Abstract During the last glacial period, the sluggish deep Ocean circulation sequestered carbon into the abyss leading to the lowering of atmospheric CO2. The impact of this redistribution on biologically essential nutrients remains poorly constrained. Using sedimentary δ 30 Si of diatoms and biogenic accumulation rates in the Eastern Equatorial Pacific (EEP), we present evidences for the remobilisation of dissolved Silica (DSi) along with carbon from the deep ocean during the Last Deglaciation. Because DSi is essential for diatoms growing in the surface ocean, its concentration in the abyss during the glacial periods amounts to a negative feedback on the oceanic CO2 uptake. However, this effect can be muted by the increased Fe inputs during glacial periods which reduces diatom Si requirements in Fe limited regions such as the EEP. Our results from the EEP suggest that the efficiency of the biological CO2 pump and the size of the local CO2 source is tightly controlled by changes in DSi utilisation driven by Fe availability across the last glacial-interglacial transition. We use a modified PANDORA box model to illustrate that the inventory of DSi in the global ocean surface is controlled by Fe availability in HNLC areas rather than by straightforward Si supply though upwelling. The Holocene is characterised by a fast mode of Si cycling driven by high biological requirement for Si under conditions of iron limitation and efficient overturning, promoting CO2 outgassing and an inefficient biological C pump via the rapid exhaustion of DSi in the surface. The last glacial period saw slower marine Si cycling as a result of decreased DSi biological requirement under Fe-replete conditions in the sea surface and increased Si and CO2 sequestration in the abyssal ocean. The switch between the two modes of Si cycling happened at 15 ka BP, i.e. mid-deglaciation, and resulted in contrasting biological carbon drawdown responses in the EEP and globally between both phases of the deglacial CO2 rise. This illustrates that in addition to deep-sea CO2 storage and overturning, the efficiency of the biological pump also plays a crucial role in determining ocean-atmosphere CO2 exchange and shows the dual controls of ocean circulation and Fe-Si availability in this process.

中文翻译：

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来自深海的冰期硅再动员揭示了对冰期大气 CO2 水平的生物地球化学和物理控制

摘要 在末次冰期，缓慢的深海环流将碳封存到深渊，导致大气 CO2 降低。这种重新分配对生物必需营养素的影响仍然很少受到限制。使用东赤道太平洋 (EEP) 的硅藻沉积 δ 30 Si 和生物成因积累率，我们提供了在末次冰消期期间溶解二氧化硅 (DSi) 与深海碳再动员的证据。因为 DSi 对生长在表层海洋中的硅藻至关重要，所以它在冰期期间在深渊中的浓度相当于对海洋 CO2 吸收的负反馈。然而，这种影响可以通过在冰河时期增加铁输入而减弱，这会减少铁限制区域（如 EEP）对硅藻硅的需求。我们从 EEP 获得的结果表明，生物 CO2 泵的效率和当地 CO2 源的大小受到 DSi 利用率变化的严格控制，这些变化由上次冰期-间冰期过渡期间 Fe 可用性驱动。我们使用修改后的 PANDORA 盒模型来说明全球海面 DSi 的库存受 HNLC 地区 Fe 可用性控制，而不是通过上升流直接供应 Si。全新世的特点是在铁限制和有效翻转的条件下，由对 Si 的高生物需求驱动的快速 Si 循环模式，通过表面 DSi 的快速消耗促进 CO2 脱气和低效的生物 C 泵。由于在海面富铁条件下 DSi 生物需求降低以及深海海洋中 Si 和 CO2 封存量增加，最后一个冰川期的海洋 Si 循环变慢。Si 循环的两种模式之间的转换发生在 15 ka BP，即冰消期中期，并导致 EEP 和全球冰消期 CO2 上升两个阶段之间的生物碳下降响应形成对比。这说明除了深海 CO2 的储存和倾覆外，生物泵的效率在决定海洋-大气 CO2 交换方面也起着至关重要的作用，并显示了在这个过程中海洋环流和 Fe-Si 可用性的双重控制。Si 循环的两种模式之间的转换发生在 15 ka BP，即冰消期中期，并导致 EEP 和全球冰消期 CO2 上升两个阶段之间的生物碳下降响应形成对比。这说明除了深海 CO2 储存和倾覆外，生物泵的效率在决定海洋-大气 CO2 交换方面也起着至关重要的作用，并表明在这个过程中海洋环流和 Fe-Si 可用性的双重控制。Si 循环的两种模式之间的转换发生在 15 ka BP，即冰消期中期，并导致 EEP 和全球冰消期 CO2 上升两个阶段之间的生物碳下降响应形成对比。这说明除了深海 CO2 储存和倾覆外，生物泵的效率在决定海洋-大气 CO2 交换方面也起着至关重要的作用，并表明在这个过程中海洋环流和 Fe-Si 可用性的双重控制。