NOAA/WDS Paleoclimatology - One Tree Island, Great Barrier Reef, Porites sp. trace metals 1990-2012 CE

The use of X-Ray Fluorescence (XRF) Core Scanning for continuous high-resolution analysis of Sr/Ca in corals is investigated here as a new method for analyzing coral material. Corals are valuable archives for generating high resolution palaeoclimate records of sea surface temperatures of the tropical oceans, but traditional methods of analyzing coral geochemistry involve extensive subsampling and wet chemistry techniques to obtain high precision elemental records. More recent developments of micro-beam techniques have limitations in the length of core that can be scanned at any one time. XRF core scanning provides a fast, non-destructive method of analyzing long sections of coral cores whilst maintaining a high sampling resolution. Here we apply this method to two modern corals, from the Sunda Strait, Indonesia and One Tree Island, Great Barrier Reef Australia. We find that results show that XRF core scanning of corals produce Sr/Ca records that capture the annual cycle, particularly from reef sites with a large sea surface temperature range. Coupled density measurements of the coral skeleton also aid in increasing the utility of XRF measurements obtained from coral material, although difficulties remain in reliably reconstructing interannual temperature variability using XRF Sr/Ca determinations. We recommend that XRF can provide a valuable method of quick and non-destructive screening of coral material, prior to more targeted analysis using traditional destructive geochemical analysis.

本研究探讨了采用X射线荧光（X-Ray Fluorescence, XRF）岩心扫描技术对珊瑚中的锶钙比（Sr/Ca）进行连续高分辨率分析的可行性，将其作为一种新型珊瑚样品分析方法。珊瑚是获取热带海洋海表温度（sea surface temperatures, SST）高分辨率古气候记录的宝贵档案载体，但传统的珊瑚地球化学分析方法需开展大量子采样与湿化学实验，方可获得高精度的元素序列记录。近年发展的微束分析技术在单次可扫描的岩心长度上存在局限，而XRF岩心扫描技术则可在维持高采样分辨率的前提下，实现对长段珊瑚岩心的快速无损分析。本研究将该方法应用于两处现代珊瑚样品，分别采自印度尼西亚巽他海峡与澳大利亚大堡礁的一树岛（One Tree Island）。研究结果显示，通过XRF岩心扫描得到的珊瑚Sr/Ca记录可捕捉年周期变化信号，在海表温度波动幅度较大的礁区站点表现尤为显著。珊瑚骨骼的密度耦合测量也有助于提升珊瑚样品XRF测量结果的应用价值，但依托XRF Sr/Ca分析可靠重建年际温度变化仍存在一定技术挑战。本研究建议，在采用传统破坏性地球化学分析开展针对性研究之前，XRF技术可作为一种快速无损的珊瑚样品初筛手段，具备重要应用价值。