英国伯明翰大学地球科学与环境科学学院Ian Fairchild教授学术报告会

地球系统科学论坛第531期：海报Ian Fairchild教授学术报告会

应遊雅堂 競馬胡超涌教授邀请，英国伯明翰大学地球科学与环境科学学院Ian Fairchild教授来校访问并做学术报告。

报告时间：2017年6月12日（周一）下午4:00

报告地点：地质斋（主楼308）

报告题目：Speleothem Archives and the Anthropocene

报告人介绍：Ian Fairchild，国际著名地球化学家，主要从事地球表生系统、第四纪和新元古代地球历史及气候变化研究。在Science, Geology, Quaternary Science Review, Earth Sciences Review，Geochimica et Cosmochimica Acta等期刊发表SCI论文100多篇，总引用五千多次，出版洞穴石笋研究专著1部。

报告主要内容如下：

Consideration is being given to defining a new Anthropocene epoch, starting in the mid-20th century. Geochemical markers are likely to be crucial in defining the boundary and include radiogenic isotopes, organic pollutants and N and S species. A sub-set of these geochemical parameters can be determined in archives of speleothems (calcareous cave deposits). The concept of the Anthropocene also draws attention to the human-modified nature of modern environments that are monitored to serve as modern analogues for palaeoenvironmental archives. Thus, modern cave environments, and the surface environments that they indirectly characterize, can be modified in a variety of ways from their natural condition.

Currently, the Anthropocene working group, the international body responsible for making proposals regarding its formal stratigraphic status, is seeking to find a definitive boundary section in an annually layered archive, together with comparator sections in different archives and across geographic regions. One of the best documented speleothem sites for this purpose is the Grotta di Ernesto in northern Italy. Here distinct mid-20thcentury signals have been documented in radiocarbon, sulphate concentration, and S stable isotope composition. These reflect widespread atmospheric changes, but mediation by the vegetation-soil ecosystem leads to attenuation and lag of the atmospheric signal. Conversely there is no signal from the widely used parameters of carbon and oxygen stable isotopes. The Suess effect, leading to lowering carbon isotope values in atmospheric carbon dioxide, is swamped by local fractionation effects. Also, the oxygen isotope composition of speleothems is now known to be primarily related to changing water isotope compositions rather than temperature. The main temperature signal at Ernesto is a mid 19th-century threshold in soil carbon dioxide production leading to non-linear increases in growth rate of stalagmites and stalactites. Another anthropogenic signal is related to deforestation. On the long-term this is seen in a rise in delta values of carbon isotopes in the late Holocene. Short-term deforestation in the early 20thcentury is encapsulated in increases in colloid-transported trace elements which peak annually during autumn recharge.

Some other case examples illustrate the types of environmental change associated directly or indirectly with human activity that can be captured by speleothem records. Reduction in rainfall in regions that are already water-stressed may be picked up by changes in carbon isotopes, or Mg or Sr concentration, caused by increased precipitation of CaCO3along a flowline to a given site. At the Golgotha cave site in SW Australia, specific changes in nutrient elements related to changes in net biomass are seen to be important on the sub-decadal scale. At other sites, it has been shown that vegetation change can lead to effects on oxygen isotope composition also because of modifications in surface temperature or evaporation. At sites subject to anthropogenic pollution, including artificial pipes and channels, distinct signals of local environmental disturbance may be recorded, reflecting changes in atmospheric composition or ground disturbance. Finally, modifications to patterns of air circulation in caves can have a variety of consequences, including the capture of pollutant aerosols.

Study of modern cave environments has proved to be a powerful method of understanding the processes that lead to capture of signals of changing environments in speleothems. The specific processes that are documented however are those of the Anthropocene, rather than the Holocene.

遊雅堂 競馬

BGEG国家重点实验室

2017年6月