妄学植物

版权声明：转载时请以超链接形式标明文章原始出处和作者信息及本声明
http://botany.blogbus.com/logs/28450721.html

Science 27 April 2001: Vol. 292. no. 5517, pp. 686 - 693 DOI: 10.1126/science.1059412

Review

Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present

James Zachos, Mark Pagani, Lisa Sloan, Ellen Thomas, Katharina Billups

摘要：自6500万年前以来，地球的气候经历了显著和复杂的演变，通过对深海沉积物钻孔的研究，其细节正日益清晰。该演变包括由地质构造驱动的在10⁵至10⁷年尺度上的变暖和变冷的渐进趋势、由地球轨道进程驱动的10⁴至10⁶年的节律性或周期性旋回、以及持续10³至10⁵年的罕见快速异常变化和极端气候瞬变。本文中综述了有关新生代以来全球气候变化的最新进展。我们主要集中在该时代早期（由最新的深海同位素记录所限制的）变异性的周期和异常组分。我们还考虑了这一改进过的视角将如何导致对以前不可预见气候转变机制的识别。

原文来自Science。

Cenozoic Climate: From Greenhouse to Icehouse
Our benthic compilation shows a total δ¹⁸O range of 5.4‰ over the course of the Cenozoic (Fig. 2). Roughly ~3.1‰ of this reflects deep-sea cooling, the remainder growth of ice-sheets, first on Antarctica (~1.2‰), and then in the Northern Hemisphere (~1.1‰). We consider the climate evolution depicted by this record under three categories: (i) longterm (~10⁶ to 10⁷ years), (ii) short-term or orbital-scale (~10⁴ to 10⁵ years), and (iii) aberrations or event-scale (~10³ to 10⁴ years).

Long-term trends. The δ¹⁸O record exhibits a number of steps and peaks that reflect on episodes of global warming and cooling, and ice-sheet growth and decay (Fig. 2). The most pronounced warming trend, as expressed by a 1.5‰ decrease in δ¹⁸O, occurred early in the Cenozoic, from the mid-Paleocene (59 Ma) to early Eocene (52 Ma), and peaked with the early Eocene Climatic Optimum (EECO; 52 to 50 Ma). The EECO was followed by a 17-My-long trend toward cooler conditionsas expressed by a 3.0‰ rise in δ¹⁸O withmuch of the change occurring over the earlymiddle(50 to 48 Ma) and late Eocene (40 to36 Ma), and the early Oligocene (35 to 34Ma). Of this total, the entire increase in δ¹⁸O prior to the late Eocene (~1.8‰) can beattributed to a 7.0°C decline in deep-sea temperature(from ~12° to ~4.5°C). All subsequent δ¹⁸O change reflects a combined effectof ice-volume and temperature (40), particularlyfor the rapid .1.0‰ step in δ¹⁸O at 34Ma. On the basis of limits imposed by bottom-water and tropical temperatures, it hasbeen estimated that roughly half this signal (~0.6‰) must reflect increased ice volume (24, 41), though independent constraints on temperature derived from benthic foraminiferal Mg/Ca ratios argue for a slightly greater ice-volume component (~0.8 to 1.0‰) (42). This long-term pattern of deep-sea warming and cooling is consistent with reconstructions of early Cenozoic subpolar climates based on both marine and terrestrial geochemical and fossil evidence (43–47).

Following the cooling and rapid expansion of Antarctic continental ice-sheets in the earliest Oligocene, deep-sea δ¹⁸O values remained relatively high (>2.5‰), indicating a permanent ice sheet(s), likely temperate in character (48), with a mass as great as 50% of that of the present-day ice sheet and bottom temperatures of ;4°C (18). These ice sheets persisted until the latter part of the Oligocene (26 to 27 Ma), when a warming trend reduced the extent of Antarctic ice. From this point until the middle Miocene (~15 Ma), global ice volume remained low and bottom water temperatures trended slightly higher (49, 50), with the exception of several brief periods of glaciation (e.g., Mi-events) (39). This warm phase peaked in the late middle Miocene climatic optimum (17 to 15 Ma), and was followed by a gradual cooling and reestablishment of a major ice-sheet on Antarctica by 10 Ma (51, 52). Mean δ¹⁸O values then continued to rise gently through the late Miocene until the early Pliocene (6 Ma), indicating additional cooling and small-scale icesheet expansion on west-Antarctica (53) and in the Arctic (54). The early Pliocene is marked by a subtle warming trend (55) until ;3.2 Ma, when δ¹⁸O again increased reflecting the onset of Northern Hemisphere Glaciation (NHG) (56, 57).