Abstract The oceanography of the western Indian sector of the Southern Ocean is extremely complex due to the presence of several subantartic islands and plateaus that alter the zonal flow of the Antarctic Circumpolar Current. The circulation is even more complex around the Kerguelen Islands (KI) as the hydrological fronts merge with the Agulhas Return Current, the latter transporting warm surface waters from the low latitudes to the Subantarctic Zone (SAZ) east of KI. Here we present new sea-surface and sub-surface temperatures, based on diatom and radiolarian census counts respectively, in two cores covering the last 40,000 years (40 kyrs) to infer past oceanographic changes in the KI region. In core MD11-3353, located in the Polar Front Zone (PFZ) west of KI, both sea-surface and sub-surface temperatures follow the expected glacial-interglacial pattern, with a constant difference of ∼3 °C, suggesting that the structure of the top 500 m of the water column did not change drastically over this period. In core MD12-3396CQ, located in the SAZ east of KI, the sub-surface temperature record again follows the expected glacial-interglacial pattern while the diatom-based reconstruction shows a strong warming during the 40-24 kyrs period, with a mean difference between the two of ∼9 °C. The temperature difference subsequently reverts to ∼3 °C during the glacial termination and Holocene. We suggest that the large difference between surface and sub-surface temperatures during the 40-24 kyrs period resulted from the injection of warm surface waters from the Indian low latitudes. This signal was transported to the core site by a strengthened Agulhas Return Current during the glacial, when the Agulhas leakage to the Atlantic was reduced. Our study thus proposes that the surface conditions in the SAZ of the KI region are shaped by the interplay between the migration of the Southern Ocean hydrological fronts and the Agulhas (Return) Current, both being climatically modulated.

中文翻译：

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Agulhas 回流对南大洋凯尔盖朗高原地区海洋学的影响，在过去 40 kyrs

摘要 由于几个亚南极岛屿和高原的存在改变了南极绕极流的纬向流动，南大洋西印度部分的海洋学极其复杂。凯尔盖朗群岛 (KI) 周围的环流更加复杂，因为水文锋与厄加勒斯回流汇合，后者将温暖的地表水从低纬度输送到 KI 以东的亚南极区 (SAZ)。在这里，我们分别基于硅藻和放射虫普查计数，在涵盖过去 40,000 年 (40 kyrs) 的两个核心中呈现新的海面和亚表层温度，以推断 KI 地区过去的海洋变化。在位于 KI 以西的极锋区 (PFZ) 的核心 MD11-3353 中，海表和次表层温度都遵循预期的冰期-间冰期模式，恒定差异约为 3 °C，表明水柱顶部 500 m 的结构在此期间没有发生剧烈变化。在位于 KI 以东的 SAZ 的核心 MD12-3396CQ 中，次表层温度记录再次遵循预期的冰-间冰期模式，而基于硅藻的重建显示在 40-24 kyrs 期间强烈变暖，平均差异在 ∼9 °C 的两者之间。在冰川结束和全新世期间，温差随后恢复到~3°C。我们认为，40-24 kyrs 期间地表和次地表温度之间的巨大差异是由于来自印度低纬度地区的温暖地表水的注入造成的。在冰川期间，当厄加勒斯向大西洋的泄漏减少时，该信号被加强的厄加勒斯回流传输到核心站点。因此，我们的研究提出，KI 地区 SAZ 的地表条件是由南大洋水文锋的迁移和厄加勒斯（回流）流之间的相互作用形成的，两者都受到气候调节。