Pacific circulation during the middle Miocene climate transition: Monitoring ocean overturning and the east-west hydrographic gradient

大约1390万年前，地球上的S气候在经历了一段较长时间的相对温暖后急剧降温。这是地球S气候和生物演化的关键转折，标志着新生代逐步冷却的最后阶段，仍然是地球S新生代气候史上最神秘的事件之一。虽然有证据表明轨道强迫和大气二氧化碳变化强烈地影响了气候演变，但海洋环流作为气候变化的增强器或驱动力的作用尚不清楚。我们的主要目标是研究中中新世温暖气候阶段太平洋环流的变化以及随后的全球变冷。特别是，我们将检验这一假设，即在-13.9 Ma，全球变冷和冰盖膨胀与太平洋环流的根本重组和西太平洋暖池系统的启动相吻合。我们的研究将提供海洋化学指标的综合，这将使太平洋不同区域的古海洋学事件能够进行详细的对比，并有助于限制对过去和未来气候的模拟研究。此外，中新世早期气候最佳是研究全球变暖的原因和后果的特殊类比，特别是在快速变暖期间深水水源的潜在开关。

About 13.9 million years ago, the Earth s climate cooled dramatically after an extended period of relative warmth. This key transition in Earth s climatic and biotic evolution, which marked the final stage of stepwise Cenozoic cooling, remains one of the most enigmatic episodes in Earth s Cenozoic climate history. While there is evidence that orbital forcing and atmospheric CO2 variations strongly influenced climate evolution, the role of the ocean circulation as enhancer or driver of climate change remains unclear. Our primary goals are to investigate circulation changes in the Pacific during the middle Miocene warm climate phase and subsequent global cooling. In particular, we will test the hypothesis that global cooling and ice-sheet expansion at - 13.9 Ma coincided with a fundamental re-organization in Pacific circulation and initiation of a West Pacific Warm Pool system. Our investigation will provide a synthesis of ocean chemistry proxies that will allow detailed correlation of paleoceanographic events in different regions of the Pacific and help constrain modeling studies of past and future climate. Furthermore, the early middle Miocene climate optimum represents an exceptional analogue to study the causes and consequences of global warming, in particular the potential switches in deep-water sources during intervals of rapid warming.