Effective graviton mass in de Sitter space

We calculate the effective mass of gravitational perturbations induced by the interaction of the classical gravitational field with quantum matter in the background of the Poincar\'e patch of de Sitter space. Using the Schwinger-Keldysh diagrammatic technique, the one-loop effective action is calculated and it is shown that the graviton does not acquire mass for the most symmetric Bunch-Davies state. However, we have shown that even in this case, there is a nontrivial modification of the theory at one loop in the scalar sector of gravity.Comment: 35 pages, 5 figure

Advancing planktonic foraminifera Mg/Ca thermometry: a microanalytical perspective

Microanalytical techniques, specifically laser ablation - inductively coupled plasma mass spectrometry (LA-ICPMS) and electron microprobe analysis(EMPA), have been used to determine Mg/Ca compositional variation within and between tests of planktonic foraminifera. Micro-scale characterization of this increasingly widely-used seawater temperature proxy has allowed scrutiny of the factors that limit its applicability as well as the development of new microanalysis-based Mg/Ca proxy calibrations for sea surface temperature and thermocline temperatures...This study illustrates the potential for using novel microanalytical techniques to advance Mg/Ca thermometry, by both providing a framework for better understanding the nature of Mg/Ca dependence on seawater temperature and the effects of complicating factors (e.g. seafloor dissolution, seasonality), as well as providing insight into the underlying biomineralization mechanisms that control Mg incorporation into and the formation of foraminiferal calcite.Australian Research Council- via an ARC Discovery Grant DP0450358 to Prof. De Deckker and Dr. Eggins. The Australian National University by a tuition fee scholarship

Intraspecific variation in recent populations of Globigerinoides ruber from the eastern Indian Ocean: evidence from test morphology and geochemistry

Abstrac

Unmovable Detection Unit of the Thermal Neutron Flux in the Source Range of the Reactor

This paper presents the results of theoretical and experimental research of the new unmovable detection unit of the thermal neutron flux in the source range of the reactor. The design features and the main parameters of this unit are also shown

The effect of ocean alkalinity and carbon transfer on deep-sea carbonate ion concentration during the past five glacial cycles

Glacial–interglacial deep Indo-Pacific carbonate ion concentration ([CO32−]) changes were mainly driven by two mechanisms that operated on different timescales: 1) a long-term increase during glaciation caused by a carbonate deposition reduction on shelves (i.e., the coral reef hypothesis), and 2) transient carbonate compensation responses to deep ocean carbon storage changes. To investigate these mechanisms, we have used benthic foraminiferal B/Ca to reconstruct deep-water [CO32−] in cores from the deep Indian and Equatorial Pacific Oceans during the past five glacial cycles. Based on our reconstructions, we suggest that the shelf-to-basin shift of carbonate deposition raised deep-water [CO32−], on average, by 7.3 ± 0.5 (SE) μmol/kg during glaciations. Oceanic carbon reorganisations during major climatic transitions caused deep-water [CO32−] deviations away from the long-term trend, and carbonate compensation processes subsequently acted to restore the ocean carbonate system to new steady state conditions. Deep-water [CO32−] showed similar patterns to sediment carbonate content (%CaCO3) records on glacial–interglacial timescales, suggesting that past seafloor %CaCO3 variations were dominated by deep-water carbonate preservation changes at our studied sites

Li Partitioning Into Coccoliths of Emiliania huxleyi : Evaluating the General Role of “Vital Effects” in Explaining Element Partitioning in Biogenic Carbonates

Emiliania huxleyi cells were grown in artificial seawater of different Li and Ca concentrations and coccolith Li/Ca ratios determined. Coccolith Li/Ca ratios were positively correlated to seawater Li/Ca ratios only if the seawater Li concentration was changed, not if the seawater Ca concentration was changed. This Li partitioning pattern of E. huxleyi was previously also observed in the benthic foraminifer Amphistegina lessonii and inorganically precipitated calcite. We argue that Li partitioning in both E. huxleyi and A. lessonii is dominated by a coupled transmembrane transport of Li and Ca from seawater to the site of calcification. We present a refined version of a recently proposed transmembrane transport model for Li and Ca. The model assumes that Li and Ca enter the cell via Ca channels, the Li flux being dependent on the Ca flux. While the original model features a linear function to describe the experimental data, our refined version uses a power function, changing the stoichiometry of Li and Ca. The version presented here accurately predicts the observed dependence of DLi on seawater Li/Ca ratios. Our data demonstrate that minor element partitioning in calcifying organisms is partly mediated by biological processes even if the partitioning behavior of the calcifying organism is indistinguishable from that of inorganically precipitated calcium carbonate

Late Holocene droughts in the Fertile Crescent recorded in a speleothem from northern Iraq

Droughts have had large impacts on past and present societies. High-resolution paleoclimate data are essential to place recent droughts in a meaningful historical context and to predict regional future changes with greater accuracy. Such records, however, are very scarce in the Middle East in general, and the Fertile Crescent in particular. Here we present a 2400 year long speleothem-based multiproxy record from Gejkar Cave in northern Iraq. Oxygen and carbon isotopes and magnesium are faithful recorders of effective moisture. The new Gejkar record not only shows that droughts in 1998–2000 and 2007–2010, which have been argued to be a contributing factor to Syrian civil war, were extreme compared to the current mean climate, but they were also superimposed on a long-term aridification trend that already started around or before 950 C.E. (Common Era). This long-term trend is not captured by tree ring records and climate models, emphasizing the importance of using various paleoclimate proxy data to evaluate and improve climate models and to correctly inform policy makers about future hydroclimatic changes in this drought-prone region

Wildfires enhance phytoplankton production in tropical oceans

Unidad de excelencia María de Maeztu CEX2019-000940-MWildfire magnitude and frequency have greatly escalated on a global scale. Wildfire products rich in biogenic elements can enter the ocean through atmospheric and river inputs, but their contribution to marine phytoplankton production is poorly understood. Here, using geochemical paleo-reconstructions, a century-long relationship between wildfire magnitude and marine phytoplankton production is established in a fire-prone region of Kimberley coast, Australia. A positive correlation is identified between wildfire and phytoplankton production on a decadal scale. The importance of wildfire on marine phytoplankton production is statistically higher than that of tropical cyclones and rainfall, when strong El Niño Southern Oscillation coincides with the positive phase of Indian Ocean Dipole. Interdecadal chlorophyll-a variation along the Kimberley coast validates the spatial connection of this phenomenon. Findings from this study suggest that the role of additional nutrients from wildfires has to be considered when projecting impacts of global warming on marine phytoplankton production

Elemental Uptake by Calcite Slowly Grown From Seawater Solution: An in-situ Study via Depth Profiling

Crystal growth rate has not been sufficiently explored to understand element partitioning between calcite and seawater solutions. We investigated the uptake of Li, B, Mg, Sr, and Ba by Mg-bearing calcite slowly grown on a calcite cleavage fragment. Experiments were conducted by elevating the alkalinity of an artificial seawater solution. Growth rates were evaluated by addition of lanthanum spike. At the end of each experiment, cleavage fragments were extracted and examined with micro-Raman spectroscopy, scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using depth profiling technique. Distribution of Li, B, Mg, Sr, and Ba in calcite overgrowth as well as partition coefficients of those elements were evaluated

Deglacial-Holocene Pulses of Old Carbon-Enriched Mediterranean Water Masses: Implications for Aragonite Mounds Growth and Global Carbon Cycle

Major changes in the Mediterranean Thermohaline Circulation (MedTHC) related to deglaciation and monsoon dynamics have been documented, while in turn, Mediterranean waters have been proposed to play a role back in global climate variability, ocean circulation and carbon cycle budgets, for instance via changes in water mass residence times. The 14C offset between coeval planktonic and benthic foraminifera over time is a very useful tool to infer variations in the water column ventilation (with no biological interference) that becomes more accurate when combined with local paired 14C-U/Th analyses in cold-water corals (CWC). Here, we present a multi-proxy-archive study (i.e., estimates of reservoir ages, εNd, [CO3 2-], O2 and current speed) carried out on the on-mound sediment core MD13-3452 (305 m, West Melilla, Alboran Sea, Western Mediterranean), which investigates potential deglacial changes and triggers in deep reservoir ages, as well as possible impacts on CWC aragonite mound growth and on global carbon cycle.Our combined foraminifera-CWC radioactive isotopes results show: 1) the arrival of two pulses of aged waters at intermediate depth corresponding to the Younger Dryas (YD) and to the end of the last sapropel (S1), when low CWC mound growth rates dominated, and 2) a very well-ventilated water mass between those two events, parallel to a CWC mound flourishing stage. In combination with the other proxies, poorer ventilated water pulses seem to have had a different origin, but common higher content in respired carbon. Our results allow, for the first time, changes in ventilation rates to be shown, quantified, and timed in association with a periodical MedTHC weakening, as well as suggesting significant aragonite dissolution as a cause of decreased mound growth rate when higher CO2 episodes. Our findings may have implications for past hydrographic interconnexions between Mediterranean basins and for global marine carbon storage and alkalinity budget in particular