Volcano- and climate-driven changes in atmospheric dust sources and fluxes since the Late Glacial in Central Europe

Atmospheric dusts are an important part of the global climate system, and play an important role in the marine and terrestrial biogeochemical cycles of major and trace nutrient elements. A peat bog record of atmospheric deposition shows considerable variation in dust deposition during the past 15 k.y., with abrupt changes in fl uxes at 12, 9.2, 8.4, 7.2, and 6 cal. kyr B.P. Using Nd isotopes and rare earth elements, it is possible to clearly distinguish between volcanic inputs and those driven by climate change, such as the long-term aridifi cation of the Sahara and regional erosion due to forest clearing and soil cultivation activities. Our results indicate that a major dust event in North Africa and Europe preceded the 8.2 kyr B.P. cold event by 200 yr. This dust event may have played an active role in the following climate cooling of the 8.2 kyr B.P. event. Nd isotope evidence also indicates a relatively slow change in dust regime over Europe from 7 to 5 kyr B.P. due to Sahara expansion. These fi ndings show that the inorganic fraction in high-resolution peat records can provide remarkably sensitive indicators of dust load and sources. Our study supports the priority to better identify the impact of dust loading during the Holocene in terms of direct and indirect impacts on environmental and climate changes. INTRODUCTION Atmospheric mineral dusts from diverse natural sources affect the biogeochemical cycles of many elements in marine (Meskhidze et al., 2003) as well as terrestrial ecosystems (Goudie and Middleton, 2001). For example, in highly weathered soils of Hawaii, dusts from Asia have been found to represent an important source of phosphorus (P) to plants (Chadwick et al., 1999). Dust modifi es the radiation budget and thus plays an important role in Earth’s climate system (Goudie and Middleton, 2001; Harrison et al., 2001). The fl uxes of these dusts are linked to their source areas (Grousset and Biscaye, 2005), mainly desert and arid regions, by the intensity and frequency of the transporting weather systems (Goudie and Middleton, 2001). Superimposed on the dust background are the episodic additions of particles from explosive volcanoes (Oppenheimer, 2003), and from large continental deserts during abrupt global cold events, as recorded in polar ice cores for the 8.2 kyr B.P. and the Younger Dryas events (Goudie and Middleton, 2001; Alley and Agustdottir, 2005). Detailed knowledge of the natural variations in atmospheric dust deposition is crucial for understanding the response of dust to climate change and the effects on ecosystems, but also to better understand the feedbacks that dust loading may have on climate. To date, despite the obvious importance of atmospheric mineral dusts, there are remarkably few continental records of their changing rates and sources. To help narrow this knowledge gap, a peat profi le from Etang de la Gruère, a well-studied bog in the Jura Mountains of Switzerland, is used as an archive of atmospheric dust deposition in Central Europe. MATERIALS AND METHODS Etang de la Gruère is a raised ombrotrophic bog that receives inputs exclusively from the atmosphere. It consists of as much as 650 cm of peat directly overlying lacustrine clay. In an early study using peat cores from this bog, atmospheric Pb deposition was reconstructed using Pb isotopes, but the sampling thickness of these cores provided limited temporal resolution (Shotyk et al., 1998). A subsequent report employing a second set of cores from the same bog provided much better sampling resolution, but the focus of that study was Hg deposition (Roos-Barraclough et al., 2002). We use the Ti concentrations from this high-resolution peat core and the numerous 14C age dates to create a detailed, high-resolution reconstruction of total dust deposition (see Figs. DR1–DR5 and text in the GSA Data Repository1). To distinguish between soil-derived mineral dusts and volcanic inputs, and to identify possible source areas, the rare earth elements (REE) were measured along with 143Nd/144Nd isotope ratios, with emphasis on the peat samples dating from the early to mid-Holocene, when abrupt dust pulses occurred. The dust fl uxes and REE and 143Nd/144Nd results are compared with pollen data (see the Data Repository, including Fig. DR7) to try to resolve the sequence of changes in dust deposition and vegetation change with a view to identifying possible causes and effects. ABRUPT DUST EVENTS DURING THE LATE GLACIAL AND THE HOLOCENE Combining the Ti concentrations (Fig. 1A) with the peat accumulation rates allows the dust fl ux to the bog to be estimated (Fig. 1B) (see the Data Repository, including Fig. DR6 and Table DR1). Some of the periods of most rapid change, i.e., ca. 12, 9.2, 8.4, 7.2, and 6 kyr B.P., are discussed in detail here. Younger Dryas A large peak of dust (>8 g m–2 yr–1) is recorded from 12.8 k.y. to 11.7 kyr B.P., consistent with the Younger Dryas (YD) time window *Current address: Institute for Transuranium Elements of the European Commission’s Joint Research Centre (JRC), Postfach 2340, D-76125 Karlsruhe, Germany. †Current address: Department of Renewable Resources, University of Alberta, Edmonton, Alberta T6G 2H1, Canada. Volcanoand climate-driven changes in atmospheric dust sources and fl uxes since the Late Glacial in Central Europe Gaël Le Roux1,2, Nathalie Fagel1, Francois De Vleeschouwer1,2, Michael Krachler3*, Vinciane Debaille4, Peter Stille5, Nadine Mattielli4, W.O. van der Knaap6, Jacqueline F.N. van Leeuwen6, and William Shotyk3† AGEs, Department of Geology, Liège University B18, Sart-Tilman, Allée du 6 Août, B-4000 Liège, Belgium EcoLab, UMR5245 CNRS–Université de Toulouse, campus ENSAT avenue de l’Agrobiopôle, 31326 Castanet-Tolosan, France Institute of Earth Sciences, University of Heidelberg, Im Neuenheimer Feld 236, D-69120 Heidelberg, Germany 4 Laboratoire G-Time, Université Libre Bruxelles, CP160/02, Avenue F.D. Roosevelt 50, 1050 Bruxelles, Belgium LhyGeS-UMR7517, EOST, Université de Strasbourg, INSU/CNRS, 1 rue Blessig, F-67084 Strasbourg, France 6 University of Bern, Institute of Plant Sciences and Oeschger Centre for Climate Change Research, Altenbergrain 21, CH-3013