Volcanic ash layer description and thickness analysis from different DSDP, ODP, IODP and JAMSTAC Holes

Ocean drilling provides a global record of deposits throughout the oceans. An international collaborative ocean research programme was established in 1966, and the International Ocean Discovery Program (IODP) is the most recent manifestation of this. During each expedition a large amount of data are generated and collected by the shipboard science team. It could be suggested that due to the different staff and objectives during each expedition there would be significant variations in the consistency of data recorded in the shipboard visual core descriptions (VCDs). Use of shipboard VCD data in a global study of volcanism through time required the ground truthing of VCD data, to assess the consistency of ash layer reporting and to identify the amount of under/over recording of volcanic ash layers in cores. Approximately 1400 ash layers in DSDP, ODP, IODP and JAMSTEC cores were examined and it was found that on average 70-75% of recorded volcanic ash layers were present as described, an average of 17-20% were over recorded and 10-15% were under recorded. A number of factors could contribute to this variability, such as VCD format, lack of time for shipboard sampling of every ash layer, significant ash layer colour changes since time of coring, or differences in VCD recording and volcanic ash layer identification and description schemes between expeditions. These findings are important and will allow greater confidence in further studies based on data compiled from shipboard VCDs.

海洋钻探可获取全球海域范围内的海底沉积记录。1966年，一项国际协作海洋研究计划正式启动，国际大洋发现计划（International Ocean Discovery Program, IODP）正是该计划的最新延续形式。每一次钻探航次期间，船载科学团队都会生成并收集海量数据。有研究指出，由于各航次的工作人员配置与研究目标存在差异，船载岩芯目视描述（Shipboard Visual Core Descriptions, VCDs）中记录数据的一致性存在显著差异。若要基于船载VCD数据开展全球尺度的长时序火山活动研究，需对VCD数据进行实地校验，以评估火山灰层记录的一致性，并量化岩芯中火山灰层的漏记与多记比例。研究团队对深海钻探计划（Deep Sea Drilling Project, DSDP）、大洋钻探计划（Ocean Drilling Program, ODP）、国际大洋发现计划（International Ocean Discovery Program, IODP）以及日本海洋地球科学技术机构（Japan Agency for Marine-Earth Science and Technology, JAMSTEC）获取的岩芯中约1400层火山灰层开展了核查，结果显示：平均而言，70%~75%的记录火山灰层与实际赋存状态一致，17%~20%存在多记情况，10%~15%存在漏记情况。造成这一差异的因素包括：VCD记录格式不统一、船载团队无充足时间对每一层火山灰层开展采样、取芯后火山灰层颜色发生显著变化，以及不同航次间VCD记录规范、火山灰层识别与描述方案存在差异。上述研究结论具有重要学术价值，可为后续基于船载VCD汇编数据开展的相关研究提供更高的可信度保障。