张文防^1,2,,
李高军²,
陈骏²
1. 中国科学院南京地理与湖泊研究所, 湖泊与环境国家重点实验室, 江苏 南京 210008
2. 南京大学地球科学与工程学院, 表生地球化学教育部重点实验室, 江苏 南京 210023

基金项目: 国家自然科学基金项目（批准号：41702191）资助


详细信息

作者简介: 张文防, 男, 34岁, 助理研究员, 地球化学专业, E-mail:wfzhang@niglas.ac.cn

中图分类号: P722;P534.6;P532

收稿日期:2019-01-03
修回日期:2019-03-13
刊出日期:2019-05-30

The abrupt change of aeolian dust in North Pacific sediments during major Northern Hemisphere glaciations at ca. 2.73 Ma

Zhang Wenfang^1,2,,
Li Gaojun²,
Chen Jun²
1. State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, Jiangsu
2. Key Laboratory of Surficial Geochemistry, Ministry of Education, Department of Earth and Planetary Sciences, Nanjing University, Nanjing 210023, Jiangsu


MSC: P722;P534.6;P532

--> Received Date: 03 January 2019
Revised Date: 13 March 2019
Publish Date: 30 May 2019


摘要
摘要:距今约2.73 Ma，北半球高纬地区冰盖急剧发展，北半球大冰期来临，成为最引人注目的事件。北半球大冰期成因已有诸多解释，其中之一是大陆干旱化加剧，输入到大洋的粉尘增多引起海洋铁肥效应增强和生物量增多，吸收了更多大气CO₂，使得地球变冷和冰盖增加。作为全球第二大粉尘释放中心，亚洲内陆干旱区释放的粉尘是北太平洋沉积物中主要陆源组分之一。开展北半球大冰期前后西北太平洋沉积物记录的亚洲粉尘研究，有助于深入认识风尘铁肥效应对北半球大冰期形成的可能贡献。文章依据大洋钻探计划（Ocean Drilling Program，简称ODP）198航次西北太平洋1208钻孔（共钻取沉积物392.3 m；本研究深度121.3 m至130.1 m，时间段为2.62 Ma至2.85 Ma）北半球大冰期前后的高分辨率（约2500年）样品，提取了沉积物中的"风尘组分"，计算了风尘通量，研究了风尘通量变化和海洋生产力之间的关联。研究结果显示，约2.73 Ma以来，1208钻孔风尘通量快速增加，已发表的该孔的海洋生产力也表现出快速增加，海水表面温度也快速降低，说明粉尘对海洋的铁肥效应可能是触发北半球大冰期形成的重要因素。文章还测试了"风尘组分"的Nd和Sr同位素，研究了粉尘物源变动。结果显示，塔克拉玛干沙漠是北半球大冰期前后1208钻孔粉尘的主要物源，其中2.73 Ma至2.85 Ma期间Nd和Sr同位素波动较大，推测与火山灰含量较多和戈壁粉尘沉积有关，位置偏北的西风可能是部分戈壁粉尘长距离运输至北太平洋的主要营力。2.73 Ma以来，北极冰盖大量发育，西风位置南移，主要运输塔克拉玛干沙漠粉尘至北太平洋，使得Nd和Sr同位素波动较小，但其中2.72 Ma至2.70 Ma期间出现的Nd同位素偏正、Sr同位素变小很可能是火山灰的突然大量沉积造成的。
关键词: 亚洲粉尘/
北半球大冰期/
西北太平洋/
1208钻孔

Abstract:The Earth's climate underwent a striking change ca. 2.73 Ma(million years) ago, characterizing by the onset and intensification of the major Northern Hemisphere glaciations(iNHG). A few factors have been considered in the driving the iNHG, one of which is the marine biological pump as a result of the increase of eolian dust in the ocean, transferring atmospheric CO₂ into the deep ocean during the onset of iNHG. The central Asian interior is the second largest center of dust emission all over the world. Once launched into the atmosphere, Asian dust is then transported to a distal accumulation center, e.g. the North Pacific Ocean via high-altitude westerly winds, becoming an important component in north Pacific sediments. The aeolian deposits in the North Pacific Ocean(NPO) serve as important archives for the paleoenvironmental change in the arid Asian interior, helping to better understand the possible role of the marine biological pump played in the onset of iNHG. This work extracts "operationally defined aeolian dust"(ODED) from the sediments recovered at Ocean Drilling Program(ODP) site 1208(36°07.6'N, 158°12.1'E) on the Shatsky Rise in NPO spanning the Pliocene-Pleistocene climate transition. Coring at site 1208 drilled a total of 392.3 m(meters below the sea floor), of which the section between 0.0 and 328.15 m is of Cenozoic age and is characterized by rhythmically alternating intervals of nannofossil ooze/chalk and nannofossil clay/claystone with diatoms and radiolarians that are punctuated by occasional volcanic ash layers. This work collected eight-nine samples continuously every ca. 10 cm from 121.3 m to 130.1 m. The chronologic framework of the high-resolution samples has been developed by correlating the benthic-foraminiferal δ¹⁸O at site 1208 to the global δ¹⁸O stack(LR04), allowing the samples in this study have a time interval of 2.62 Ma and 2.85 Ma with roughly one sample every 2500 years. The resulting ODED flux, shows a rapid increase since about 2.73 Ma, concurrent with the increase of the changes in productivity, cooling of the sea surface and the iNHG, implying that biological pump hypothesis is possibly a plausible mechanism for triggering the iNHG. This work also studied the source change of Asian dust archived in site 1208 sediments by measuring the Nd and Sr isotopes of ODED fraction. The results show that the Asian dust archived in site 1208 sediments is mainly derived from Taklimakan Desert throughout the studied time interval. The higher-amplitude fluctuations of Nd and Sr isotopes from 2.73 Ma to 2.85 Ma are attributable to the higher contributions of volcanic ash as a result of the relatively low dust flux and/or the deposition of Gobi dust. The westerly wind might be the main agent to transport the Gobi dust during this interval, as it possibly located in the relatively northern position during the late Pliocene. The position of westerly wind might have moved southward since 2.73 Ma associated with the development of iNHG, mainly transporting Taklimakan dust to the North Pacific Ocean, which resulted in the lower-amplitude fluctuations of Nd and Sr isotopes. It is worthy to note that the more radiogenic Nd isotope and less radiogenic Sr isotope between 2.72 Ma and 2.70 Ma, was probably caused by the abrupt increase of volcanic ash.
Key words:Asian dust/
major Northern Hemisphere glaciations/
northwest Pacific Oceans/
ODP site 1208



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