Ice core methods: Studies of radiocarbon in ice

Abstract

The early history of ice core and radiocarbon (14C) research are closely intertwined. 14C is a radioactive isotope of carbon that exists in trace amounts (10−12 abundance) and decays with a half-life of 5730years. Before well-dated deep ice cores from accumulation sites were available, early efforts to measure 14C in natural glacial ice were focused on using 14C dating to prove that trapped air in glacial ice contains preserved old air from Earth's past atmosphere. Technological advances and improvement in measurement techniques over the past 60years allow for more than a factor of 1000 reduction in sample requirement for 14C analysis in ice. Furthermore, they allow for 14C measurements in trace compounds such as methane (CH4), carbon monoxide (CO), and organics. Today measurements of 14C in ice can be used for several paleo-environmental applications. For example, measurements of biogenic organic materials trapped in alpine ice can be used for absolute dating. 14C in methane (14CH4) can be used to constrain the past contribution of fossil CH4 sources to the atmosphere. Likewise, 14C in organics can be used for source apportionment of past carbonaceous aerosol emissions. 14C in carbon monoxide (14CO) has the potential to constrain the oxidative capacity of Earth's past atmosphere. However, the interpretation of 14C studies in ice can be complicated by in situ production of 14C by cosmic rays directly in the ice lattice. This chapter will provide an overview of successful applications of 14C analysis in ice and discuss recent advances in our understanding of 14C in situ production in ice.