Development of Accurate Radiocarbon Chronologies for Antarctic Margin Sediments

该奖项由极地方案办公室南极地质和地球物理方案提供，为改进确定海底沉积层年龄的方法的开发提供资金。这些方法尤其适用于南极沿海环境的样品。这一结果将导致更好地重建过去2万年来南极冰缘的位置。反过来，这些信息将有助于更好地了解南极冰盖与全球气候之间的关系，包括过去和未来的海平面变化。目前对过去20,000年间南极环境变化时间的估计主要是基于有机物质的放射性碳年代。在南极大陆，这些日期大多来自可识别的生物材料残留物，其来源很清楚。相比之下，当样品来自沿海海洋沉积物时，大多数数据都是基于对总(“酸不溶”)有机碳的分析，有机碳可能来自多种来源。特别是，从大陆侵蚀的旧有机物质与来自海洋表面水域的新鲜产品混合在一起，可能导致沉积层的表观年龄大大超过其沉积以来所经历的时间。这种影响在多大程度上解释了南极洲大陆和海洋年表之间的差异尚不清楚。解决这些差异对于减少南极对气候和海平面变化影响的不确定性至关重要。海底沉积物中有机物质的准确日期已经可以通过分离单一有机化合物并提交进行放射性碳分析的化学技术来获得。然而，考虑到需要大量的数据，这种技术在样本大小、操作员专业知识和时间方面的要求高得令人望而却步。为了绕过这个问题，该项目将开发一种简化的程序，在该程序中，安全地确定为新鲜海洋产品的生物相关化合物组被分离出来进行测年。这些将包括特定类别的化合物，以及在一个平行项目中，捕获在源于海洋的无机基质中的材料，即由硅藻产生的蛋白石。样品吞吐量应该会有非常大的增长。将使用特定于化合物的放射性碳分析来指导这些技术的开发并检查结果。所有碳14丰度的测定都将使用加速器质谱仪。

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for development of improved methods for determination of the ages of sea-floor sediment layers. These methods are needed particularly for use with samples from Antarctic coastal environments. The results will lead to better reconstruction of the locations of the Antarctic ice margins during the past 20,000 years. In turn, that information will lead to a better understanding of relationships between the Antarctic ice sheets and global climate, including sea-level changes both in the past and in the future. Present estimates of the timing of Antarctic environmental changes during the past 20,000 years are based largely on radiocarbon ages of organic materials. On the Antarctic continent, most of these dates have come from recognizable remnants of biological materials for which the origin is clear. In contrast, when samples have come from coastal oceanic sediments, most dates have been based on the analysis of total ("acid-insoluble") organic carbon, which can derive from multiple sources. In particular, the mixing of old organic material, eroded from the continent, with fresh products from oceanic surface waters can lead to sediment layers with apparent ages significantly greater than the time that has elapsed since their deposition. The extent to which such effects explain discrepancies between continental and oceanic chronologies in Antarctica is not known. Resolution of these discrepancies is crucial to reduction of uncertainties regarding Antarctic effects on climate and sea-level change.Accurate dates for organic materials in sea-floor sediments can already be obtained by use of chemical techniques in which single organic compounds are isolated and submitted for radiocarbon analysis. The requirements of such techniques in terms of sample size, operator expertise, and time are, however, prohibitively high, given that large numbers of dates are needed. To circumvent that problem, this project will develop a streamlined procedure in which biologically related groups of compounds, securely identified as fresh, oceanic products, are isolated for dating. These will include both specific classes of compounds and, in a parallel project, materials trapped within an inorganic matrix of marine origin, namely the opal produced by diatoms. Very substantial increases in sample throughput should result. Compound-specific radiocarbon analyses will be used to guide the development of these techniques and to check the results. Accelerator mass spectrometry will be used for all determinations of the abundance of carbon-14.