Lateglacial lake-level changes at Montilier-Strandweg, lake Morat, Switzerland and their climatic significance [Les variations du niveau du lac de Morat (Montilier-Strandweg, Suisse) pendant le Tardiglaciaire et leur signification climatique]

Using pollen and sediment analyses, cores from Montilier-Strandweg, lake Morat (Swiss Plateau), were studied to reconstruct lake-level fluctuations during the Bølling-Allerød interstadial and the Younger Dryas stadial. Lake-level appears to have been low during the early and mid-Bølling at ca 12 275 BP (Juniperus and early Betula phases), the early and late Allerød (at 1 1 845 and 1 1 250 BP respectively), and the second part of the Younger Dryas. Rises in lake-level occurred during the late Bølling and the Bølling-Allerød transitions at ca 1 2 000 BP (late Betula phase and Older Dryas), the mid- Alterød, and the Younger Dryas start. The palaeohydrological changes reconstructed at Montilier-Strandweg show a possible response in west-central Europe to the oscillations of the deglacial ocean-system such as recognized in the North Atlantic area.L'analyse palynologique et sédimentologique de sondages réalisés à Montilier-Strandweg, au bord du lac de Morat (Plateau suisse), permet de reconstituer tes fluctuations du niveau du lac pendant l'interstade Bølling-Allerød et le Dryas récent. De bas niveaux sont mis en évidence pendant la première partie du Bølling vers 12 275 BP (phases à Juniperus et début de la phase à Betula), le début et la fin de l'Allerød (vers 11 845 et 11 250 BP), et la seconde partie du Dryas récent. Des hausses du plan d'eau surviennent pendant la seconde partie du Bølling et à la transition Bølling-Alterød vers 12 000 BP (fin de la phase à Betula et Dryas moyen), au milieu de l'Allerød, et au début du Dryas récent. Les variations paléohydrologiques reconstituées à Montilier-Strandweg, au centre de l'Europe, pourraient être la réponse aux changements survenus dans l'Atlantique Nord pendant la déglaciation.Magny Michel, Richoz Isabelle. Lateglacial lake-level changes at Montilier-Strandweg, lake Morat, Switzerland and their climatic significance [Les variations du niveau du lac de Morat (Montilier-Strandweg, Suisse) pendant le Tardiglaciaire et leur signification climatique]. In: Quaternaire, vol. 11, n°2, 2000. Le Tardiglaciaire en France septentrionale. pp. 129-144

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

Stable isotopes and element concentrations of samples from the Wadi Bih, United Arab Emirates

Ocean acidification triggered by Siberian Trap volcanism was a possible kill mechanism for the Permo-Triassic Boundary mass extinction, but direct evidence for an acidification event is lacking. We present a high-resolution seawater pH record across this interval, using boron isotope data combined with a quantitative modeling approach. In the latest Permian, increased ocean alkalinity primed the Earth system with a low level of atmospheric CO2 and a high ocean buffering capacity. The first phase of extinction was coincident with a slow injection of carbon into the atmosphere, and ocean pH remained stable. During the second extinction pulse, however, a rapid and large injection of carbon caused an abrupt acidification event that drove the preferential loss of heavily calcified marine biota