19th century glacier retreat in the Alps preceded the emergence of industrial black carbon deposition on high-alpine glaciers

Light absorbing aerosols in the atmosphere and cryosphere play an important role in the climate system. Their presence in ambient air and snow changes the radiative properties of these systems, thus contributing to increased atmospheric warming and snowmelt. High spatio-temporal variability of aerosol concentrations and a shortage of long-term observations contribute to large uncertainties in properly assigning the climate effects of aerosols through time.Starting around AD&thinsp;1860, many glaciers in the European Alps began to retreat from their maximum mid-19th century terminus positions, thereby visualizing the end of the Little Ice Age in Europe. Radiative forcing by increasing deposition of industrial black carbon to snow has been suggested as the main driver of the abrupt glacier retreats in the Alps. The basis for this hypothesis was model simulations using elemental carbon concentrations at low temporal resolution from two ice cores in the Alps.Here we present sub-annually resolved concentration records of refractory black carbon (rBC; using soot photometry) as well as distinctive tracers for mineral dust, biomass burning and industrial pollution from the Colle Gnifetti ice core in the Alps from AD&thinsp;1741 to 2015. These records allow precise assessment of a potential relation between the timing of observed acceleration of glacier melt in the mid-19th century with an increase of rBC deposition on the glacier caused by the industrialization of Western Europe. Our study reveals that in AD&thinsp;1875, the time when rBC ice-core concentrations started to significantly increase, the majority of Alpine glaciers had already experienced more than 80&thinsp;% of their total 19th century length reduction, casting doubt on a leading role for soot in terminating of the Little Ice Age. Attribution of glacial retreat requires expansion of the spatial network and sampling density of high alpine ice cores to balance potential biasing effects arising from transport, deposition, and snow conservation in individual ice-core records.</p

A Holocene black carbon ice-core record of biomass burning in the Amazon Basin from Illimani, Bolivia

The Amazon Basin is one of the major contributors to global biomass burning emissions. However, regional paleofire trends remain particularly unknown. Due to their proximity to the Amazon Basin, Andean ice cores are suitable to reconstruct paleofire trends in South America and improve our understanding of the complex linkages between fires, climate and humans. Here we present the first refractory black carbon (rBC) ice-core record from the Andes as a proxy for biomass burning emissions in the Amazon Basin, derived from an ice core drilled at 6300&thinsp;m&thinsp;a.s.l. from the Illimani glacier in the Bolivian Andes and spanning the entire Holocene back to the last deglaciation 13&thinsp;000 years ago. The Illimani rBC record displays a strong seasonality with low values during the wet season and high values during the dry season due to the combination of enhanced biomass burning emissions in the Amazon Basin and less precipitation at the Illimani site. Significant positive (negative) correlations were found with reanalyzed temperature (precipitation) data for regions in eastern Bolivia and western Brazil characterized by substantial fire activity. rBC long-term trends indirectly reflect regional climatic variations through changing biomass burning emissions as they show higher (lower) concentrations during warm–dry (cold–wet) periods, in line with climate variations such as the Younger Dryas, the 8.2&thinsp;ka event, the Holocene Climatic Optimum, the Medieval Warm Period and the Little Ice Age. The highest rBC concentrations of the entire record occurred during the Holocene Climatic Optimum between 7000 and 3000&thinsp;BCE, suggesting that this exceptionally warm and dry period caused high levels of biomass burning activity, unprecedented in the context of the past 13&thinsp;000 years. Recent rBC levels, rising since 1730&thinsp;CE in the context of increasing temperatures and deforestation, are similar to those of the Medieval Warm Period. No decrease in fire activity was observed in the 20th century, in contradiction to global biomass burning reconstructions based on charcoal data.</p

An 800-year high-resolution black carbon ice core record from Lomonosovfonna, Svalbard

Produced by the incomplete combustion of fossil fuel and biomass, black carbon (BC) contributes to Arctic warming by reducing snow albedo and thus triggering a snow-albedo feedback leading to increased snowmelt. Therefore, it is of high importance to assess past BC emissions to better understand and constrain their role. However, only a few long-term BC records are available from the Arctic, mainly originating from Greenland ice cores. Here, we present the first long-term and high-resolution refractory black carbon (rBC) record from Svalbard, derived from the analysis of two ice cores drilled at the Lomonosovfonna ice field in 2009 (LF-09) and 2011 (LF-11) and covering 800 years of atmospheric emissions. Our results show that rBC concentrations strongly increased from 1860 on due to anthropogenic emissions and reached two maxima, at the end of the 19th century and in the middle of the 20th century. No increase in rBC concentrations during the last decades was observed, which is corroborated by atmospheric measurements elsewhere in the Arctic but contradicts a previous study from another ice core from Svalbard. While melting may affect BC concentrations during periods of high temperatures, rBC concentrations remain well preserved prior to the 20th century due to lower temperatures inducing little melt. Therefore, the preindustrial rBC record (before 1800), along with ammonium (NH4+), formate (HCOO−) and specific organic markers (vanillic acid, VA, and p-hydroxybenzoic acid, p-HBA), was used as a proxy for biomass burning. Despite numerous single events, no long-term trend was observed over the time period 1222–1800 for rBC and NH4+. In contrast, formate, VA, and p-HBA experience multi-decadal peaks reflecting periods of enhanced biomass burning. Most of the background variations and single peak events are corroborated by other ice core records from Greenland and Siberia. We suggest that the paleofire record from the LF ice core primarily reflects biomass burning episodes from northern Eurasia, induced by decadal-scale climatic variations.</p

REDUCTION OF THE NOISE RADIATED BY SUBMERGED STRUCTURES : OPTIMISATION OF LAYERED COATINGS

We propose an optimization process in order to design optimal viscoelastic (isotropic or transverse-isotropic) layered coatings for submerged structures. These coatings are optimized in order to reduce the far-field pressure radiated by the structure when subjected to time-harmonic prescribed forces or displacements. These coatings have to satisfy three inequality constraints, maximum thickness, maximum and minimum mean value mass density, maximum mean value compressibility. In order to define a fast and efficient optimization process, we have considered the structure to be an infinite plate radiating in a semi-infinite fluid and the coating to be an infinite layered medium. The optimization has to provide coatings feasible with respect to the constraints and inducing the maximum far-field radiated noise attenuation in the largest frequency range. We present the software named OPTIMASQ we have developped for this purpose and some of the results we have obtained which prove the efficiency of the optimization process even for severe constraints

Thin film in-plane actuator: Assessment of monolayer and bilayer mechanical output

This article shows that in an in-plane configuration a thin film and a bulk actuators deliver the same amount of mechanical power under the same voltage. This opens the possibility to reach more powerful actuators while keeping the same geometric dimensions by simply stacking these films. It also demonstrates that the effective transverse-plane piezoelectric coefficient is constant with electric field which is a crucial result for this actuator

rf-sputtering of PMNT thin films

We report on the realization of relaxor ferroelectric thin films by rf magnetron sputtering deposition. We investigated fabrication of films in the solid solution of PMN (Pb(Mg1/3Nb2/3)O3) with PT (PbTiO3). This material is the most studied among the relaxor ferroelectric family for applications in the field of microelectronics and microsystems. We chose the composition with 30% of PT, close to the morphotropic phase boundary between relaxor and normal ferroelectric behavior which exhibits good piezoelectric properties suited to actuators. We have grown the films in a cold deposition process. The substrates used were Si/SiO2 coated by Ti/Pt electrodes. This allowed to synthesize pyrochlore-free PMNT ceramic thin films at temperatures between 450 and 675°C in a postdeposition conventional annealing. We performed dielectric and ferroelectric characterizations of the films with Pt upper electrodes. Dielectric constant was measured as a function of temperature (up to 155°C) and frequency (1 kHz ~ 1 MHz). We obtained relative dielectric constant of the order of 1500. Relaxor behavior and ferroelectric properties are evidenced and are shown to be enhanced by annealing temperature