The Les Echets sediment sequence has recently been the subject of a high-resolution, multi-proxy study which revealed shifts in lake productivity linked to Greenland stadials and interstadials over the last 40 ka . Rapid ecosystem response to abrupt climate changes during the last glacial period in western Europe, 40-16 ka. Geology 36: 407-410). Here we present new elemental data for this sequence as acquired using an X-ray fluorescence core scanning system which provides in situ high-resolution, continuous, multi-element analyses. It was found that the strength of associations between the studied elements (Ti, Rb, K, Zr, Si, Ca, Sr, Mn and Fe) varied over time with changes in lake status which are ultimately driven by changes in climate. Increases in fine-grained, detrital input (as indicated by Ti, Rb, K and Zr/Rb) overlap with independently established periods of lower lake productivity and are interpreted to represent more arid conditions. Several of these arid periods are coincident with low diatom concentrations and the timing of Heinrich events H4, H3 and H2. The duration of the environmental impacts linked to the H events varied by proxy with elemental data (Ti and Zr/Rb) estimating shorter events than the diatom data. Periods of lower detrital input and coarser grain sizes agreed in time with periods of higher lake productivity. The elemental data provide new insights into hydrological changes and related sediment processes within the catchment, and highlight the need for multi-element and multi-proxy approaches when reconstructing climate change using lacustrine sediment sequences.

International audienceWe present a high-resolution and independently dated multiproxy lake sediment record from the paleolake at Les Échets in southeastern France that displays synchronous changes in independent limnic and terrestrial ecosystem proxies, in concert with millennial-scale climate oscillations during the last glacial period. Distinct lake-level fluctuations, low lake organic productivity, and open, treeless vegetation indicate cold and dry conditions in response to Heinrich events. Alternating phases of higher and low lake organic productivity, stratified surface waters and long-lasting lake ice cover, decreased or increased catchment erosion, and tree-dominated or herb-dominated vegetation resemble Dansgaard-Oeschger interstadialstadial variability. Transitions between different ecological states occurred in as little as 40–230 yr and seem to have been controlled by the position of the Polar Front. Ecosystem response after 30 ka suggests that local climate conditions became more important. Our results demonstrate that all parts of the terrestrial system responded to the abrupt and dramatic climatic changes associated with Dansgaard-Oeschger and Heinrich events, and that regional factors modulated ecosystem response

Several large abrupt climate fluctuations during the last glacial have been recorded in Greenland ice cores and archives from other regions. Often these DansgaardOeschger events are assumed to have been synchronous over wide areas, and then used as tiepoints to link chronologies between the proxy archives. However, it has not yet been tested independently whether or not these events were indeed synchronous over large areas. Here, we compare DansgaardOeschgertype events in a welldated record from southeastern France with those in Greenland ice cores. Instead of assuming simultaneous climate events between both archives, we keep their age models independent. Even these welldated archives possess large chronological uncertainties, that prevent us from inferring synchronous climate events at decadal to multicentennial time scales. If possible, comparisons between proxy archives should be based on independent, nontuned timescales.

M., 2015: Regional deglaciation and postglacial lake development as reflected in a 74 m sedimentary record from Lake Vättern, southern Sweden.Abstract: The withdrawal of the Late Weichselian ice sheet and rapid isostatic uplift in southern Scandinavia led to the entrainment of large volumes of melt water within the proglacial Baltic Ice Lake (BIL). The eventual western outpost of BIL, Lake Vättern, has been a focal point for studying the dynamic retreat history of the Late Weichselian ice sheet in south central Sweden. This part of the deglacial history is described from an abundance of terrestrial studies, but, to date, no complimentary long sediment cores from Lake Vättern have been available. Here, we present the results from a unique, 74 m borehole in southern Lake Vättern that recovered a Late Pleistocene to Holocene sedimentary sequence. Physical and chemical analyses of the sediment and pore water, together with geophysical mapping, reveal glacial as well as postglacial imprints implying an oscillating ice sheet margin, evidence for neotectonic activity and one or more marine incursions into the lake during deglaciation. We attribute the glaciotectonic deformation of the sediments at 54 m below the lake floor to an ice readvance that likely occurred at the same time or before the advance that formed the Levene moraine (,. After this event, potential readvances were likely restricted to a more northerly position in the basin. We identify the final drainage of the BIL, but find evidence for an earlier marine incursion into the Vättern basin (,13.0 cal. ka BP), indicating water exchange between the North Atlantic and the Baltic Ice Lake during the late Alleröd.

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Abstract. We describe the results of an inter-laboratory investigation into the identification and quantification of the Arctic sea ice biomarker proxy IP 25 in marine sediments. Seven laboratories took part in the study, which consisted of the analysis of IP 25 in a series of sediment samples from different regions of the Arctic, sub-Arctic and Antarctic, additional sediment extracts and purified standards. The results obtained allowed 4 key outcomes to be determined. First, IP 25 was identified by all laboratories in sediments from the Canadian Arctic with inter-laboratory variation in IP 25 concentration being substantially larger than within individual laboratories. This greater variation between laboratories was attributed to the difficulty in accurately determining instrumental response factors for IP 25 , even though laboratories were supplied with appropriate standards. Second, the identification of IP 25 by 3 laboratories in sediment from SW Iceland that was believed to represent a blank, was interpreted as representing a better limit of detection or quantification for such laboratories, contamination or mis-identification. These alternatives could not be distinguished conclusively with the data available, although it is noted that the precision of these data was significantly poorer compared with the other IP 25 concentration measurements. Third, 3 laboratories reported the occurrence of IP 25 in a sediment sample from the Antarctic Peninsula even though this biomarker is believed to be absent from the Southern Ocean. This anomaly is attributed to a combined chromatographic and mass spectrometric interference that results from the presence of a di-unsaturated highly branched isoprenoid (HBI) pseudo-homologue of IP 25 that occurs in Antarctic sediments. Finally, data are presented that suggest that extraction of IP 25 is consistent between Accelerated Solvent Extraction (ASE) and sonication methods and that IP 25 concentrations based on 7-hexylnonadecane as an internal standard are comparable using these methods. Recoveries of some more unsaturated HBIs and the internal standard 9-octylheptadecene, however, were lower with the ASE procedure, possibly due to partial degradation of these more reactive chemicals as a result of higher temperatures employed with this method. For future measurements, we recommend the use of reference sediment material with known concentration(s) of IP 25 for determining and routinely monitoring instrumental response factors. Given the significance placed on the presence (or otherwise) of IP 25 in marine sediments, some further recommendations pertaining to quality control are made that should also enable the two main anomalies identified here to be addressed.

Lake Vättern, Sweden, is within a graben that formed through rifting along the boundary between two Precambrian terrains. Geophysical mapping and geological coring show that substantial tectonic movements along the Lake Vättern graben occurred at the very onset of the Holocene. This is evident from deformation structures in the soft sediment accumulated on the lake fl oor. Our interpretation of these structures suggests as much as 13 m of vertical tectonic displacements along sections of a >80-km-long fault system. If these large displacements are from one tectonic event, Lake Vättern must have had an earthquake with seismic moment magnitudes to 7.5. In addition, our geophysical mapping shows large landslides along sections of the steep lake shores. Pollen analysis of sediment infi llings of some of the most prominent sediment deformation structures places this major seismic event at the Younger Dryas-Preboreal transition, ca. 11.5 ka. We suggest that this event is mainly related to the rapid release of ice-sheet load following the deglaciation. This paleoseismic event in Lake Vät-tern ranks among the larger known intraplate tectonic events in Scandinavia and attests to the signifi cance of glacio-isostatic unloading.

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