Sediments of Lake Vens (SW European Alps, France) record large-magnitude earthquake events

We studied sediment cores from Lake Vens (2,327 m asl), in the Tinée Valley of the SW Alps, to test the paleoseismic archive potential of the lake sediments in this particularly earthquake-sensitive area. The historical earthquake catalogue shows that moderate to strong earthquakes, with intensities of IX–X, have impacted the Southern Alps during the last millennium. Sedimentological (X-ray images, grain size distribution) and geochemical (major elements and organic matter) analyses show that Lake Vens sediments consist of a terrigenous, silty material (minerals and organic matter) sourced from the watershed and diatom frustules. A combination of X-ray images, grain-size distribution, major elements and magnetic properties shows the presence of six homogenite-type deposits interbedded in the sedimentary background. These sedimentological features are ascribed to sediment reworking and grain sorting caused by earthquake-generated seiches. The presence of microfaults that cross-cut the sediment supports the hypothesis of seismic deposits in this system. A preliminary sediment chronology is provided by 210Pb measurement and AMS 14C ages. According to the chronology, the most recent homogenite events are attributable to damaging historic earthquakes in AD 1887 (Ligure) and 1564 (Roquebillière). Hence, the Lake Vens sediment recorded large-magnitude earthquakes in the region and permits a preliminary estimate of recurrence time for such events of ~400 years.

Quantitative high-resolution warm season rainfall recorded in varved sediments of Lake Oeschinen, northern Swiss Alps: calibration and validation AD 1901–2008

High-resolution, well-calibrated records of lake sediments are critically important for quantitative climate reconstructions, but they remain a methodological and analytical challenge. While several comprehensive paleotemperature reconstructions have been developed across Europe, only a few quantitative high-resolution studies exist for precipitation. Here we present a calibration and verification study of lithoclastic sediment proxies from proglacial Lake Oeschinen (46°30′N, 7°44′E, 1,580 m a.s.l., north–west Swiss Alps) that are sensitive to rainfall for the period AD 1901–2008. We collected two sediment cores, one in 2007 and another in 2011. The sediments are characterized by two facies: (A) mm-laminated clastic varves and (B) turbidites. The annual character of the laminae couplets was confirmed by radiometric dating (210Pb, 137Cs) and independent flood-layer chronomarkers. Individual varves consist of a dark sand-size spring-summer layer enriched in siliciclastic minerals and a lighter clay-size calcite-rich winter layer. Three subtypes of varves are distinguished: Type I with a 1–1.5 mm fining upward sequence; Type II with a distinct fine-sand base up to 3 mm thick; and Type III containing multiple internal microlaminae caused by individual summer rainstorm deposits. Delta-fan surface samples and sediment trap data fingerprint different sediment source areas and transport processes from the watershed and confirm the instant response of sediment flux to rainfall and erosion. Based on a highly accurate, precise and reproducible chronology, we demonstrate that sediment accumulation (varve thickness) is a quantitative predictor for cumulative boreal alpine spring (May–June) and spring/summer (May–August) rainfall (rMJ = 0.71, rMJJA = 0.60, p < 0.01). Bootstrap-based verification of the calibration model reveals a root mean squared error of prediction (RMSEPMJ = 32.7 mm, RMSEPMJJA = 57.8 mm) which is on the order of 10–13 % of mean MJ and MJJA cumulative precipitation, respectively. These results highlight the potential of the Lake Oeschinen sediments for high-resolution reconstructions of past rainfall conditions in the northern Swiss Alps, central and eastern France and south-west Germany.

UNESCO World Heritage „Prehistoric pile-dwellings around the Alps“: Chances and Challenges for Management and Research of Cultural Heritage Under Water

Research in prehistoric sites of lakes and bogs around the Alps started more than 150 years ago. In 2004 Switzerland took the initiative to propose an international UNESCO world heritage nomination, which was successful in 2011. Six countries – Austria, France, Germany, Italy, Slovenia and Switzerland – joined forces to obtain the precious label for an invisible cultural heritage of outstanding universal value. Archaeological sites under water or in bogs are of special importance because objects made of organic material like wood, bark, plant fibres and others survive in this milieu for hundred or thousands of years. The alpine pile-dwelling sites offer a highly precise dating possibility by using dendrochronology. All in all these sites have a high scientific potential but run also risks of long term conservation. Beside the scientific chances there are risks to consider: public access is difficult and a major challenge. New ideas are demanded to keep alive public interest.

Transient sediment supply in a high-altitude Alpine environment evidenced through a 10Be budget of the Etages catchment (French Western Alps)

Although beryllium-10 (10Be) concentrations in stream sediments provide useful synoptic views of catchment-wide erosion rates, little is known on the relative contributions of different sediment supply mechanisms to the acquisition of their initial signature in the headwaters. Here we address this issue by conducting a 10Be-budget of detrital materials that characterize the morphogenetic domains representative of high-altitude environments of the European Alps. We focus on the Etages catchment, located in the Ecrins-Pelvoux massif (southeast France), and illustrate how in situ 10Be concentrations can be used for tracing the origin of the sand fraction from the bedload in the trunk stream. The landscape of the Etages catchment is characterized by a geomorphic transient state, high topographic gradients, and a large variety of modern geomorphic domains ranging from glacial environments to scarcely vegetated alluvial plains. Beryllium-10 concentrations measured in the Etages catchment vary from similar to 1 x 104 to 4.5 x 105 atoms per gram quartz, while displaying consistent 10Be signatures within each representative morphogenetic unit. We show that the basic requirements for inferring catchment-wide denudation from 10Be concentration measurements are not satisfied in this small, dynamic catchment. However, the distinct 10Be signature observed for the geomorphic domains can be used as a tracer. We suggest that a terrestrial cosmogenic nuclide (TCN) budget approach provides a valuable tool for the tracing of material origin in basins where the let nature do the averaging' principles may be violated.

Synchronous Holocene climatic oscillations recorded on the Swiss Plateau and at timberline in the Alps

Eight synchronous pre-Roman cold phases were found at 9600–9200, 8600–8150, 7550–6900, 6600– 6200, 5350–4900, 4600–4400, 3500–3200 and 2600–2350 radiocarbon years BP by reconstructing past climate at two sites on the Swiss Plateau and at timberline in the Alps. The cooling events during the early-and mid-Holocene represent temperature values similar to today, and apparently the onset of cooling events represents a deviation from today's mean annual temperature of about 1°C and is triggered at a 1000-year periodicity. At Wallisellen-Langachermoos (440 m), a former oligotrophic lake near Zürich, the correlation between sum mertime lake levels and the seed production of the amphi-Atlantic aquatic plantNajas flexilis was used to reconstruct lake levels over a 3000-year period during the first part of the Holocene. At Lake Seedorf on the western Swiss Plateau (609 m) the sedimentological, palynological and macrofossil record revealed fluctuations of lake levels for the complete Holocene. From Lago Basso in the southern Alps (2250 m, Val San Giacomo near Splügen Pass, Northern Italy) the terrestrial plant macrofossils – especiallyPinus cembra andLarix – allowed the reconstruction of timberline fluctuations controlled by climate. A similar climatic pattern was found at Gouillé Rion pond in the central Swiss Alps (2343 m, Val d'Hérémence) with plant macrofossils and pollen concentrations and percentages. We postulate that these climatic events are detectable throughout central Europe by independent methods in combination with precise AMS-radiocarbon datings on terrestrial plant remains. Our data fit other proxy records of regional climatic change, such as cool intervals from Greenland ice cores, glacier movements in the Swiss and Austrian Alps, and dendro-densitometry on subfossil wood, as well as the palaeoclimatic data from the Jura Mountains of France obtained by sedimentological analyses. Thus our data indicate that the Northern Hemisphere climate was less stable during the Holocene than previously believed.