Synchronous tropical and polar temperature evolution in the Eocene
Synchronous tropical and polar temperature evolution in the Eocene
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DOI：
10.1038/s41586-018-0272-2
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发表时间：
2018-07-19
期刊：
影响因子：
64.8
通讯作者：
Sluijs, Appy
中科院分区：
文献类型：
--
作者：
Cramwinckel, Margot J.;Huber, Matthew;Sluijs, Appy
气候温暖、大气二氧化碳浓度高的时期的古气候重建对于更好地预测未来气候变化至关重要。深海 (1,2) 和高纬度 (3) 古温度代理表明，始新世（56 至 3400 万年前）涵盖了过去 6600 万年中最温暖的时期，随后逐渐冷却，最终在南极洲形成冰盖。始新世极地温暖已经确定，因此量化关键气候参数（例如全球平均温度变化及其极地放大）演变的主要障碍是缺乏连续的高质量热带温度重建。在这里，我们基于应用于大西洋沉积物的生物标记古体温测量，提出了连续的始新世赤道海面温度记录。我们将此记录与稀疏的现有数据 (4-6) 结合起来，构建了始新世热带气候演化的 2600 万年多代理、多地点堆栈。我们发现，在长期气候趋势和短期事件的影响下，热带和深海温度平行变化。这与温室气体强迫(7,8)，而不是海洋环流的变化(9,10)，是始新世气候的主要驱动力的假设是一致的。此外，我们观察到热带和深海温度之间存在很强的线性关系，这意味着在整个无冰的始新世中存在恒定的极地放大系数。与全耦合气候模型模拟的定量比较表明，始新世早、中早、中晚和晚始新世全球平均气温分别约为29、26、23和19摄氏度，而工业化前气温为14.4摄氏度。最后，将基于代理和模型的温度估计与可用的二氧化碳重建相结合(8)，得出始新世地球系统敏感性为 0.9 至 2.3 开尔文每瓦每平方米的概率为 68%，与之前估计的上限一致(11)。
Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO2 concentrations are crucial for developing better projections of future climate change. Deep-ocean(1,2) and high-latitude(3) palaeotemperature proxies demonstrate that the Eocene epoch (56 to 34 million years ago) encompasses the warmest interval of the past 66 million years, followed by cooling towards the eventual establishment of ice caps on Antarctica. Eocene polar warmth is well established, so the main obstacle in quantifying the evolution of key climate parameters, such as global average temperature change and its polar amplification, is the lack of continuous high-quality tropical temperature reconstructions. Here we present a continuous Eocene equatorial sea surface temperature record, based on biomarker palaeothermometry applied on Atlantic Ocean sediments. We combine this record with the sparse existing data(4-6) to construct a 26-million-year multi-proxy, multi-site stack of Eocene tropical climate evolution. We find that tropical and deep-ocean temperatures changed in parallel, under the influence of both long-term climate trends and short-lived events. This is consistent with the hypothesis that greenhouse gas forcing(7,8), rather than changes in ocean circulation(9,10), was the main driver of Eocene climate. Moreover, we observe a strong linear relationship between tropical and deep-ocean temperatures, which implies a constant polar amplification factor throughout the generally ice-free Eocene. Quantitative comparison with fully coupled climate model simulations indicates that global average temperatures were about 29, 26, 23 and 19 degrees Celsius in the early, early middle, late middle and late Eocene, respectively, compared to the preindustrial temperature of 14.4 degrees Celsius. Finally, combining proxy- and model-based temperature estimates with available CO2 reconstructions(8 )yields estimates of an Eocene Earth system sensitivity of 0.9 to 2.3 kelvin per watt per square metre at 68 per cent probability, consistent with the high end of previous estimates(11).