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

该奖项由极地方案办公室南极地质和地球物理方案提供，支持测试和开发利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消长以及其他古气候信息，但这些沉积物的准确年表很难获得。这些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30-4万年，注--下面的“ka”指的是1000年)，14C年龄可能不准确，因为可变的14C储集层效应，而超过30-40ka的方法很少适用。温带地区风成和水系沉积物的光子激发发光沉积物测年(光子测年)的范围从几十到数百ka不等，但南极洲及其周围的海洋沉积物造成了特别的困难，因为大多数碎屑颗粒在沉积之前可能受到日光照射(时钟调零过程)。这一提议将在具有代表性的南极冰晶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。在北温带和极地纬度，利用冰晶和海洋沉积物进行了有限发光测年和信号归零实验，但从未详细研究过不同冰晶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，因此有特定的过程在那里运行。例如，通过中性浮力的“冷舌”(水中)羽流输送陆源悬浮物在南极洲周围可能很常见，但这种输送对发光调零的影响尚不清楚。南极洲附近的典型海洋岩心可能含有一小部分来自冷舌和近海底悬浮的碎屑颗粒。因此，南极洲周围的极地冰晶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(如果颗粒在沉积之前不暴露在日光下，就会导致年龄高估)。该项目将从南极半岛内各种“零年龄”(现代)海洋沉积环境中收集碎屑颗粒，在那里记录了具有代表性的南极沉积过程，并且后勤允许进入。悬浮物将从代表从极地到亚极地的横断面的四个峡湾收集。悬浮物将从两个站点收集，每个站点最多从3个深度(表层和2个深度羽流)收集悬浮物。沉积物捕集器将部署在其中两个峡湾。此外，还将从几个地点收集岩心顶部的沉积物。所有样品都将被遮挡在光中，并被运送到内华达州的里诺进行发光分析。对南极冰川环境中发光时钟归零的有效性的系统研究将确定光子测年是否可以可靠地应用于未来的南极海洋沉积物。预计该项目将为未来的光子测年样品选择完善的沉积学标准。光子测年能力将提供一个数字地质计时器，远远超出14C测年的年龄范围。这种能力将允许回答一些更广泛的问题，即南极大陆架附近和附近过去冰川的时间和范围。

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.