A continuous high-resolution dust record for the reconstruction of wind systems in central Europe (Eifel, Western Germany) over the past 133 ka

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1 GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L20712, doi: /2009gl039716, 2009 A continuous high-resolution dust record for the reconstruction of wind systems in central Europe (Eifel, Western Germany) over the past 133 ka Klemens Seelos, 1 Frank Sirocko, 1 and Stephan Dietrich 1 Received 24 June 2009; revised 25 August 2009; accepted 2 September 2009; published 31 October [1] The last glacial cycle in Central Europe is dominated by processes of aeolian dust transport and accumulation. These dust deposits are preserved in soils and lake sediments and provide detailed information about the climate variability during cold and dry periods. Especially the transitions from warm into cold periods are characterized by turbulent climate conditions. The main problems of terrestrial paleoclimate reconstructions are the completeness of the core material and a sampling resolution. To detect single dust storms we use a particle detection method, which allows high resolution, sub-annual analyses of sediment structures in undisturbed samples. The ELSA (Eifel Laminated Sediment Archive) stack is a compilation of four different lake sediment cores of the Eifel region (Western Germany) and comprise the period of the last 133 ka. The results of our analyses show high frequencies of dust storm events during the first cold events C24 and C23 after the last warm stage. In opposition, the coldest periods of the last glacial cycle OIS-4 (70 60 ka BP) and OIS-2 (35 14 ka BP) are characterized by stable climate conditions that provide the accumulation of homogenous dust sediments. Citation: Seelos, K., F. Sirocko, and S. Dietrich (2009), A continuous high-resolution dust record for the reconstruction of wind systems in central Europe (Eifel, Western Germany) over the past 133 ka, Geophys. Res. Lett., 36, L20712, doi: /2009gl Introduction [2] Laminated sediments are useful climate proxy archives for warm stages and interstadials and glacial/ interglacial transitions, in particular if the laminations are annual varves [Zolitschka, 1998]. The last deglaciation (14,400 12,600 ka BP) is documented by changing varve thicknesses and varve facies in laminated lake sediments in Central Europe [Brauer et al., 1999, 2008; Goslar et al., 1993]. For the LGM (Last Glacial Maximum) and the cold and dry stadials during the last glacial, it is mostly impossible to count single varves and analyse their internal structure. Here we need other techniques to reconstruct the climate conditions, which are dominated by dust storms over a nearly vegetation free landscape and permafrost soils [Zöller and Semmel, 2001; Schaber and Sirocko, 2005]. Especially the parameters wind strength and wind direction are essential indicators for the development and stability of 1 Institute for Geosiences, Johannes Gutenberg University, Mainz, Germany. Copyright 2009 by the American Geophysical Union /09/2009GL pressure cells over the North Atlantic and Europe [Isarin et al., 1997; Hostetler et al., 1999; Renssen et al., 2006]. [3] Continuous dust and loess sequences in the region of past braided river systems are well studied and trace the trends of climate variations during the last glacial cycle in Central Europe. The Nussloch loess-palaeosol sequence in the Upper Rhine Area shows a first appearance of remarkable aeolian dust accumulation around 70/68 ka BP and a reduction of loess sedimentation during OIS 3, ka BP [Bibus et al., 2007; Antoine et al., 2001]. Increasing dust accumulations during the transition OIS-5a OIS-4 (70 ka BP) are also detected in the Achenheim sequence, France [Rousseau et al., 1998]. Studies on the site of Koblenz- Metternich in the Middle Rhine Area and a loess record of an old volcanic crater near Tönchesberg, Germany show, that the last interglacial soils in both sequences are covered by at least 10 paleosols [Boenigk and Frechen, 2001; Frechen, 1994]. These paleosol horizons are developed during the warm Dansgaard-Oeschger phases during the last glacial. The stratigraphical correctness of the Tönchesberg sequence is verified by high-resolution palaeomagnetic studies [Reinders and Hambach, 1995]. In both records a marker loess layer at the transition OIS 5a-4 is detectable and underlines the connection to the sequence of Nussloch and Achenheim and other European records in Austria, Czech Republic, Hungary [Zöller et al., 1994] and Serbia [Marković et al., 2008]. Analyses of loess samples on a transect from Tadjikistan to the Tibet Plateau, in combination with atmospheric simulations, show, that the transport paths of dust during the last interglacial was strongly influenced by westerly wind systems [Vandenberghe et al., 2006]. [4] In addition to surface loess sites all over Europe, dust sediments can also be found in lakes and rivers [Creer and Morris, 1996; Muhs et al., 2003]. In Germany and France the maar lakes are ideal sediment traps for glacial sediments and represent the sedimentary succession of the environment. They are characterised by deep water volumes and an anoxic, hostile water chemism on the lake beds - ideal conditions for a good sediment preservation [Negendank, 1989]. A comparison of annually laminated and varve counted maar lake records from the Eifel/Germany, with a laminated lake sediment record from Northern Germany (Rederstall) shows, that high-resolution lake cores can be correlated across Central Europe by dust content, if the resolution of grain size data is on the order of decades/ centuries [Menke and Tynni, 1984; Seelos and Sirocko, 2007]. Phases of widespread dust dispersal are the same as the cold events in the Greenland ice and North Atlantic sea surface temperature patterns. The first occurrence of L of6

2 Figure 1. Geological map of the Eifel region, based on the geological map of Germany 1:1,000,000 [Bundesanstalt für Geowissenschaften und Rohstoffe, 1993] coordinate system: GCS Deutsches Hauptdreiecksnetz, Gauss zone 2, Bessel dust in Northern Germany and in the Eifel is during the Late Eemian Aridity Pulse (LEAP) which is called C26 in ocean records [Sirocko et al., 2005]. [5] Based on these results we developed a long dust time series for the Eifel region, Germany. The complete stack (0 133 ka) is a compilation of four different sediment cores (HL2 dry maar west of Hoher List; De3 Dehner Maar; OW3 Oberwinkler Maar; Sm3 Schalkenmehren) with a sampling interval of 500 mm. The dry maars Dehner Maar, Oberwinkler Maar and Maar west of Hoher List and the recent maar lake Schalkenmehren are located in the Eifel region, Western Germany (Figure 1). 2. Methods [6] The particle analysis method RADIUS - Rapid Particle Analysis of digital Images by ultra-high-resolution scanning of thin sections [Seelos and Sirocko, 2005], was developed to analyse and identify the different sediment structures in sediment cores, especially for cores of the ELSA archive (Eifel Laminated Sediment Archive) [Sirocko et al., 2005]. The application allows the detection of climate controlled sedimentation processes like storm events under cool and dry conditions or fine laminated sequences during warm periods and spontaneous events like volcanic eruptions, slumps and turbidites. Table 1 shows the particle analysis parameters and the thresholds for separating the detectable sediment structures by a weighting system (probability in percent). Especially the gradients of grain sizes and the correlation coefficients of compared datasets are important detection parameters to separate dust sequences and turbidites. The mean and maximum diameters of bright and dark particles are the key values to identify tephra layers and organic rich sequences. [7] After the detection procedure is finished, the dataset is getting time correlated and all identified turbidites and volcanic events are eliminated by a Matlab based ager module (The Mathworks Inc., USA). The results are adjusted records for dust and organics on a time scale. [8] The RADIUS storm detection module allows a frequency analysis of the storm activity for the complete dust stack. The algorithm works in the following way: if the dust detection value is high and the analysed sequence is surrounded by other sediment types like organic rich material or varves, the module detects a storm layer. In sequences of aeolian transported material, mostly during the cold and dry stadials, layers of strong storm events are detected by increased grain sizes in comparison to the surrounding dust sequences. In the end, all detected storm layers are counted and allocated to a fixed time interval of 100 years. 3. Stratigraphy and Variability of the ELSA Dust Stack [9] Datings and tuning used for the ELSA greyscale stack [Sirocko et al., 2005] are also the basis for the new dust stack. Because of better sediment conservation, we replaced the sections De2 and SM2 (41,000 0 ka BP) and added the core sequences De3 and SM3 for the same period. New 14 C-datings for the De3 core (Figure 2) and chemical tephra correlations of the Lake Laach Tephra [van den Bogaard and Schmincke, 1985; van den Bogaard, 1995] for the SM3 and De3 core stabilized the stratigraphy of ELSA stack noticeable. [10] The dust stack over the last glacial cycle is characterised by a high variability of different dust sequences during the whole period (Figure 2). The noticeable similar- 2of6

3 Table 1. Weighting Factors a Detection Float. gradient analysis (depends on sampling steps, gradient) no vertical particle-size gradient (±0.05) Dust Turbidite Tephra Organics Details WF Details WF Details WF Details WF 1 3 increasing particle sizes from top to bottom 5 10 no significance - no significance - Floating correlation analysis (depends on sampling steps, correlation factor) high positive correlation: mean size versus max size for bright particles 1 5 negative. correlation: silt of total versus silt of all classes high positive correlation for the top area: silt of total versus mean particle size 1 5 high positive correlation: max size of bright particles versus max size of dark particles high negative correlation: max size of dark particles versus max size of bright particles 1 10 Mean particle sizes (500 mm sample segment) mm 5 mean sizes (top): mm 3 mean sizes (min. size bright particles: mm): mean sizes for dark particles: mm 2 >350 mm mm mm 6 >60 mm 3 mean sizes (bottom): mm <30 mm mm (dark) mm (dark) mm (dark) mm 2 Modes 40 ± 5 mm bimodality: 1 5 top: 30 ± 5 mm ± 5 mm (dark & bright) 2 no significance - bottom: 60 ± 5 mm 1 bimodality: 5 Skewness of distribution 0.0 ± ± >0.5 3 no significance ± ± Distribution width (1/38 classification) 0.0 ± ± <28 (bright) 5 > (bright) 3 >48 (bright & dark) 5 no significance - < < < Silt content (20 63 mm) >60% (bright) 5 no significance - 5 8% 3 <5% 6 >50% 3 <8% (dark p.) 1 5 8% (bright p.) 3 >40% 1 <30% 3 >5% (dark) 3 Sorting (bright) 3 no significance - >1.9 (bright & dark) (dark) > > Percentile 95 percentile 10 for bright particles: no significance - for dark & bright particles: no significance mm mm mm mm 1 Max. particle sizes <80 mm (bright) mm (bright) 2 >130 mm (dark) 2 >200 mm (dark) 2 Maximum sum a WF, maximum 36 points comply with a probability of 100% for the detected sediment type. 3of6

4 Figure 2. Comparison of climate proxy records for the period ka BP: (a) NorthGRIP d 18 O-record as a temperature proxy for the last glacial cycle in Greenland; (b) the NorthGRIP microparticles record, measured particle diameters > 2 mm; (c) ELSA dust detection stack as a normalized probability record (see methods and Table 1); (d) frequency of single dust storms in a 100-years-segmentation; (e) ELSA organic detection stack (see methods and Table 1); (f) the four core sequences of the stack, SM3 is a sediment core of a recent maar lake, DE3, OW1 and HL2 are cores from dry maars; (g) datings (AMS 14C and OSL 9 and tephra chronology as age control for the stack, Lake Laach tephra dated by van den Bogaard [1995]. The asterisk indicates a piece of wood (DE m, spruce) dated 2008, Leibnitz Institut, Kiel. ity to the NorthGRIP d 18 O and the NorthGRIP microparticles record [North Greenland Ice Core Project members, 2004; Ruth et al., 2003] underlines the direct coupling between the conditions in North Atlantic and the climate situation in Central Europe. [11] During the 468 years lasting LEAP ± 118 ka BP) 52 single storms layers could be detected (Figures 2c 2d) [Sirocko et al., 2005]. This was the first appearance of an intensive aridity phase during the Eemian ( 18,500 ka BP). At the very end of the last warm stage (111 ka BP), two very strong dust events (C24, C23) occur and the transition from relatively warm and wet conditions into the cool and dry period happened in between decades. These cool events are characterized by a congeries of single dust storms in an environment, that was dominated by herbage and shrub vegetation [Sirocko et al., 2005]. The frequency of storm events is higher than 40 storm events per century during C24 and higher than 15 events in C23 (Figure 2d). During the next phase ( ka BP), single dust storm sediments are replaced by a continuous dust accumulation. The content of organics decreases until the long-lasting DO21 event (86 82 ka BP), that represents a warm period with a completely developed vegetation cover (Figure 2e). The first maximum of dust accumulation rates appears during OIS 4 and lasts for about 10,000 years (Figure 2c). The transition into the warm phase OIS-3 (60 ka BP) is characterized by a strong variability of organic rich sediments during the DO events 17-7 and high dust contents during the stadials. The maximum content of organics is observed during the 6000 years lasting DO14 event. The following stadial is characterized by high dust accumulation rates and a rapidly increasing dust storm frequency. OIS-3 ends around 32 ka BP. The content of homogenous dust sediments increases rapidly and reaches the absolute maximum during the LGM (18 ka BP). The content of organics is very low during this period and increases once again with Figure 3. Comparison of different sediment types of core HL2: (a) core sequence 111, ,781 a BP, fine laminated varves with a mean thickness of 150 mm and a low content of quartz particles; (b) core sequence 110, ,011 a BP, 5 dust storms and 2 turbidites are detected by the RADIUS particle analysis module 10, storm layers are not graded and very well sorted, turbidites show gradation and coarse particles on the basis; and (c) core sequence 70,248 70,187 a BP, homogenous sediment structure, well sorted and no gradation, characteristic of loess-like sediments. 4of6

5 the Bölling transition 14 ka BP. The entrance into the Holocene is represented by high contents of organics and a very low dust activity. 4. Conclusions [12] It is obvious, that the frequency of single dust storms is very high during the LEAP (118 ka BP) and the first cold events (C24, C23) after the last interglacial. The reason for this phenomenon can be explained by analysing highresolution microscopy images (Figure 3). The ending Eemian is characterized by annually laminated, undisturbed varves sequences (Figure 3a). Dust storms are very seldom and hence the content of clastic components in the lake deposits is extremely low. The sediment structure of the following cold event C24 is completely different (Figure 3b). It is visible that the internal structure of dust storm layers is characterized by a good sorting, no gradation and relatively coarse grain sizes. The surrounding sediments are mostly varves with a relatively high amount of clastic particles. During these periods the landscape still has a closed vegetation cover [Sirocko et al., 2005], which constricts the wind to pick up particles and transport them to the next sediment trap. Only storms with high velocities are able to erode and pick up particles from the river basins and mountain slopes of the nearer surrounding. The frequency of more than 40 dust storms per century for the C24 event shows that the climate conditions at the very end of the last warm stage are characterized by extreme short time variations. [13] The sediment structure of wind transported material during OIS-4 is apparently different in comparison to the cold events C23 and C24 (Figure 3c). Because of missing forest vegetation, which disturbs the continuous material transport over the surface and stable climate conditions, we recognize homogenous dust sequences without a separation into single storm events. The situation during OIS-3 is similar to the end phase of the Eemian and in analogy to OIS-4, the LGM is dominated by homogenous dust sediments. [14] The ELSA dust stack shows, that the climate situation at the end of the last interglacial is, in spite of a boreal forest vegetation, characterized by extreme storm events. There is also evidence, that longer lasting warm phases like the interstadials DO-21 and DO-14 entail increasing storm frequencies in the following stadials. The results of the ELSA dust stack and the reconstruction of the storm activity during the last glacial should be the basis for further reaching research projects. Especially the detection of numerous storm events during the cold stages C24 and C23 could be an interesting challenge for modelers to control the results by time transient simulations. [15] Acknowledgments. We wish to thank Klaus Schwibus and Günter Ritschel, the technicians of our working group, for the preparation of excellent thin sections. We thank the Johannes Gutenberg-University of Mainz for funding the ELSA core repository. This research was supported by grants to the University of Mainz from the German Research Foundation (DFG), the German Climate Research program of the Federal Ministry of Education and Research (DEKLIM), and the Stiftung Rheinland-Pfalz für Innovation. A special thank goes to the Editor, the Editor s Assistants of GRL, and the two Reviewers, who helped us with their factual comments. References Antoine, P., D.-D. Rousseau, L. Zöller, A. Lang, A.-V. Munaut, C. Hatté, and M. Fontugne (2001), High-resolution record of the last interglacialglacial cycle in the Nussloch loess-palaeosol sequences, Upper Rhine area, Germany, Quat. Int., 76/77, , doi: /s (00)00104-x. Bibus, E., M. Frechen, M. Kösel, and W. Rähle (2007), Das jungpleistozäne Lößprofil von Nußloch (SW-Wand) im Aufschluss der Heidelberger Zement AG, Quat. Sci. J., 56, Boenigk, W., and M. Frechen (2001), The loess record in sections at Koblenz-Metternich and Tönchesberg in the Middle Rhine area, Quat. Int., 76/77, , doi: /s (00) of6

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(1998), Paläoklimatische Bedeutung laminierter Sedimente Holzmaar (Eifel, Deutschland), Lake C2 (Nordwest-Territorien, Kanada) und Lago Grande di Monticchio (Basilikata, Italien), Gebrüder Bornträger, Berlin. Zöller, L., and A. Semmel (2001), 175 years of loess research in Germany Long records and unconformities, Earth Sci. Rev., 54, 19 28, doi: /s (01) Zöller, L., E. A. Oches, and W. D. McCoy (1994), Towards a revised chronostratigraphy of loess in Austria with respect to key sections in the Czech Republic and in Hungary, Quat.Sci.Rev., 13, , doi: / (94) S. Dietrich, K. Seelos, and F. Sirocko, Institute for Geosiences, Johannes Gutenberg University, D Mainz, Germany. (seelos@uni-mainz.de) 6of6