Search

Author(s): EPICA Community Members; EPICA Community Members; C. Barbante [1, 2]; J.-M. Barnola [3]; S. Becagli [4]; J. Beer [5]; M. Bigler [6, 7]; C. Boutron [3]; T. Blunier [6]; [...]

Author(s): E. W. Wolff (corresponding author) [1]; H. Fischer [2]; F. Fundel [2]; U. Ruth [2]; B. Twarloh [2]; G. C. Littot [1]; R. Mulvaney [1]; R. Rothlisberger [1]; M. [...]

In this work, an evaluation of an intense biomass burning event observed over Ny-Ålesund (Spitsbergen, European Arctic) in July 2015 is presented. Data from the multi-wavelengths Raman-lidar KARL, a sun photometer and radiosonde measurements are used to derive some microphysical properties of the biomass burning aerosol as size distribution, refractive index and single scattering albedo at different relative humidities. Predominantly particles in the accumulation mode have been found with a bi-modal distribution and dominance of the smaller mode. Above 80% relative humidity, hygroscopic growth in terms of an increase of particle diameter and a slight decrease of the index of refraction (real and imaginary part) has been found. Values of the single scattering albedo around 0.9 both at 355 nm and 532 nm indicate some absorption by the aerosol. Values of the lidar ratio are around 26 sr for 355 nm and around 50 sr for 532 nm, almost independent of the relative humidity. Further, data from the photometer and surface radiation values from the local baseline surface radiation network (BSRN) have been applied to derive the radiative impact of the biomass burning event purely from observational data by comparison with a clear background day. We found a strong cooling for the visible radiation and a slight warming in the infra-red. The net aerosol forcing, derived by comparison with a clear background day purely from observational data, obtained a value of -95 W/m2 per unit AOD500. [ABSTRACT FROM AUTHOR]

The causes of the recent increase in Antarctic sea ice extent, characterised by large regional contrasts and decadal variations, remain unclear. In the Ross Sea, where such a sea ice increase is reported, 50% of the sea ice is produced within wind-sustained latent-heat polynyas. Combining information from marine diatom records and sea salt sodium and water isotope ice core records, we here document contrasting patterns in sea ice variations between coastal and open sea areas in Western Ross Sea over the current interglacial period. Since about 3600 years before present, an increase in the efficiency of regional latent-heat polynyas resulted in more coastal sea ice, while sea ice extent decreased overall. These past changes coincide with remarkable optima or minima in the abundances of penguins, silverfish and seal remains, confirming the high sensitivity of marine ecosystems to environmental and especially coastal sea ice conditions. [ABSTRACT FROM AUTHOR]

PM10 aerosol samples were collected during summer 2013 within the framework of the Chemistry and Aerosol Mediterranean Experiment (ChArMEx) at two sites located North (Capo Granitola, 36.6° N, 12.6° E) and South (Lampedusa Island, 35.5° N, 12.6° E), respectively, of the main Mediterranean shipping route in the Sicily Channel.

The PM10 samples were collected with 12 hour time resolution at both sites. Selected metals, main anions, cations, and elemental and organic carbon were determined.

The evolution of soluble V and Ni concentrations (typical markers of heavy fuel oil combustion) was related to meteorology and ship traffic intensity in the Sicily Channel, using a high resolution regional model for back trajectories calculation. Elevated concentration of V and Ni were associated with transport from the Sicily Channel and coincidences between trajectories and positions of large ships, both at Capo Granitola and Lampedusa; the vertical structure of the planetary boundary layer also appears to play a role, with high V values associated with strong inversions and stable boundary layer. The V concentration was generally lower at Lampedusa than at Capo Granitola, where it reached a peak value of 40 ng/m³.

Concentrations of rare earth elements, La and Ce in particular, were used to identify possible contributions from refineries, whose emissions are also characterized by elevated V and Ni amounts; refinery emissions are expected to display high La/Ce and La/V ratios, due to the use of La in the fluid catalytic converter systems. In general, low La/Ce and La/V ratios were observed in the PM samples, allowing to unambiguously identify the large role of the ship source in the Sicily Channel.

Based on the sampled aerosols, ratios of the main aerosol species arising from ship emission with respect to V were estimated with the aim of deriving a lower limit for the total ship contribution to PM10. The estimated minimum ship emission contributions to PM10 was 1.9 μg/m³ at Lampedusa, and 2.8 μg/m³ at Capo Granitola, corresponding to 11 % and 8.2 % of PM10, respectively. [ABSTRACT FROM AUTHOR]

The Mediterranean basin is characterized by large concentrations of aerosols from both natural and anthropogenic sources. These aerosols affect tropospheric photochemistry by modulating the photolytic rates. Three simulations of the atmospheric composition at basin scale have been performed with the CHIMERE chemistry-transport model for the period from 6 June to 15 July 2013 covered by the ADRIMED campaign, a campaign of intense measurements in the western Mediterranean basin. One simulation takes into account the radiative effect of the aerosols on photochemistry, the second one does not, and the third one is designed to quantify the model sensitivity to a bias in the ozone column. These simulations are compared to satellite and groundbased measurements, with a particular focus on the area of Lampedusa. Values of the aerosol optical depth (AOD) are obtained from the MODIS instrument on the AQUA and TERRA satellites as well as from stations in the AERONET network and from the MFRSR sun photometer deployed at Lampedusa. Additional measurements from instruments deployed at Lampedusa either permanently or exceptionally are used for other variables: MFRSR sun photometer for AOD, diode array spectrometer for actinic fluxes, LIDAR for the aerosol backscatter, sequential sampler for speciation of aerosol and Brewer spectrophotometer for the total ozone column. It is shown that CHIMERE has a significant ability to reproduce observed peaks in the AOD, which in Lampedusa are mainly due to dust outbreaks during the ADRIMED period, and that taking into account the radiative effect of the aerosols in CHIMERE considerably improves the ability of the model to reproduce the observed day-to-day variations of the photolysis rate of ozone to O2 and O.1D/, J .O1D/, and that of NO2 to NO and O.3P/, J .NO2/. While in the case of J .O1D/ other variation factors such as the stratospheric ozone column are very important in representing correctly the day-to-day variations, the day-to-day variations of J .NO2/ are captured almost completely by the model when the optical effects of the aerosols are taken into account. Finally, it is shown that the inclusion of the direct radiative effect of the aerosols in the CHIMERE model leads to reduced J .O1D/ and J .NO2/ values over all the simulation domain, which range from a few percents over continental Europe and the north-east Atlantic Ocean to about 20% close to and downwind from Saharan dust sources. The effect on the modelled ozone concentration is 2-fold: the effect of aerosols leads to reduced ozone concentrations over the Mediterranean Sea and continental Europe, close to the sources of NOx, but it also leads to increased ozone concentrations over remote areas such as the Sahara and the tropical Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Nature 440, 491-496 (2006); doi:10.1038/nature04614. In calculating the fluxes used in this paper, we made a mistake in the snow accumulation rate used. We calculated fluxes assuming that snow accumulation [...]

The Mediterranean Basin atmosphere is influenced by both strong natural and anthropogenic aerosol emissions and is also subject to important climatic forcings. Several programs have addressed the study of the Mediterranean basin; nevertheless important pieces of information are still missing. In this framework, PM10 samples were collected on a daily basis on the island of Lampedusa (35.5° N, 12.6° E; 45ma.s.l.), which is far from continental pollution sources (the nearest coast, in Tunisia, is more than 100 km away). After mass gravimetric measurements, different portions of the samples were analyzed to determine the ionic content by ion chromatography (IC), the soluble metals by inductively coupled plasma atomic emission spectrometry (ICP-AES), and the total (soluble + insoluble) elemental composition by particle-induced x-ray emission (PIXE). Data from 2007 and 2008 are used in this study. The Positive Matrix Factorization (PMF) model was applied to the 2-year long data set of PM10 mass concentration and chemical composition to assess the aerosol sources affecting the central Mediterranean basin. Seven sources were resolved: sea salt, mineral dust, biogenic emissions, primary particulate ship emissions, secondary sulfate, secondary nitrate, and combustion emissions. Source contributions to the total PM10 mass were estimated to be about 40% for sea salt, around 25% for mineral dust, 10% each for secondary nitrate and secondary sulfate, and 5% each for primary particulate ship emissions, biogenic emissions, and combustion emissions. Large variations in absolute and relative contributions are found and appear to depend on the season and on transport episodes. In addition, the secondary sulfate due to ship emissions was estimated and found to contribute by about one-third to the total sulfate mass. Results for the seasalt and mineral dust sources were compared with estimates of the same contributions obtained from independent approaches, leading to an estimate of the water content bound to the sea salt in the marine source. [ABSTRACT FROM AUTHOR]

An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (δD-δ18Oice, δ18Oatm, total air content, CO2, CH4, N2O, dust, high-resolution chemistry, ice texture) of the bottom 60m of the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core from central Antarctica. These bottom layers were subdivided into two distinct facies: the lower 12m showing visible solid inclusions (basal dispersed ice facies) and the upper 48 m, which we will refer to as the "basal clean ice facies". Some of the data are consistent with a pristine paleoclimatic signal, others show clear anomalies. It is demonstrated that neither large-scale bottom refreezing of subglacial water, nor mixing (be it internal or with a local basal end term from a previous/initial ice sheet configuration) can explain the observed bottom-ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom-ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides. This stress field change, combined with bottom-ice temperature close to the pressure melting point, induces accelerated migration recrystallization, which results in spatial chemical sorting of the impurities, depending on their state (dissolved vs. solid) and if they are involved or not in salt formation. This chemical sorting effect is responsible for the progressive build-up of the visible solid aggregates that therefore mainly originate "from within", and not from incorporation processes of debris from the ice sheet's substrate. We further discuss how the proposed mechanism is compatible with the other ice properties described. We conclude that the paleoclimatic signal is only marginally affected in terms of global ice properties at the bottom of EPICA Dome C, but that the timescale was considerably distorted by mechanical stretching of MIS20 due to the increasing influence of the subglacial topography, a process that might have started well above the bottom ice. A clear paleoclimatic signal can therefore not be inferred from the deeper part of the EPICA Dome C ice core. Our work suggests that the existence of a flat monotonic ice-bedrock interface, extending for several times the ice thickness, would be a crucial factor in choosing a future "oldest ice" drilling location in Antarctica. [ABSTRACT FROM AUTHOR]

Size-segregated particle samples were collected in the Arctic (Ny-Ålesund, Svalbard) in April 2011 both at ground level and in the free atmosphere exploiting a tethered balloon equipped also with an optical particle counter (OPC) and meteorological sensors. Individual particle properties were investigated by scanning electron microscopy coupled with energy dispersive microanalysis (SEM-EDS). Results of the SEM-EDS were integrated with particle size and optical measurements of the aerosols properties at ground level and along the vertical profiles. Detailed analysis of two case studies reveals significant differences in composition despite the similar structure (layering) and the comparable texture (grain size distribution) of particles in the air column. Differences in the mineral chemistry of samples point at both local (plutonic/metamorphic complexes in Svalbard) and remote (basic/ultrabasic magmatic complexes in Greenland and/or Iceland) geological source regions for dust. Differences in the particle size and shape are put into relationship with the mechanism of particle formation, that is, primary (well sorted, small) or secondary (idiomorphic, fine to coarse grained) origin for chloride and sulfate crystals and transport/settling for soil (silicate, carbonate and metal oxide) particles. The influence of size, shape, and mixing state of particles on ice nucleation and radiative properties is also discussed. [ABSTRACT FROM AUTHOR]

The Mediterranean basin is characterized by large concentrations of aerosols from both natural and anthropogenic sources. These aerosols change the optical properties of the atmosphere, therefore affecting tropospheric photochemistry through the photolytic rates. Two simulations of the atmospheric composition at basin-scale have been performed with the CHIMERE chemistry-transport model for the period from 1 June to 15 July 2013 covered by the ADRIMED campaign, a campaign of intense measurements in the western Mediterranean basin. One simulation takes into account the radiative effect of the aerosols on photochemistry, the other one does not. These simulations are compared to satellite and ground-based measurements, with a particular focus on the area of Lampedusa. Values of the Aerosol Optical Depth (AOD) are obtained from the MODIS instrument on the AQUA and TERRA satellites as well as from stations in the AERONET network and from the MFRSR sun photometer deployed at Lampedusa. Additional measurements from instruments deployed at Lampedusa either permanently or exceptionnally are used for other variables: MFRSR sun photometer for AOD, diode array spectrometer for actinic fluxes, LIDAR for the aerosol backscatter, sequential sampler for speciation of aerosol and Brewer spectrophotometer for the total ozone column. It is shown that CHIMERE has a significant ability to reproduce observed peaks in the AOD, which in Lampedusa are mainly due to dust outbreaks during the ADRIMED period, and that taking into account the radiative effect of the aerosols in CHIMERE improves considerably the ability of the model to reproduce the observed day-to-day variations of J(O¹D) and J(NO2). While in the case of J(O¹D) other variation factors such as the stratospheric ozone column are very important in representing correctly the day-to-day variations, the day-to-day variations of J(NO2) are captured almost completely by the model when the optical effects of the aerosols are taken into account. Finally, it is shown that the inclusion of the direct radiative effect of the aerosols in the CHIMERE model leads to reduced J(O¹D) and J(NO2) values over all the simulation domain, which ranges from a few percents over continental Europe and the northeast Atlantic Ocean to about 20% close to and downwind from saharan dust sources. The effect on the modelled ozone concentration is twofold, with the effect of aerosols leading to reduced ozone concentrations over the Mediterranean Sea and continental Europe, close to the sources of NOx, and on the contrary to increased ozone concentrations over remote areas such the Sahara and the tropical Atlantic Ocean. [ABSTRACT FROM AUTHOR]