Abstract Time-series analyses of satellite images reveal that sea ice extent in the Ross Sea has experienced significant changes over the last 40 years, likely triggered by large-scale atmospheric anomalies. However, resolving how sea ice in the Ross Sea has changed over longer timeframes has until now remained more elusive. Here we used a laminated sediment piston core (14.6 m) collected from the Edisto inlet (Western Ross Sea) to reconstruct fast ice dynamics over the last 2.6 ka. Our goal was to first understand the climate expression of selected well-defined sediment laminae and then use these characteristics for reconstructing past sea ice behaviour across the whole sedimentary sequence. We used the recently established sea ice diatom biomarker proxy IPSO25 in combination with diatom census counts and bulk analyses. Analyses performed on a suite of discrete laminae revealed statistically significant differences between dark and light laminae reflecting different depositional conditions. Based on their respective biogeochemical fingerprints, we infer that dark laminae accumulated during sea ice thaws in early summer. Under these conditions, laminae contain relatively high concentrations of IPSO25 and display an enriched δ13C composition for the bulk organic matter (OM). While diatom assemblages in dark laminae are relatively homogenous, as the thaw continues later in the summer, Corethron pennatum becomes the dominant diatom species, resulting in the formation of light laminae characterized by low IPSO25 concentrations. Since C. pennatum can migrate vertically through the water column to uptake nutrients and avoid competition in oligotrophic waters, its high concentration likely reflects stratified and ice-free surface waters typical of late summer. Down-core trends show that the correlation between sediment brightness and geochemical fingerprint (i.e., IPSO25 and δ13C) holds throughout the record. Based on the knowledge gained at lamina level, our down-core high-resolution reconstruction shows that the summer fast ice coverage changed dramatically during the late Holocene. Specifically, we conclude that the Edisto inlet experienced regular early summer opening between 2.6 ka, and ca. 0.7 ka, after which, coastal fast ice persisted during summer months and ice-free conditions became less frequent. Comparison with previous regional ice core data suggests that the sudden cooling recorded over the Victoria Land Coast region since 0.7 ka might potentially explain our observation of persistent summer fast ice in the Western Ross Sea. Our study has shown that multi-proxy data derived from laminated sediments can provide hitherto unknown detail regarding past summer sea ice dynamics in coastal Antarctic regions.

中文翻译：

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解决过去 2.6 ka 期间罗斯海西北部的海冰动态：从季节性到千年时间尺度

摘要 卫星图像的时间序列分析表明，罗斯海的海冰范围在过去 40 年中经历了重大变化，这可能是由大规模大气异常引发的。然而，直到现在，解决罗斯海的海冰如何在更长的时间范围内发生变化仍然难以捉摸。在这里，我们使用从埃迪斯托入口（西罗斯海）收集的层状沉积物活塞芯（14.6 m）来重建过去 2.6 ka 的快速冰动力学。我们的目标是首先了解选定的明确定义的沉积层的气候表现，然后使用这些特征来重建整个沉积序列中过去的海冰行为。我们使用最近建立的海冰硅藻生物标志物代理 IPSO25 结合硅藻普查计数和批量分析。对一组离散薄层进行的分析揭示了反映不同沉积条件的深色和浅色薄层之间的统计学显着差异。根据它们各自的生物地球化学指纹，我们推断在初夏海冰融化期间积累了深色薄层。在这些条件下，薄层含有相对高浓度的 IPSO25，并显示出大量有机物质 (OM) 的丰富 δ13C 组成。虽然深色薄层中的硅藻组合相对均匀，但随着夏季晚些时候解冻的继续，Corethron pennatum 成为主要的硅藻物种，导致形成以低 IPSO25 浓度为特征的浅色薄层。由于 C. pennatum 可以通过水体垂直迁移以吸收养分并避免在贫营养水域中竞争，它的高浓度可能反映了夏末典型的分层和无冰地表水。下芯趋势表明沉积物亮度和地球化学指纹（即 IPSO25 和 δ13C）之间的相关性在整个记录中保持不变。基于在叶片层面获得的知识，我们的下核高分辨率重建表明，在全新世晚期，夏季快速冰覆盖率发生了巨大变化。具体来说，我们得出结论，埃迪斯托入口在 2.6 ka 和大约 2.6 之间经历了定期的初夏开放。0.7 ka，此后，沿海快速冰在夏季持续存在，无冰条件变得不那么频繁。与之前区域冰芯数据的比较表明，维多利亚陆地海岸地区自 0. 7 ka 可能可以解释我们对西罗斯海持续存在的夏季快速冰的观察。我们的研究表明，来自叠层沉积物的多代理数据可以提供有关南极沿海地区过去夏季海冰动态的迄今为止未知的细节。