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Evolution of nutricline dynamics in the equatorial Pacific during the late Pliocene

机译：上新世晚期赤道太平洋营养盐动态的演变

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The tropics have played a central role in modulating Earth's climate throughout the Plio-Pleistocene, with tropical productivity fluctuations a key mechanism in the operation of the global carbon cycle and linkage of high- and low-latitude climates. Published records of tropical sea surface temperatures (SSTs) during the Plio-Pleistocene appear to vary primarily in tune with high-latitude climate on both orbital and secular timescales. However, contemporaneous changes in equatorial primary productivity are less well constrained,particularly at sites where climate is not dominated by upwelling or monsoon systems. Furthermore, the role of thermocline dynamics (tilt and mean depth changes) in forcing SST and productivity on orbital timescales remains uncertain. Here we report new, high-resolution calcareous nannofossil records from two Ocean Drilling Program sites in the western and eastern equatorial Pacific during marine isotope stages 95-101,about 2400-2600 kyr ago. Our records of paleoproductivity and nutricline depth reveal synchronous, largeamplitude glacial-interglacial productivity variations at both ends of the equatorial Pacific indicating (1)remote (high-latitude) forcing of primary productivity and (2) no primary role for east–west tilting of the equatorial Pacific thermocline, with important implications regarding the operation of El Nino–like dynamics in the Pliocene Pacific. Instead, the paleoproductivity variations and phase relationships that we document suggest the interaction of two mechanisms operating on obliquity timescales: a "bottom-up" forcing transmitted via the upwelling of high-latitude source waters in conjunction with the "top-down" forcing of atmospheric greenhouse gases.
机译：热带地区在整个上新世的地球气候调节中发挥了核心作用，热带生产力的波动是全球碳循环和高低纬度气候联系的关键机制。在上新世更新世期间，已发布的热带海表温度（SST）记录似乎在轨道和世俗时间尺度上均与高纬度气候的变化有关。但是，同期赤道初级生产力的变化受到的限制较小，特别是在气候不受上升流或季风系统支配的地区。此外，在跃迁轨道尺度上，温跃层动力学（倾斜和平均深度变化）在强迫海温和生产力方面的作用仍然不确定。在这里，我们报告了大约95年至101年（大约2400年至2600年）的海洋同位素阶段，赤道西太平洋和东太平洋两个海洋钻探计划站点的新的高分辨率钙质纳米化石记录。我们的古生产力和营养深度记录表明，赤道太平洋两端的冰山-冰川间生产力同步变化，表明（1）主要生产力的远程（高纬度）强迫，（2）东西向倾斜没有主要作用。赤道太平洋高温跃层，对上新世太平洋类似厄尔尼诺现象的动力学产生重要影响。取而代之的是，我们记录的古生产力变化和相位关系暗示了在倾斜时标上运行的两种机制之间的相互作用：通过高纬度水源上升流传输的“自下而上”强迫与“纬度自上而下”强迫共同作用。大气温室气体。

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