ESH: Development of Luminescene Banding in Speleothems as a High Resolution Climatic Record

先前的研究表明，腐殖质，主要是黄腐酸，结合到洞穴中的次生方解石晶体中，会产生明显的发光条带。在圆柱形石笋的纵向切面以及从平面花石沉积中切割出来的岩芯或板材中，条带最容易被观察到。这些带的宽度约为10-100微米，似乎代表了每年的干湿循环，其中每个带代表石笋一年的生长。在条带中还有很多额外的细节。一块1米高的石笋可能包含代表2万年沉积的条带。因此，发光带有可能成为非常高分辨率的气候记录。这一提议的目的是为洞穴中发光带的古气候解释奠定可靠的基础。主要有三个目标：(I)建造一台沿洞穴纵向剖面测量激光激发发光强度的装置，具有高测光精度、几微米的空间分辨率和几微米范围内的空间位置跟踪。这将通过使用现有的微焦点拉曼光谱仪作为基本仪器并构建一个计算机控制的机械平台来平移石笋板材来实现。(Ii)进行一系列广泛的测量，相互比较从同一标本的多个横断面获得的记录、从同一洞穴内同一地点收集的标本以及从小地理区域内的洞穴收集的标本。需要这些测量来确定发光带状记录的重复性，并测试匹配重叠但不相同年龄的洞穴群记录的方法。(Iii)建立最近洞穴带生长的发光带状剖面，以与当代气候记录进行比较。这是一个校准步骤，将发光强度的具体变化与历史记录中已知的降水和其他气候事件联系起来。(Iv)建立跨越晚全新世洞穴的剖面，以便将发光带的细节与其他最近的古气候记录进行比较。(V)如果第(i-iv)项按计划进行，该项目将为更广泛地研究更早地延伸到更新世的洞穴记录奠定基础。

9809138WhitePrevious research has shown that humic substances, mainly fulvic acid, incorporated into the secondary calcite crystals of cave speleothems produce a distinct luminescence banding. The bands are best observed in longitudinal sections of cylindrical stalagmites and in cores or slabs cut from planar flowstone deposits. The bands have widths on the order of 10 - 100 micrometers and appear to represent annual wet and dry cycles where each band represents one year's growth of the stalagmite. There is much additional detail within the banding. A 1-meter high stalagmite might contain bands representing 20,000 years of deposition. The luminescence bands, therefore, have the potential for being a very high resolution climatic record.The intent of this proposal is to establish a sound basis for the paleoclimatic interpretation of the luminescence banding in speleothems. There are three main objectives.(i) Construct an apparatus that will measure laser excited luminescence intensity along longitudinal sections of speleothems with high photometric accuracy, spatial resolution of a few micrometers, and tracking of spatial position within a few micrometers. This is to be accomplished by using an existing microfocus Raman spectrometer as a base instrument and constructing a computer controlled mechanical stage to translate the slab of stalagmite.(ii) Conduct an extensive series of measurements intercomparing the records obtained from multiple transects of the same specimen, specimens collected from the same location within the same cave, and specimens collected from caves within a small geographic area. These measurements are needed to establish the reproducibility of luminescence banding records and to test methods for matching the records for speleothems of overlapping but not identical ages.(iii) Construct luminescence-banding profiles for very recent speleothem growth to compare with contemporary climatic records. This is a calibration step to correlate specific variations in luminescence intensity with known precipitation and other climatic events in the historical record.(iv) Construct profiles spanning late Holocene speleothems so that the details of luminescence banding may be compared with other recent paleoclimatic records.(v) If items (i - iv) work out as planned, this project would lay the groundwork for a more extensive study of speleothem records extending farther back into the Pleistocene.