Abstract The Antarctic Circumpolar Current (ACC) is an influential component of the global climate system, and therefore it is essential to clarify the history of the oceanic fronts associated with it. However, there have been only a few attempts to reconstruct their history during the Neogene, as most previous studies focused on Quaternary ages. This study uses the late Miocene to Pliocene (ca. 9–3 Ma) fossil records of diatoms from the Atlantic sector of the Southern Ocean (Deep Sea Drilling Project Site 513 and Ocean Drilling Program Site 689) to reconstruct the paleo-location of the Subantarctic Front (SAF), which represents the northern limit of the ACC. The abundance of subtropical diatoms at Site 513 shows significant fluctuations during ca. 9–5 Ma, which strongly suggest that there have been repetitive north-south migrations of the SAF across Site 513 during at least ca. 9–5 Ma. In order to reconstruct the SAF migration history in more detail, changes in abundance of a typical subtropical diatom (i.e., Thalassionema nitzschioides var. parva Heiden emend. Moreno-Ruiz) recorded at Sites 513 and 689 are compared to abundance patterns of the same taxon at several drilling sites (Ocean Drilling Program Sites 697, 699, and 704) published in previous data reports. Results suggest several phases of SAF migration involving the following shifts in SAF position (direction of shift is indicated in brackets): ca. 8.5 Ma (northward), 8.0 Ma (northward), 7.0 Ma (southward), 6.1 Ma (northward), 5.4 Ma (the direction differs region by region), 4.9 Ma (northward), 4.6 Ma (southward), 3.8 Ma (northward). The results also show that SAF has experienced north-south migrations with a latitudinal amplitude of ca. 5° or more. Comparison between changes in fossil diatom assemblages at Site 689 and the inferred SAF shifts suggest that the northward/southward shift of the SAF could be induced by the cooling/warming in the high-latitude regions.

中文翻译：

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基于硅藻重建中新世晚期和上新世亚南极锋迁移

摘要 南极环极流（ACC）是全球气候系统的重要组成部分，因此阐明与之相关的洋锋的历史至关重要。然而，在新近纪重建它们的历史的尝试很少，因为以前的大多数研究都集中在第四纪。本研究使用中新世晚期至上新世（约 9-3 Ma）来自南大洋大西洋部分（深海钻探项目站点 513 和海洋钻探计划站点 689）的硅藻化石记录来重建该地区的古位置。亚南极锋 (SAF)，代表 ACC 的北界。Site 513 的亚热带硅藻丰度在大约 20 年期间显示出显着波动。9–5 毫安，这强烈表明至少在大约 10 年的时间里，SAF 在 Site 513 上发生了重复的南北迁移。9-5 马。为了更详细地重建 SAF 迁移历史，将在站点 513 和 689 记录的典型亚热带硅藻（即 Thalassionema nitzschioides var. parva Heiden emend. Moreno-Ruiz）的丰度变化与相同分类群的丰度模式进行比较在之前的数据报告中公布的几个钻井站点（海洋钻井计划站点 697、699 和 704）。结果表明 SAF 迁移的几个阶段涉及 SAF 位置的以下移动（移动方向在括号中表示）：8.5 Ma（北）、8.0 Ma（北）、7.0 Ma（南）、6.1 Ma（北）、5.4 Ma（方向因地区而异）、4.9 Ma（北）、4.6 Ma（南）、3.8 Ma（向北）。结果还表明，SAF 经历了南北向迁移，纬度幅度约为 5°以上。Site 689 化石硅藻组合的变化与推断的 SAF 偏移之间的比较表明，SAF 的北/南偏移可能是由高纬度地区的冷却/变暖引起的。