous hydrogen as a function of mass and particle size was also investigated. RESULTS: The δ(2)HVSMOW-SLAP values of NBS 30 obtained by three laboratories were as much as 21 ‰ too high compared with the accepted value of -65.7 ‰, determined by conventional off-line measurements. The experiments showed a strong correlation between grain size and the δ(2)HVSMOW-SLAP value of NBS 30 biotite, but not of biotites with lower iron content. The δ(2)HVSMOW-SLAP values of NBS 30 as a function of particle size show a clear trend toward -65.7 ‰ with finer grain size. CONCLUSIONS: Determination of the δ(2)HVSMOW-SLAP values of hydrous minerals and of NBS 30 biotite by on-line HTC systems coupled to isotope-ratio mass spectrometers may be unreliable because hydrogen in this biotite may not be converted quantitatively into molecular hydrogen. Extreme caution in the use and interpretation of δ(2)HVSMOW-SLAP on-line measurements of hydrous minerals is recommended.

Opportunistic feeding strategy for the earliest old world hypsodont equids: evidence from stable isotope and dental wear proxies.

BACKGROUND: The equid Hippotherium primigenium, with moderately hypsodont cheek teeth, rapidly dispersed through Eurasia in the early late Miocene. This dispersal of hipparions into the Old World represents a major faunal event during the Neogene. The reasons for this fast dispersal of H. primigenium within Europe are still unclear. Based on its hypsodonty, a high specialization in grazing is assumed although the feeding ecology of the earliest European hipparionines within a pure C3 plant ecosystem remains to be investigated. METHODOLOGY/PRINCIPAL FINDINGS: A multi-proxy approach, combining carbon and oxygen isotopes from enamel as well as dental meso- and microwear analyses of cheek teeth, was used to characterize the diet of the earliest European H. primigenium populations from four early Late Miocene localities in Germany (Eppelsheim, Höwenegg), Switzerland (Charmoille), and France (Soblay). Enamel δ(13)C values indicate a pure C3 plant diet with small (<1.4‰) seasonal variations for all four H. primigenium populations. Dental wear and carbon isotope compositions are compatible with dietary differences. Except for the Höwenegg hipparionines, dental microwear data indicate a browse-dominated diet. By contrast, the tooth mesowear patterns of all populations range from low to high abrasion suggesting a wide spectrum of food resources. CONCLUSIONS/SIGNIFICANCE: Combined dental wear and stable isotope analysis enables refined palaeodietary reconstructions in C3 ecosystems. Different H. primigenium populations in Europe had a large spectrum of feeding habits with a high browsing component. The combination of specialized phenotypes such as hypsodont cheek teeth with a wide spectrum of diet illustrates a new example of the Liem's paradox. This dietary flexibility associated with the capability to exploit abrasive food such as grasses probably contributed to the rapid dispersal of hipparionines from North America into Eurasia and the fast replacement of the brachydont equid Anchitherium by the hypsodont H. primigenium in Europe.

Bronze Age volcanic event recorded in stalagmites by combined isotope and trace element studies.

Stable isotope analyses of speleothems (carbonate deposits formed in caves) have been widely used to reconstruct paleoenvironmental conditions. Recent improvements in geochemical techniques have enabled us to analyze climate-influenced deposits at high temporal resolution so that hitherto unrecognized environmental conditions may be identified. Stable H, C and O isotope analyses on carbonate and inclusion water have been combined with multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) age dating and laser-ablation ICP-MS trace element analyses on a stalagmite from southern Hungary. The study reveals significant changes in chemical and isotopic compositions of the speleothem between approx. 3800 and 3500 years BP ('Before Present') indicating coupled changes in the temperature and precipitation regime under which the speleothem formed. Stable isotopic and trace element correlations within this time period correlate with similar studies of stalagmites of comparable age from the Alpine-Mediterranean region. Our studies suggest that traces of deposition of volcanic dust, possibly related to the Thera eruption of Santorini (Greece) ca. 1650 BC (approximately 3650 BP), and environmental changes can be detected at a distance of several thousand kilometers.

The stable hydrogen and oxygen isotope variation of water stored in polyethylene terephthalate (PET) bottles.

A set of bottled waters from a single natural spring distributed worldwide in polyethylene terephthalate (PET) bottles has been used to examine the effects of storage in plastic polymer material on the isotopic composition (delta18O and delta2H values) of the water. All samples analyzed were subjected to the same packaging procedure but experienced different conditions of temperature and humidity during storage. Water sorption and the diffusive transfer of water and water vapor through the wall of the PET bottle may cause isotopic exchange between water within the bottle and water vapor in air near the PET-water interface. Changes of about +4 per thousand for delta2H and +0.7 per thousand for delta18O have been measured for water after 253 days of storage within the PET bottle. The results of this study clearly indicate the need to use glass bottles for storing water samples for isotopic studies. It is imperative to transfer PET-bottled natural waters to glass bottles for their use as calibration material or potential international working standards.