Fluvial response to the last Holocene rapid climate change in the Northwestern Mediterranean coastlands

The variability of fluvial activity in the Northwestern Mediterranean coastal lowlands and its relationship with modes of climate change were analysed from the late 9th to the 18th centuries CE. Geochemical analyses were undertaken from a lagoonal sequence and surrounding sediments in order to track the fluvial inputs into the lagoon. An index based on the K/S and Rb/S ratios was used to evidence the main periods of fluvial activity. This index reveals that the Medieval Climate Anomaly (MCA) was a drier period characterized by a lower fluvial activity, while the Little Ice Age (LIA) was a wetter period with an increase of the river dynamics. Three periods of higher than average fluvial activity were evidenced at the end of the first millennium CE (ca. 900–950calyrCE), in the first half of the second millennium CE (ca. 1150–1550calyrCE), and during the 1600s–1700s CE (ca. 1650–1800calyrCE). The comparison of these fluvial periods with other records of riverine or lacustrine floods in Spain, Italy, and South of France seems to indicate a general increase in fluvial and flood patterns in the Northwestern Mediterranean in response to the climate change from the MCA to the LIA, although some episodes of flooding are not found in all records. Besides, the phases of higher than average fluvial dynamics are in good agreement with the North Atlantic cold events evidenced from records of ice-rafted debris. The evolution of fluvial activity in the Northwestern Mediterranean coastlands during the last millennium could have been driven by atmospheric and oceanic circulation patterns. •A lagoonal record of fluvial activity in the NW Mediterranean coastlands•Increase of river floods from the Medieval Climate Anomaly to the Little Ice Age•High fluvial activity synchronous with the North Atlantic cold events•Fluvial sedimentary archives compared with historical sources of flood events•Elemental ratios K/S and Rb/S used to track the fluvial dynamics