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Alexander, B.; Park, R.J.; Jacob, D.J.; Li, Q.B.; Yantosca, R.M.; Savarino, J.; Lee, C.C.W.; Thiemens, M.H. (2005). Sulfate formation in sea-salt aerosols: Constraints from oxygen isotopes. J. Geophys. Res., 110.
Abstract: We use observations of the mass-independent oxygen isotopic composition (?17O) of sulfate in the marine boundary layer (MBL) to quantify the sulfate source from aqueous SO2 (S(IV)) oxidation by O3 in alkaline sea-salt aerosols. Oxidation by O3 imparts a large ?17O signature to the resulting sulfate (8.8‰) relative to oxidation by H2O2 (0.9‰) or by OH or O2 (0‰). Ship data from two Indian Ocean Experiment (INDOEX) cruises in the Indian Ocean indicate ?17O values usually <1‰ in the submicron sulfate aerosol but considerable variability in the supermicron sulfate with frequent occurrences above 1‰ and up to 6.7‰. The large ?17O values are associated with high concentrations of sea-salt aerosols, providing evidence for the S(IV) + O3 pathway. We use a global chemical transport model (GEOS-CHEM) to interpret quantitatively the INDOEX observations and to assess the global importance of sulfate production in sea-salt aerosols. The model accounts for titration of sea-salt alkalinity in the MBL by uptake of acid gases (SO2, H2SO4, and HNO3), shutting down the S(IV) + O3 pathway. We find that this titration occurs rapidly over much of the oceans except at high latitudes (strong sea-salt emission) and is due to both the S(IV) + O3 reaction and HNO3 (g) condensation; that is, sulfate formation in sea-salt aerosols is limited by the alkalinity flux from the ocean and by competition for this alkalinity supply from HNO3 (g). The model is consistent with the ?17O magnitudes and patterns in the INDOEX data. Titration of alkalinity is critical for the success of the model simulation. Regeneration of sea-salt aerosol alkalinity by OH uptake is inconsistent with the ?17O observations in INDOEX. Model results indicate that sulfate production in sea-salt aerosols decreases MBL SO2 concentrations and gas phase H2SO4 production rates by typically 10–30% (up to >70%) and increases MBL sulfate concentrations by typically >10% (up to 30%). Globally, this mechanism contributes 9% of atmospheric sulfate production and 1% of the sulfate burden. The impact on H2SO4 (g) formation and implications for the potential formation of new particles in the MBL warrants inclusion in models examining the radiative effects of sulfate aerosols.
Keywords: atmospheric chemistry; aerosol formation; isotopes; 0305 Atmospheric Composition and Structure: Aerosols and particles; 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes; 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0490 Biogeosciences: Trace gases; 1041 Geochemistry: Stable isotope geochemistry
Programme: 399
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Nishitani, N.; Ogawa, T.; Sato, N.; Yamagishi, H.; Pinnock, M.; Villain, J.-P.; Sofko, G.; Troshichev, O. (2002). A study of the dusk convection cell's response to an IMF southward turning. J. Geophys. Res., 107.
Abstract: One example of the response of ionospheric convection and the polar cap boundary to a sudden change in the interplanetary magnetic field (IMF) orientation has been studied by using ground magnetometers, the Super Dual Auroral Radar Network (SuperDARN), and Defense Meteorological Satellite Program (DMSP) particle detectors when the IMF suddenly changed from northward (+6 nT) to strongly southward (?19 nT) at 1716 UT on 5 September 1995. The Bz component was fairly constant for ?2 hours before and ?25 min after the sudden IMF change. The convection flow changed almost simultaneously over a global extent. This initial change of the convection pattern can be characterized by a sudden formation of a large flow vortex in the afternoon sector. This agrees with the earlier findings by Ruohoniemi and Greenwald [1998] and Ridley et al. [1998]. On the other hand, the response of the polar cap boundary (or its proxy) is more complicated. The Saskatoon radar, located in the late morning sector, observed an equatorward shift of the cusp scatter region simultaneously with the initial response of the convection flows. The DMSP particle data also showed a simultaneous equatorward expansion of the auroral oval in the 2100 magnetic local time (MLT) sector. The radar and particle data indicate the immediate equatorward expansion of the precipitation regions in the noon and premidnight sectors. About 10–20 min after the initial change, there were changes observed in the dusk region, namely, an equatorward expansion of the current reversal boundary observed by the Greenland magnetometer chain in the dusk sector between 1740 and 1750 UT and an equatorward expansion of the convection reversal boundary detected by the Stokkseyri, Halley, and Syowa radars. The delayed responses were observed 18-8 min before a substorm onset was recorded at midlatitude stations at 1756 UT. These observations indicate that there were two kinds of ionospheric responses to the southward turning of the IMF; the first response is the formation of the convection vortex and the equatorward shift of the polar cap boundary at noon and at ?2100 MLT, and the second response is the equatorward expansion of the convection reversal boundary in the dusk sector. We make the case that the first response is associated with the propagation of magnetosonic waves and that the second response is consistent with the Cowley and Lockwood [1992] picture of the redistribution of the newly created open flux in the polar cap region.
Keywords: 2463 Ionosphere: Plasma convection; 2431 Ionosphere: Ionosphere/magnetosphere interactions; 2437 Ionosphere: Ionospheric dynamics; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions
Programme: 312;911
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Dominé, F.; Rey-Hanot, L. (2002). Adsorption isotherms of acetone on ice between 193 and 213 K. Geophysical research letters, 29.
Abstract: The adsorption isotherms of acetone on ice were measured at 193, 203 and 213 K using a volumetric method with mass spectrometric detection. Henry's law applies for values of the acetone partial pressure, Pacetone, lower than 10?3 Pa. Where Henry's law applies, the number of acetone molecules adsorbed per cm2 of ice, is: nads = 90.53 × Pacetone × exp (6610.2/T), with Pacetone in Pa and T in K. The measured enthalpy of adsorption of acetone on ice is ?Hads = ?55±7 kJ/mol. Acetone values previously measured in Arctic snow are too high to be due to adsorbed acetone. Acetone was then probably dissolved in ice or in organic aerosols contained in snow. Adsorption of acetone in the snowpack or on ice crystals in cirrus clouds is insufficient to affect Pacetone above the snow or in the clouds.
Keywords: 1863 Hydrology: Snow and ice; 3947 Mineral Physics: Surfaces and interfaces; 0320 Atmospheric Composition and Structure: Cloud physics and chemistry
Programme: 437
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Biessy, G.; Dauteuil, O.; Van Vliet-Lanoë, B.; Wayolle, A. (2008). Fast and partitioned postglacial rebound of southwestern Iceland. Tectonics, 27.
Abstract: Located both on the Mid-Atlantic Ridge and above a mantle plume, Iceland is subject to horizontal and vertical motions. Many studies described these deformations in terms of rifting episodes that have combined both extensional tectonics and magmatism. However, few studies have described the glacio-isostatic response induced by the retreat of the Weichselian ice cap. The melting of this ice cap induced a postglacial rebound for the whole of Iceland that may be controlled by the geodynamic setting and the rheological layering of the lithosphere. This study is devoted to (1) understanding the Holocene rebound on the southwestern coast and (2) estimating the asthenosphere viscosity and depth beneath Iceland. Two stages of holocene evolution were determined by means of GPS profiles, morphological observations, and data compilation. The first stage corresponds to a vertical uplift of 67.5 to 157.5 m. It started at 10,000 years BP and ended at 8500 years BP implying uplift rates between 4.5 and 10.5 cm/a. It was a quick isostatic response to the fast ice retreat. The second stage had vertical motion of tens of meters with a probable tectonic origin and started at 8500 years BP. The uplift rate is 1 to 2 orders of magnitude slower than the one during the first stage. Uplift partitioning during the first stage was controlled by the thermal state of the lithosphere, the highest geothermal flux inducing the maximum uplift rates. The relaxation time for uplift provides a viscosity estimate of 5.4–5.8 × 1019 Pa s for the asthenosphere. This value is similar to those determined for glacial areas in different continental contexts. However, the flexural wavelength indicates a shallower asthenosphere than that occurring in continental domains. Therefore this study highlights a coupling between the thermal structure of the Icelandic asthenosphere and the glacial rebound.
Keywords: glacio-isostasy; rebound; rheology; 5475 Planetary Sciences: Solid Surface Planets: Tectonics; 5416 Planetary Sciences: Solid Surface Planets: Glaciation; 4556 Oceanography: Physical: Sea level: variations and mean; 8033 Structural Geology: Rheology: mantle
Programme: 316
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Caillon, N.; Jouzel, J.; Severinghaus, J.P.; Chappellaz, J.; Blunier, T. (2003). A novel method to study the phase relationship between Antarctic and Greenland climate. Geophysical research letters, 30.
Abstract: A classical method for understanding the coupling between northern and southern hemispheres during millennial-scale climate events is based on the correlation between Greenland and Antarctic ice core records of atmospheric composition. Here we present a new approach based on the use of a single Antarctic ice core in which measurements of methane concentration and inert gas isotopes place constraints on the timing of a rapid climate change in the North and of its Antarctic counterpart. We applied it to the Marine Isotope Stage (MIS) 5d/c transition early in the last glaciation ?108 ky BP. Our results indicate that the Antarctic temperature increase occurred 2 ky before the methane increase, which is used as a time marker of the warming in the Northern Hemisphere. This result is in agreement with the “bipolar seesaw” mechanism used to explain the phase relationships documented between 23 and 90 ky BP [
Blunier and Brook, 2001].
Keywords: 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; 4267 Oceanography: General: Paleoceanography; 1827 Hydrology: Glaciology; 4870 Oceanography: Biological and Chemical: Stable isotopes; 1620 Global Change: Climate dynamics
Programme: 902
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Karlöf, L.; Winther, J.-G.; Isaksson, E.; Kohler, J.; Pinglot, J.F.; Wilhelms, F.; Hansson, M.; Holmlund, P.; Nyman, M.; Pettersson, R.; Stenberg, M.; Thomassen, M.P.A.; van der Veen, C.; van de Wal, R.S.W. (1999). A 1500 year record of accumulation at Amundsenisen western Dronning Maud Land, Antarctica, derived from electrical and radioactive measurements on a 120 m ice core. J. Geophys. Res., 105.
Abstract: During the Nordic EPICA pre-site survey in Dronning Maud Land in 1997/1998 a 120 m long ice core was retrieved (76°00'S 08°03'W, 2400 m above sea level). The whole core has been measured using the electric conductivity measurement (ECM) and dielectric profiling (DEP) techniques, and the core chronology has been established by detecting major volcanic eruptions. In a nearby shallow core radioactive traces from nuclear tests conducted during the 1950s and 1960s have been identified. Altogether, 13 ECM and DEP peaks in the long core are identified as originating from specific volcanic eruptions. In addition two peaks of increased total ? activity are identified in the short core. Accumulation is calculated as averages over the time periods between these dated events. Accumulation rate is 62 millimetres (w. eq./yr) for the last 181 years (1816 A.D. to present) and 61 mm w. eq./yr for the last 1457 years (540 A.D. to present). Our record shows an 8% decrease in accumulation between 1452 and 1641 A.D. (i.e. part of the Little Ice Age), compared to the long-term mean.
Programme: 265
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Geirsson, H.; Árnadóttir, T.; Völksen, C.; Jiang, W.; Sturkell, E.; Villemin, T.; Einarsson, P.; Sigmundsson, F.; Stefánsson, R. (2006). Current plate movements across the Mid-Atlantic Ridge determined from 5 years of continuous GPS measurements in Iceland. J. Geophys. Res., 111.
Abstract: We analyze data spanning up to 5 years from 18 continuous GPS stations in Iceland, computing daily positions of the stations with three different high-level geodetic processing software packages. We observe large-scale crustal deformation due to plate spreading across Iceland. The observed plate divergence between the North American and the Eurasian plates is in general agreement with existing models of plate motion. Spreading is taken up within a ?100–150 km wide plate boundary zone that runs through the island. Of the two parallel branches of the plate boundary in south Iceland, the eastern volcanic zone is currently taking up the majority of the spreading and little is left for the western volcanic zone. The plate boundary deformation field has been locally and temporarily affected in south Iceland by two M w = 6.5 earthquakes in June 2000, inflation at Katla volcano during 2000 to 2004, and an eruption of Hekla volcano in February 2000. All stations with significant vertical velocities are moving up relative to the reference station REYK, with the highest velocity exceeding 20 mm/yr in the center of the island.
Keywords: Iceland crustal deformation; continuous GPS; 1240 Geodesy and Gravity: Satellite geodesy: results; 8150 Tectonophysics: Plate boundary: general; 1242 Geodesy and Gravity: Seismic cycle related deformations; 8158 Tectonophysics: Plate motions: present and recent; 7245 Seismology: Mid-ocean ridges
Programme: 316
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Fain, X.; Ferrari, C.P.; Gauchard, P.-A.; Magand, O.; Boutron, C. (2006). Fast depletion of gaseous elemental mercury in the Kongsvegen Glacier snowpack in Svalbard. Geophysical research letters, 33.
Abstract: Gaseous elemental mercury (GEM, Hg°) was measured in the snowpack interstitial air on the Kongsvegen Glacier (Svalbard) between the surface and 190 cm depth. A rapid depletion of GEM from ?5 to 0.4 ng.m?3 in the snowpack air was measured in less than 8 hours at a calculated depletion rate of ?0.5–0.7 ng.m?3.h?1 while concentration of GEM above the snow stayed constant about 1.7 ng.m?3. This depletion could only be explained by chemical processes and this study suggests that Br. could be the most important reactant for the oxidation of GEM in the interstitial snow air. The lifetime of GEM was estimated to be ?10 minutes with second order reaction rate constant between GEM and Br. of about ?2 × 10?11 cm?3.molecule?1.s?1. These first experimental kinetic values for GEM oxidation in the snow air are in good agreement with both theoretical and modelling studies previously reported.
Keywords: 0317 Atmospheric Composition and Structure: Chemical kinetic and photochemical properties; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0330 Atmospheric Composition and Structure: Geochemical cycles; 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0736 Cryosphere: Snow
Programme: 399
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Andersen, O.B.; Hinderer, J. (2005). Global inter-annual gravity changes from GRACE: Early results. Geophysical research letters, 32.
Abstract: Fifteen monthly gravity field solutions from the GRACE twin satellites launched more than two years ago have been studied to estimate gravity field changes between 2002 and 2003.The results demonstrate that GRACE is capable of capturing the changes in ground water on inter-annual scales with an accuracy of 0.4 ?Gal corresponding to 9 mm water thickness on spatial scales longer than 1300 km. Four of the most widely used global hydrological models have been investigated for their spatial comparison with GRACE observations of inter-annual gravity field variations due to changes in continental water storage. The Global Land Data Assimilation System model has a spatial correlation coefficient with GRACE observations of 0.65 over the northern hemisphere. This demonstrates that the observed gravity field changes on these scales are largely related to changes in continental water storage.
Keywords: 1217 Geodesy and Gravity: Time variable gravity; 1855 Hydrology: Remote sensing; 1640 Global Change: Remote sensing; 1655 Global Change: Water cycles
Programme: 337
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Andersen, O.B.; Seneviratne, S.I.; Hinderer, J.; Viterbo, P. (2005). GRACE-derived terrestrial water storage depletion associated with the 2003 European heat wave. Geophysical research letters, 32.
Abstract: The GRACE twin satellites reveal large inter-annual terrestrial water-storage variations between 2002 and 2003 for central Europe. GRACE observes a negative trend in regional water storage from 2002 to 2003 peaking at ?7.8 cm in central Europe with an accuracy of 1 cm. The 2003 excess terrestrial water storage depletion observed from GRACE can be related to the record-breaking heat wave that occurred in central Europe in 2003. We validate the measurements from GRACE using two independent hydrological estimates and direct gravity observations from superconducting gravimeters in Europe. All datasets agree well with the GRACE measurements despite the disparity of the employed information; the difference between datasets tends to be within GRACE margin of error. The April-to-August terrestrial water storage depletion is found to be significantly larger in 2003 than in 2002 from both models and observations.
Keywords: 1640 Global Change: Remote sensing; 1655 Global Change: Water cycles; 1836 Hydrology: Hydrological cycles and budgets; 1812 Hydrology: Drought
Programme: 337
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