Megasplice of benthic d18O records over the last 35 Ma

Earth's climate has undergone different intervals of gradual change as well as abrupt shifts between climate states. Here we aim to characterize the corresponding changes in climate response to astronomical forcing in the icehouse portion of the Cenozoic, from the latest Eocene to the present. As a tool, we use a 35-m.y.-long d18Obenthic record compiled from different high-resolution benthic isotope records spliced together (what we refer to as a megasplice).We analyze the climate response to astronomical forcing during four 800-k.y.- long time windows. During the mid-Miocene Climatic Optimum (ca. 15.5 Ma), global climate variability was mainly dependent on Southern Hemisphere summer insolation, ampli ed by a dynamic Antarctic ice sheet; 2.5 m.y. later, relatively warm global climate states occurred during maxima in both Southern Hemisphere and Northern Hemisphere summer insolation. At that point, the Antarctic ice sheet grew too big to pulse on the beat of precession, and the Southern Hemisphere lost its overwhelming in uence on the global climate state. Likewise, we juxtapose response regimes of the Miocene (ca. 19 Ma) and Oligocene (ca. 25.5 Ma) warming periods. Despite the similarity in d18Obenthic values and variability, we nd different responses to precession forcing. While Miocene warmth occurs during summer insolation maxima in both hemispheres, Oligocene global warmth is consistently triggered when Earth reaches perihelion in the Northern Hemisphere summer. This pattern is in accordance with previously published paleoclimate modeling results, and suggests an amplifying role for Northern Hemisphere sea ice.

地球气候经历了多段渐进式变化时期，以及不同气候态间的突发性跃迁。本研究旨在刻画新生代（Cenozoic）冰室气候阶段（从始新世最晚期至今）中，气候对天文强迫（astronomical forcing）的响应特征变化。本研究采用一套时长35百万年的底栖有孔虫氧同位素（d18Obenthic）记录作为分析工具，该记录由多份高分辨率底栖同位素记录拼接整合而成（我们将其称为巨型拼接序列（megasplice））。我们针对四个时长80万年的时间窗口，分析了气候对天文强迫的响应特征。在中新世中期气候最佳期（mid-Miocene Climatic Optimum，约15.5 Ma），全球气候变率主要受控于南半球夏季日照辐射，动态南极冰盖进一步放大了这一效应；时隔2.5百万年，当南北半球夏季日照辐射均处于峰值时，全球进入相对暖的气候态。彼时，南极冰盖规模已过大，无法随岁差（precession）周期发生脉动式变化，南半球也因此丧失了对全球气候态的主导性影响。与此类似，本研究还对比了中新世（约19 Ma）与渐新世（约25.5 Ma）两次升温时期的气候响应模态。尽管两次升温期的底栖有孔虫氧同位素数值与变率特征相似，但其对岁差强迫的响应却存在显著差异。中新世暖期对应南北半球夏季日照辐射峰值时段，而渐新世的全球暖化则始终发生在北半球夏季地球运行至近日点（perihelion）的时刻。该响应模式与已发表的古气候模拟（paleoclimate modeling）研究结果相符，同时揭示了北半球海冰的气候放大作用。