River response to late quaternary environmental change in Corsica

Mediterranean river systems are particularly sensitive to environmental change and often provide good archives to reconstruct fluvial histories. This study investigates river response to environmental change in two steep land river catchments in Corsica. Late Pleistocene alluviation and pedogenic weathering is explored within the Tavignano River basin (-775 km2) and river response to Late Holocene (including Little Ice Age) environmental change is examined in the Figarella catchment (-132 km2). A range of geochronological controls has been employed including optically stimulated luminescence (OSL) dating, a profile development index (POI) determined from pedogenic properties, and lichenometry. This study also examines the potential of a relatively new absolute dating teclmique, terrestrial insitu cosmogenic nuclide dating, for establishing the timing of recent glacial activity in Corsica. Two cosmogenic lOBe nuclide exposure ages of 14.09 ± 1.04 k and 12.70 ± 0.96 k cal. years suggest that Corsica was glaciated during the Lateglacial period. Although more samples are required to confirm these ages, support for this interpretation is evident from other palaeoenvironmental data in the western Mediterranean and a simple snowpack model simulating Younger Dryas conditions in Corsica. Analysis of the Tavignano alluvial units indicates that Pleistocene glaciation is likely to have had a strong impact on the river regime and sedimentation style. The timing of the major alluviation phases has been estimated using an age model derived from OSL ages and the POI. Deposition is broadly coeval with the Late Pleistocene cold stages and climate change is therefore considered to be the dominant control on river behaviour during the Late Pleistocene. Lichenometric dating of coarse flood deposits on the Figarella valley floor has established the timing of flood periods since ca. AD 1570. At least ten distinct periods of enhanced flooding are evident over the last five centuries. Flooding was particularly prominent during the 1500s, mid-late 1700s and throughout the 1800s in the Figarella, corresponding to particularly cold and wet periods. The apparent synchrony of flood events across the Mediterranean region during the Little Ice Age suggests that climate variability over the past 500 years has been the overriding control on flood frequency in Corsica. Analyses of twentieth century rainfall records show a strong correlation between heavy precipitation events in the western Mediterranean and a strong negative winter North Atlantic Oscillation.