Identifying sedimentary signatures of tsunamis within long-term records (hundreds to thousands of years) is time and labour intensive using existing techniques. The lack of rapid identification restricts our ability to reconstruct past (palaeo-) tsunamis on the large spatial and temporal scales necessary for accurate hazard and risk assessment needed by vulnerable, low-lying populations. Here we pioneer the use of portable optically stimulated luminescence (POSL) in rapidly assessing in the field the occurrence and imprint of palaeotsunamis in sedimentary records. Pescadero Marsh (California) has a 2000-year sedimentary record of high-energy events constrained by a robust chronology derived from multiple techniques (luminescence dating, pollution markers). Tsunamis on the Californian coast rework nearshore sediments that have well reset luminescence signals. In slowly-accreting settings with well reset baseline signals, it is difficult to identify tsunamis remobilising locally-derived, well-reset sediments. However, tsunami signatures are readily detectable under rapidly-accreting, back-barrier saltmarsh conditions where they contrast the intercalating, poorly-reset luminescence signals of the marsh sediments deposited under tidal and fluvial conditions. Thus, POSL can allow for rapid, in-the-field assessment of tsunami deposits because their luminescence properties differ from the baseline sedimentary signal. POSL also documents changes in environmental conditions arising from a tsunami event, such as marsh recovery after an erosional and/or co-seismic subsidence event. Where there is a contrast in properties of the tsunami signatures and the baseline sediments, the rapid POSL assessment will allow for landscape-wide datasets to be obtained that can fully capture tsunami signatures globally as the minerals used for measurements are almost ubiquitous on Earth.

Salt marshes provide valuable nature-based, low-cost defences protecting against coastal flooding and erosion. Storm sedimentation can improve the resilience of salt marshes to accelerating rates of sea-level rise, which poses a threat to salt marsh survival worldwide. It is therefore important to be able to accurately detect the frequency of storm activity in longer-term sediment records to quantify how storms contribute to salt marsh resilience. Luminescence is able to infer how long mineral grains were exposed to sunlight prior to burial (e.g., the presence or absence of sediment processing). This study used sediment cores collected from the Ribble Estuary, North West England, to show that luminescence properties of sand-sized K-feldspar grains can diagnose the differential modes of deposition across intertidal settings (i.e., sandflat, mudflat and salt marsh) in longer-term sediment records by detecting the variability in sediment bleaching potential between settings (i.e., sediment exposure to sunlight), thus establishing a framework for the interpretation of luminescence properties of intertidal sediments. It then used modern sediment samples collected before and after a storm event to show how such properties can diagnose changes in sediment processing (i.e., bleaching potential) of mudflat sediments caused by storm activity, despite no changes in sediment composition being recorded by geochemical and particle size distribution analyses. This new luminescence approach can be applied to longer-term sediment records to reveal (and date) changes in the environment of deposition and/or depositional dynamics where there is no obvious stratigraphic evidence of such.