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

9909665Berger 该奖项由极地项目办公室的南极地质和地球物理项目提供，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。南极洲周围的第四纪（最近 200 万年）海洋沉积物记录了冰架和冰盖的增减，以及其他古气候信息，但很难获得这些沉积物的准确年代。这些年代学为研究过去的地质过程提供了重要的基础。在放射性碳 (14C) 测年范围内（小于 30-40 万年，注意 - 下面的“ka”表示 1000 年），由于可变的 14C 储库效应，14C 日期可能不准确，而超过 30-40 ka 则很少有方法适用。温带地区风成沉积物和水域沉积物的光子激发发光沉积物测年（光子测年）的范围从数十年到数百ka，但南极洲及其周围的海洋沉积物造成特别困难，因为大多数碎屑颗粒在沉积前暴露在日光下（时钟调零过程）可能受到限制。该提案将在具有代表性的南极冰川沉积环境中测试时钟归零假设，从而确定南极海洋沉积物光子测年的潜在可靠性。在北温带和极地纬度地区已经进行了利用冰川矿物和海洋沉积物的有限发光测年和信号归零测试，但从未详细研究过不同冰川矿物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，中性浮力“冷舌”（中水）羽流对陆源悬浮液的输送在南极洲周围可能很常见，但这种输送对发光归零的影响尚不清楚。南极洲附近的典型海洋岩心可能含有未知部分的来自冷舌和近底悬浮液的碎屑颗粒。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测年的潜在准确性尚不清楚（如果颗粒在沉积前没有暴露在日光下，则会导致年龄高估）。该项目将从南极半岛内的各种“零年龄”（现代）海洋沉积环境中收集碎屑颗粒，这些区域已记录了代表性的南极沉积过程，并且物流允许进入。将从代表从极地到亚极地条件的横断面的四个峡湾收集悬浮液。将从两个监测站以及每个监测站最多 3 个深度（表面和 2 个深层羽流）收集悬浮液。其中两个峡湾将部署沉积物收集器。此外，还将从多个地点收集岩心顶部沉积物。所有样本都将避光并运送到内华达州里诺进行发光分析。对南极冰川海洋环境中发光时钟归零有效性的系统研究将确定光子测年对于未来对南极海洋沉积物的应用是否可靠。该项目预计将为未来光子测年样品的选择提供完善的沉积学标准。光子测年能力将提供远远超出 14C 测年年龄范围的数字地球计时仪。这种能力将有助于回答一些更广泛的问题，涉及南极大陆架附近和过去冰川作用的时间和范围。

9909665BergerThis 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.