Radiocarbon in Stalagmites: Indicator of Climate Variability and Key to Atmospheric Radiocarbon Reconstruction

Due to their ability to record climate change over large periods of time, stalagmites remain a primary focus of paleoclimatology. Utilizing high-precision age determination methods such as U-series dating, it is possible to measure climate-induced variations of the geochemical composition of speleothems over the time of their growth periods. This dissertation focuses on the investigation of radiocarbon (14C) concentration in several stalagmites. To this end, a new setup for the chemical preparation of carbonate samples for 14C measurements was planned and successfully put into operation. The incorporation of 14C into stalagmites is dependent on various climate-related processes in the soil and in the karst host rock above the cave. Using stable isotope ratios and trace element concentrations, this was investigated in two case studies with high-resolution 14C measurements. Reduced 14C concentration was observed in a stalagmite originating from Moomi Cave on Socotra Island which is indicative of aged soil organic matter influencing the stalagmite formation. It was demonstrated that a combination of higher soil humidity and denser vegetation towards the end of the last glacial period caused higher stalagmite 14C concentration. In a second study on a stalagmite from Sofular Cave in Turkey, the 14C signature allowed for the observation of various aspects of soil carbon dynamics from the last glacial period through into the Holocene. Moreover, the record suggests an increase of atmospheric 14C concentration coincident with the geomagnetic minimum approximately 41000 years ago. This may contribute to the ongoing effort to improve radiocarbon calibration datasets, on which the 14C dating method is based. Lastly, a summary of various stalagmite studies conducted at the Institute of Environmental Physics and a review of the relevant processes of stalagmite 14C incorporation is presented

Climate-induced speleothem radiocarbon variability on Socotra Island from the Last Glacial Maximum to the Younger Dryas

In this study, the dead carbon fraction (DCF) variations in stalagmite M1-5 from Socotra Island in the western Arabian Sea were investigated through a new set of high-precision U-series and radiocarbon (14C) dates. The data reveal an extreme case of very high and also climate-dependent DCF. For M1-5, an average DCF of 56.2±3.4% is observed between 27 and 18kyrBP. Such high DCF values indicate a high influence of aged soil organic matter (SOM) and nearly completely closed-system carbonate dissolution conditions. Towards the end of the last glacial period, decreasing Mg/Ca ratios suggest an increase in precipitation which caused a marked change in the soil carbon cycling as indicated by sharply decreasing DCF. This is in contrast to the relation of soil infiltration and DCF as seen in stalagmites from temperate zones. For Socotra Island, which is influenced by the East African-Indian monsoon, we propose that more humid conditions and enhanced net infiltration after the Last Glacial Maximum (LGM) led to dense vegetation and thus lowered the DCF by increasing 14CO2 input into the soil zone. At the onset of the Younger Dryas (YD) a sudden change in DCF towards much higher, and extremely variable, values is observed. Our study highlights the dramatic variability of soil carbon cycling processes and vegetation feedback on Socotra Island manifested in stalagmite DCF on both long-term trends and sub-centennial timescales, thus providing evidence for climate influence on stalagmite radiocarbon. This is of particular relevance for speleothem studies that aim to reconstruct past atmospheric 14C (e.g., for the purposes of 14C calibration), as these would rely on largely climate-independent soil carbon cycling above the cave. © 2020 Copernicus GmbH. All rights reserved

Foodborne Botulism in the Republic of Georgia

In the Republic of Georgia, high rates of foodborne botulism are largely caused by home-preserved vegetables

Is Hair Just Hair? : The Role of Hair in Identity Processes and Contestations of Black Women in Sweden

This bachelor thesis provides an analysis of hair and its role for the racial and ethnic identity of Black women living in Sweden. This is achieved by analyzing interviews with five women who reside in different urban areas throughout Sweden. In the analysis, the concept of Othering and social identity theory by Fiske and Taylor (2016) have been used to examine the position of the interviewees within Swedish society and the role of hair in their racial and ethnic identity. The results of the analysis show, that hair is a significant part of the interviewed women’s racial and ethnic identity. Furthermore, the results also show the ambivalence of hair for the women; though their hair is crucial for their self-identification and self-esteem, women are in a constant struggle with insecurities stemming from perceived external identification processes through negative labels attached to their hair

Is Hair Just Hair? : The Role of Hair in Identity Processes and Contestations of Black Women in Sweden

This bachelor thesis provides an analysis of hair and its role for the racial and ethnic identity of Black women living in Sweden. This is achieved by analyzing interviews with five women who reside in different urban areas throughout Sweden. In the analysis, the concept of Othering and social identity theory by Fiske and Taylor (2016) have been used to examine the position of the interviewees within Swedish society and the role of hair in their racial and ethnic identity. The results of the analysis show, that hair is a significant part of the interviewed women’s racial and ethnic identity. Furthermore, the results also show the ambivalence of hair for the women; though their hair is crucial for their self-identification and self-esteem, women are in a constant struggle with insecurities stemming from perceived external identification processes through negative labels attached to their hair

Femmes ingénieurs «FI»

Therre Marie-Hélène. Femmes ingénieurs «FI». In: Diplômées, n°232, 2010. 1920-2010 l'AFFDU du XXe au XXIe siecle. pp. 8-10