熊尚发-第四纪环境变化机制

Climatic proxy
100kyr 周期成因的解释
Broecker: 海洋－大气系统重组，淡水注入，海洋盐 度分布，NADW Imbrie: 100kyr周期产生于气候系统内部的非线性 响应机制，与北半球大陆冰盖产生的气候 惰性有关 Shackleton: 在100kyr周期上，CO2变化早于冰量变 化，说明100kyr周期并非起源于冰盖动力 学变化，而可能与全球碳循环变化导致的 大气CO2浓度变化有关 Muller & MacDonald: 轨道面倾角(orbital inclination) （引发的宇宙尘变化 Interplanetary dust） 与冰期旋回有关 Clark: 冰盖下覆的地基不稳定性导致冰盖周期性 坍塌 Raymo, Paillard: 太阳辐射的阈值引发冰期循环
驱动和记录的对比：第四纪冰期旋回理论的一块基石
最大的问题－100kyr周期问题
Termination I
Termination II
明显的100kyr周期
Termination III
Termination IV
S1 S2 S3
黄土记录的100kyr周期
S4
S5
Stratigraphic interpretation
第四纪气候变化机制问题： The 100kyr problem The “Stage-11 problem” The causality problem The transition problem (1Ma) The 41kyr problem The sudden termination problem
第四纪气候变化机制
中国科学院地质与地球物理研究所
熊尚发
第四纪气候变化过程与机制
－构造尺度 －轨道尺度 －亚轨道尺度 第四纪气候变化研究中的几个难题 －冰期旋回机制，Milankovitch理论 －气候突变与快速气候变化机制 －南北半球气候变化耦合机制 －冰期热带降温幅度问题
气候变化信息从哪里来－－ 记录-Climatic Proxies
Precession (春分点进动)--These are two components of procession: that relating to the elliptical orbit of the Earth, and that related to its axis of rotation. Time of perihelion, Earth-Sun distance in June. 23kyr, 19kyr.
Obliquity (轨道倾角)--The tilt of the Earth’s axis of rotation with respect to the plane of its orbit (the plane of the ecliptic) varies between 21.8o and 24.4o over a period of 41kyr. The greater the angle of tilt, the greater the difference between summer and winter.
-History:
冰 期 旋 回 理 论 的 简 史
Agassiz (1838)was among the first to recognize that glaciation was the most natural explanation for the erratic boulders, moraines, and deeply scratched bedrocks that could be found in many places in the Alps, Scotland, and North America. Croll (1875) elaborated the first astronomical theory of paleoclimate. Croll hypothesized that precessional forcing, though only seasonal, might be crucial and that winter insolation might be critical. Interest in an astronomical theory of glacial cycles was renewed with the work of ankovitch between 1920 and 1941, in which he computed the solar radiation at the top of the atmosphere for different latitudes, taking into account the changes in eccentricity, precession, and tilt of the Earth. In contrast to Croll ’s theory, Milankovitch argued that the summer season was critical. Colder summers enable the persistence throughout the year of snowfields in some high latitude regions, leading to a net accumulation of ice and to the building of ice sheets. The first continuous records of the ice ages from marine sediment cores came in the 1950s (Arrhé nius, 1952; Ericson et al., 1956), and Emiliani (1955) provided the first record of the isotopic composition of fossil shells of foraminifers in these cores. For the first time, cyclicity was demonstrated, and Emiliani assigned each individual cycle a “marine isotopic stage number”. Shackleton (1967) and Duplessy et al. (1970) suggested that most of Emiliani ’s signal was caused by ice volume changes, not by temperature changes. With the study of foraminiferal assemblages in marine sediment cores, Imbrie and Kipp (1971) could confirm these results and provide quantitative estimates of the glacial-interglacial temperature changes. Dating methods based on the radioisotopes of uranium, thorium, and potassium were also developed at this time. When applied to fossil coral reefs (Broecker, 1966; Broecker et al., 1968), as well as to magnetic reversals (Cox et al., 1963, 1964), a cyclicity of 100 kyr was clearly demonstrated (Broecker and van Donk, 1970; Hays et al., 1969; Kukla, 1975). However, the Milankovitch theory stated that the main cycles should be at 23 and 41 kyr. Careful spectral analysis of marine sediment cores led to the clear confirmation of the astronomical theory. Indeed, besides the 100kyr cycle, three other cycles could be identified: 41, 23, and 19 kyr (Hays et al., 1976). Ice age cycles are therefore undoubtedly linked in some fashion to Earth’s orbital variations. (2002/4/26)
Marine diment
Tree ring Pollen
Ice Core
Terrestrial record and Geomorphology
Coral reef
长记录－跨越第四纪
多个冰期－间冰期旋回的气候记录
Age (ka)
10 20 30 40 50 60 70 80 90
末次冰期(Last Glacial Period) 的气候记录
存第 在四 冰纪 期气 －候 间变 冰化 期的 的最 转大 换特 征 是
大冰盖的消退
16,000,000km2
ICE SHEET
Eccentricity (偏心率)---
轨 道 参 数 及 其 谱 分 布
The shape of the Earth’s orbit changes from near circular to an ellipse over a period of about 95kyr with a longer cycle of change of about 400kyr. Changes in eccentricity cause only a 0.03% variation in total annual insolation, but they have significant seasonal effect.