Natural 32Si for the study of environmental processes

Published November 5th, 2000 - 02:00 GMT

The need for an effective dating tool to cover the historical past is pressing. Cosmogenic 32Si, with a half-life of 140 years, is ideally suited to provide time information in the range 50-1000 years. Detection of 32Si is, however, very difficult due to extremely low natural concentrations and isotopic ratios.  


At GNS we have developed improved methods for radiometric detection of natural 32Si, and in collaboration with Australian National University, have succeeded in measuring natural 32Si by accelerator mass spectrometry (AMS). With AMS the necessary sample size can be reduced by a factor of ca. 1000.  


Glacier ice dating : 

Glaciers play a fundamental role as archives for global climate history. They contain a variety of proxies for climate forcing and climate response. Accurate dating of ice cores is crucial to make full use of this information.  


Cosmogenic 32Si, stored in the ice, provides a precise natural clock for this purpose. AMS is suitable for analysing ice core samples with only ca. 1 kg of water required for measurement. 


Sediment dating using 32-silicon: 

Dating of sediments is of special importance because sediments as a natural climate archive accumulate a wealth of environmental information, and they can normally be found close to human settlements.  


32Si dating of sediments is therefore essential for studies of palaeoenvironmental change covering the last millennium, especially for identifying human impacts on environmental processes.  


We have applied scintillation spectrometry for detection of natural 32Si in sediments with extremely selective radiochemical purification procedures. This makes 32Si now a standard tool for sediment dating. Ca. 0.5 kg of sediment is necessary for analysis. 


Other applications: 

32Si is also useful for study of oceanic circulation, study of atmospheric circulation (exchange processes between stratosphere and troposphere), understanding groundwater flow, and dating of marine siliceous biota (e.g. glass sponges). 

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