古气候中的沙尘变化及其气候影响

doi:10.13745/j.esf.sf.2021.9.51

摘要/Abstract

摘要：

大气中的沙尘通过对太阳光的吸收和散射对地表温度产生影响,进而对大气环流和降水等也产生影响,但是在地球的不同历史时期尤其是深时地球大气中的沙尘量如何变化以及如何影响气候还有很多不清楚的地方。本文通过模式模拟对地球上4个不同时期的沙尘变化及其气候影响进行了研究,这4个时期分别是陆地植被还没有出现的前寒武时期、有植被且全球气温较高的盘古超大陆时期、大陆分布接近现代但气候较寒冷的末次盛冰期和气候较温暖的中全新世。在前寒武时期,由于陆地起沙面积大,大气中的沙尘含量可以达到现代地球的近10倍,使得全球地表温度下降也有近10 ℃。在盘古超大陆时期,由于在副热带的陆地面积比现代稍大,因此大气沙尘量也比现代稍大,对全球平均温度的影响很小。在末次盛冰期,由于寒冷干燥,沙尘量是现代的约两倍,但是它对全球有强烈的增温作用,如果没有沙尘,全球温度可能降低约2.5 ℃。在中全新世,观测显示全球沙尘量比现代少很多,模拟显示,采用现代沙尘和把沙尘全部去掉对全球平均温度的影响可以忽略,但是大西洋经向翻转流有显著变化。

关键词: 沙尘, 古气候, 植被, 大西洋经向翻转流, 超大陆

Abstract:

Dust in the atmosphere can affect the Earth's surface temperature by absorbing and scattering sunlight, and thus further affects the atmospheric circulation and precipitation. However, the mechanism of atmospheric dust loading variability and its effects on the climate during different geological periods, especially the deep time, remain unclear. This paper investigates the change of atmospheric dust loading and its climate effects during four different geological periods via numerical modeling. The four periods are the Precambrian when there was no terrestrial vegetation; the Pangea supercontinent period with terrestrial vegetation and a global temperature significantly higher than the present day; the Last Glacial Maximum with continental configuration close to the modern one but a much colder climate than the present day; and the mid-Holocene with a slightly warmer climate than the present day. Compared to the present day, the Precambrian atmospheric dust loading was nearly 10 times as much due to larger dust source area, which led to a decrease in global surface temperature by about 10 ℃. In the Pangea supercontinent period, the dust loading was slightly higher because of slightly larger land area in the subtropical zone, and its impact on the global mean temperature was small. During the Last Glacial Maximum, dust loading was about twice as much due to a colder and drier climate, yet dust had a strong warming effect—without it, the global temperature would have decreased by about 2.5 ℃. In the mid-Holocene, global dust loading was much less as shown by observational evidence, while simulation results suggest that the effect of removing global dust on the global mean temperature can be ignored for this period even as the Atlantic Meridional Overturning Circulation changed significantly.

Key words: dust, paleoclimate, vegetation, Atlantic meridional ocean circulation, supercontinent

中图分类号:

P467

刘永岗, 张铭, 林琪凡, 刘鹏, 胡永云. 古气候中的沙尘变化及其气候影响[J]. 地学前缘, 2022, 29(5): 285-299.

LIU Yonggang, ZHANG Ming, LIN Qifan, LIU Peng, HU Yongyun. Variation of atmospheric dust loading and its climate impacts in different geological periods[J]. Earth Science Frontiers, 2022, 29(5): 285-299.

图/表 13

图1 模拟得到的工业革命前(1850年)大气沙尘的年平均分布 a—真实植被和地表侵蚀系数;b—真实植被和全球均一的侵蚀系数;c—模拟的植被和全球均一的侵蚀系数。

Fig.1 Annual mean atmospheric dust loading during the pre-industrial obtained from model simulations

表1 各试验中的边界条件和地表侵蚀系数

Table 1 Boundary conditions and soil erodibility factors for all experiments

时期	轨道参数对应年份	CO₂含量/ 10^-6	太阳常数/ (W·m^-2)	海陆分布	沙尘设置	地表侵蚀系数k
中全新世	6 ka	280	1 361	现代	固定为现代观测值
中全新世	6 ka	280	1 361	现代	全球无沙尘
末次盛冰期	21 ka	185	1 361	ICE-6G	在线模拟	同现代
末次盛冰期	21 ka	185	1 361	ICE-6G	全球无沙尘	全球设为0
盘古超大陆时期	1990	7 000	1 334	据[48]	在线模拟	全球均一(0.013)
盘古超大陆时期	1990	7 000	1 334	据[48]	全球无沙尘	全球设为0
前寒武纪	1990	2 000	1 285	据[49]	在线模拟	全球均一(0.30)
	1990	2 000	1 285	据[49]	在线模拟	全球均一(0.15)
	1990	2 000	1 285	据[49]	在线模拟	全球均一(0.075)
	1990	2 000	1 285	据[49]	在线模拟	全球均一(0.037 5)
	1990	2 000	1 285	据[49]	全球无沙尘	全球设为0

图2 中全新世去掉沙尘后4个季节的地表温度变化

Fig.2 Changes of surface temperature after dust removal for 4 seasons during the mid-Holocene

图3 中全新世去掉沙尘后4个季节的降水变化

Fig.3 Changes of precipitation rate after dust removal for 4 seasons during the mid-Holocene

图4 末次盛冰期去掉沙尘后年平均和4个季节的地表温度变化

Fig.4 Changes of annual mean and seasonal mean surface temperature after dust removal during the last glacial maximum

图5 末次盛冰期去掉沙尘后年平均和4个季节的降水变化

Fig.5 Changes of annual mean and seasonal mean precipitation rates after dust removal during the last glacial maximum

图6 盘古超大陆时期模式模拟的植被覆盖率

Fig.6 Model simulated fraction of vegetation cover during the Pangea supercontinent era

图7 盘古超大陆时期大气中沙尘在4个季节的分布

Fig.7 Atmospheric dust loading for 4 seasons during the Pangea supercontinent era

图8 盘古超大陆时期有沙尘时年平均和4个季节的温度变化

Fig.8 Changes of annual mean and seasonal mean surface temperature when considering dust during the Pangea supercontinent era

图9 盘古超大陆时期有沙尘时年平均和4个季节的降水变化

Fig.9 Changes of annual mean and seasonal mean precipitation rates when considering dust during the Pangea supercontinent era

图10 前寒武时期大气中沙尘在4个季节的分布(k=0.15)

Fig.10 Seasonal distribution of atmospheric dust loading in the Precambrian era (k=0.15)

图11 不同地表侵蚀系数条件下的全球年平均温度

Fig.11 Annual mean surface temperature under different erodibilities

图12 不同地表侵蚀系数条件下的全球年平均降水率

Fig.12 Annual mean precipitation rate under different erodibilities

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