Last millennium decoupling of the South American Summer Monsoon and local hydroclimate of central Brazil

Thesis advisor: Corinne I. WongThe South American Monsoon System is the dominant convective system over tropical South America during austral summer that is critical to a region heavily dependent on agricultural and hydroelectric production. An understanding of the controls on moisture conditions throughout Brazil is critical to assessing recurrent droughts and global climate change responses. An increasing number of monsoon reconstructions from δ¹⁸O records provide insight into last millennium variation of regional monsoon intensity. However, the relationship between past variations in monsoon intensity and local moisture conditions has yet to be investigated. In this study, we develop speleothem ⁸⁷Sr/⁸⁶Sr values as a paleo-moisture proxy from a cave site located in central Brazil. Increasing speleothem ⁸⁷Sr/⁸⁶Sr values and decreasing δ²³⁴U values over the last millennium indicate progressively wetter conditions. A similar trend in monsoon intensity is not evident in δ¹⁸O records from the region, suggesting that monsoon intensity is decoupled from the local moisture conditions through the late Holocene. The potential decoupling between the monsoon and local moisture conditions suggests that processes independent from those governing monsoon intensity may play a critical role in dictating moisture variability in the region.Thesis (MS) — Boston College, 2016.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Earth and Environmental Sciences

Transfluthrin indoor air concentration and inhalation exposure during application of electric vaporizers

International audienceDifferent household insecticide applications via two electric vaporizers emitting transfluthrin were realized in a full-scale experimental room under controlled air exchange rate conditions. On-line high-time resolved measurements of the gas-phase concentrations of the active substance during and immediately after the spreading periods were performed with a High Sensitivity Proton-Transfer-Reaction Mass Spectrometer (HS-PTR-MS). Experimental and modelled data from the ConsExpo 4.0 software were also compared to evaluate the sources of differences. Different application scenarios were also compared. Averaged inhaled concentrations over 1h, 1week, and 5months were estimated to be 8.3, 1.8, and 1.8μg.m(-3), respectively. Corresponding margins of exposures range from 1000 to 10,000, claiming for the absence of effect. Dermal and dust ingestion pathways, although roughly estimated, seems being non-negligible. This claims for a more in-depth integrated risk assessment

Deweyan tools for inquiry and the epistemological context of critical pedagogy

This article develops the notion of resistance as articulated in the literature of critical pedagogy as being both culturally sponsored and cognitively manifested. To do so, the authors draw upon John Dewey\u27s conception of tools for inquiry. Dewey provides a way to conceptualize student resistance not as a form of willful disputation, but instead as a function of socialization into cultural models of thought that actively truncate inquiry. In other words, resistance can be construed as the cognitive and emotive dimensions of the ongoing failure of institutions to provide ideas that help individuals both recognize social problems and imagine possible solutions. Focusing on Dewey\u27s epistemological framework, specifically tools for inquiry, provides a way to grasp this problem. It also affords some innovative solutions; for instance, it helps conceive of possible links between the regular curriculum and the study of specific social justice issues, a relationship that is often under-examined. The aims of critical pedagogy depend upon students developing dexterity with the conceptual tools they use to make meaning of the evidence they confront; these are background skills that the regular curriculum can be made to serve even outside social justice-focused curricula. Furthermore, the article concludes that because such inquiry involves the exploration and potential revision of students\u27 world-ordering beliefs, developing flexibility in how one thinks may be better achieved within academic subjects and topics that are not so intimately connected to students\u27 current social lives, especially where students may be directly implicated

The SISAL database: a global resource to document oxygen and carbon isotope records from speleothems

Stable isotope records from speleothems provide information on past climate changes, most particularly information that can be used to reconstruct past changes in precipitation and atmospheric circulation. These records are increasingly being used to provide “out-of-sample” evaluations of isotope-enabled climate models. SISAL (Speleothem Isotope Synthesis and Analysis) is an international working group of the Past Global Changes (PAGES) project. The working group aims to provide a comprehensive compilation of speleothem isotope records for climate reconstruction and model evaluation. The SISAL database contains data for individual speleothems, grouped by cave system. Stable isotopes of oxygen and carbon (δ 18O, δ 13C) measurements are referenced by distance from the top or bottom of the speleothem. Additional tables provide information on dating, including information on the dates used to construct the original age model and sufficient information to assess the quality of each data set and to erect a standardized chronology across different speleothems. The metadata table provides location information, information on the full range of measurements carried out on each speleothem and information on the cave system that is relevant to the interpretation of the records, as well as citations for both publications and archived data. The compiled data are available at https://doi.org/10.17864/1947.147

Evaluating model outputs using integrated global speleothem records of climate change since the last glacial

Although quantitative isotopic data from speleothems has been used to evaluate isotope-enabled model simulations, currently no consensus exists regarding the most appropriate methodology through which to achieve this. A number of modelling groups will be running isotope-enabled palaeoclimate simulations in the framework of the Coupled Model Intercomparison Project Phase 6, so it is timely to evaluate different approaches to use the speleothem data for data-model comparisons. Here, we illustrate this using 456 globally-distributed speleothem δ18O records from an updated version of the Speleothem Isotopes Synthesis and Analysis (SISAL) database and palaeoclimate simulations generated using the ECHAM5-wiso isotope-enabled atmospheric circulation model. We show that the SISAL records reproduce the first-order spatial patterns of isotopic variability in the modern day, strongly supporting the application of this dataset for evaluating model-derived isotope variability into the past. However, the discontinuous nature of many speleothem records complicates procuring large numbers of records if data-model comparisons are made using the traditional approach of comparing anomalies between a control period and a given palaeoclimate experiment. To circumvent this issue, we illustrate techniques through which the absolute isotopic values during any time period could be used for model evaluation. Specifically, we show that speleothem isotope records allow an assessment of a model’s ability to simulate spatial isotopic trends. Our analyses provide a protocol for using speleothem isotopic data for model evaluation, including screening the observations to take into account the impact of speleothem mineralogy on 18O values, the optimum period for the modern observational baseline, and the selection of an appropriate time-window for creating means of the isotope data for palaeo time slices

Investigating climate dynamics in CA: A multi-proxy approach to stalagmite paleoclimate reconstruction

Stalagmite records of stable isotope (18Occ) variability from across the Southwestern United States change in-step with Northern Hemisphere temperature over the last deglaciation. The interpretations of 18Occ records, however, is complicated due to the multiple influences on 18Occ. These influences include seasonality of precipitation, regional temperature change, and variability in precipitation source, among others. To isolate the influence of temperature in 18Occ records, we must develop quantitative and independent records of temperature. Here, I use a multi-proxy approach in a previously studied stalagmite, ML-1, from western Sierra Nevada. We employ high-resolution 3-dimensional neutron computed tomography and x-ray computed tomography to map fluid inclusion distribution in the stalagmite. Water-rich regions in ML-1 occur contemporaneously with the lowest values of 18Occ. We also use ML-1 fluid inclusions to determine a noble gas temperature for the Last Glacial Maximum (18.8 0.3 ka), indicating a 5.2 1.7 (2) C cooling relative to today. Noble gas concentrations were measured using a progressive step-crushing technique originally developed for understanding noble gas abundances in basalt. The progressive step-crushing technique and a robust water calibration reduces uncertainty in the resulting NGT relative to previous studies that utilize pre-crushing techniques. The temperature from the Last Glacial Maximum is used to correct for temperature variability in 18Occ. Variability in 18Occ is ~2.0 ‰ on the centennial scale originally interpreted to reflect temperature and precipitation source shifts. Finally, a record of 45 stable isotope measurements from the stalagmite fluid inclusions reveal periods of increased kinetic fractionation at 18, 15.2, and 13.2 ka. The results of the stable isotope analysis reveal that these periods are times of lower effective moisture locally. The combined results from these three approaches illustrate that, in the western Sierra Nevada, temperature variability only accounts for a fraction of total 18Occ changes on the centennial scale and points to variability in precipitation source region and effective moisture as major influences on stalagmite paleoclimate records. Additionally, I conclude that the central Sierra Nevada is sensitive to changing precipitation dynamics in the western U.S. that are teleconnected to circulation and temperature variability in the Pacific and the Atlantic

An integrated approach to understand disequilibrium effects in a stalagmite record from a central Sierra Nevada cave

Stalagmite records of stable isotope (delta (super 18) O (sub cc) ) variability from across the Southwestern United States change in-step with Northern Hemisphere temperature over the last deglaciation. The interpretations of delta (super 18) O (sub cc) , however, is complicated due to the multiple influences on delta (super 18) O (sub cc) . These influences include seasonality of precipitation, regional temperature change, and variability in precipitation source, among others. To isolate the influence of temperature in delta (super 018) O (sub cc) records, we must develop quantitative and independent records of temperature. Here, we use a multi-proxy approach in a previously studied stalagmite, ML-1, from the central Sierra Nevada. We employ high-resolution 3-dimensional neutron computed tomography and x-ray computed tomography to map fluid inclusion distribution in the stalagmite. Water-rich regions in ML-1 occur contemporaneously with the lowest values of delta (super 18) O (sub cc) . We also use ML-1 fluid inclusions to create a record of 45 stable isotope measurements from the stalagmite fluid inclusions. The stable isotope results from the fluid inclusions reveal periods of anomalous temperature, d-excess, and fractionation at 18.0, 15.0, and 13.2 ka. To better constrain these periods, we use the forward proxy system model, Karstolution, integrated with isotope enabled climate modeling outputs of the western U.S. (iCESM1.3). The output of the Karstolution model reveals periods of disagreement between the predicted stalagmite record of delta (super 18) O (sub cc) and the measured delta (super 18) O (sub cc) from stalagmite ML-1 at 18.0, 15.0, and 13.2 ka. We interpret these integrated results as being caused by evaporative conditions and disequilibrium fractionation at these periods. Two of the three periods occur during warm interstadials during the deglaciation, suggesting that warm temperatures in California led to dry conditions in the central Sierra Nevada. This finding is in agreement with records of hydroclimate from across the Southwestern United States. The novel approach of integrating x-ray and neutron computed tomography, stable isotope measurements of fluid inclusions, and forward proxy system modeling, helps us understand the complex processes that impact stalagmite records of delta (super 18) O (sub cc) in seasonal and arid climates

Nitrous acid production and uptake by Zea mays plants in growth chambers in the presence of nitrogen dioxide

International audienceNitrous acid (HONO) photolysis is an important atmospheric reaction that leads to the formation of hydroxyl radicals (OH), the main diurnal atmospheric oxidants. The process of HONO formation remains unclear, and comparisons between field measurements and model results have highlighted the presence of unknown HONO sources. HONO production on plant surfaces was recently suggested to contribute to atmospheric HONO formation, but there is limited information on the quantification of HONO production and uptake by plants. To address this gap in the existing knowledge, the current study investigated HONO exchange on living Zea mays plants. Experiments were conducted in growth chambers under controlled experimental conditions (temperature, relative humidity, NO2 mixing ratio, light intensity, CO2 mixing ratio) at temperatures ranging between 283 and 299 K. To investigate the effect of drought on HONO plant-atmosphere exchanges, experiments were carried out on two sets of Zea mays plants exposed to two different water supply conditions during their growth: optimal watering (70% of the field capacity) and water stress (30% of the field capacity). Results indicated that the uptake of HONO by control Zea mays plants increased linearly with ambient temperature, and was correlated with CO2 assimilation for temperatures ranging from 283 to 299 K. At 299 K, HONO production on the leaves offset this uptake and Zea mays plants were a source of HONO, with a net production rate of 27 ± 7 ppt h-1. Deposition velocities were higher for HONO than CO2, suggesting a higher mesophyll resistance for CO2 than HONO. As water stress reduced the stomatal opening, it also decreased plant-atmosphere gas exchange. Thus, climate change, which may limit the availability of water, will have an impact on HONO exchange between plants and the atmosphere

Measurement report: Fourteen months of real-time characterisation of the submicronic aerosol and its atmospheric dynamics at the Marseille-Longchamp supersite

International audienceThis study reports results of PM1 chemical composition determined using a Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM) over a 14-month period (1 February 2017–13 April 2018) at the Marseille–Longchamp supersite (MRS-LCP) in France. Parallel measurements were performed with an aethalometer, an ultrafine particle monitor and a suite of instruments to monitor regulated pollutants (PM2.5, PM10, NOx, O3 and SO2). The average PM1 chemical composition over the period was dominated by organic aerosol (OA; 49.7 %) and black carbon (BC; 17.1 %), while sulfate accounted for 14.6 %, nitrate for 10.2 %, ammonium for 7.9 % and chloride for 0.5 % only. Wintertime was found to be the season contributing the most to the annual PM1 mass concentration (30 %), followed by autumn (26 %), summer (24 %) and spring (20 %). During this season, OA and BC concentrations were found to contribute 32 % and 31 % of their annual concentrations, respectively, as a combined result of heavy urban traffic, high emissions from residential heating and low planetary boundary layer (PBL) height. Most (75 %) of the 15 days exceeding the target daily PM2.5 concentration value recommended by the World Health Organization (WHO) occurred during this season. Local and long-range pollution episodes with contrasting chemical composition could be distinguished, accounting for 40 % and 60 % of the exceedance days, respectively. Enhanced OA and BC concentrations, mostly originating from domestic wood burning under nocturnal land breeze conditions, were observed during local pollution episodes, while high levels of oxygenated OA and inorganic nitrate were associated with medium-/long-range transported particles.In summertime, substantially higher concentrations of sulfate were found, with an average and a maximum contribution to the PM1 mass of 24 % and 66 %, respectively. Results from k-means clustering analysis of daily profiles of sulfate concentrations clearly reveal the significant influence of local harbour/industrial activities on air quality in addition to the more regional contribution of shipping traffic that originates from the Mediterranean basin