Simone A. Kasemann

MPI‐DING reference glasses for in situ microanalysis: New reference values for element concentrations and isotope ratios

We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties (at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive (isotope dilution) and comparative bulk (e.g., INAA, ICPMS, SSMS) and microanalytical (e.g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented.

Ocean acidification and the Permo-Triassic mass extinction

Ocean acidification and mass extinction The largest mass extinction in Earths history occurred at the Permian-Triassic boundary 252 million years ago. Several ideas have been proposed for what devastated marine life, but scant direct evidence exists. Clarkson et al. measured boron isotopes across this period as a highly sensitive proxy for seawater pH. It appears that, although the oceans buffered the acidifiying effects of carbon release from contemporary pulses of volcanism, buffering failed when volcanism increased during the formation of the Siberian Traps. The result was a widespread drop in ocean pH and the elimination of shell-forming organisms. Science, this issue p. 229 A rapid injection of massive amounts of carbon into the atmosphere acidified the oceans, causing mass extinction. Ocean acidification triggered by Siberian Trap volcanism was a possible kill mechanism for the Permo-Triassic Boundary mass extinction, but direct evidence for an acidification event is lacking. We present a high-resolution seawater pH record across this interval, using boron isotope data combined with a quantitative modeling approach. In the latest Permian, increased ocean alkalinity primed the Earth system with a low level of atmospheric CO2 and a high ocean buffering capacity. The first phase of extinction was coincident with a slow injection of carbon into the atmosphere, and ocean pH remained stable. During the second extinction pulse, however, a rapid and large injection of carbon caused an abrupt acidification event that drove the preferential loss of heavily calcified marine biota.

Surviving mass extinction by bridging the benthic/planktic divide

Evolution of planktic organisms from benthic ancestors is commonly thought to represent unidirectional expansion into new ecological domains, possibly only once per clade. For foraminifera, this evolutionary expansion occurred in the Early–Middle Jurassic, and all living and extinct planktic foraminifera have been placed within 1 clade, the Suborder Globigerinina. The subsequent radiation of planktic foraminifera in the Jurassic and Cretaceous resulted in highly diverse assemblages, which suffered mass extinction at the end of the Cretaceous, leaving an impoverished assemblage dominated by microperforate triserial and biserial forms. The few survivor species radiated to form diverse assemblages once again in the Cenozoic. There have, however, long been doubts regarding the monophyletic origin of planktic foraminifera. We present surprising but conclusive genetic evidence that the Recent biserial planktic Streptochilus globigerus belongs to the same biological species as the benthic Bolivina variabilis, and geochemical evidence that this ecologically flexible species actively grows within the open-ocean surface waters, thus occupying both planktic and benthic domains. Such a lifestyle (tychopelagic) had not been recognized as adapted by foraminifera. Tychopelagic are endowed with great ecological advantage, enabling rapid recolonization of the extinction-susceptible pelagic domain from the benthos. We argue that the existence of such forms must be considered in resolving foraminiferal phylogeny.

Neoproterozoic ice ages, boron isotopes, and ocean acidification: implications for a snowball Earth

The Neoproterozoic Earth underwent at least two severe glaciations, each extending to low paleomagnetic latitudes and punctuating warmer climates. The two widespread older and younger Cryogenian glacial deposits in Namibia are directly overlain by cap carbonates deposited under inferred periods of high atmospheric carbon dioxide concentrations. Oceanic uptake of carbon dioxide decreases ocean pH; here we present a record of Cryogenian interglacial ocean pH, based on boron (B) isotopes in marine carbonates. Our data suggest a largely constant ocean pH and no critically elevated p CO 2 throughout the older postglacial and interglacial periods. In contrast, a marked ocean acidification event marks the younger deglaciation period and is compatible with elevated postglacial p CO 2 concentration. Our data are consistent with the presence of two panglacial climate states in the Cryogenian, but indicate that each had its own distinct environmental conditions.

Boron in central Andean ignimbrites: implications for crustal boron cycles in an active continental margin

Abstract Calc-alkaline pumices and lavas from the Neogene–Pleistocene central Andean Altiplano–Puna Volcanic Complex (APVC) contain quartz phenocrysts with abundant primary melt inclusions. Melt inclusions represent the melt composition of dacitic to rhyodacitic magmas prior to eruption and they are widely protected from eruptive degassing, low-temperature vapor-phase alteration and post-depositional contamination with boron-rich dusts and aerosols. The average boron isotopic compositions of melt inclusion and matrix glasses are uniform in the units studied (overall average δ 11 B=−3.8±2.8‰, 1 SD) and overlap with the range of local basement rocks ( δ 11 B=−11‰ to −5‰). B is enriched in glasses (55±14 ppm, 1 SD), whereas whole-rock contents range between 10 and 40 ppm. At similar B contents, incompatible trace element ratios like B/Nb are generally higher in the ignimbrites and lavas (B/Nb=2.4 and 4.0) than in crustally derived Paleozoic to Cretaceous granitoids from NW-Argentina (B/Nb=1.0–2.7). This suggests a minor contribution of high-B/Nb arc andesites and is consistent with petrogenetic models in which APVC dacites originated from hybridization of dominantly crustally derived melts with andesitic magmas. Boron-rich hydrothermal brines and salt-lake water from within the APVC have δ 11 B=−4.1 to +5.7‰. These values are close to the APVC ignimbrite values and contrast with hydrothermal brines from the eastern Puna and eastern Cordillera, which have lower δ 11 B=−10‰ to −17‰ and occur in an area of little volcanic cover. This regional pattern suggests that borate enrichments resulted from the leaching of local country rocks: ignimbrites in the W Altiplano–Puna and Paleozoic basement in the eastern Puna and eastern Cordillera.

Dynamic anoxic ferruginous conditions during the end-Permian mass extinction and recovery

The end-Permian mass extinction, ∼252 million years ago, is notable for a complex recovery period of ∼5 Myr. Widespread euxinic (anoxic and sulfidic) oceanic conditions have been proposed as both extinction mechanism and explanation for the protracted recovery period, yet the vertical distribution of anoxia in the water column and its temporal dynamics through this time period are poorly constrained. Here we utilize Fe–S–C systematics integrated with palaeontological observations to reconstruct a complete ocean redox history for the Late Permian to Early Triassic, using multiple sections across a shelf-to-basin transect on the Arabian Margin (Neo-Tethyan Ocean). In contrast to elsewhere, we show that anoxic non-sulfidic (ferruginous), rather than euxinic, conditions were prevalent in the Neo-Tethys. The Arabian Margin record demonstrates the repeated expansion of ferruginous conditions with the distal slope being the focus of anoxia at these times, as well as short-lived episodes of oxia that supported diverse biota.

Ocean acidification in the aftermath of the Marinoan glaciation

Boron isotope patterns preserved in cap carbonates deposited in the aftermath of the younger Cryogenian (Marinoan, ca. 635 Ma) glaciation confirm a temporary ocean acidification event on the continental margin of the southern Congo craton, Namibia. To test the significance of this acidification event and reconstruct Earth’s global seawater pH states at the Cryogenian-Ediacaran transition, we present a new boron isotope data set recorded in cap carbonates deposited on the Yangtze Platform in south China and on the Karatau microcontinent in Kazakhstan. Our compiled δ11B data reveal similar ocean pH patterns for all investigated cratons and confirm the presence of a global and synchronous ocean acidification event during the Marinoan deglacial period, compatible with elevated postglacial p CO2 concentrations. Differences in the details of the ocean acidification event point to regional distinctions in the buffering capacity of Ediacaran seawater.

Deformation-controlled cation diffusion in tourmaline: A microanalytical study on trace elements and boron isotopes

Abstract Plastic deformation of variable intensity has modified primary textures, composition, and element distribution in tourmaline from a mylonitic pegmatite from the NW Argentinean Sierras Pampeanas. The primary concentric tourmaline zonation has been overprinted and partly destroyed by synkinematic cation diffusion that occurred under amphibolite-facies P-T conditions. Textural changes include bending of crystals, formation of subgrains, and subgrain rotation, leading locally to recrystallization of tourmaline. Some parts of deformed crystals were less affected or unaffected by plastic deformation and secondary cation diffusion. Two principal processes, intracrystal trace-element diffusion and matrix exchange of trace-elements, caused the compositional variations in deformed tourmaline domains. Intracrystal diffusion partly or completely destroyed the primary trace-element zonation by cation diffusion from zones of high to low concentration. Small cations occupying the Y-position are readily mobilized even by weak deformation, whereas large cations on the X-site require higher deformation intensity to be mobilized and show less pronounced or no homogenization of the primary zonation. Matrix exchange between tourmaline and co-existing solid or fluid phases generally leads to trace-element loss from deformed tourmaline domains. The extent of the matrix exchange is primarily controlled by the compatibility of mobilized cation species with matrix phases during mylonitization. In contrast, the B-isotopic compositions in deformed and undeformed crystal domains are uniform, indicating absence of significant B diffusion and isotope fractionation during crystal growth and plastic deformation; i.e., the activation energy to move B in tourmaline must be too high even for intense plastic deformation to overcome.

The influences of growth rates on planktic foraminifers as proxies for palaeostudies – a review

Abstract Size dependent changes in element concentrations in planktic foraminifers have long been recognized to influence their reliability as an archive for climate change. Traditionally, these changes have been interpreted as changes in element partitioning during the ontogeny of the organism with faster growth rates in the earlier part of the development. These changes, in the light of new culture experiments, can also be interpreted as changes in growth rate throughout the entire life of the organism, with larger, faster-growing specimens discriminating less efficiently against trace element incorporation into the calcite shell. Growth rates of foraminifera are influenced by the environment and hence change geographically and temporally at various scales, e.g. glacial-interglacial or rapid millennial events such as the Younger Dryas. These changes in growth rate can account for some changes in element to calcium ratio between glacial and interglacials, which were previously linked to changes in seawater element ratios.

The stable isotope composition of nitrogen and carbon and elemental contents in modern and fossil seabird guano from Northern Chile – Marine sources and diagenetic effects

Seabird excrements (guano) have been preserved in the arid climate of Northern Chile since at least the Pliocene. The deposits of marine organic material in coastal areas potentially open a window into the present and past composition of the coastal ocean and its food web. We use the stable isotope composition of nitrogen and carbon as well as element contents to compare the principal prey of the birds, the Peruvian anchovy, with the composition of modern guano. We also investigate the impact of diagenetic changes on the isotopic composition and elemental contents of the pure ornithogenic sediments, starting with modern stratified deposits and extending to fossil guano. Where possible, 14C systematics is used for age information. The nitrogen and carbon isotopic composition of the marine prey (Peruvian anchovy) of the birds is complex as it shows strong systematic variations with latitude. The detailed study of a modern profile that represents a few years of guano deposition up to present reveals systematic changes in nitrogen and carbon isotopic composition towards heavier values that increase with age, i.e. depth. Only the uppermost, youngest layers of modern guano show compositional affinity to the prey of the birds. In the profile, the simultaneous loss of nitrogen and carbon occurs by degassing, and non-volatile elements like phosphorous and calcium are passively enriched in the residual guano. Fossil guano deposits are very low in nitrogen and low in carbon contents, and show very heavy nitrogen isotopic compositions. One result of the study is that the use of guano for tracing nitrogen and carbon isotopic and elemental composition in the marine food web of the birds is restricted to fresh material. Despite systematic changes during diagenesis, there is little promise to retrieve reliable values of marine nitrogen and carbon signatures from older guano. However, the changes in isotopic composition from primary marine nitrogen isotopic signatures towards very heavy values generate a compositionally unique material. These compositions trace the presence of guano in natural ecosystems and its use as fertilizer in present and past agriculture.