Latitudinal Migrations of the Subtropical Front at the Agulhas Plateau Through the Mid‐Pleistocene Transition
Latitudinal Migrations of the Subtropical Front at the Agulhas Plateau Through the Mid‐Pleistocene Transition
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DOI：
10.1029/2020pa004084
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发表时间：
2021-07
影响因子：
3.5
通讯作者：
A. Cartagena-Sierra;M. Berke;R. Robinson;B. Marcks;I. Castañeda;A. Starr;I. Hall;S. Hemming;L. Levay
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作者：
A. Cartagena-Sierra;M. Berke;R. Robinson;B. Marcks;I. Castañeda;A. Starr;I. Hall;S. Hemming;L. Levay
南半球副热带锋（STF）的经向变化与南大洋的扩张或收缩有关，可能通过调节印度洋-大西洋门户的水交换幅度（即所谓的厄加勒斯泄漏），在全球海洋环流中发挥了重要作用。在这里，我们展示了阿加勒斯高原 IODP 站点 U1475、STF 附近和阿加勒斯反射路径内海洋沉积物的上层水柱温度（U37K' 和 TEX86）和初级生产力（二氢卟酚和烯酮）的新生物标志物记录。我们使用这些 1.4 至 0.3 Ma 的多代理时间序列记录来检查更新世中期过渡（MPT，约 1.2-0.8 Ma）上层海洋条件的隐含变化。我们的重建，结合过去 350 ka 期间 STF 迁移的先前证据，表明在西南印度洋，STF 可能在中更新世过渡状态（MPIS，MIS 23-12）期间从厄加勒斯高原进一步向南移动，并在 MIS 34-24 和 MIS 10 期间到达最北端的位置。开普盆地表明，只有 STF 最极端的向北迁移才与阿加勒斯泄漏的减少有关。在 MPIS 期间，STF 迁移似乎并不能控制厄加勒斯泄漏变异性，我们认为先前模拟的西风转移可能是造成观察到的模式的原因。 STF 迁移与厄加勒斯泄漏之间的分离，除了引起西风转变之外，也可能有助于解释 MPIS 期间看到的二氧化碳通风的变化。
The meridional variability of the Subtropical Front (STF) in the Southern Hemisphere, linked to expansions or contractions of the Southern Ocean, may have played an important role in global ocean circulation by moderating the magnitude of water exchange at the Indian‐Atlantic Ocean Gateway, so called Agulhas Leakage. Here we present new biomarker records of upper water column temperature ( U37K' and TEX86 ) and primary productivity (chlorins and alkenones) from marine sediments at IODP Site U1475 on the Agulhas Plateau, near the STF and within the Agulhas retroflection pathway. We use these multiproxy time‐series records from 1.4 to 0.3 Ma to examine implied changes in the upper oceanographic conditions at the mid‐Pleistocene transition (MPT, ca. 1.2–0.8 Ma). Our reconstructions, combined with prior evidence of migrations of the STF over the last 350 ka, suggest that in the Southwestern Indian Ocean the STF may have been further south from the Agulhas Plateau during the mid‐Pleistocene Interim State (MPIS, MIS 23–12) and reached its northernmost position during MIS 34–24 and MIS 10. Comparison to a Globorotalia menardii‐derived Agulhas Leakage reconstruction from the Cape Basin suggests that only the most extreme northward migrations of the STF are associated with reduced Agulhas Leakage. During the MPIS, STF migrations do not appear to control Agulhas Leakage variability, we suggest previously modeled shifting westerly winds may be responsible for the patterns observed. A detachment between STF migrations and Agulhas Leakage, in addition to invoking shifting westerly winds may also help explain changes in CO2 ventilation seen during the MPIS.