摘要
新仙女木(Younger Dryas,简称YD)事件是末次冰消期末期升温过程中北半球高纬一次剧烈的突变降温事件,主流机制为淡水注入北大西洋减缓了北大西洋翻转环流,使得北半球普遍降温、热带辐合带南移等全球范围的气候重组.虽然该事件研究程度较高,然而其在南半球、尤其在西南印度洋的气候变化模态尚不明朗.本研究利用来自罗德里格斯岛(罗岛)高分辨率、高精度定年的石笋氧同位素(δ18O)记录,重建了过去13. 3~10. 8 ka期间(对应石笋样品100~169 mm)西南印度洋亚热带地区的气候变化.结果表明,在YD事件期间罗岛石笋δ18O相对偏重,指示降水相对减少.与印度洋北岸的地质记录对比显示, YD时期罗岛石笋记录与众多亚洲季风石笋氧同位素记录共同展现出偏重的"谷状结构",并且显示出"缓进快出"的不对称特征.与印度洋东岸的地质记录对比结果显示,罗岛石笋δ18O与印太暖池南北边缘记录共同显示出偏干状态,而与近赤道记录的气候特征不同.与印度洋西岸的地质记录对比结果显示,东非热带赤道地区至南部亚热带地区呈现"北干南湿"的特征.罗岛与东非赤道地区的气候变化也具有一致性. YD时期,热带辐合带南移而罗岛降水却减少,可能原因是热带辐合带强度减弱,削弱了对流降水,使得亚洲季风从源区至下游地带水汽传输均发生减弱.
The Younger Dryas (YD) event is an abrupt cooling event in the Northern Hemisphere occurred during the last deglaciation, which is triggered likely by fresh water injecting into the North Atlantic Ocean, resulting slowdown of the Atlantic Meridional Overturning Circulation (AMOC) and southward shift Intertropical Convergence Zone (ITCZ).While a large number of YD records have been reconstructed from Northern Hemisphere, the YD records from Southern Hemisphere remain sporadic, especially in southwestern Indian Ocean.This impeded our understanding about climate variations across the YD event to a global extent.Here, we present a high-resolution and precisely dated speleothem (PATA-1) oxygen isotope (δ18O) record from Patate Cave (19°45'30"S, 63°23'11"E;ca.20 m a.s.l.) in Rodrigues Island, southwestern subtropical Indian Ocean.The sample is pure calcite around 334 mm long and 95 mm wide with clear yellow, white, dark red or brown layers.The length between 100~169 mm was selected to study, covering the time period from ca.13.3 ka to 10.8 ka ago, including the YD event.We obtained 19 U-Th dates and 684 δ18O data, which allows a high-resolution (ca.3.7 a) reconstruction of a new speleothem δ18O record to characterize the hydroclimate variability across the YD event in the southwestern subtropical Indian Ocean.Our analyses show that the PATA-1δ18O record reflects mainly changes in the precipitation amount resulting from local to large scale atmospheric circulations, including ITCZ shift and El Ni?o -Southern Oscillation (ENSO). The YD variation in the PATA-1 record is characterized by a heavier (or drier) excursion with a gradual onset and a rapid termination, similar to Greenland ice core δ18O records and speleothem δ18O records from vast Asian summer monsoon regions.In eastern coast of the Indian Ocean, the existing records also show a drier condition during the YD event, such as the stalagmite records from Palawan and Ball Gown caves located respectively in the northern and southern edges of the Indo-Pacific warming pool (IPWP, defined between 10°N^18°S and 110°~140°E).However, the records near the equator in the IPWP show different climate change during the YD event compared with our PATA-1 record.Along west coast of the Indian Ocean, the climate show a pattern of "dry in north and wet in south" from equatorial eastern Africa to subtropical southern Africa.The hydroclimate variations during the YD event inferred from the PATA-1 record in Rodrigues are in line with the records near equatorial eastern Africa.Although the hypothesis of a ITCZ shift farther south across Rodrigues may explain the drier YD condition observed in our record, it requires a ITCZ shift of more than 11° to south from its modern position, which appears to be difficult in terms of atmospheric physics.Alternatively, a weakened ITCZ intensity and thus its convective activity during the YD event may explain the drier YD condition in Rodrigues, as well as along the Asian summer monsoon pathway in both hemispheres.
作者
李瀚瑛
Ashish Sinha
程海
Spotl Christoph
宁有丰
Li Hanying;Sinha Ashish;Cheng Hai;Spotl Christoph;Ning Youfeng(Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an 710054, Shaanxi;Department of Earth Science, California State University Dominguez Hills, California 90747, USA;Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA;Institute of Geology, University of Innsbruck, Innsbruck 6020, Austria)
出处
《第四纪研究》
CAS
CSCD
北大核心
2019年第4期1006-1017,共12页
Quaternary Sciences
基金
国家自然科学基金项目(批准号:41472140、41731174和41888101)
中国科学院地球环境研究所黄土与第四纪地质国家重点实验室开放基金(批准号:SKLLQG1414)共同资助.
关键词
新仙女木事件
罗德里格斯岛
印度洋
石笋
热带辐合带
Younger Dryas event
Rodrigues Island
Indian Ocean
stalagmite
Intertropical Convergence Zone
作者简介
第一作者简介:李瀚瑛,女,26岁,博士研究生,地球环境科学与工程专业,E-mail:leehom20114@stu.xjtu.edu.cn;通讯作者:Ashish Sinha,E-mail:asinha@csudh.edu;通讯作者:程海,E-mail:cheng021@xjtu.edu.cn.
