Tropical Warming and Intensification of the West African Monsoon During the Miocene Climatic Optimum

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Paleoceanography and Paleoclimatology Pub Date : 2024-05-01 DOI:10.1029/2023pa004767

E. Wubben, Bianca R. Spiering, T. Veenstra, Remco Bos, Zongyi Wang, Joost van Dijk, I. Raffi, Jakub Witkowski, Frederik J. Hilgen, F. Peterse, F. Sangiorgi, A. Sluijs

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Abstract

Studying monsoon dynamics during past warm time periods such as the Miocene Climatic Optimum (MCO; ∼16.9–14.5 Ma) could greatly aid in better projecting monsoon intensity, in the context of future greenhouse warming. However, studies on regional MCO temperature change and its effect on the monsoons during this time period are lacking. Here, we present the first high‐resolution, low‐latitude record of sea surface temperature (SST) and paleoceanographic change covering the Miocene Climatic Optimum, in the eastern equatorial Atlantic, at Ocean Drilling Program Site 959, based on TEX86 paleothermometry. SSTs were ∼1.5°C warmer at the onset of the MCO (16.9 Ma) relative to the pre‐MCO (∼18.3–17.7 Ma). This warming was accompanied by a transient increase in %total organic carbon. Prior to the MCO, sediment composition, geochemical proxy data as well as dinoflagellate cyst assemblages imply a productive surface ocean at Site 959. Immediately following the MCO onset (∼16.9–16.5 Ma), we record an intensification of the West African Monsoon (WAM) characterized by higher amplitude variability in all proxy records on precession to obliquity timescales. We interpret increased orbital‐scale SST, biogenic Ba and dinocyst assemblage variability to represent intensification of equatorial upwelling, forced by the WAM strength. Furthermore, higher SSTs during eccentricity maxima correlate to increased relative abundances of the warm and stratification‐favoring dinocyst Polysphaeridium zoharyi, during periods of low WAM intensity. Finally, while long‐term SSTs decline toward the middle Miocene, maximum SSTs and Polysphaeridium zoharyi abundances occur during MCO peak warming at ∼15.6 Ma.

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中新世气候最适宜期的热带变暖和西非季风加剧

研究中新世气候最适宜期（MCO；16.9-14.5 Ma）等过去温暖时期的季风动态，对更好地预测未来温室变暖背景下的季风强度大有帮助。然而，目前还缺乏对这一时期区域MCO温度变化及其对季风影响的研究。在此，我们基于 TEX86 古温度测定法，在大洋钻探计划第 959 号站点首次展示了中新世气候最适宜期赤道大西洋东部海面温度（SST）和古海洋学变化的高分辨率、低纬度记录。在中新世气候最适宜期开始时（16.9 Ma），相对于中新世气候最适宜期之前（18.3-17.7 Ma），海温升高了 1.5 °C。在变暖的同时，总有机碳含量也出现了短暂的增加。在 MCO 发生之前，沉积物成分、地球化学代用数据以及甲藻孢囊群表明 959 号地点的表层海洋是富饶的。紧接着 MCO 开始之后（16.9-16.5 Ma），我们记录到西非季风（WAM）的加强，其特点是所有代用记录在前向到斜向时间尺度上的振幅变化更大。我们将轨道尺度的海温、生物钡和恐龙囊集合体变率的增加解释为在 WAM 强度的作用下赤道上升流的加强。此外，在偏心率最大值期间，较高的 SST 与在 WAM 强度较低期间，温暖且有利于分层的双胞藻 Polysphaeridium zoharyi 的相对丰度增加有关。最后，虽然长期海温在中新世中期有所下降，但最大海温和Polysphaeridium zoharyi丰度出现在15.6 Ma的MCO变暖高峰期。

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来源期刊

Paleoceanography and Paleoclimatology Earth and Planetary Sciences-Atmospheric Science

CiteScore

6.20

自引率

11.40%

发文量

107

期刊介绍： Paleoceanography and Paleoclimatology (PALO) publishes papers dealing with records of past environments, biota and climate. Understanding of the Earth system as it was in the past requires the employment of a wide range of approaches including marine and lacustrine sedimentology and speleothems; ice sheet formation and flow; stable isotope, trace element, and organic geochemistry; paleontology and molecular paleontology; evolutionary processes; mineralization in organisms; understanding tree-ring formation; seismic stratigraphy; physical, chemical, and biological oceanography; geochemical, climate and earth system modeling, and many others. The scope of this journal is regional to global, rather than local, and includes studies of any geologic age (Precambrian to Quaternary, including modern analogs). Within this framework, papers on the following topics are to be included: chronology, stratigraphy (where relevant to correlation of paleoceanographic events), paleoreconstructions, paleoceanographic modeling, paleocirculation (deep, intermediate, and shallow), paleoclimatology (e.g., paleowinds and cryosphere history), global sediment and geochemical cycles, anoxia, sea level changes and effects, relations between biotic evolution and paleoceanography, biotic crises, paleobiology (e.g., ecology of “microfossils” used in paleoceanography), techniques and approaches in paleoceanographic inferences, and modern paleoceanographic analogs, and quantitative and integrative analysis of coupled ocean-atmosphere-biosphere processes. Paleoceanographic and Paleoclimate studies enable us to use the past in order to gain information on possible future climatic and biotic developments: the past is the key to the future, just as much and maybe more than the present is the key to the past.