古近纪晚期东亚低纬度年际和年代际气候变化的木化石记录

It is a grand challenge to decipher the Paleogene climate variabilities on the interannual and interdecadal timescale, because such study is highly depending on particular fossils which growths were strictly according to the annual time series. This hampers our understanding on some critical paleoclimatic issues. For example, whether the tropical Pacific and its surrounding continents remained under a state of permanent El Niño or with a robust El Niño-like variety is considered as one of the essential to decode the warm phases during the Paleogene. However, there is a notorious lacking of direct physical evidence to test this hypothesis. Recently, our team discovered a late Oligocene plant Lagerstätte in the Nanning Basin of Guangxi, in which plenty of mummified woods are perfectly preserved. In the project, we investigate the components of the mummified wood fossil flora based on anatomical studies. After this, the nearest living relative (NLR) of each fossil species will be further sampled by core drilling, where the local climatic data will also collected accordingly, such as temperatures and precipitations. The late Oligocene climates will be reconstructed based on both of fossil and NLR tree-ring width and its oxygen and hydrogen isotopes along the time series, which will demonstrate the interannual and interdecadal climatic variations. The coupled climate modeling experiments will further help to find out if there was the El Niño-like variety in late Paleogene and its global impact.

以年际和年代际分辨率精细刻画古近纪气候是极富挑战性的课题。由于高度依赖于特殊保存的、具有年际性生长序列的化石，使得该时期的诸多气候谜题始终难以解开。其中，低纬度太平洋及周边大陆保持在“永久厄尔尼诺(permanent El Niño)”状态或存在“类厄尔尼诺(El Niño-like)”周期性震荡，是认识古近纪暖期气候机制的关键，但却一直缺乏直接证据。最近，申请人等在广西南宁发现了一处罕见的晚渐新世特异埋藏木乃伊化木化石群。本项目拟通过详细解剖研究查明木化石群的组成，并综合确定各组分的现生最近亲缘类群。进而系统获取亲缘类群的树芯，同时深入调查温度和降水等主控环境因子。以化石与亲缘类群的树轮及其氧、氢同位素的序列性对照分析，反演晚渐新世东亚低纬度气候特征，揭示其温度和降水在年际和年代际尺度上的波动性质，并以全耦合的气候模拟综合阐明古近纪晚期是否发育“类厄尔尼诺”现象及其影响这一重要科学问题。

以年际和年代际分辨率精细刻画古近纪气候是极富挑战性的课题。由于高度依赖于特殊保存的、具有年际性生长序列的化石，使得该时期的诸多气候谜题始终难以解开。其中，低纬度太平洋及周边大陆保持在“永久厄尔尼诺(permanent El Niño)”状态或存在“类厄尔尼诺(El Niño-like)”周期性震荡，是认识古近纪暖期气候机制的关键，但却一直缺乏直接证据。最近，申请人等在广西南宁发现了一处罕见的晚渐新世特异埋藏木乃伊化木化石群。本项目拟通过详细解剖研究查明木化石群的组成，并综合确定各组分的现生最近亲缘类群。进而系统获取亲缘类群的树芯，同时深入调查温度和降水等主控环境因子。以化石与亲缘类群的树轮及其氧、氢同位素的序列性对照分析，反演晚渐新世东亚低纬度气候特征，揭示其温度和降水在年际和年代际尺度上的波动性质，并以全耦合的气候模拟综合阐明古近纪晚期是否发育“类厄尔尼诺”现象及其影响这一重要科学问题。项目针对上述科学问题展开一系列研究工作，建立了和南宁木姜子木(新属新种; Litseoxylon nanningensis gen. et sp. nov.)。新建立的木姜子木属被置于樟科关键类群月桂族中的木姜子种系，与现生木姜子Litsea、山胡椒Lindera、黄肉楠Actinodaphne、新木姜子Neolitsea有密切关系。详细描述和报道了产于邕宁组上部的广西栲Castanopsis guangxiensis、南宁栲Castanopsis nanningensis、和南宁柯木Lithocarpoxylon nanningensis。报道了南宁瓜馥木Fissistigma nanningense sp. nov. (番荔枝科; Annonaceae)叶化石。基于南宁盆地保存完好的渐新世木乃伊化木化石，系统描述了南宁木兰（Magnolia nanningensis）。该类群的特征显示其与广义木兰属玉兰亚属白兰组极为接近。单物种气孔频度随海拔的变化趋势在高海拔地区是空白领域，这严重阻碍了植物在极端环境下适应的研究。课题组对青藏高原喜马拉雅松草沿3723-5081 m海拔梯度的气孔变化做了详细分析。结果发现，其气孔密度由542 ± 81.8 mm2增加到303 ± 55.6 mm2，气孔指数由29.6%降低到21.0%。