Steps in the intensification of Benguela upwelling over the Walvis Ridge during Miocene and Pliocene

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• 作者：Sebastian Hoetzel ; Lydie M. Dupont…
• 关键词：Dinoflagellate cysts ; Benguela upwelling ; Miocene–Pliocene ; Eastern South Atlantic
• 刊名：International Journal of Earth Sciences
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：106
• 期：1
• 页码：171-183
• 全文大小：
• 刊物类别：Earth and Environmental Science
• 刊物主题：Geology; Geophysics/Geodesy; Sedimentology; Structural Geology; Mineral Resources; Geochemistry;
• 出版者：Springer Berlin Heidelberg
• ISSN：1437-3262
• 卷排序：106

文摘

Upwelling is a significant part of the ocean circulation controlling largely the transport of nutrient-rich cold waters to the surface and therefore influencing ocean productivity and global climate. The Benguela upwelling system (BUS) is one of the major upwelling areas in the world. Previous reconstructions of the BUS mainly focused on the onset and intensification in southern and central parts, but changes of the northern part have been rarely investigated in detail. Using the Late Miocene to Pliocene organic-walled dinoflagellate cyst record of ODP Site 1081, we reconstruct and discuss the early upwelling history over the Walvis Ridge with a special focus on the movement of the Angola-Benguela Front (ABF). We suggest that during the Late Miocene the Angola Current flowed southwards over the Walvis Ridge more frequently than today because the ABF was probably located further south as a result of a weaker meridional temperature gradient. A possible strengthening of the meridional gradient during the latest Miocene to early Pliocene in combination with uplift of south-western Africa intensified the upwelling along the coast and increased the upwelling’s filaments over the Walvis Ridge. An intermediate period from 6.2 to 5.5 Ma is shown by the dominance of Habibacysta tectata, cysts of a cool-tolerant dinoflagellate known from the northern Atlantic, indicating changing oceanic conditions contemporaneous with the Messinian Salinity Crisis. From 4.3 Ma on, the upwelling signal got stronger again and waters were well-mixed and nutrient-rich. Our results indicate a northward migration of the ABF as early as 7 Ma and the initial stepwise intensification of the BUS.