Studies Related to Establishing a Valid Radiocarbon Ventilation Rate for the Glacial Ocean

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ABSTRACTOCE-0435703Determining how ocean ventilation rates changed during the last glacial and deglacial periods is fundamental to reconstructing global changes in ocean circulation related to major shifts in the Earth's climate. In this project, researchers at the Lamont-Dougherty Earth Observatory of Columbia University will attempt to resolve some of the major problems that have confronted scientists studying these phenomena.The main objective of the project is to use radiocarbon ages from contemporaneous planktonic (surface dwelling) and benthic (bottom dwelling) foraminifera to define the age of deep waters over the period 21,000 - 14,000 14C years before the present time. To this end it will be necessary to make multiple radiocarbon dates on samples from various depths and locations. Recent work has suggested that some core locations may be unsuitable for precise radiocarbon dating due to the presence of secondary carbonate phases forming within the sediment column. A second theme of this project is to investigate the presence of these phases and if possible, determine which sites are ultimately more or less valid for determining ocean ventilation rates. This goal will be addressed by carrying out dissolution experiments on samples that are known to yield anomalous 14C ages, the aim being to isolate and date individually the different phases. Changes in carbon storage and ocean circulation will be investigated by reconstructing changes in deep sea carbonate ion concentrations using the foraminiferal shell weight proxy developed by Lohmann (1995). A further aim of the project will be to use land-based evidence to investigate the relative timing of events occurring at the close of the last glacial period and during deglaciation. This work will be based on precise dating of glacial features and exposure dating of moraines left by retreating glaciers at the end of glacial times.Broader impacts: This study should provide answers to some fundamental questions concerning changes in global climate -- how different was ocean circulation during glacial time and how, if at all, have changes in ocean circulation affected climate in the past. The results from these studies will provide important constraints for paleo- and future climate models.