BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:Record of abrupt changes of last climate cycle in European glacial dust deposits - Denis-Didier Rousseau - Laboratoire de Meteorologie Dynam ique &\; CERES-ERTI DTSTART:20180426T163000Z DTEND:20180426T173000Z UID:TALK100564@talks.cam.ac.uk CONTACT:Heather L. Ford DESCRIPTION:This presentation is an overview to the project ACTES\, suppor ted by the French ANR\, and previous projects I conducted on European loes s sequences. The main aim was to study the record of abrupt climate change s\, corresponding to the Dansgaard-Oeschger and Heinrich events\, in Europ ean terrestrial records\, especially loess sequences. Loess is an eolian m aterial that can be considered in a first order as “paleodust”. This s tudy was designed as a data-model comparison to investigate how these sequ ences recorded the DO events in a periglacial environment\, how the dust w as emitted and deposition occurred\, and from which source zones.\n\nEurop e has been strongly impacted by the millennial climate changes related to variations in the sea-ice extent and therefore also affected the moisture sources of precipitation on the Greenland ice sheet. These variations in t he extent of the sea ice during the last climatic cycle (LCC\, about 130-1 5 kyr) impacted the westerlies and the position of the polar jet stream\, and consequently storm track trajectories. Furthermore\, the presence of i ce sheets and ice caps over Great Britain\, Scandinavia and the Alps enhan ced the zonal circulation\, as recorded by the European paleodust deposits located along the 50°N parallel. \n\nLoess sequences are well developed all over Europe\, but especially in the so-called loess belt between 48° and 52°N. Such intensive deposition of paleodust over Europe has been fav ored by the reduced arboreal cover (even practically absent in NW Europe d uring both GS and GIs\, by sea-level lowering\, exposing large areas of th e continental shelves to eolian erosion\, and by strong increases in fluvi al transport and sedimentation by periglacial braided rivers. Extensive in vestigations of European loess series along a longitudinal transect at 50 °N reveal that the millennial-scale climate variations observed in the No rth-Atlantic marine and Greenland ice-core records are well preserved in l oess sequences. Among them\, the Nussloch loess site yields an important r ecord of the LCC although its paleosol-loess unit couplet succession is no t unique\, but observed with a variable thickness and a diverse nature of the paleosols in sequences ranging from Western Europe eastward to Ukraine over more than 1800 km. \nRecent numerical simulations of the past global dust cycle for the first time included glaciogenic dust sources and\, com pared to earlier attempts\, resulted in an improved performance when confr onted to data available for the Last Glacial Maximum. Still\, even the imp roved modeling failed to capture spatial and temporal dynamics of past dus t deposition. We achieve recently a step increase in understanding sub-con tinental scale climate change by identifying dust sources and constraining dust residence time in the atmosphere. Using dust deposition over Europe during the last glacial cycle\, geochemical fingerprinting\, and numerical dust emission simulations we identify the main aerosol sources for differ ent depositional areas. Dust was transported at low elevation and over reg ional distances only. The glaciogenic sources considered so far in climate modeling\, like frontal moraines and outwash plains of the European ice-s heets\, were of considerably less relevance for the global dust budget tha n proposed earlier. The main contributors were regions between 48°and 52 °N\, with variable hot spots depending on climate conditions. Loess units are interpreted to correspond to coarse paleodust transported at rather l ow elevations\, in the active layer of the atmosphere (about 300 to maximu m 3000 m) at regional to local scales\, while finer paleodust deposited at high latitudes seems transported at much higher elevations.\n\nA recent s tudy raised the problem in correctly estimating the sedimentation (SR) and mass accumulation (MAR) rates of the sequences for comparison with model estimates\, which cannot be estimated by just taking into account the whol e thickness of the considered deposits as classically performed. To solve this issue\, Greenland ice and northwestern European eolian deposits are c ompared in order to establish a link between GI and the soil development i n European mid-latitudes\, as recorded in loess sequences. For the differe nt types of observed paleosols\, the precise correlation with the Greenlan d records is applied to propose estimates of the maximum time lapses neede d to achieve the different degrees of maturation and development. To ident ify these time lapses more precisely\, two independent ice-core records ar e compared: d180 and dust concentration\, indicating variations of tempera ture and atmospheric dustiness respectively in the Greenland area. This me thod slightly differs from the definition of a GI event duration applied i n other studies where the sharp end of the d18O decrease gives the end of a GI. The same methodology is applied to both records (i.e.\, the GI last from the beginning of the abrupt d18O increase or dust concentration decre ase until when d18O or dust reach again their initial value) determined bo th visually and algorithmically\, and compare them to GI published estimat es. LOCATION:Bawden Room\, West Court\, Jesus College END:VEVENT END:VCALENDAR