Refining tephra dispersal in Japan to understand the impact of past volcanic eruptions and synchrony of past climate changes

Lake Suigetsuis located in a small tectonic basin and forms the largest of the 'Mikata Five Lakes', Honshu, Japan(see: Figure 1). The Suigetsu archive records continuous sediment deposition over the last ~ 150 ka (Nakagawa et al.,2012)and has been intensely studied over two decades. It is widely regarded as one of the key high-resolution and precisely dated palaeoenvironmental archives ineast Asia, including a detailed record of explosive volcanism for Japan, South Korea and China (McLean et al.,2016; Smith et al.,2011). Whilst the chronology for this record is well constrained for the past ~ 60 ka by hundreds of radiocarbon dates(Ramsey et al.,2012)and annual and seasonal laminae (varves)(Marshall et al.,2012; Schlolaut etal.,2018),a robust chronology is lacking for older sections of the core. This has limited the ability to accurately correlate the pre-60 ka sediments of the Suigetsu record with other high-resolution archives within the east Asia/Pacific region and beyond. Thus, improving the chronology for the older section of the core has the potential to revolutionise our understanding of spatial leads and lags in palaeoclimate change in this region. The use of time-parallel stratigraphic (isochronous) markers offers the potential to overcome issues associated with the comparison ofpalaeoenvironmental records on independent timescales. Volcanic ash (tephra)iswidely dispersed during explosive eruptions and deposited near instantaneously. These tephra layerspreserved within sedimentary sequences areroutinely employed as isochronous markers for the synchronisation of disparate records.Methodological developments have facilitated the isolation of non-visible tephra (cryptotephra; < 125 qm) deposits, enabling research to be conducted in increasingly distal locations,allowing sedimentary archives from a greater spatial area to be used. Identifying tephra in distal records has enabled greater understanding in the tempo of volcanism, ash dispersal (Albert et al.,2018), the environmental impacts of explosive volcanic eruptions (Matthews et al.,2012)and the synchronicity of palaeoenvironmental response to climate change over continental and inter-continental distances(Lane et al.,2013).Cryptotephra investigations of the late Pleistocene and Holocene section of the Lake Suigetsu sedimentary archive haveshown that there are up to four times morenon-visiblelayers than can beenseen in core sections(McLean et al.,2018)which has significantly extended our knowledge of tephra dispersal (McLean et al.,2016, 2018). Therefore there is significant potential for tephrochronology in the east Asian/Pacific region due to the number and the distribution spreadof ash fall events across Japan. Evaluating the eruptive histories of volcanoes in this part of the world is essential for accurate hazard assessments. The east Asian/Pacific region is home to over ~ 30% of the global population (Cook et al.,2010; Ha et al.,2012)and the location of a large number of volcanoes -some of which have produced a number of the largest magnitude volcanic eruptions over the last 200 ka (Newhall et al.,2018). Across the islands of Japan, there are over 110 volcanic centres which are known to have been active during the late Quaternary (Machida and Arai, 2003; Figure 1). Thus, it is crucial that the tempo of volcanism is well understood as well as the scale of potential environmental impacts of large explosive volcanic eruptions for the local population.