The Miocene epoch witnessed major changes in climate. The marine oxygen isotope record, our best single continuous representation of the time interval, contains large shifts indicating substantial changes in the glaciation of Antarctica and/or deep ocean temperatures, with the interval of the most depleted isotopic composition occurring between ~18 and 13.9 Ma (mid‐Miocene Climatic Optimum [MCO]). We present here a record of alkenone unsaturation estimates from a borehole penetrating marine sediments spanning most of the Miocene at ~56°N. Marine temperatures reconstructed for the Miocene are up to 20°C warmer than present day. A maximum occurs at the time of the MCO. The record is strikingly similar to discontinuous alkenone results published from other North Atlantic sites. As in the southern hemisphere, ocean temperature gradients were extraordinarily low in the North Atlantic in comparison to today. Our findings suggest that the MCO was a global temperature maximum and link the partial deglaciation of the Antarctic and subsequent “refrigeration” to a global forcing process. However, the small magnitude of the ocean cooling from ~14 to 10 Ma suggests a highly nonlinear (threshold) relationship between East Antarctic ice volume and global temperature.

中文翻译：

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从丹麦北海看中新世气候最适宜的双半球变暖

中新世时期见证了气候的重大变化。海洋氧同位素记录是我们对时间间隔的最佳连续记录，它包含较大的变化，表明南极洲的冰川作用和/或深海温度发生了实质性变化，最耗竭的同位素组成的时间间隔在〜18和13.9 Ma之间（中新世中期气候最佳[MCO]）。我们在这里提供了一个贯穿贯穿中新世大部分地区（约56°N）的海洋沉积物的钻孔中烯酮不饱和度估计值的记录。为中新世重建的海洋温度比今天高出20°C。在MCO发生最大值时。该记录与从其他北大西洋站点发布的不连续烯酮结果惊人地相似。和南半球一样，与今天相比，北大西洋的海洋温度梯度异常低。我们的发现表明，MCO是全球最高温度，并将南极的部分冰消和随后的“制冷”与全球强迫过程联系起来。但是，从约14Ma到10Ma的海洋降温幅度较小，这表明南极东部冰量与全球温度之间存在高度非线性（阈值）关系。