Reconstructing intermediate and deep ocean circulation during the Pliocene warm period

海洋正在吸收今天由人类活动引入气候系统的大部分热量和二氧化碳排放。然而，我们目前正在地球上进行的这项‘实验’的长期影响还知之甚少。大约300万年前，在上新世暖期，气温高于现代水平，大气中的二氧化碳水平与今天相似。过去的这个时代可能会为未来的气候变化提供线索，我们想要了解的一个关键反应是，海洋环流将如何在变暖的世界中发挥作用。今天，北大西洋的表层水变得比周围的水更稠密，并下沉到海洋内部，形成了一个深水团，作为大西洋子午线翻转环流的一部分。这种大西洋经向翻转环流在全球气候和英国的气候/天气中起着重要作用。另一方面，北太平洋太新鲜了，因此今天那里没有形成深水。上新世深海环流的形态尚不清楚：一些化石证据表明大西洋经向翻转环流很强，而气候模型表明大西洋经向翻转环流很弱，北太平洋发生了太平洋经向翻转环流。这种分歧对整个海洋的热量传输和碳、氧和营养物质的循环有着深远的影响。为了解决这种数据模型不匹配的问题，该项目旨在利用在海洋沉积物中发现的微型化石的化学成分，重建上新世暖期大西洋和太平洋的中水和深水环流。然后将这些记录与上新世最先进的气候模型进行比较，以帮助理解对保持上新世温暖很重要的气候动力学。这些记录将有助于描述全球变暖气候状态下的热量输送、碳循环和中深海环流的特征，并可能有助于确定全球变暖的一些长期后果。

The ocean is absorbing much of the heat and carbon dioxide emissions introduced to the climate system today by human activity. However, long-term impacts of the 'experiment' we are currently carrying out with our planet earth are poorly understood. Approximately three million years ago, during the Pliocene warm period, temperatures were elevated over modern levels and atmospheric carbon dioxide levels were similar to today. This past era could present clues to future climate change and a key response we would like to understand is how ocean circulation will function in a warmer world. Today, surface waters in the North Atlantic become denser than the surrounding water and sink to the ocean's interior forming a deep-water mass as part of Atlantic Meridional Overturning Circulation. This Atlantic Meridional Overturning Circulation plays a major role in global climate and climate/weather in the United Kingdom. The North Pacific on the other hand is too fresh, and hence no deep waters are formed there today. The configuration of deep ocean circulation during the Pliocene is unclear: some fossil evidence suggests that Atlantic Meridional Overturning Circulation was strong, whereas climate models suggest Atlantic Meridional Overturning Circulation was weak and a Pacific Meridional Overturning Circulation occurred in the North Pacific. This disagreement has profound implications for heat transport and the cycling of carbon, oxygen, and nutrients throughout the oceans. To address this data-model mismatch, this project aims to reconstruct intermediate and deep-water circulation in the Atlantic and Pacific during the Pliocene warm period using the chemistry of microfossils found within marine sediment. These records will then be compared to state of the art climate models for the Pliocene to help understand the climate dynamics important in maintaining Pliocene warmth. These records will help characterize heat transport, carbon cycling and intermediate to deep ocean circulation during a globally warm climate state and may help identify some of the long-term consequences of global warming.