Vertical thermal gradient history in the eastern equatorial Pacific during the early to middle Miocene: Implications for the equatorial thermocline development
Vertical thermal gradient history in the eastern equatorial Pacific during the early to middle Miocene: Implications for the equatorial thermocline development
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DOI：
10.1002/2016pa003058
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发表时间：
2017-07
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通讯作者：
H. Matsui;H. Nishi;A. Kuroyanagi;H. Hayashi;M. Ikehara;R. Takashima
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作者：
H. Matsui;H. Nishi;A. Kuroyanagi;H. Hayashi;M. Ikehara;R. Takashima
了解赤道温跃层对于了解热带太平洋的气候变化至关重要。多物种浮游有孔虫分析提供了一种方法来检查温度分布，从而温跃层的结构。虽然长期温跃层的发展已被记录到晚中新世，早中新世至中中新世的时间间隔很少被检查。此外，与动态南极冰盖的关系仍不清楚。在这里，我们调查的垂直热梯度在上层水柱在综合大洋钻探计划网站U1337在赤道东太平洋（EEP）整个早中期中新世（23.1至11.7马）。在中新世气候适宜期，梯度增加，而在东南极冰盖扩张期（EAIE），梯度下降。EEP记录与其西赤道太平洋（WEP）对应的比较表明，海表温度更稳定的WEP比在EEP。我们进一步估计赤道温跃层从两个对角梯度之间的EEP和WEP：温跃层变浅，从16.7至15.7 Ma和倾斜减弱之间的16.5和13.8 Ma。“蒙特雷漂移”的开始和南极冰盖体积的减少将分别影响温跃层深度和倾斜度。温跃层的深度可能比上新世到现代的条件要深得多。此外，使用基于4点的等温线分布（4DI指数）作为等温线分布的均匀性或不均匀性的度量。4DI指数在EAIE和其他Mi事件附近显著降低，反映了在冰川化程度更高的南极洲下均匀分布的等温线。
Knowledge of the equatorial thermocline is essential for understanding climate changes in the tropical Pacific. Multispecies planktic foraminiferal analyses provide a way to examine temperature distributions and thus the structure of the thermocline. Although the secular thermocline development has been documented back to the late Miocene, the early to middle Miocene interval has rarely been examined. In addition, relationships with the dynamic Antarctic ice sheets remain unclear. Here we investigate the vertical thermal gradient in the upper water column at Integrated Ocean Drilling Program Site U1337 in the eastern equatorial Pacific (EEP) throughout the early to middle Miocene (23.1 to 11.7 Ma). The gradient increased over the Miocene Climatic Optimum, whereas it decreased during the East Antarctic Ice Sheet Expansion (EAIE). Comparison of the EEP record with its western equatorial Pacific (WEP) counterpart suggests that sea surface temperature was more stable in the WEP than in the EEP. We further estimated equatorial thermocline from two diagonal gradients between the EEP and the WEP: thermocline shoaled from 16.7 to 15.7 Ma and tilt weakened between 16.5 and 13.8 Ma. The onset of the “Monterey Excursion” and the reduced Antarctic ice sheet volume would have affected thermocline depth and tilt, respectively. Thermocline depth was likely much deeper compared to Pliocene-to-modern conditions. Furthermore, a 4-point-based distribution of isotherms (4DI index) was used as a metric of the evenness or unevenness of the isotherm distributions. The 4DI index considerably reduced at around the EAIE and other Mi-events, reflecting the evenly distributed isotherms under a more glaciated Antarctica.