Browsing by Author "Eynaud, Frederique"
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- Marine Isotope Stage 4 (71–57 ka) on the Western European margin: insights to the drainage and dynamics of the Western European Ice SheetPublication . Toucanne, Samuel; Rodrigues, Teresa; Menot, Guillemette; Soulet, Guillaume; Cheron, Sandrine; Billy, Isabelle; Eynaud, Frederique; Antoine, Pierre; Sinninghe Damste, Jaap S.; Bard, Edouard; Sanchez Goñi, Maria-FernandaMarine Isotope Stage (MIS) 4 (ca. 71–57 ka; within the Middle Weichselian Substage) is considered a significant Pleistocene glaciation, but it remains poorly constrained in comparison to that of the Late Weichselian Last Glacial Maximum (LGM; ca. 29–19 ka, during MIS 2), or even the Late Saalian MIS 6 (ca. 190–130 ka). Most MIS 4 glacial landforms in Europe were erased by the more extensive LGM ice advance, precluding a robust recon struction of its extent and dynamic through time. Marine sedimentary archives, in preserving the source-to-sink sediment transfer signals of ice-sheet and glacier processes, help to bridge this gap. Here, the signals west of the European Ice Sheet (EIS) are tracked for MIS 4 from the deep Bay of Biscay (NE Atlantic), which was the outlet for Fennoscandian Ice Sheet (FIS) sediment-laden meltwater during extensive glaciations, specifically when the British-Irish Ice Sheet (BIIS) and the FIS coalesced into the North Sea (as during MIS 6 and the LGM). Sedi mentological, geochemical, and mineralogical proxies reveal the absence of FIS-derived material in Bay of Biscay sediment throughout MIS 4, which indicates that FIS meltwater and huge river systems from the North European Plain never drained into the Bay of Biscay at that time. This suggests that contrary to MIS 6 and the LGM, the BIIS and FIS were not likely large enough to coalesce and form a (grounded) ice bridge onto the North Sea, thus confirming geomorphic evidence for a significant, but relatively limited, glaciation in Europe during MIS 4. Closer to the Bay of Biscay, ice-marginal fluctuations of the BIIS are identified in the Celtic-Irish Sea region from the deep-sea record. More specifically, our findings suggest an early retreat of the Irish Sea Ice Stream as soon as ca. 68–65 ka, a few millennia before the demise of the EIS, and the Northern Hemisphere ice sheets as a whole, during Heinrich Stadial (HS) 6. This pattern is similar to that already recorded during MIS 2. Finally, this study reveals that the MIS 4 period in Western Europe corresponds, as for MIS 2, to a complex combination of general ice advance interspersed by preliminary-to-final EIS demises highlighted by HS conditions.
- Palaeohydrological changes over the last 50 ky in the central Gulf of Cadiz: complex forcing mechanisms mixing multi-scale processesPublication . Penaud, Aurelie; Eynaud, Frederique; Luise Voelker, Antje Helga; Turon, Jean-LouisNew dinoflagellate cyst (dinocyst) analyses were carried out at high resolution in core MD99-2339, retrieved from a contouritic field in the central part of the Gulf of Cadiz, for the Marine Isotope Stage (MIS) 3 interval, allowing for discussion of palaeohydrological changes over the last 50 ky in the subtropical NE Atlantic Ocean. Some index dinocyst taxa, according to their (palaeo) ecological significance, shed light on significant sea-surface changes. Superimposed on the general decreasing pattern of dinocyst export to the seafloor over the last 50 ky, paralleling the general context of decreasing aeolian dust fertilization, a complex variability in dinocyst assemblages was detected at the millennial timescale. Enhanced fluvial discharges occurred during Greenland Interstadials (GIs), especially GI 1, 8 and 12, while enhanced upwelling cell dynamics were suggested during the Last Glacial Maximum and Heinrich Stadials. Finally, during the early Holocene, and more specifically during the Sapropel 1 interval (around 7-9 ka BP), we evidenced a strong decrease in dinocyst fluxes, which occurred synchronously to a strong reduction in Mediterranean Outflow Water strength and which we attributed to an advection of warm and nutrient-poor subtropical North Atlantic Central Waters. Over the last 50 ky, our study thus allows for capturing and documenting the fine tuning existing between terrestrial and marine realms in North Atlantic subtropical latitudes, in response to not only the regional climate pattern but also monsoonal forcing interfering during precession-driven Northern Hemisphere insolation maxima. This mechanism, well expressed during the Holocene, is superimposed on the pervasive role of the obliquity as a first major trigger for explaining migration of dinocyst productive centres in the NE Atlantic margin to the subtropical (temperate) latitudes during glacial (interglacial) periods.