Age determinations, biomarker analyses, and accumulation rates of three sediment cores from the Fram Strait

A reconstruction of Holocene sea ice conditions in the Fram Strait provides insight into the palaeoenvironmental and palaeoceanographic development of this climate sensitive area during the past 8,500 years BP. Organic geochemical analyses of sediment cores from eastern and western Fram Strait enable the identification of variations in the ice coverage that can be linked to changes in the oceanic (and atmospheric) circulation system. By means of the sea ice proxy IP25, phytoplankton derived biomarkers and ice rafted detritus (IRD) increasing sea ice occurrences are traced along the western continental margin of Spitsbergen throughout the Holocene, which supports previous palaeoenvironmental reconstructions that document a general cooling. A further significant ice advance during the Neoglacial is accompanied by distinct sea ice fluctuations, which point to short-term perturbations in either the Atlantic Water advection or Arctic Water outflow at this site. At the continental shelf of East Greenland, the general Holocene cooling, however, seems to be less pronounced and sea ice conditions remained rather stable. Here, a major Neoglacial increase in sea ice coverage did not occur before 1,000 years BP. Phytoplankton-IP25 indices ("PIP25-Index") are used for more explicit sea ice estimates and display a Mid Holocene shift from a minor sea ice coverage to stable ice margin conditions in eastern Fram Strait, while the inner East Greenland shelf experienced less severe to marginal sea ice occurrences throughout the entire Holocene.对弗拉姆海峡（Fram Strait）全新世（Holocene）海冰状况的重建，为揭示这一气候敏感区域距今8500年以来的古环境与古海洋学演化提供了关键视角。研究团队通过对弗拉姆海峡东西两侧沉积物岩芯（sediment cores）开展有机地球化学分析（organic geochemical analyses），得以识别海冰覆盖度的变化特征，并将其与海洋（及大气）环流系统的演变建立关联。借助海冰代用指标IP25（sea ice proxy IP25）、浮游植物源生物标志物（phytoplankton derived biomarkers）以及冰筏碎屑（ice rafted detritus, IRD），可追踪到全新世期间斯匹次卑尔根岛（Spitsbergen）西部大陆边缘海冰发生频次的增加趋势，该结果佐证了此前记录整体降温过程的古环境重建成果。新冰期（Neoglacial）期间的又一次显著冰进过程，伴随有明显的海冰波动，这表明该区域的大西洋水平流（Atlantic Water advection）或北极水流出（Arctic Water outflow）存在短期扰动。然而在东格陵兰（East Greenland）大陆架（continental shelf）区域，全新世的整体降温趋势并不显著，海冰状况始终相对稳定。该区域直至距今1000年才出现新冰期阶段海冰覆盖度的显著增长。研究人员采用浮游植物-IP25指数（PIP25-Index）开展更精准的海冰定量估算，结果显示弗拉姆海峡东部在全新世中期发生了从轻度海冰覆盖到稳定冰缘环境的转变；而东格陵兰内陆架区域在整个全新世期间仅存在轻度至边缘性海冰出现情况。