A new orbital‐scale record of bulk sediment biogenic silica (opal) content from Ocean Drilling Program (ODP) Site 745B spans the past 630 kyr (Marine Isotope Stages (MIS) 1–16). Together with the published portion of the record (MIS 16–31, Billups et al., 2018), we obtain a 1 million year orbital‐scale record of paleoproductivity in the Antarctic Zone of the Indian Ocean sector of the Southern Ocean. A coherent age model is based on tuning variations in the opal content to the benthic foraminiferal δ¹⁸O stack of Lisiecki and Raymo (2005). Consistent with other sites from the Antarctic Zone of the Southern Ocean, we align opal maxima with interglacial and opal minima with glacial intervals. Opal variations are significant at all three primary periodicities (100, 40, and 23 kyr), coherent (>95%), and in‐phase with the tuning target on the scale of individual cycles as well as their amplitude modulation. This supports the assumption of global ice volume‐related changes in Southern Ocean paleoproductivity in the derivation of the age model. Between MIS 11 and 4, however, the opal record lacks minima corresponding to the glacial extremes of MIS 10, 8, and 6. During this interval of time, opal fluctuates primarily with a 23 kyr precession signal. We suggest that the productivity response to precession reflects an ice‐free sea surface that remains sensitive to wind‐driven upwelling of nutrients. Results from Site 745B illustrate the potential importance of regional climate forcing factors on longer time scales and their interplay with global climate background conditions.

中文翻译：

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南洋印度洋地区生物硅的百万年记录：区域对全球初级生产力的强迫

来自海洋钻探计划（ODP）站点745B的一条新的大规模沉积物生物硅（蛋白石）含量的轨道尺度记录跨越了过去的630年（海洋同位素阶段（MIS）1–16）。连同记录的已发布部分（MIS 16–31，Billups等人，2018），我们获得了南洋印度洋南极地区古生产力的一百万年轨道规模记录。相干年龄模型是基于在蛋白石内容调谐变化到底栖有孔虫δ ¹⁸O堆栈的Lisiecki和Raymo（2005）。与来自南大洋南极地区的其他站点一致，我们将蛋白石最大值与冰间期对齐，并将蛋白石最小值与冰川间隔对齐。蛋白石的变化在所有三个主要周期（100、40和23 kyr），相干（> 95％），并且在各个周期以及它们的幅度调制范围内与调整目标同相时均很显着。这支持了年龄模型推导中与全球冰量有关的南大洋古生产力变化的假设。但是，在MIS 11和4之间，蛋白石记录缺少与MIS 10、8和6的冰河极端相对应的极小值。在此时间间隔内，蛋白石主要以23年岁差信号波动。我们建议生产力对岁差的反应反映出无冰的海面对风驱动的养分上升仍然敏感。站点745B的结果说明了区域气候强迫因素在较长时间尺度上的潜在重要性及其与全球气候背景条件的相互影响。