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Abstract. Anthropogenic emission of SO 2 and conversion into SO42-is argued to be the most important factor damping and modulating the global greenhouse effect. Recent estimates of the relative strength of the three important sources of volatile sulfur (SO2 from fossil fuel combustion -78 Tg S/yr, from biomass burning -2 Tg S/yr, and from natural sources ~ 25 Tg S/yr) suggest an overwhelming effect of the anthropogenic emissions for climate forcing. However, the radiatively relevant product SO42-may have different patterns due to the distribution of the sources (some very dense areas near the surface for anthropogenic SO 2, formation of SO 2 from dimethylsulfide in the marine boundary layer, and emission of volcanic SO2 mostly in the free atmosphere in rural areas). In this paper we study the relative contribution of volcanic SO2 emissions to the atmospheric sulfur budget applying an atmospheric general circulation model including a full sulfur cycle and prescribed source distributions. An off-line analysis tool is applied to determine the radiative forcing of sulfate aerosols. The results show that natural S sources are at least as important as the anthropogenic ones, even though their source strength is much smaller. The reasons are different lifetimes due to different production and emission processes. Therefore, we should improve our knowledge about the volcanic volatile sources and their time-space variability.

[1] This study presents a novel approach to develop a combined organic-inorganic sub-micron sea-spray source function for inclusion in large-scale models. It requires wind speed and surface ocean chlorophyll-a concentration as input parameters. The combined organic-inorganic source function is implemented in the REMOTE regional climate model and sea-spray fields are predicted with particular focus on the North East Atlantic. The model predictions using the new source functions compare well with observations of total sea-spray mass and organic carbon fraction in sea-spray aerosol. During winter (periods of low oceanic biological activity), sea-salt dominates the sea-spray mass while in summer (when biological activity is high), water soluble organic carbon contributes between 60-90% of the submicron sea-spray mass.

Abstract. Iron is a key limiting micro-nutrient for marine primary productivity. It can be supplied to the ocean by atmospheric dust deposition. Volcanic ash deposition into the ocean represents another external and so far largely neglected source of iron. This study demonstrates strong evidence for natural fertilisation in the iron-limited oceanic area of the NE Pacific, induced by volcanic ash from the eruption of Kasatochi volcano in August 2008. Atmospheric and oceanic conditions were favourable to generate a massive phytoplankton bloom in the NE Pacific Ocean which for the first time strongly suggests a connection between oceanic iron-fertilisation and volcanic ash supply.

Abstract:The first results of a regional circulation model REMO iso fitted with water isotope diagnostics are compared with various isotope series from central Europe. A 2 year case study is conducted from March 1997 to February 1999 centred over Europe, analysing daily and monthly measurements. Isotope signals over Europe are dominated by the typical isotopic effects such as temperature, continental and altitude effects, both on annual and seasonal scales. These well-known isotopic effects are successfully reproduced by REMO iso , using two different boundary data sets. In a first simulation, the European Centre for Medium-range Weather Forecasts (ECMWF) analyses serve as boundary conditions, where water isotopes were parameterized by a simple temperature dependence. In a second simulation, boundary conditions both for climatic and isotopic variables are taken from the ECHAM iso general circulation model output. The comparison of both simulations shows a very high sensitivity of the simulated υ 18 O signal to boundary conditions. The ECMWF-nested simulation shows an average offset of 4Ð5‰ in mean υ18 O values and exaggerated seasonal amplitude. The ECHAM-nested simulation represents correctly the observed mean υ18 O values, although with a dampened seasonality. REMO iso 's isotope module is further validated against daily υ 18 O measurements at selected stations (Nordeney, Arkona and Hohenpeissenberg) situated in Germany.