Collaborative Research: Development of a Luminescence Dating Capability for Antarctic Glaciomarine Sediments: Tests of Signal Zeroing at the Antarctic Peninsula

合作研究：南极冰川沉积物发光测年能力的开发：南极半岛信号归零测试

• 批准号: 0003060
• 负责人: Eugene Domack
• 金额: $ 1.26万
• 依托单位: Hamilton College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-09-15 至 2003-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0003060&HistoricalAwards=false
• 关键词: Collaborative; Research; Development; Luminescence; Dating

0003060 DomackThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports project to test and develop approaches for using thermoluminescence techniques to determine the age of Antarctic marine sediments. Quaternary (last 2 million yrs) marine sediments surrounding Antarctica record the waxing and waning of ice shelves and ice sheets, and also other paleoclimatic information, yet accurate chronologies of these sediments are difficult to obtain. Such chronologies provide the essential foundation for study of geological processes in the past. Within the range of radiocarbon (14C) dating (less than 30-40 thousand yrs, note - "ka" below means 1000 yrs) 14C dates can be inaccurate because of a variable 14C reservoir effect, and beyond 30-40 ka few methods are applicable. Photon-stimulated-luminescence sediment dating (photonic dating) of eolian and waterlain deposits in temperate latitudes spans the range from decades to hundreds of ka, but marine sediments in and around Antarctica pose special difficulty because of the potentially restricted exposure to daylight (the clock-zeroing process) of most detrital grains before deposition. This proposal will test the clock-zeroing assumption in representative Antarctic glaciomarine depositional settings, and thereby determine the potential reliability of photonic dating of Antarctic marine sediments.Limited luminescence dating and signal-zeroing tests using glaciomarine and marine deposits have been conducted in the northern temperate and polar latitudes, but the effects on luminescence of the different glaciomarine depositional processes have never been studied in detail. Furthermore, the depositional settings around Antarctica are almost entirely polar, with consequent specific processes operating there. For example, transport of terrigenous suspensions by neutrally buoyant "cold-tongue" (mid-water) plumes may be common around Antarctica, yet the effect of such transport on luminescence zeroing is unknown. Typical marine cores near Antarctica may contain an unknown fraction of detrital grains from cold-tongue and near-bottom suspensions. Thus the extent to which the polar glaciomarine depositional processes around Antarctica may limit the potential accuracy of photonic dating of marine cores is unknown (age overestimates would result if grains are not exposed to daylight before deposition).This project will collect detrital grains from a variety of "zero-age" (modern) marine depositional settings within the Antarctic Peninsula, where representative Antarctic depositional processes have been documented and where logistics permit access. Suspensions will be collected from four fjords representing a transect from polar through subpolar conditions. Suspensions will be collected from two stations and from up to 3 depths (surface and 2 deep plumes) at each station. Sediment traps will be deployed at two of these fjord settings. As well, core-top sediments will be collected from several sites. All samples will be shielded from light and transported to Reno, Nevada, for luminescence analyses.Systematic study of the effectiveness of luminescence-clock-zeroing in Antarctic glaciomarine settings will determine if photonic dating can be reliable for future applications to Antarctic marine sediments. Refined sedimentological criteria for the selection of future samples for photonic dating are expected from this project. A photonic-dating capability would provide a numeric geochronometer extending well beyond the age range of 14C dating. Such a capability would permit answering a number of broader questions about the timing and extent of past glaciations near and on the Antarctic shelves.

该奖项由极地计划办公室的南极地质和地球物理计划提供，支持测试和开发使用热释光技术确定南极海洋沉积物年龄的方法的项目。南极洲周围第四纪（最近200万年）的海洋沉积物记录了冰架和冰原的盛衰，以及其他古气候信息，但这些沉积物的准确年表很难获得。这样的年表为研究过去的地质过程提供了必要的基础。在放射性碳（14C）测年范围内（小于3 -4万年，注：“ka”以下表示1000年），由于14C储集层效应的变化，14C测年可能不准确，超过30-40 ka的方法很少适用。对温带地区风成和水成沉积物进行光子刺激发光沉积物测年（光子测年）的时间范围从几十年到几百年不等，但南极洲及其周围的海洋沉积物面临着特殊的困难，因为大多数碎屑颗粒在沉积前暴露在日光下的时间可能有限（时钟归零过程）。这一建议将在具有代表性的南极冰海沉积环境中检验时钟归零假设，从而确定南极海洋沉积物光子测年的潜在可靠性。在北温带和极纬度地区，利用冰川海和海洋沉积物进行了有限的发光测年和信号零化试验，但从未详细研究过不同冰川海沉积过程对发光的影响。此外，南极洲周围的沉积环境几乎完全是极地的，因此在那里发生了特定的过程。例如，通过中性浮力的“冷舌”（中水）羽流运输陆源悬浮物在南极洲周围可能很常见，但这种运输对发光零化的影响尚不清楚。南极洲附近典型的海洋岩心可能含有来自冷舌和近海底悬浮物的未知比例的碎屑颗粒。因此，南极洲周围的极地冰川海洋沉积过程可能在多大程度上限制海洋岩心光子定年的潜在准确性是未知的（如果颗粒在沉积前没有暴露在日光下，就会导致年龄高估）。该项目将收集南极半岛内各种“零年代”（现代）海洋沉积环境中的碎屑颗粒，在南极半岛有代表性的南极沉积过程被记录下来，并且物流允许进入。悬浮液将从四个峡湾收集，代表从极地到亚极地条件的样带。悬浮气体将从两个气象站收集，每个气象站最多从3个深度（地表羽流和2个深层羽流）收集。沉积物捕集器将部署在其中两个峡湾。同时，将从几个地点收集岩心顶部的沉积物。所有的样品将被遮光并运送到内华达州里诺市进行发光分析。对南极冰川期海洋环境中发光时钟调零的有效性进行系统研究，将决定光子测年在未来南极海洋沉积物中的应用是否可靠。该项目有望为今后选择光子测年样品提供更精确的沉积学标准。光子测年能力将提供一个远远超出14C测年年龄范围的数字地球计时器。这种能力将使我们能够回答一些更广泛的问题，如南极冰架附近和南极冰架上过去冰川作用的时间和范围。