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

水月湖位于一个小型构造盆地中，是日本本州“三田五湖”中最大的一个（见：图1）。Suigetsu档案记录了过去约150 ka的连续沉积物沉积（Nakagawa等人，2012)二十多年来一直被深入研究。它被广泛认为是东亚地区关键的高分辨率和精确定年的古环境档案之一，包括日本、韩国和中国爆发性火山活动的详细记录（姆克林等人，2016; Smith等人，2011年）。虽然这一记录的年代学在过去~ 60 ka受到数百个放射性碳年代的限制（Ramsey等人，2012)以及一年生和季节性纹层（纹层）（马歇尔等人，2012; Schlolaut埃塔尔，2018年），一个强大的年表是缺乏较旧的部分的核心。这限制了准确地将水月记录的60 ka前沉积物与东亚/太平洋地区及其他地区的高分辨率档案相关联的能力。因此，改进岩芯较老部分的年代学有可能彻底改变我们对该地区古气候变化的空间领先和滞后的理解。时间平行地层（等时线）标志的使用提供了克服与独立时间尺度上的古环境记录的比较相关的问题的潜力。火山灰（火山灰）在爆炸性喷发过程中广泛散布，并在瞬间沉积下来。这些火山灰层保存在沉积序列中，通常被用作不同记录同步的同位素标记。方法学的发展促进了不可见火山灰（隐火山灰; < 125 qm）沉积物的分离，使研究能够在越来越远的位置进行，允许使用来自更大空间区域的沉积档案。在远距离记录中识别火山灰使人们能够更好地理解火山活动的克里思、火山灰的散布（Albert等人，2018年），火山爆发的环境影响（马修斯等人，2012)以及古环境对大陆和洲际距离上气候变化的同步性（Lane等人，2013).对水月湖沉积档案的晚更新世和全新世部分的隐石层调查显示，非可渗透层比岩心部分多四倍（姆克林等人，2018)这显著地扩展了我们对火山灰散布的知识（姆克林等人，2016年，2018年）。因此，由于日本各地火山灰坠落事件的数量和分布范围，东亚/太平洋地区的火山灰年代学具有很大的潜力。评估世界这一地区火山喷发的历史对于准确的危险评估至关重要。东亚/太平洋地区是全球人口超过30%的家园（Cook等人，2010; Ha等人，2012)以及大量火山的位置-其中一些在过去200 ka中产生了许多最大规模的火山爆发（Newhall等人，2018年）。在日本各岛屿上，已知有110多个火山中心在第四纪晚期活跃（町田和荒井，2003年;图1）。因此，必须充分了解火山活动的克里思以及大规模火山爆发对当地居民的潜在环境影响的规模。

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.