An improved boron isotope pH proxy calibration for the deep-sea coral Desmophyllum dianthus through sub-sampling of fibrous aragonite
An improved boron isotope pH proxy calibration for the deep-sea coral Desmophyllum dianthus through sub-sampling of fibrous aragonite
复制标题
DOI：
10.1016/j.chemgeo.2016.10.029
复制
发表时间：
2016-12
期刊：
影响因子：
3.9
通讯作者：
J. Stewart;E. Anagnostou;G. Foster
中科院分区：
文献类型：
--
作者：
J. Stewart;E. Anagnostou;G. Foster
海相碳酸盐中硼的同位素组成(δ11B)被认为是过去海洋pH的替代指标，然而，它在古环境中的强大应用依赖于物种特异性校正的产生。现有的利用深海珊瑚(DSC)Desmophyllumdianthus的校准突出了这种普遍存在的物种在中等深度水域的pH重建方面的潜在应用。然而，从这些大量的骨骼δ11B测量中估计海水的pH值仍然存在相当大的不确定性，这可能是由于δ11B的微观结构不均一所致。石榴花。以规避这一问题，从而提高THED的可靠性。石榴石δ11B-pH定标，我们提出了一种新的δ11B定标方法，对该物种的微量纤维文石样品进行了定标。从大西洋、太平洋和南大洋采集的现代珊瑚样品，通过微钻孔、微粉碎和激光切割提取，分析了微量元素(B/Ca、Mg/Ca、Sr/Ca和U/Ca)和硼同位素组成。我们发现，针对当地环境海水中的硼酸盐的δ11B(pH的函数，取自水文数据集；pH范围为7.57至8.05)的最佳校准方法是使用δ11B对每个珊瑚样本的纤维进行测量，这些纤维的生长速度可能较慢，且来自邻近微结构的污染最小(通过低镁/钙确定)。与散装珊瑚δ11B相比，这一新的校准显示出对周围海水pH的更强、更明确的依赖；δ11B纤维=(0.93±0.17)×δ11B硼酸盐+(12.02±22.63)。我们认为，测量的δ11B的大部分变异是来自AD的纤维文石的复制条带之间的差异。硅灰石样品可以解释为显微取样过程中非纤维文石和表面杂质的少量掺入以及生长速度的影响。这项研究证实了D。如果采用适当的采样策略，Dianthusas是精确的古pH档案(±0.07个pH单位)。
The isotopic composition of boron (δ11B) in marine carbonates is well established as a proxy for past ocean pH, however, its robust application to palaeo-environments relies on the generation of species-specific calibrations. Existing calibrations utilising the deep-sea coral (DSC)Desmophyllumdianthushighlight the potential application of this pervasive species to pH reconstructions of intermediate depth waters. Nevertheless, considerable uncertainty remains regarding the estimation of seawater pH from these bulk skeletal δ11B measurements, likely resulting from microstructural heterogeneities in δ11B ofD. dianthus. To circumvent this problem, thus improving the reliability of theD. dianthusδ11B-pH calibration, we present a new δ11B calibration of micro-sampled fibrous aragonite from this species.Modern coral specimens recovered from the Atlantic, Pacific, and Southern Oceans, micro-sampled using microdrilling, micromilling, and laser cutting extraction, were analysed for trace element (B/Ca, Mg/Ca, Sr/Ca, and U/Ca) and boron isotopic composition. We find the best calibration against the δ11B of borate in local ambient seawater (a function of pH and taken from hydrographic data sets; pH range 7.57 to 8.05) utilises δ11B measurements of fibres with likely slow growth rates and minimal contamination from adjacent microstructures (identified by low Mg/Ca) for each coral specimen. This new calibration exhibits a stronger, and better-defined dependence on ambient seawater pH compared to bulk coral δ11B; δ11Bfibre= (0.93± 0.17) × δ11Bborate+ (12.02± 2.63). We suggest that the majority of the variability in measured δ11B between replicate bands of fibrous aragonite from aD. dianthusspecimen can be explained by small incorporation of non-fibrous aragonite and surface impurities during microsampling and growth rate effects. This study confirms the utility ofD. dianthusas an archive of precise palaeo-pH (± 0.07 pH units), provided that suitable sampling strategies are applied.