Pliocene sediment and silicon isotope record of ODP Site 145-882@en

Increases in the low-field mass-specific magnetic susceptibility (chi), dropstones and the terrigenous sediment component from Ocean Drilling Program (ODP) Site 882 (~45°N) have been interpreted to indicate a major onset of ice-rafting to the sub-Arctic northwest Pacific Ocean during marine isotope stage (MIS) G6 (from ~2.75 Ma). In contrast, studies of the terrigenous content of sediments cored downwind of ODP Site 882 indicate that dust and disseminated volcanic ash deposition in the sub-Arctic Pacific increased markedly during MIS G6. To investigate the relative contribution of dust, volcanic ash and ice rafting to the Pliocene chi increase, we present new high-resolution environmental magnetic and ice-rafted debris records from ODP Sites 882 and 885. Our results demonstrate that the chi increase at both sites across MIS G6 is predominantly controlled by a previously overlooked mixture of aeolian dust and volcanic ash. Our findings call into question the reliability of chi as a proxy for ice-rafting to the North Pacific. They also highlight a previously undocumented link between iron fertilisation and biogeochemical cycling in the North Pacific at a key stage during intensification of late Pliocene northern hemisphere glaciation.大洋钻探计划（Ocean Drilling Program, ODP）882站位（约45°N）的低场质量磁化率（low-field mass-specific magnetic susceptibility, chi）、冰筏砾石以及陆源沉积物组分的升高，曾被解读为指示海洋同位素阶段（marine isotope stage, MIS）G6（约2.75 Ma）期间，北太平洋亚北极海域出现大规模冰筏沉积事件。与之相反，对ODP 882站位下风区沉积物岩芯的陆源组分研究显示，亚北极太平洋海域的风尘与弥散状火山灰沉积在MIS G6期间显著增加。为探究风尘、火山灰与冰筏沉积对上新世磁化率升高的相对贡献，我们获取了ODP 882与885站位的新的高分辨率环境磁学与冰筏碎屑（ice-rafted debris）记录。研究结果表明，MIS G6时期两个站位的磁化率升高主要受此前被忽视的风尘与火山灰混合组分控制。本研究结果对磁化率作为北太平洋冰筏沉积替代指标的可靠性提出了质疑。同时，本研究还揭示了上新世晚期北半球冰川作用增强关键阶段中，北太平洋海域铁施肥与生物地球化学循环之间此前未被记录的关联。