Optical Dating Tests of Quaternary Sediments from the Central Arctic Ocean

BergerOPP-98-18070北极地区被预测对全球气候变化非常敏感。北冰洋沉积的沉积物可能记录了过去北极环境变化的信号，如环北极固定冰盖的消长、融水排放以及北冰洋中部海冰覆盖范围和组成的变化。然而，自最近的冰川/间冰期(过去的几十万年)以来，这些沉积物很难或不可能确定其年龄。北冰洋沉积物的绝对测年在很大程度上仍然是一个谜，因此对北冰洋中部的古海洋和古气候更新世记录知之甚少。放射性碳(14C)测年仅限于最近30-40ka，直到最近才发展出高精度的测年。氧同位素和古地磁地层学依赖于均匀和连续的沉积。氧同位素地层学是有问题的，因为有孔虫在北极的丰度是不连续的。然而，为了准确对比北冰洋与其他海洋和环北极陆地的沉积历史，数字测年是必不可少的。例如，孤立的有孔虫丰度峰可能表示没有广泛的海冰覆盖，因此确定有孔虫的年龄对于北半球的古气候学研究至关重要。首席调查者将测试和开发一种替代的绝对测年技术-热释光(TL)测年，其时间范围为0-400ka。他将在北冰洋西部的三个地点进一步发展他的热释光测年技术，通过广泛测试长石特定红外受激发光(IR-OSL)光学测年版本的信号归零和剂量学假设。IR-OSL技术具有比TL更高的固有灵敏度和精密度。他将对分布在北冰洋的岩心上部的沉积物和具有相关14C日期的沉积物进行归零测试。此外，还将对具有代表性的岩心进行剂量学测试。最后，将对北大西洋测年准确的岩心的沉积物进行三项光学测年测试，以便从更简单的环境中提供基线比较。该项目将为以下工作奠定基础：1)将北冰洋中部的绝对测年年表扩大到AMS(加速质谱仪)14C测年范围之外；2)直接测定保存下来的最后一次北极冰川/间冰期的记录，显示有孔洞丰度峰值；3)为北极陆地-海洋对比的区域对比提供高质量的年表。对有孔虫丰度峰值的直接测年将回答有关北冰洋海冰覆盖历史的重要问题。

AbstractBergerOPP-98-18070The Arctic region has been predicted to be very sensitive to global climatic changes. Sediments deposited in the Arctic Ocean may record signals of past Arctic environmental changes such as growth and decay of circum-Arctic grounded ice sheets, meltwater discharges, and changes in extent and composition of central Arctic Ocean sea-ice cover. However, since recent glaciations/interglaciations (the last several hundred thousand (ka) years), these sediments have been difficult or impossible to date. Absolute dating of Arctic Ocean sediments has remained largely an enigma, and therefore the paleoceanographic and paleoclimatic Pleistocene record of the central Arctic Ocean is poorly known.Radiocarbon (14C) dating is restricted to the last 30-40 ka and only recently has high precision dating been developed. Oxygen-isotope and paleomagnetic stratigraphy depend on uniform and continuous sedimentation. Oxygen-isotope stratigraphy is problematic because foraminiferal abundances are discontinuous in the Arctic. Nevertheless, for accurate correlation of the depositional history of the Arctic Ocean with other oceans and circum-Arctic lands, numeric dating is essential. For example, isolated foraminifera abundance peaks probably represent an absence of extensive sea-ice cover, and so it is critical to determine the forams' ages for paleoclimatological studies in the Northern Hemisphere.The Principal Investigator will test and develop an alternate, absolute dating technology, thermoluminescence (TL)-dating which has a time range of 0-400 ka for terrestrial sediments. He will further develop his TL-dating technique at three sites in the western Arctic Ocean by broadly testing the signal-zeroing and dosimetry assumptions of the feldspar-specific infrared-optically-stimulated-luminated (IR-OSL) version of optical dating. The IR-OSL technique has greater inherent sensitivity and precision than TL. He will perform zeroing tests with sediments from upper parts of cores distributed across the Arctic Ocean and sediments having associated 14C dates. Also, dosimetry tests will be conducted on representative cores. Finally, three optical-dating tests will be conducted on sediments from well-dated cores from the North Atlantic to provide a baseline comparison from a simpler environment.This project will provide a foundation for: 1) extending absolute-dating chronologies for the central Arctic Ocean beyond the range of AMS(accelerated mass spectrometry) 14C dating; 2) direct dating of the preserved record of the last Arctic glacial/interglacial periods manifested by foram abundance peaks; and 3) providing a high-quality chronology for regional correlations for Arctic land-ocean correlations. Direct dating of foraminifera abundance peaks on will answer important questions about the history of Arctic Ocean sea-ice cover.