River runoff reconstructions from novel spectral luminescence scanning of massive coral skeletons
River runoff reconstructions from novel spectral luminescence scanning of massive coral skeletons
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DOI：
10.1007/s00338-010-0629-y
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发表时间：
2010-09-01
期刊：
影响因子：
3.5
通讯作者：
Brummer, G. Jan A.
中科院分区：
文献类型：
--
作者：
Grove, C. A.;Nagtegaal, R.;Brummer, G. Jan A.
近岸块状珊瑚经常显示出明亮的发光线，这些发光线与流入沿海集水区的河流洪水羽流有关，因此有可能提供内陆降水的长期记录。珊瑚发光被认为是由于在主要的洪水事件中，土壤来源的腐殖酸被运送到珊瑚礁。远离陆地来源的珊瑚通常只显示出暗淡的相对较宽的发光带，这是由于珊瑚密度的季节性变化。因此，我们测试的假设，光谱比，而不是传统的发光强度提供了一个定量的代理记录的河流径流没有季节性密度变化的混杂影响。为此，我们开发了一种新的，快速光谱发光扫描（SLS）技术，分裂成红色，绿色和蓝色域（RGB）的发射强度为整个核心前所未有的线性分辨率为71.4 μ m。由于腐殖酸比珊瑚文石具有更长的发射波长，因此光谱发射的归一化应产生腐殖酸径流的灵敏的光学腐殖酸/文石比率，即，G/B比率。事实上，G/B比，而不是强度与Ba/Ca，沉积物径流的地球化学珊瑚代理，并与降雨量数据，例如从马达加斯加的珊瑚记录。珊瑚芯也显示最近发光强度下降的趋势，其他地方的珊瑚也报告了这种趋势。这种趋势似乎与现代骨骼密度的下降有关。相比之下，G/B光谱比不仅标志着个别气旋的影响，但也意味着腐殖酸径流增加，在马达加斯加在过去的几十年里，而珊瑚骨骼密度下降。因此，SLS技术反卷积腐殖酸掺入和珊瑚密度之间的长期相互作用，混淆了早期尝试使用发光强度作为河流径流的代理。
Inshore massive corals often display bright luminescent lines that have been linked to river flood plumes into coastal catchments and hence have the potential to provide a long-term record of hinterland precipitation. Coral luminescence is thought to result from the incorporation of soil-derived humic acids transported to the reef during major flood events. Corals far from terrestrial sources generally only exhibit dull relatively broad luminescence bands, which are attributed to seasonal changes in coral density. We therefore tested the hypothesis that spectral ratios rather than conventional luminescence intensity provide a quantitative proxy record of river runoff without the confounding effects of seasonal density changes. For this purpose, we have developed a new, rapid spectral luminescence scanning (SLS) technique that splits emission intensities into red, green and blue domains (RGB) for entire cores with an unprecedented linear resolution of 71.4 mu m. Since humic acids have longer emission wavelength than the coral aragonite, normalisation of spectral emissions should yield a sensitive optical humic acid/aragonite ratio for humic acid runoff, i.e., G/B ratio. Indeed, G/B ratios rather than intensities are well correlated with Ba/Ca, a geochemical coral proxy for sediment runoff, and with rainfall data, as exemplified for coral records from Madagascar. Coral cores also display recent declining trends in luminescence intensity, which are also reported in corals elsewhere. Such trends appear to be associated with a modern decline in skeletal densities. By contrast, G/B spectral ratios not only mark the impact of individual cyclones but also imply that humic acid runoff increased in Madagascar over the past few decades while coral skeletal densities decreased. Consequently, the SLS technique deconvolves the long-term interplay between humic acid incorporation and coral density that have confounded earlier attempts to use luminescence intensities as a proxy for river runoff.