ALBERT

Description: Dust can affect the radiative balance of the atmosphere by absorbing or reflecting incoming solar radiation; it can also be a source of micronutrients, such as iron, to the ocean. It has been suggested that production, transport and deposition of dust is influenced by climatic changes on glacial-interglacial timescales. Here we present a high-resolution record of aeolian dust from the EPICA Dome C ice core in East Antarctica, which provides an undisturbed climate sequence over the past eight climatic cycles. We find that there is a significant correlation between dust flux and temperature records during glacial periods that is absent during interglacial periods. Our data suggest that dust flux is increasingly correlated with Antarctic temperature as the climate becomes colder. We interpret this as progressive coupling of the climates of Antarctic and lower latitudes. Limited changes in glacial-interglacial atmospheric transport time suggest that the sources and lifetime of dust are the main factors controlling the high glacial dust input. We propose that the observed approximately 25-fold increase in glacial dust flux over all eight glacial periods can be attributed to a strengthening of South American dust sources, together with a longer lifetime for atmospheric dust particles in the upper troposphere resulting from a reduced hydrological cycle during the ice ages.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lambert, F -- Delmonte, B -- Petit, J R -- Bigler, M -- Kaufmann, P R -- Hutterli, M A -- Stocker, T F -- Ruth, U -- Steffensen, J P -- Maggi, V -- England -- Nature. 2008 Apr 3;452(7187):616-9. doi: 10.1038/nature06763.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18385736" target="_blank"〉PubMed〈/a〉

Description: Aerosol-climate interactions constitute one of the major sources of uncertainty in assessing changes in aerosol forcing in the anthropocene, as well as understanding glacial-interglacial cycles. Here we focus on improving the representation of mineral dust in the Community Atmosphere Model and assessing the impacts of the improvements in terms of direct effects on the radiative balance of the atmosphere. We simulated the dust cycle using different parameterization sets for dust emission, size distribution, and optical properties. Comparing the results of these simulations with observations of concentration, deposition, and aerosol optical depth allows us to refine the representation of the dust cycle and its climate impacts. We propose a tuning method for dust parameterizations to allow the dust module to work across the wide variety of parameter settings which can be used within the Community Atmosphere Model. Our results include a better representation of the dust cycle, most notably for the improved size distribution. The estimated net top of atmosphere direct dust radiative forcing is -0.23 ± 0.14 W/m 2 for present day and -0.32 ± 0.20 W/m 2 at the Last Glacial Maximum. From our study and sensitivity tests we also derive some general relevant findings, supporting the concept that the magnitude of the modeled dust cycle is sensitive to the observational datasets and size distribution chosen to constrain the model as well as the meteorological forcing data, even within the same modeling framework, and that the direct radiative forcing of dust is strongly sensitive to the optical properties and size distribution used.

Description: During the I997-98 Italian Antarctic Programme (PNRA) summer season, two snow pits were dug 3km north-westward of the ltalian-French Dome C Station (East Antarctica, 75o 09'S, 123o 06'E, 3200m a.s.l.) and the EPICA project drilling site. These 4 m depth pits were done upwind of the station to avoid the risk of pollution. In the first pit, after cleaning of walls, a high resolution sampling was carried out for chemical (anions, cations, organic acids), stable isotope ( d 180 and d D), tritium and dust (concentration, size distribution, AI concentration) measurements. In the second pit, dug 50cm apart, visual stratigraphy was done. The concentration/depth profiles and any eventual correlation between chemical components were examined to obtain environmental information about primary and secondary aerosol sources, transport phenomena and any evidence of relevant trends in the temporal series of some components. Particular attention was spent on the relative contribution of sea spray components (Na+, Cl-, Mg2+) and substances from biogenic origin (nssSO42- and MSA) to atmospheric aerosol. Using Na+ and MSA as source tracers, fractionating phenomena induced variations of CI-/Na+ and nssSO42-/MSA ratios were valued. nssSO42-/MSA relationship with MSA reveals the importance of long range transport effects and the presence of other nssSO42- sources. Temporal data series for Ca2+, K+, No3-, F- and some short chain carboxylic acids are also reported. For almost all the components ng/g or sub-ng/g concentration levels were found, as expected for a station located at a very long distance from the most part of aerosol sources and at high altitude. Tritium analyses were carried out in order to identify the peak related to the thermonuclear tests performed in the atmosphere in the early sixties as a reference horizon for dating purpose. The seasonal signal in the stable isotopes was not observed due to the low accumulation of this site, but nevertheless the main trends were compared to other Antarctic sites and to temperature records available from the main East Antarctica automatic weather stations. The dust concentration, size distribution (Particles Counter) and AI (Atomic Absorption) measurements show records of continental influences on the Dome C insoluble aerosols. The very low annual accumulation rate, 3 to 3.5 cm (W.E.) and, probable, wind erosion are the main reasons of the absence of seasonal variations. Because of this limitation, of more interest is the correlation of the measured records with the visual stratigraphy. The main topics from these pits measurements can provide: 1) the sutdy of the last tens years of atmospheric deposition in the Dome C area, 2) define the atmosphere-snow transport processes, also on the comparison with EPICA ice core, 3) identification of primary and secondary sources at this site.