Reconnaissance of historic (post-AD 1000) high-energy deposits along the Atlantic coasts of southwest Britain, Ireland and Brittany, France

Sand and gravel deposits from the Atlantic coasts of southwest Britain, Brittany and western Ireland are identified as potential indicators of historic (post-AD 1000) ocean-sourced high-energy events, such as storm surges and tsunami. This is an important historic period as it includes the climatic perturbations of the Medieval Warm Period and the Little Ice Age, and also seismogenic events, such as the Lisbon tsunami of 1755. Ten new sites are identified from various coastal settings and dated using eight new radiocarbon dates alongside previously published data. Generally, sites do not appear to record multiple high-energy events, suggesting that either only the most extreme and/or recent events are registered. A number of radiocarbon dates from marine shell yield modern ages when corrected for the marine reservoir effect. Rather than necessarily indicating recent deposition, this may reflect a poor understanding of terrestrial carbon input into coastal and estuarine waters, and the practice of applying broad regional Δ R values at the local scale. Two groupings of radiocarbon dates are recognised; a Medieval Group and a Post-Medieval Group, which might reflect events within known climatic perturbations and/or tsunami occurrences. These events may include the Lucia Flood of 1287, the All Saint's Day Flood of 1570, the 1607 Flood, the Great Storm of 1703, and the Lisbon tsunami. Some older (pre-AD 1000) deposits indicate the potential to construct frequency/magnitude records of high-energy events throughout the Holocene. Data presented here support the view that salt marshes within the Bristol Channel and Severn Estuary were completely eroded away early in the 17th century.