Holocene hydrological changes in the Rhone River (NW Mediterranean) as recorded in the marine mud belt

摘要

Expanded marine Holocene archives are relatively scarce in the Mediterranean Sea because most of the sediments were trapped in catchment areas during this period. Mud belts are the most suitable targets to access expanded Holocene records. These sedimentary bodies represent excellent archives for the study of sea-land interactions and notably the impact of the hydrological activity on sediment accumulation. We retrieved a 7.2m long sediment core from the Rhone mud belt in the Gulf of Lions in an area where the average accumulation rate is ca. 0.70 m 1000 yr(-1). This core thus provides a continuous and high-resolution record of the last 10 ka cal BP. A multiproxy dataset (XRF core scan, C-14 dates, grain size and organic-matter analysis) combined with seismic stratigraphic analysis was used to document decadal to centennial changes in the Rhone hydrological activity. Our results show that (1) the early Holocene was characterized by high sediment delivery likely indicative of local intense (but short-duration) rainfall events, (2) important sediment delivery around 7 ka cal BP presumably related to increased river flux, (3) a progressive increase in continental/marine input during the mid-Holocene despite increased distance from river outlets due to sea-level rise possibly related to higher atmospheric humidity caused by the southward migration of the storm tracks in the North Atlantic, (4) multidecadal to centennial humid events took place in the late Holocene. Some of these events correspond to the cold periods identified in the North Atlantic (Little Ice Age, LIA; Dark Ages Cold Period) and also coincide with time intervals of major floods in the northern Alps. Other humid events are also observed during relatively warm periods (Roman Humid Period and Medieval Climate Anomaly).