ALBERT

Description: The middle Miocene is a crucial period for the evolution of apes, and it corresponds to their appearance in Europe. The dispersion of apes was made possible by tectonic changes and the expansion of their habitat, (sub-) tropical forest, in Europe. The context in which the middle Miocene climatic optimum occurred still lacks constraints in terms of atmospheric pCO2 and ice-sheet volume and extent. Using a coupled atmosphere-ocean general circulation model (GCM) and dynamic vegetation model, we investigated the sensitivity of Miocene climate and vegetation to pCO2 levels and Antarctic ice-sheet configurations. Our results indicate that higher than present pCO2 is necessary to simulate subtropical forest in Western and Central Europe during the middle Miocene, but that a threshold at high pCO2 makes subtropical forest partly collapse. Moreover, removing ice over Antarctica modifies oceanic circulation and induces warmer and slightly wetter conditions in Europe, which are consistent with the expansion of subtropical forest. These results suggest that a small East Antarctic Ice Sheet (25% of present-day ice volume) together with higher than present pCO2 values are in better agreement with available European middle Miocene data.

Description: Ice dynamics, tectonic setting, and sediment supply are the key parameters controlling the architecture of high-latitude margins and the formation of trough mouth fans (TMFs). Current understanding of these archives of paleo–ice streams is based on studies of ice sheets adjacent to stable, passive margins, while the behavior of active, convergent glacier-influenced margins remains relatively unconstrained. We integrate high-resolution seismic data and chronology from Integrated Ocean Drilling Program Expedition 341 cores in southeast Alaska across the actively converging Yakutat terrane margin to examine the late Quaternary evolution of the Bering Glacier, the largest outlet glacier of the poorly understood Cordilleran Ice Sheet (CIS). We interpret at least eight glacial advances to the shelf break since the end of the mid-Pleistocene transition, showing a more dynamic CIS than hitherto realized. During the past ~130 k.y., the temperate, meltwater-charged Bering Glacier delivered ~925 km 3 of sediment to the shelf and slope, providing one of the highest rates of sustained sediment accumulation (5–10 m/k.y.) ever reported globally. Rapid formation of a TMF, reaching ~600 m thick in ~130 k.y., emphasizes the extreme sediment flux that can be produced by wet-based glacial systems, and its critical role in the development of high-latitude margin stratigraphy. TMF formation despite initially steep, tectonically controlled slopes in this active setting reflects an autogenic shift in the evolution of the Bering Trough, suggesting that major transitions between sedimentary regimes need not reflect some externally driven change in climate variability.