Reconstruction of Radiocarbon Distribution in the Glacial Ocean
Since its discovery about four decades ago, radiocarbon has been an important isotope tracer for studying the ventilation rates of deep seawater and the rain rate of calcite toward the deep-sea floor (Broecker & Peng 1982). After their production in the atmosphere, 14C atoms invade the surface water of the ocean. The 14C in surface water is then slowly transported to the deeper ocean as surface water is mixed with deep water. The difference in 14C/12C ratios between surface water and deep water depends on how fast the deep water is replaced by the surface water through ocean circulation and mixing processes. The distribution of 14C in the water column of the present-day ocean can be measured by counting the 14C atoms in CO2 gas extracted from the dissolved inorganic carbon in seawater. The 14C atoms in seawater are also preserved in calcite shells of marine microorganisms. For example, planktonic foraminifera that live in near-surface waters produce calcite shells that contain 14C derived from water that is close to equilibrium with the atmosphere. These shells eventually sink to the sea floor and provide valuable materials for dating deep-sea sediments. The rain rate of calcite can thus be estimated from results of such 14C datings.
KeywordsRain Rate Benthic Foraminifera Accelerator Mass Spectrometry Planktonic Foraminifera Accelerator Mass Spectrometry
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