The 4.2 ka event that occurred during the period from 4 500–3 900 a BP was characterized by cold and dry climates and resulted in the collapse of civilizations around the world. The cause of this climatic event, howe...The 4.2 ka event that occurred during the period from 4 500–3 900 a BP was characterized by cold and dry climates and resulted in the collapse of civilizations around the world. The cause of this climatic event, however, has been under debate. We collected four corals(Porites lutea) from Yongxing Island, Xisha Islands, South China Sea, dated them with the U-series method, and measured the annual coral growth rates using X-ray technology. The dating results showed that the coral growth ages were from 4 500–3 900 a BP, which coincide well with the period of the4.2 ka event. We then reconstructed annual sea surface temperature anomaly(SSTA) variations based on the coral growth rates. The growth rate-based SSTA results showed that the interdecadal SSTA from 4 500–3 900 a BP was lower than that during modern times(1961–2008 AD). A spectral analysis showed that the SSTA variations from4 500–3 900 a BP were under the influence of El Nino-Southern Oscillation(ENSO) activities. From 4 500–4 100 a BP, the climate exhibited La Nina-like conditions with weak ENSO intensity and relatively stable and lower SSTA amplitudes. From 4 100–3 900 a BP, the climate underwent a complicated period of ENSO variability and showed alternating El Nino-or La Nina-like conditions at interdecadal time scales and large SSTA amplitudes. We speculate that during the early and middle stages of the 4.2 ka event, the cold climate caused by weak ENSO activities largely weakened social productivity. Then, during the end stages of the 4.2 ka event, the repeated fluctuations in the ENSO intensity caused frequent extreme weather events, resulting in the collapse of civilizations worldwide. Thus, the new evidence obtained from our coral records suggests that the 4.2 ka event as well as the related collapse of civilizations were very likely driven by ENSO variability.展开更多
Annual skeletal extension rates of the sclera-actinian corals Porites species were investigated in 32 colonies from the northern Gulf of Aqaba fringing reef at various depths (1 - 42 m). All corals reveal clear and re...Annual skeletal extension rates of the sclera-actinian corals Porites species were investigated in 32 colonies from the northern Gulf of Aqaba fringing reef at various depths (1 - 42 m). All corals reveal clear and regular skeletal density banding patterns. Results showed that the high-density annual growth bands were formed during winter and the low-density annual growth bands during summer. The mean annual extension rates of the studied corals reveal a large inter-colony variability with values ranged between 2.36 to 20.0 mm/year. While a general trend of decreasing coral extension rate with depth was observed and best explained by a simple exponential model, the rates clustered into two groups: 10.86 ± 2.54 mm/year in water depths less than 10 m, and 5.23 ± 1.99 mm/year below 12 m. Light intensity seems to be the primary environmental factor responsible for decreasing coral extension rate with depth since the effect of other environmental parameters could be neglected from the Gulf of Aqaba. Time series record of the mean annual coral extension rate showed a slight increasing linear trend which could be linked to increase seawater temperature over the period of time represented.展开更多
珊瑚生长率是珊瑚古气候研究的重要指标,其反映珊瑚生长快慢,并提供高分辨率的海水表层温度变化信息。中全新世作为当前全球变暖的地质历史相似型,利用珊瑚生长率重建该时期的气候环境状况对于理解现代气候变化的过程及其机制具有重要...珊瑚生长率是珊瑚古气候研究的重要指标,其反映珊瑚生长快慢,并提供高分辨率的海水表层温度变化信息。中全新世作为当前全球变暖的地质历史相似型,利用珊瑚生长率重建该时期的气候环境状况对于理解现代气候变化的过程及其机制具有重要的参考价值。文章对采自海南潭门珊瑚岸礁的23段中全新世(6143—4356 a BP)滨珊瑚进行生长率分析,并基于该区域现代(2005—2021 AD)滨珊瑚生长率与SST的关系重建了中全新世期间共406 a的年均SST序列。结果显示:1)中全新世滨珊瑚生长率的变化范围为0.607~1.670 cm/a,均值为1.079 cm/a,且存在明显的波动变化过程;2)基于生长率重建的中全新世平均SST为25.7±0.54℃,这与全球变暖程度加剧背景下的现代海温相近;中全新世年均SST的变化范围为24.7~26.8℃,其中5860、5660和5160 a BP为3个显著的低温期;3)对比现代与中全新世(5427—5394、5243—5209、4515—4456和4404—4356 a BP)珊瑚生长率的频谱周期,发现现代与中全新世珊瑚的生长率均存在显著的3~7 a ENSO周期,但中全新世ENSO主周期改变且频率显著降低,表明中全新世的ENSO活动总体偏弱;概率密度函数统计进一步显示中全新世期间ENSO变率存在逐渐增强的趋势。展开更多
基金The National Natural Science Foundation of China under contract No.91428203the Guangxi Scientific Projects under contract Nos AD17129063 and AA17204074the Bagui Fellowship from Guangxi of China
文摘The 4.2 ka event that occurred during the period from 4 500–3 900 a BP was characterized by cold and dry climates and resulted in the collapse of civilizations around the world. The cause of this climatic event, however, has been under debate. We collected four corals(Porites lutea) from Yongxing Island, Xisha Islands, South China Sea, dated them with the U-series method, and measured the annual coral growth rates using X-ray technology. The dating results showed that the coral growth ages were from 4 500–3 900 a BP, which coincide well with the period of the4.2 ka event. We then reconstructed annual sea surface temperature anomaly(SSTA) variations based on the coral growth rates. The growth rate-based SSTA results showed that the interdecadal SSTA from 4 500–3 900 a BP was lower than that during modern times(1961–2008 AD). A spectral analysis showed that the SSTA variations from4 500–3 900 a BP were under the influence of El Nino-Southern Oscillation(ENSO) activities. From 4 500–4 100 a BP, the climate exhibited La Nina-like conditions with weak ENSO intensity and relatively stable and lower SSTA amplitudes. From 4 100–3 900 a BP, the climate underwent a complicated period of ENSO variability and showed alternating El Nino-or La Nina-like conditions at interdecadal time scales and large SSTA amplitudes. We speculate that during the early and middle stages of the 4.2 ka event, the cold climate caused by weak ENSO activities largely weakened social productivity. Then, during the end stages of the 4.2 ka event, the repeated fluctuations in the ENSO intensity caused frequent extreme weather events, resulting in the collapse of civilizations worldwide. Thus, the new evidence obtained from our coral records suggests that the 4.2 ka event as well as the related collapse of civilizations were very likely driven by ENSO variability.
文摘Annual skeletal extension rates of the sclera-actinian corals Porites species were investigated in 32 colonies from the northern Gulf of Aqaba fringing reef at various depths (1 - 42 m). All corals reveal clear and regular skeletal density banding patterns. Results showed that the high-density annual growth bands were formed during winter and the low-density annual growth bands during summer. The mean annual extension rates of the studied corals reveal a large inter-colony variability with values ranged between 2.36 to 20.0 mm/year. While a general trend of decreasing coral extension rate with depth was observed and best explained by a simple exponential model, the rates clustered into two groups: 10.86 ± 2.54 mm/year in water depths less than 10 m, and 5.23 ± 1.99 mm/year below 12 m. Light intensity seems to be the primary environmental factor responsible for decreasing coral extension rate with depth since the effect of other environmental parameters could be neglected from the Gulf of Aqaba. Time series record of the mean annual coral extension rate showed a slight increasing linear trend which could be linked to increase seawater temperature over the period of time represented.
文摘珊瑚生长率是珊瑚古气候研究的重要指标,其反映珊瑚生长快慢,并提供高分辨率的海水表层温度变化信息。中全新世作为当前全球变暖的地质历史相似型,利用珊瑚生长率重建该时期的气候环境状况对于理解现代气候变化的过程及其机制具有重要的参考价值。文章对采自海南潭门珊瑚岸礁的23段中全新世(6143—4356 a BP)滨珊瑚进行生长率分析,并基于该区域现代(2005—2021 AD)滨珊瑚生长率与SST的关系重建了中全新世期间共406 a的年均SST序列。结果显示:1)中全新世滨珊瑚生长率的变化范围为0.607~1.670 cm/a,均值为1.079 cm/a,且存在明显的波动变化过程;2)基于生长率重建的中全新世平均SST为25.7±0.54℃,这与全球变暖程度加剧背景下的现代海温相近;中全新世年均SST的变化范围为24.7~26.8℃,其中5860、5660和5160 a BP为3个显著的低温期;3)对比现代与中全新世(5427—5394、5243—5209、4515—4456和4404—4356 a BP)珊瑚生长率的频谱周期,发现现代与中全新世珊瑚的生长率均存在显著的3~7 a ENSO周期,但中全新世ENSO主周期改变且频率显著降低,表明中全新世的ENSO活动总体偏弱;概率密度函数统计进一步显示中全新世期间ENSO变率存在逐渐增强的趋势。
