Antarctic sea-ice extent, primary productivity and ocean circulation represent interconnected systems that form important components of the global carbon cycle. Subdecadal to centennial-scale variability can influence the characteristics and interactions of these systems, but observational records are too short to evaluate the impacts of this variability over longer timescales. Here, we use a 170-m-long sediment core collected from Integrated Ocean Drilling Program Site U1357B, offshore Adélie Land, East Antarctica to disentangle the impacts of sea ice and subdecadal climate variability on phytoplankton bloom frequency over the last ~11,400 years. We apply X-ray computed tomography, Ice Proxy for the Southern Ocean with 25 carbon atoms, diatom, physical property and geochemical analyses to the core, which contains an annually resolved, continuously laminated archive of phytoplankton bloom events. Bloom events occurred annually to biennially through most of the Holocene, but became less frequent (~2–7 years) at ~4.5 ka when coastal sea ice intensified. We propose that coastal sea-ice intensification subdued annual sea-ice break-out, causing an increased sensitivity of sea-ice dynamics to subdecadal climate modes, leading to a subdecadal frequency of bloom events. Our data suggest that projected loss of coastal sea ice will impact the influence of subdecadal variability on Antarctic margin primary productivity, altering food webs and carbon-cycling processes at seasonal timescales.

南极海冰范围、初级生产力和海洋环流代表了相互关联的系统，它们构成了全球碳循环的重要组成部分。亚十年到百年尺度的变率会影响这些系统的特征和相互作用，但观测记录太短，无法评估这种变率在较长时间尺度上的影响。在这里，我们使用从南极洲东部阿德利地近海的综合海洋钻探计划站点 U1357B 收集的 170 米长的沉积岩芯来解开过去约 11,400 年海冰和年代际气候变化对浮游植物开花频率的影响。我们对核心应用 X 射线计算机断层扫描、具有 25 个碳原子的南大洋冰代理、硅藻、物理性质和地球化学分析，其中包含每年解决的、浮游植物水华事件的连续分层档案。Bloom 事件在全新世的大部分时间里每年到每两年发生一次，但当沿海海冰加剧时，在约 4.5 ka 时变得不那么频繁（约 2-7 年）。我们提出沿海海冰强化抑制了每年的海冰爆发，导致海冰动力学对亚年代际气候模式的敏感性增加，从而导致水华事件的亚年代际频率。我们的数据表明，预计沿海海冰的减少将影响次年代际变化对南极边缘初级生产力的影响，改变季节性时间尺度的食物网和碳循环过程。5 ka 当沿海海冰加强时。我们提出沿海海冰强化抑制了每年的海冰爆发，导致海冰动力学对亚年代际气候模式的敏感性增加，从而导致水华事件的亚年代际频率。我们的数据表明，预计沿海海冰的减少将影响次年代际变化对南极边缘初级生产力的影响，改变季节性时间尺度的食物网和碳循环过程。5 ka 当沿海海冰加强时。我们提出沿海海冰强化抑制了每年的海冰爆发，导致海冰动力学对亚年代际气候模式的敏感性增加，从而导致水华事件的亚年代际频率。我们的数据表明，预计沿海海冰的减少将影响次年代际变化对南极边缘初级生产力的影响，改变季节性时间尺度的食物网和碳循环过程。